Ionizing radiation modulates vascular endothelial growth factor (VEGF) expression through multiple mitogen activated protein kinase dependent pathways.

We investigated the role of radiation-induced mitogen activated protein kinase (MAPK) pathway activity in the regulation of proliferation, cell survival and vascular endothelial growth factor (VEGF) production in primary astrocytes and in T9 and RT2 glioblastoma cells derived from Fisher 344 rats. In these cells, ionizing radiation (2 Gy) caused activation of the MAPK pathway which was blocked by specific inhibitor drugs. Blunting of radiation-induced MAPK activity weakly enhanced radiation-induced apoptosis 24 h after exposure in RT2 cells. Furthermore, blunting of MAPK activation weakly enhanced the ability of radiation to reduce RT2 cell growth in clonogenic growth assays. These findings argue that inhibition of MAPK signaling reduces proliferation and enhances cell killing by ionizing radiation in transformed astrocytes. Proliferation and survival of cancer cells has been linked in vivo to enhanced expression of angiogenic growth factors. Recently we demonstrated that the gene product of a novel rodent radiation-responsive gene, progression elevated gene 3 (PEG-3), could enhance vascular endothelial growth factor (VEGF) promoter activity in rodent fibroblasts, leading to increased VEGF protein levels and tumorigenic behavior in vivo. Thus PEG-3 and VEGF expression could be expected to directly correlate with the oncogenic potential of transformed cells. RT2 cells expressed more PEG-3 and VEGF protein than T9 cells, and were more tumorigenic in vivo than T9 cells. Radiation activated the PEG-3 promoter via MAPK signaling and ectopic over-expression of PEG-3 enhanced both basal MAPK activity and basal VEGF promoter activity. Basal MAPK activity partially correlated with basal VEGF promoter activity and VEGF protein levels in primary astrocytes, T9 and RT2 cells. Radiation increased the activity of the VEGF promoter and VEGF protein levels in primary astrocytes, T9 and RT2 cells which were dependent upon MAPK function. Furthermore, inhibition of AP-1 transcription factor signaling by dominant negative c-Jun (TAM67) also significantly reduced basal, and to a lesser extent radiation-induced, VEGF promoter function in RT2 cells. Collectively, our data demonstrate that radiation-induced MAPK signaling can both protect cells from radiation-induced cell death as well as enhance protein levels of pro-angiogenic factors such as VEGF. Enhanced VEGF expression in RT2 cells may be mediated via MAPK and JNK pathway signaling which converges upon the AP-1 transcription factor complex.

PEG-3, a nontransforming cancer progression gene, is a positive regulator of cancer aggressiveness and angiogenesis.

Cancer is a progressive disease culminating in acquisition of metastatic potential by a subset of evolving tumor cells. Generation of an adequate blood supply in tumors by production of new blood vessels, angiogenesis, is a defining element in this process. Although extensively investigated, the precise molecular events underlying tumor development, cancer progression, and angiogenesis remain unclear. Subtraction hybridization identified a genetic element, progression elevated gene-3 (PEG-3), whose expression directly correlates with cancer progression and acquisition of oncogenic potential by transformed rodent cells. We presently demonstrate that forced expression of PEG-3 in tumorigenic rodent cells, and in human cancer cells, increases their oncogenic potential in nude mice as reflected by a shorter tumor latency time and the production of larger tumors with increased vascularization. Moreover, inhibiting endogenous PEG-3 expression in progressed rodent cancer cells by stable expression of an antisense expression vector extinguishes the progressed cancer phenotype. Cancer aggressiveness of PEG-3 expressing rodent cells correlates directly with increased RNA transcription, elevated mRNA levels, and augmented secretion of vascular endothelial growth factor (VEGF). Furthermore, transient ectopic expression of PEG-3 transcriptionally activates VEGF in transformed rodent and human cancer cells. Taken together these data demonstrate that PEG-3 is a positive regulator of cancer aggressiveness, a process regulated by augmented VEGF production. These studies also support an association between expression of a single nontransforming cancer progression-inducing gene, PEG-3, and the processes of cancer aggressiveness and angiogenesis. In these contexts, PEG-3 may represent an important target molecule for developing cancer therapeutics and inhibitors of angiogenesis.

Inhibition of the growth of glioblastomas by CGP 41251, an inhibitor of protein kinase C, and by a phorbol ester tumor promoter.

Protein kinase C (PKC) plays a central role in signal transduction pathways that mediate the action of certain growth factors, tumor promoters, and cellular oncogenes. To explore whether PKC might be an appropriate target for the chemotherapy of human brain tumors, cell lines were established from five glioblastomas, one mixed gliosarcoma and glioblastoma, two astrocytomas, and one choroid plexus carcinoma. The staurosporine derivative CGP 41251, an inhibitor of PKC, inhibited cell proliferation in all nine cell lines with an IC50 in the range of 0.4 micrometer. Drug withdrawal and clonogenicity assays showed that CGP 41251 induced an irreversible growth arrest. Three cell lines were examined in detail: two human glioblastoma cell lines, GB-1 and GB-2, and one gliosarcoma cell line, GS-1. All of these three cell lines were highly aneuploid and displayed morphologies and immunohistochemical markers characteristic of the glial lineage. The compound 12-O-tetradecanoylphorbol-13-acetate (TPA), a tumor promoter and activator of PKC, also inhibited the growth of these cell lines. CGP 41251 in combination with TPA caused further growth inhibition. Cultures treated with CGP 41251 displayed an increase in the fraction of cells in G2-M, a decrease of cells in S phase, and no consistent effect on G0-G1. Immunohistochemical analyses demonstrated that growth inhibition by CGP 41251 was associated with the formation of giant nuclei with extensive fragmentation and apoptotic bodies. These effects of CGP 41251 were abrogated by withdrawal of serum from the medium or by exposure of these cells to aphidicolin, actinomycin D, cycloheximide, or TPA. In contrast to the effects seen with the glioblastoma cell lines, nontransformed astrocyte lines remained viable in the presence of 0.4 and 0.8 micrometer CGP 41251 and displayed only a slight increase in the fraction of giant nuclei with fragmentation. The antitumor activity of CGP 41251 was demonstrated in vivo against xenografts of the glioblastoma cell lines U87 MG and U373 MG. These findings suggest that CGP 41251 might be a useful agent for the treatment of glioblastomas.

Expression of a cell death marker (Clusterin) in muscle target fibers.

We report, for the first time, the expression of immunoreactivity to clusterin in skeletal muscle. Clusterin, a protein probably related to the process of programmed cell death (apoptosis), was specifically very highly expressed in target fibers. All target fibers found in 50 muscle biopsy samples from a variety of neuromuscular disorders expressed a high concentration of clusterin in the middle of the targets. Clusterin was not expressed in any targetoid fibers or cores. Acute denervation, where targets are mostly seen, may be the beginning of apoptosis. Hence our findings support the concept that targets are harbingers of acute denervation.

Analysis of viral and cellular gene expression during progression and suppression of the transformed phenotype in type 5 adenovirus-transformed rat embryo cells.

Transformation of secondary Sprague-Dawley rat embryo (RE) cells with type 5 adenovirus (Ad5) results in morphologically transformed cells which can undergo a series of sequential changes resulting in enhanced expression of the transformed phenotype, a process termed progression. Selection for a progressed phenotype often occurs after growth in agar or tumor formation in nude mice, and this process is reversible following treatment of cells with 5-azacytidine. In the present study we have analyzed a series of clonal populations of Ad5-transformed RE cells representing different stages in a defined progression lineage. Progression was not associated with alterations in the steady-state levels of mRNA produced by the viral transforming genes, E1A and E1B, or the cellular gene, c-myc. In addition, the tumor-promoting agent 12-O-tetradecanoyl-phorbol-13-acetate (TPA), which induces expression of a progressed phenotype in Ad5-transformed RE cells, did not significantly alter the RNA transcription rates of the Ad5 E1A or E1B genes, the TPA-inducible gene TPA-S1 or the TPA-responsive genes Pro1 or protein kinase C. TPA did, however, increase by 1 h the steady-state level of c-fos mRNA, but this effect was similar in both progressed and unprogressed cells. Progression also did not involve a change in the RNA transcription rate of a number of cellular and viral genes, including actin, c-Ha-ras, c-myc, v-fos, erbB, TGF-alpha, TGF-beta, Pro-2, transin, TPA-R1, v-myb and c-mos, or other adenovirus genes in addition to E1A and E1B, including E2A and E4. Immunoblotting analysis using E1B polyclonal antiserum further indicated that progression was not associated with changes in the levels of an Mr 21,000 polypeptide encoded by E1B. Similarly, immunoprecipitation analysis with an Ad2 E1A monoclonal antibody indicated similar levels of the Mr 55,000 and 48,000 E1A polypeptides, as well as coprecipitated proteins of Mr 300,000, 107,000 and 105,000 [which is the retinoblastoma (Rb) protein], in E11 and E11-NMT cells. Immunoprecipitation of cell lysates with a monoclonal antibody specific for the Mr 105,000 Rb protein further demonstrated that progression also was not associated with a change in the level or state of phosphorylation of the Rb protein. However, transfection of a human Rb gene (also containing a neomycin resistance gene) into Ad5-transformed RE cells was more inhibitory, with respect to formation of G418-resistant colonies, in unprogressed than in progressed Ad5-transformed RE cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Low-level beta 1 protein kinase C expression in cloned rat embryo fibroblast cells enhances transformation induced by the adenovirus type 5 E1A gene.

Expression of the E1A gene of adenovirus type 5 (Ad5) in a cloned rat embryo fibroblast (CREF) cell line results in morphological transformation. The efficiency of E1A-mediated transformation of CREF cells is increased if a wild-type Ad5 E1A gene is cotransfected with a rat beta 1 protein kinase C (beta 1 PKC) gene. A direct demonstration of complementation between a functional-transforming Ad5 E1A gene and beta 1 PK in inducing transformation was demonstrated using Ad5 E1A cold-sensitive mutant (E1Acs) genes. The E1Acs gene enhanced transformation only at the transformation-permissive temperature of 37 degrees C and not at the nonpermissive transforming temperature of 32 degrees C. CREF cells constitutively expressing low levels of beta 1 PKC mRNA were transformed at a higher frequency than parental CREF cells after transfection with an Ad5 E1A gene or infection with wild-type Ad5 or the Ad5 host-range cold-sensitive mutant H5hr1. There was no enhancement of transformation in low-level beta 1 PKC-expressing CREF cells when cultures were grown continuously in the presence of the PKC-inhibitor 1-(5-isoquinolynsulfonyl)-2-methylpiperazine dihydrochloride. Transfected CREF cells expressing low levels of beta 1 PKC mRNA displayed CREF-like morphology and did not form colonies when grown in agar. In contrast, retroviral vector-transformed CREF cells expressing high levels of beta 1 PKC mRNA and beta 1 PKC enzyme activity were morphologically transformed and grew efficiently in agar. These findings indicate that the beta 1 PKC gene, when expressed at low levels, can cooperate with the Ad5 E1A gene in the initiation of viral oncogene-mediated transformation.

Expression and modulation by cytokines of the intercellular adhesion molecule-1 (ICAM-1) in human central nervous system tumor cell cultures.

The intercellular adhesion molecule (ICAM-1) has been shown to be important in interactions involving cells of the immune system and to be upregulated in a number of cell culture systems by cytokines, including immune interferon (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). In the present study, we have determined by fluorescence-activated cell sorter (FACS) analysis and the anti-ICAM-1 monoclonal antibody (MAb) CL203.4 the base-line expression of ICAM-1 and its modulation by recombinant IFN-beta, IFN-gamma and TNF-alpha in early passage (less than 15) human central nervous system (CNS) tumor-derived cell cultures. These cultures were established from various malignancies, including glioblastoma multiforme (GBM), astrocytoma (AST), ganglioglioma, medulloblastoma, meningioma and a pineal tumor. ICAM-1 expression was highest in the GBM- and AST-derived cell cultures and was lowest in the ganglioglioma and normal pineal cell cultures. Variable ICAM-1 expression was found, however, in tumors of the same histological group. In several cell cultures the variable expression observed by FACS was substantiated by the intensity of the molecular species immunoprecipitated by the anti-ICAM-1 MAb CL203.4 from these cells. All the cell cultures displayed variable but consistent increases in ICAM-1 expression following treatment with IFN-gamma or TNF-alpha. In general, the degree of increase in ICAM-1 expression was greatest in cultures exposed to TNF-alpha. Upregulation of ICAM-1 expression in an established glioblastoma multiforme cell line was of greater magnitude and more rapid following TNF-alpha treatment (within 2 to 3 hr) than exposure to IFN-gamma (by 24 hr). In several cultures, IFN-beta also increased ICAM-1 expression and enhanced the increase induced by TNF-alpha. The results of the present study indicate that variable expression of ICAM-1 is a common property of early passage cultures of CNS tumors and recombinant interferons and TNF-alpha can differentially upregulate ICAM-1 expression in these CNS tumor cell cultures.

Alterations in SV40 DNA integration patterns are associated with acquisition of the invasive phenotype in hamster brain tumors.

A panel of cell lines that represents a reproducible, easily manipulated experimental system which discriminates between the minimally and diffusely invasive phenotypes of brain tumors has been developed. A population of SV40-transformed glial cells derived from newborn hamster cerebral cortex (Cx) has been sequentially passaged in newborn hamsters by intracerebral inoculation followed by in vitro culture, and after each passage progressively more invasive cell lines have been established. To study the molecular basis for the observed phenotypic characteristics associated with invasiveness, cloned cells were isolated from the first (Cx4T1-derived) and third Passage (Cx4T3-derived) cells lines. After injection into hamster brain, these cloned cells produce tumors that were either minimally invasive (Cx4T1-derived) or diffusely invasive (Cx4T3-derived) into normal brain tissue. In our initial attempt to identify and characterize the cellular and molecular factors that modulate the invasive phenotype, restriction endonuclease generated SV40 DNA-containing fragment patterns of DNA from each parental cell line and each of the clonal variants were determined by Southern transfer-hybridization. The results suggest the cell lines are composed of a limited number of tumorigenic subpopulations, each of which contain characteristic arrangements of integrated SV40 DNA with repeated in vivo/in vitro passage the avvangement of intecyvated SV40 changed. Analysis of DNA from minimally and diffusely invasive cloned cells indicated strong similarities of integrated SV40 DNA arrangement to their parental cells with the greatest similarities in cells exhibiting comparable invasive phenotypes. A striking difference was seen, however, in comparisons of SV40 DNA-containing fragment patterns of DNA extracted from clones which induced marginally versus diffusely invasive tumors. These differences suggest that the invasive cells were selected from a distinct minority subpopulation or that they may have arisen as a consequence of a more dynamic process of genetic rearrangement. This cell system appears to mimic the phenotypic and genetic heterogeneity observed in human tumors of glial origin and should prove valuable in defining the biochemical and molecular basis of tumor cell invasion.

Role of the Ha-ras (RasH) oncogene in mediating progression of the tumor cell phenotype (review).

Recent experimental evidence indicates that the c-Ha-ras (rasH) oncogene may be causally involved in the etiology and evolution of specific human neoplasms. In addition, cultured cells transformed by the rasH oncogene can induce both a tumorigenic and a metastatic phenotype when expressed in appropriate cultured cells. To begin to define the molecular and biochemical mechanism(s) by which the rasH oncogene induce their effects on expression of the transformed state we have employed a cloned rat embryo fibroblast (CREF) cell line. Transformation of CREF cells with wild-type 5 adenovirus (Wt) results in transformed cells which display anchorage-independence and an increased saturation density in monolayer culture, but are non-tumorigenic in both athymic nude mice and syngeneic Fischer rats. In contrast, when CREF cells are transformed with mutant type 5 adenoviruses, such as H5hrl, or the ElA transforming gene from hrl (0-4.5), tumors are induced in both nude mice and syngeneic rats. However, hrl (0-4.5)-transformed CREF cells are not metastatic following intravenous injection into the tail vein of syngeneic rats. Insertion of an activated T24 rasH oncogene or a wild-type v-rasH oncogene into CREF, wt-transformed CREF or hrl (0-4.5)-transformed CREF cells results in acquisition of a metastatic phenotype by these cells. A mutant v-rasH oncogene (mutant 116K), which is defective in GTP binding and the induction of transformation of NIH 3T3 cells, does not induce transformation in CREF cells, but it can progress wt-transformed CREF cells to a tumorigenic-non-metastatic state. Employing this model system which displays well-defined and stable stages in the tumor cell progression lineage, we have analyzed the potential role of changes in the phosphatidylinositol (PI) cycle and phospholipase A2 (PLA2) enzyme activity during progression to a tumorigenic and metastatic phenotype. An increase in PI cycle intermediates (primarily inositol triphosphate; IP3) were observed only in the wt-transformed and hrl (0-4.5)-transformed CREF cell lines transfected with the rasH oncogene. In the case of PLA2, all rasH-transformed CREF cell lines displayed increased activity. In contrast, CREF cells transformed only by Ad5 (Wt or hrl (0-4.5)) or the 116K v-rasH oncogene did not display increased PLA2 activity similar to that observed in rasH transfected cells. Since one important metabolite generated by PLA2 is arachidonic acid, which is converted into prostaglandins and leukotrienes by cyclooxygenase or lipooxygenase, respectively, the levels of prostaglandin E2 (PGE2) in the various cell lines were monitored.(ABSTRACT TRUNCATED AT 400 WORDS)

Suppression of the progression phenotype in somatic cell hybrids occurs in the absence of altered adenovirus type 5 gene expression.

In the present study we have analyzed the genetic regulation of increased expression of transformation-associated traits, a process termed progression, in adenovirus type 5 (Ad5)-transformed secondary rat embryo cells. Somatic cell hybrids were formed between a highly progressed neomycin-resistant Ad5-transformed cloned cell line (E11-NMTneo) and an untransformed chloramphenicol-resistant rat embryo fibroblast cell line (CREFcap). Parental E11-NMTneo cells grew with high efficiency in agar, exhibited reduced 125I-epidermal growth factor (EGF) binding, and were tumorigenic in nude mice. Parental CREFcap cells exhibited phenotypes opposite to those of E11-NMTneo cells. A high proportion (84%) of the presumptive hybrid cell types obtained after fusion and genetic selection (G418 and chloramphenicol) displayed a flat morphological phenotype intermediate between CREFcap and E11-NMTneo cells, suggesting that a trans-dominant extinction phenomenon had occurred. Two hybrids with a round morphology (R), which still exhibited the progressed phenotype, and two hybrids with a flat morphology (F), which had lost the progressed phenotype, were chosen for detailed analysis. Both R hybrids grew efficiently in agar, exhibited low 125I-EGF binding, and were tumorigenic in nude mice, whereas both F hybrids grew poorly in agar, displayed increased 125I-EGF binding in comparison with E11-NMTneo and R hybrids, and were nontumorigenic in nude mice. An analysis of the viral DNA integration patterns and the rates of transcription, steady-state mRNA accumulation, and relative levels of the Ad5 E1A and E1B gene products revealed no differences among the parental and hybrid cells. These studies indicate that normal CREF cells may contain a suppressor gene(s) which can inhibit the expression of specific traits of the progression phenotype in Ad5-transformed cells and that this suppression is not associated with changes in the expression of Ad5 transforming genes.

Modulation by interferons of HLA antigen, high-molecular-weight melanoma associated antigen, and intercellular adhesion molecule 1 expression by cultured melanoma cells with different metastatic potential.

The effect of leukocyte (IFN-alpha), fibroblast (IFN-beta), and immune (IFN-gamma) interferon and/or mezerein on the expression of HLA antigens and melanoma-associated antigens by the melanoma cell line MeWo and its metastatic variant MeM 50-10 was investigated, since this information may contribute to our understanding of the molecular mechanism(s) underlying the metastatic process and of the role of cell differentiation and growth suppression in the antigenic changes induced by interferon (IFN). The three types of IFN had no effect on the expression of high-molecular-weight melanoma-associated antigen, but enhanced that of HLA Class 1 antigens and of intercellular adhesion molecule 1 on MeWo and MeM 50-10 cells. The enhancing effect of IFN-gamma was more marked than that of IFN-alpha and IFN-beta. Furthermore IFN-gamma enhanced the expression of intercellular adhesion molecule 1 by MeM 50-10 cells more than by MeWo cells. IFN-beta was shown for the first time to induce HLA Class II antigens; the effect of IFN-beta, like that of IFN-gamma, is differential on the two cell lines and on the gene products of the HLA-D region. Like IFN-gamma, IFN-beta induced only HLA-DR antigens on MeM 50-10 cells. The results of Northern blot analysis with HLA-DR beta, -DQ beta, and -DP beta probes suggest that the differential modulation of the gene products of the HLA-D region by IFN-beta and IFN-gamma reflects transcriptional and posttranscriptional events. The differential susceptibility to modulation by IFN-beta and IFN-gamma of HLA Class II antigens on MeWo and MeM 50-10 cells is an intrinsic property of each cell line, since only small differences were detected in the number and/or affinity of receptors on the two cell lines. Furthermore, the lack of marked effects of mezerein on the antigen-modulating activity of the three types of IFN, in spite of an enhancement of their differentiating activity, suggests that the changes in the antigenic profile induced by IFN do not represent a differentiation-related phenomenon.

Regulation of class II MHC gene expression by interferons: insights into the mechanism of action of interferon (review).

Modulation of class I and II MHC antigen expression by interferons has been the focus of considerable attention because the regulation of these molecules serves as a useful model system to study factors exerting transcriptional control of gene expression and because of the relevance of these molecules to expression of the neoplastic phenotype. While our knowledge of the molecular mechanisms regulating the ability of interferon to mediate enhancement of MHC genes has increased, this information is primarily based on studies employing established cell lines, and it remains to be determined whether similar controls are also exerted in short term cultured cell lines. In this short review, we have discussed the structural organization of the 5' flanking regions of the MHC genes, with special emphasis on class II genes, and the implications of these data for the transcriptional regulation of these and of other interferon inducible genes. Present evidence indicates the existence of at least four conserved upstream sequences which are shared by interferon responsive genes and which appear to be involved in the transcriptional control of these genes. The pattern of metabolic requirements for IFN-alpha and IFN-beta versus IFN-gamma upregulation of the class I and II MHC genes suggests that the regulation of gene expression by IFN-gamma requires unique regulatory molecules, i.e. newly synthesized proteins, which are not required by IFN-alpha and IFN-beta treated cells. These putative mediators of gene expression are likely to be shared by many of the biochemical induction pathways involved in the regulation of genes which exhibit interferon responsive sequences. However, in addition to common regulatory signals, other specific pathways and possibly additional regulatory sequences, are also required to account for locus--or subunit-specific patterns of antigenic modulation. Future studies are required, including those employing short term tumor cell cultures, to precisely define the molecular details of gene regulation of class I and II MHC genes, as well as other interferon--responsive--genes, by interferons. These investigations will not only prove valuable on a fundamental scientific level, but they will also be crucial for the more effective application of interferons in clinical oncology.

Differential induction by immune interferon of the gene products of the HLA-D region on the melanoma cell line MeWo and its metastatic variant MeM 50-10.

This study has shown for the first time an association between the metastatic properties of two autologous melanoma cell lines and their susceptibility to induction of HLA class II Ag by IFN-gamma. After in vitro incubation with IFN-gamma the melanoma cell line MeWo did not acquire reactivity with anti-HLA class II antibodies, whereas its metastatic variant MeM 50-10 did. The differential susceptibility to induction of HLA class II Ag on the two cell lines cannot be accounted for by either differences in the number and affinity of IFN-gamma receptors or in the sensitivity to IFN-gamma, but most likely reflects an intrinsic property of each cell line. Serologic and immunochemical investigations with anti HLA-DR, DQ, and DP mAb have indicated that only HLA-DR Ag are induced by IFN-gamma on MeM 50-10 cells. Northern blot analysis with HLA-DR beta, DQ beta, and DP beta probes suggest that different mechanisms underlie the differential susceptibility to induction by IFN-gamma of the gene products of the HLA-D region. The regulatory mechanism(s) that control the expression of HLA class II Ag appear to be different from those controlling the expression of the melanoma-associated Ag tested, inasmuch as the modulation of the latter by IFN-gamma did not differ on the two melanoma cell lines.

Effect of methyl methanesulfonate on type 5 adenovirus DNA integration and the phenotypic properties of cold-sensitive type 5 adenovirus-transformed cloned rat embryo fibroblast cells.

Pretreatment of a cloned rat embryo fibroblast cell line (CREF) with methyl methanesulfonate (MMS) prior to infection with a specific cold-sensitive type 5 adenovirus mutant, H5hr1, results in a unique carcinogen enhancement of transformation phenotype. MMS induces a dose-dependent increase in the absolute number of transformed foci in comparison with solvent-treated controls as well as an increase in transformation frequency when normalized for carcinogen-induced cell toxicity. To determine if the carcinogen enhancement of transformation phenotype was a consequence of the carcinogen altering the pattern of type 5 adenovirus (Ad5) DNA integration into the genome of CREF cells and/or if carcinogen treatment modified the phenotype of established H5hr1-transformed CREF cells, we have analyzed a series of single cell-derived H5hr1-transformed CREF cultures which were isolated from cultures pretreated with carcinogen-solvent or MMS prior to infection with H5hr1. Analysis of viral DNA integration by DNA filter-transfer hybridization (Southern blotting) indicated that MMS pretreatment did not increase the copy number of Ad5 DNA sequences which persisted in H5hr1-transformed clones or result in transformants which contained identical DNA restriction enzyme cleavage patterns. MMS-pretreated H5hr1-transformed clones also did not differ significantly from solvent-pretreated H5hr1-transformed clones in their ability to grow in agar, bind 125I-epidermal growth factor, or form tumors in athymic nude mice. MMS-pretreated H5hr1-transformed CREF clones retained a similar cold-sensitive negative regulation in the expression of the transformed cell phenotype as did H5hr1-transformed clones not exposed to carcinogens. These findings suggest that the unique carcinogen enhancement of transformation phenotype displayed by CREF cells pretreated with MMS prior to infection with H5hr1 does not result in transformants which either contain increased concentrations of Ad5 DNA or similar patterns of Ad5 DNA integration. Furthermore, carcinogen-pretreated H5hr1 transformants did not display novel phenotypes not expressed by cloned H5hr1-transformed CREF cell lines exposed to solvent prior to viral infection.

Characterization of mutant human fibroblast cultures transformed with simian virus 40.

Fibroblast cell strains derived from a normal individual and from eight patients with various genetic mutations were transformed by a small-plaque variant of simian virus 40 (SV40, strain 776), cloned and studied after long-term in vitro maintenance. Seven of the cultures continued to express the mutant phenotype. Cultures derived from a patient with phosphoglycerate kinase I deficiency exhibited reappearance of normal enzyme activity after transformation. Compared to untransformed controls, all transformed cultures displayed decreased population doubling times, an increase in the relative number of cycling cells and increased saturation density on solid substrates, and did not show evidence of cellular senescence after long-term cultivation. Unlike previous studies on wild-type SV40-transformed human fibroblasts, the majority of cultures transformed by the small-plaque variant of SV40 did not exhibit signs of crisis. The cells also exhibited a decreased dependence on serum and were able to grow in semi-solid medium. The different transformed cultures expressed variable levels of SV40 large T-antigen, synthesized some infectious SV40 virus, and contained both unique arrangements and quantities of covalently integrated and episomal SV40 DNA. No correlation was observed between the rate of growth and synthesis of infectious virus in the different transformed clones. These studies indicate that this small-plaque variant of SV40 can be used effectively to generate long-lived human cultures, which generally retain their mutant phenotype. Transformation with this SV40 variant permits the generation of large quantities of clonal cell cultures for the biochemical and molecular analysis of their genetic defects.

Regulation of thyroidal inducibility of Na,K-ATPase and binding of epidermal growth factor in wild-type and cold-sensitive E1a mutant type 5 adenovirus-transformed CREF cells.

We have analyzed the relationship between expression of the transformed phenotype and thyroid hormone (triiodothyronine, T3) inducibility of Na,K-ATPase and binding of 125I-epidermal growth factor (EGF) to cell membrane receptors in wild-type (wt) and mutant type 5 adenovirus (Ad5)-transformed CREF cells displaying a cold-sensitive (cs) expression of the transformed phenotype. CREF cells respond to thyroid hormone treatment with increased Na,K-ATPase activity and bind similar levels of 125I-EGF at 32 degrees C, 37 degrees C and 39.5 degrees C. In contrast, CREF cells transformed by wt Ad5 or the E1a plus E1b-transforming genes of wt Ad5 are refractile to T3 treatment and bind lower levels of 125I-EGF than CREF cells at all three temperatures. By employing a series of cloned CREF cell lines transformed by a host-range cold-sensitive mutant virus, H5hr1 or H5dl101, or the E1a or E1a plus E1b genes from these viruses, we have investigated expression of the transformed state and its relationship with hormone inducibility and EGF binding. When cs virus, cs E1a- or cs E1a plus E1b-transformed CREF clones were grown at 32 degrees C, a nonpermissive transforming temperature in which cs-transformed cells exhibit properties similar to untransformed CREF cells, T3 induced Na,K-ATPase activity and these cells bound similar levels of 125I-EGF as CREF cells. However, when cs virus- and cs Ela plus E1b-transformed CREF clones were incubated at 37 degrees C or 39.5 degrees C, temperatures at which cs-transformed cells exhibit properties similar to wt Ad5-transformed CREF cells, they did not respond to T3 and bound lower levels of 125I-EGF than CREF cells. In the case of cs E1a-transformed CREF clones, thyroid hormone responsiveness was observed at both 32 degrees C and 37 degrees C, but not at 39.5 degrees C. By performing temperature shift experiments--i.e. 32 degrees C to 37 degrees C, 32 degrees C to 39.5 degrees C, 37 degrees C to 32 degrees C, and 39.5 degrees C to 32 degrees C, it was demonstrated that after a shift from lower to higher temperature a 24-hr lag period was required for cs-transformed CREF cells to lose T3 inducibility and exhibit reduced EGF binding, whereas 96 hr after a shift from higher to lower temperature a 96-hr lag period was required for cs-transformed cells to regain T3 inducibility and increased 125I-EGF binding.(ABSTRACT TRUNCATED AT 400 WORDS)

Unique carcinogen enhancement of transformation phenotype displayed by cloned rat embryo fibroblast (CREF) cells treated with methyl methanesulfonate and infected with a specific host-range mutant of type 5 adenovirus.

Pretreatment of cloned rat embryo fibroblast (CREF) cells with methyl methanesulfonate (MMS) prior to infection with wild-type 5 adenovirus (H5wt) or a temperature-sensitive mutant of Ad5 (H5ts125) results in an MMS dose-dependent enhancement of viral transformation. With both viral isolates, MMS enhanced the transformation frequency when normalized for cell toxicity but did not induce a carcinogen dose-dependent increase in the absolute number of foci above solvent-treated controls. In contrast, pretreatment of CREF cells with MMS prior to infection with a host-range mutant of Ad5 (H5hr1) which contains a single basepair deletion in the E1a-transforming region of Ad5 and displays a cold-sensitive transformation phenotype, results in an MMS dose-dependent increase in the absolute number of transformed foci in comparison with solvent-treated controls as well as an increase in transformation frequency when normalized for cell toxicity. To explore the possible mechanism by which H5hr1 displays its unique carcinogen-enhancement of transformation (CET) phenotype we have examined the effect of MMS pretreatment on the frequency of transformation of CREF cells infected with mutants of Ad5 which were engineered to contain either a deletion (H5dl101) or an insertion (H5in106) mutation in the E1a gene region resulting in a cold-sensitive transformation phenotype similar to H5hr1. MMS-pretreated CREF cells infected with H5dl101 or H5in106 did not demonstrate a dose-dependent increase in the absolute number of transformed foci as was observed with carcinogen-pretreated H5hr1-infected CREF cells. These findings suggest that the unique CET phenotype displayed by H5hr1 may result from a second site mutation in a region of H5hr1 other than the E1a-transforming region and/or a novel interaction between gene products resulting from the specific mutation in E1a and other region(s) of the H5hr1 genome. Our investigations also indicate that the CREF/H5hr1 system should prove useful in analyzing chemical-viral interactions in cell transformation.

Mutations in the E1a gene of type 5 adenovirus result in oncogenic transformation of Fischer rat embryo cells.

Transformation of a specific clone of Fischer rat embryo (CREF) cells with wild-type 5 adenovirus (Ad5) or the E1a plus E1b transforming gene regions of Ad5 results in epithelioid transformants that grow efficiently in agar but that do not induce tumors when inoculated into nude mice or syngeneic Fischer rats. In contrast, CREF cells transformed by a host-range Ad5 mutant, H5hrl, which contains a single base-pair deletion of nucleotide 1055 in E1a resulting in a 28-kd protein (calculated) in place of the wild-type 51-kd acidic protein, display a cold-sensitive transformation phenotype and an incomplete fibroblastic morphology but surprisingly do induce tumors in nude mice and syngeneic rats. Tumors develop in both types of animals following injection of CREF cells transformed by other cold-sensitive Ad5 E1a mutants (H5dl101 and H5in106), which contain alterations in their 13S mRNA and consequently truncated 289AA proteins. CREF cells transformed with only the E1a gene (0-4.5 m.u.) from H5hrl or H5dl101 also produce tumors in these animals. To directly determine the role of the 13S E1a encoded 289AA protein and the 12S E1a encoded 243AA protein in initiating an oncogenic phenotype in adenovirus-transformed CREF cells, we generated transformed cell lines following infection with the Ad2 mutant pm975, which synthesizes the 289AA E1a protein but not the 243AA protein, and the Ad5 mutant H5dl520 and the Ad2 mutant H2dl1500, which do not produce the 289AA E1a protein but synthesize the normal 243AA E1a protein. All three types of mutant adenovirus-transformed CREF cells induced tumors in nude mice and syngeneic rats. Tumor formation by these mutant adenovirus-transformed CREF cells was not associated with changes in the arrangement of integrated adenovirus DNA or in the expression of adenovirus early genes. These results indicate, therefore, that oncogenic transformation of CREF cells can occur in the presence of a wild-type 13S E1a protein or a wild-type 12S E1a protein when either protein is present alone, but does not occur when both wild-type E1a proteins are present.