Dual inhibition of survivin and MAOA synergistically impairs growth of PTEN-negative prostate cancer.

BACKGROUND: Survivin and monoamine oxidase A (MAOA) levels are elevated in prostate cancer (PCa) compared to normal prostate glands. However, the relationship between survivin and MAOA in PCa is unclear. METHODS: We examined MAOA expression in the prostate lobes of a conditional PTEN-deficient mouse model mirroring human PCa, with or without survivin knockout. We also silenced one gene at a time and examined the expression of the other. We further evaluated the combination of MAOA inhibitors and survivin suppressants on the growth, viability, migration and invasion of PCa cells. RESULTS: Survivin and MAOA levels are both increased in clinical PCa tissues and significantly associated with patients' survival. Survivin depletion delayed MAOA increase during PCa progression, and silencing MAOA decreased survivin expression. The combination of MAOA inhibitors and the survivin suppressants (YM155 and SC144) showed significant synergy on the inhibition of PCa cell growth, migration and invasion with concomitant decrease in survivin and MMP-9 levels. CONCLUSIONS: There is a positive feedback loop between survivin and MAOA expression in PCa. Considering that survivin suppressants and MAOA inhibitors are currently available in clinical trials and clinical use, their synergistic effects in PCa support a rapid translation of this combination to clinical practice.

Disruption of PPARgamma signaling results in mouse prostatic intraepithelial neoplasia involving active autophagy.

Peroxisome proliferator-activated receptor-gamma (PPARgamma) regulates the interface between cellular lipid metabolism, redox status and organelle differentiation. Conditional prostatic epithelial knockout of PPARgamma in mice resulted in focal hyperplasia which developed into mouse prostatic intraepithelial neoplasia (mPIN). The grade of PIN became more severe with time. Electron microscopy (EM) showed accumulated secondary lysosomes containing cellular organelles and debris suggestive of autophagy. Consistent with this analysis the autophagy marker LC-3 was found to be upregulated in areas of PIN in PPARgamma KO tissues. We selectively knocked down PPARgamma2 isoform in wild-type mouse prostatic epithelial cells and examined the consequences of this in a tissue recombination model. Histopathologically grafted tissues resembled the conditional PPARgamma KO mouse prostates. EM studies of PPARgamma- and PPARgamma2-deficient epithelial cells in vitro were suggestive of autophagy, consistent with the prostatic tissue analysis. This was confirmed by examining expression of beclin-1 and LC-3. Gene expression profiling in PPARgamma-/gamma2-deficient cells indicated a major dysregulation of cell cycle control and metabolic signaling networks related to peroxisomal and lysosomal maturation, lipid oxidation and degradation. The putative autophagic phenotypes of PPARgamma-deficient cells could be rescued by re-expression of either gamma1 or gamma2 isoform. We conclude that disruption of PPARgamma signaling results in autophagy and oxidative stress during mPIN pathogenesis.

Prostate stem cells and cancer.

Properties shared by neoplastic and stem cells indicate a possibility that somatic stem cells or transit-amplifying cells that have reacquired stem cell properties, particularly the ability for self-renewal, represent favorable targets for malignant transformation. In this review we discuss significance of the stem cell model for understanding prostate cancer pathogenesis and describe relevant studies in animals. It is proposed that dissemination of rare cancer stem cells may lead to metastatic disease and that resistance of such cells to multiple drugs and androgen ablation make them responsible for failure of current treatments. Thus further understanding of the cancer stem cell biology is needed for development of efficient rationally designed therapy permitting better targeting and better treatment outcomes for patients with prostate neoplasms.

Genetically defined mouse models that mimic natural aspects of human prostate cancer development.

This review is focused on mouse models for prostate cancer that have been designed on the basis of genetic alterations that are frequently found in human prostate cancer. It begins with an analysis of the similarities and differences in the gross and microscopic anatomy of the mouse and human prostate glands, and extends to the pathologies induced in the genetically manipulated mouse prostate in comparison with the sporadic development of the disease in humans. Major achievements have been made in modeling human prostate cancer in mice in recent years. There are models which display slow, temporal development of increasingly severe preneoplastic lesions, which are remarkably restricted to the prostate gland, a property similar to the aging-related progression of these lesions in humans. Other models rapidly progress to local invasive adenocarcinoma, and, in some of them metastasis is manifested subsequently with defined kinetics. Global assessment of molecular changes in the prostate of the genetically manipulated mice is increasingly underscoring the validity of the models through identification of 'signature' genes which are associated with the organ-confined primary or distant metastases of human prostate cancer. Taken together, various 'natural' models depicting stages of the disease, ranging from the early preneoplastic lesions to metastatic prostate cancer, now provide new tools both for exploring the molecular mechanism underlying prostate cancer and for development or testing of new targeted therapies.

Mouse strains for prostate tumorigenesis based on genes altered in human prostate cancer.

Animal models of prostate cancer have been limited in number and in relevance to the human disease. With the advancement of transgenic and knockout technologies, combined with tissue specific promoters and tissue-specific gene ablation, a new generation of mouse models has emerged. This review will discuss various animal models and their inherent strengths and weaknesses. A primary emphasis is placed on mouse models that have been designed on the basis of genetic alterations that are frequently found in human prostate cancer. These models display slow, temporal development of increasingly severe histopathologic lesions, which are remarkably restricted to the prostate gland, a property similar to the ageing related progression of this disease in humans. The preneoplastic lesions, akin to what is considered as prostatic intraepithelial neoplasia, are consistent major phenotypes in the models, and, therefore. are discussed for histopathologic criteria that may distinguish their progressions or grades. Finally, considering that prostate cancer is a complex multifocal disease, which is likely to require multiple genetic/epigenetic alterations, many of these models have already been intercrossed to derive mice with compound genetic alterations. It is predicted that these and subsequent compound mutant mice should represent "natural" animal models for investigating the mechanism of development of human prostate diseases, as well as, for preclinical models for testing therapeutics.

A replication-competent feline leukemia virus, subgroup A (FeLV-A), tagged with green fluorescent protein reporter exhibits in vitro biological properties similar to those of the parental FeLV-A.

We previously established that lymphoid tumors could be induced in cats by intradermal injection of ecotropic feline leukemia virus (FeLV), subgroup A, plasmid DNA. In preparation for in vivo experiments to study the cell-to-cell pathway for the spread of the virus from the site of inoculation, the green fluorescent protein (GFP) transgene fused to an internal ribosome entry site (IRES) was inserted after the last nucleotide of the env gene in the ecotropic FeLV-A Rickard (FRA) provirus. The engineered plasmid was transfected into feline fibroblast cells for production of viruses and determination of GFP expression. The virions produced were highly infectious, and the infected cells could continue to mediate strong expression of GFP after long-term propagation in culture. Similar to parental virus, the transgene-containing ecotropic virus demonstrated recombinogenic activity with endogenous FeLV sequences in feline cells to produce polytropic recombinant FeLV subgroup B-like viruses which also contained the IRES-GFP transgene in the majority of recombinants. To date, the engineered virus has been propagated in cell culture for up to 8 months without diminished GFP expression. This is the first report of a replication-competent FeLV vector with high-level and stable expression of a transgene.

Generation of a prostate epithelial cell-specific Cre transgenic mouse model for tissue-specific gene ablation.

To facilitate the elucidation of the genetic events that may play an important role in the development or tumorigenesis of the prostate gland, we have generated a transgenic mouse line with prostate-specific expression of Cre recombinase. This line, named PB-Cre4, carries the Cre gene under the control of a composite promoter, ARR2PB which is a derivative of the rat prostate-specific probasin (PB) promoter. Based on RT-PCR detection of Cre mRNA in PB-Cre4 mice or Cre-mediated activation of LacZ activity in PB-Cre4/R26R double transgenic mice, it is conclusively demonstrated that Cre expression is post-natal and prostatic epithelium-specific. Although the Cre recombination is detected in all lobes of the mouse prostate, there is a significant difference in expression levels between the lobes, being highest in the lateral lobe, followed by the ventral, and then the dorsal and anterior lobes. Besides the prostate gland, no other tissues of the adult PB-Cre4 mice demonstrate significant Cre expression, except for a few scattered areas in the gonads and the stroma of the seminal vesicle. By crossing the PB-Cre4 animals with floxed RXRalpha allelic mice, we demonstrate that mice, whose conventional knockout of this gene is lethal in embryogenesis, could be propagated with selective inactivation of RXRalpha in the prostate. Taken together, the results show that the PB-Cre4 mice have high levels of Cre expression and a high penetrance in the prostatic epithelium. The PB-Cre4 mice will be a useful resource for genetic-based studies on prostate development and prostatic disease.

The effect of fibroblast growth factor 8, isoform b, on the biology of prostate carcinoma cells and their interaction with stromal cells.

Fibroblast growth factor 8, isoform b (FGF8b), has been implicated in the oncogenesis of the prostate and mammary epithelia. We examined whether overexpression of FGF8b in a weakly tumorigenic prostate carcinoma cell line, LNCaP, could alter the growth and tumorigenic properties of these cells. LNCaP cells were infected with a lentivirus vector carrying FGF8b cDNA and the green fluorescent protein (GFP) cDNA in the same construct, and the infected cell population was sorted on the basis of GFP protein expression. It was demonstrated that, in comparison with the cells transduced with GFP-vector alone, LNCaP cells with FGF8b-GFP expression manifested an increased growth rate, higher soft agar clonogenic efficiency, enhanced in vitro invasion, and increased in vivo tumorigenesis. Most strikingly, whereas parental or vector-control LNCaP cells failed to grow at all in an in vivo tumorigenesis/diaphragm invasion assay in nude mice, the cells overexpressing FGF8b proliferated as deposits of tumor cells on the diaphragm, frequently with indications of tumor cell invasion into the diaphragm. Coculturing of primary prostatic or non-prostatic stromal cells with the infected LNCaP cells led us to observe that: (a) stromal cells, irrespective of tissue origin, strongly suppressed LNCaP cell growth; (b) FGF8b producing LNCaP cells could partially evade the stromal inhibition, perhaps from the autocrine stimulatory effect of FGF8b; and (c) production of FGF8b in the coculture had a stimulatory effect on the proliferation of the stromal cells, prostatic or non-prostatic. This stimulation was not attributable to the direct action of FGF8b on stromal cells. Instead, it appears that epithelial-stromal cell-cell contact and some unknown soluble factors secreted by LNCaP cells upon stimulation of FGF8b are required for the maximal effect. Together, these results suggest that the growth rate and biological behavior of prostatic cancer cells can be altered to a more aggressive phenotype by up-regulation of FGF8b expression. These changes in phenotype also influence the interaction of the affected cells with stromal cells. The data obtained may have direct relevance to the progression of prostate cancer, recognizing that FGF8b is naturally overexpressed in advanced disease.

Inhibition of feline leukemia virus subgroup A infection by coinoculation with subgroup B.

Feline leukemia virus (FeLV) subgroup B arises de novo through recombination between the env genes of exogenous FeLV subgroup A and endogenous FeLV-like sequences. FeLV-B, which by itself is poorly infectious, will increase to high titer in the presence of FeLV-A, and is associated with FeLV-related neoplastic disease. Although the participation of FeLV-B in disease progression has not been definitively proven, circumstantial evidence supports the hypothesis that the generation of FeLV-B is linked to disease progression. The present study was designed to evaluate whether increasing the levels of FeLV-B early in FeLV-A infection could result in reduction of the incubation period for development of neoplastic disease. For this study, an isolate of FeLV-B, designated FeLV-1B3, was biologically cloned, partially sequenced, and subgroup typed. In in vivo studies, none of the neonatal cats inoculated with FeLV-1B3 alone converted to viremia positive, and all remained healthy throughout the observation period. All of the kittens inoculated with FeLV-A alone became chronically viremic, and those held for long-term observation all developed either neoplastic disease or anemia. However, kittens inoculated with the combination of FeLV-1B3 and FeLV-A showed attenuated infections whereby the majority of cats failed to develop chronic viremia. The apparent interference of FeLV-A infection by FeLV-B was time and titer dependent. This unexpected result suggests that FeLV-B may act as an attenuated virus, causing inhibition of FeLV-A possibly through an immune-mediated mechanism. Partial support for this view was provided by postmortem examination of cats inoculated with FeLV-1B3 alone. Even though none of these cats became viremic, FeLV antigen was detected as focal infections in select tissues, especially salivary gland epithelium, where enough antigen may be expressed to provide an immunizing dose against gag and pol cross-reacting antigens. This work may also provide another approach to vaccine development based on endogenous retrovirus vector systems.

Long terminal repeat regions from exogenous but not endogenous feline leukemia viruses transactivate cellular gene expression.

We have previously reported that the long terminal repeat (LTR) region of feline leukemia viruses (FeLVs) can enhance expression of certain cellular genes such as the collagenase IV gene and MCP-1 in trans (S. K. Ghosh and D. V. Faller, J. Virol. 73:4931-4940, 1999). Genomic DNA of all healthy feline species also contains LTR-like sequences that are related to exogenous FeLV LTRs. In this study, we evaluated the cellular gene transactivational potential of these endogenous FeLV LTR sequences. Unlike their exogenous FeLV counterparts, neither nearly full-length endogenous FeLV molecular clones (CFE-6 and CFE-16) nor their isolated LTRs were able to activate collagenase IV gene or MCP-1 expression in transient transfection assays. We had also demonstrated previously that production of an RNA transcript from exogenous FeLV LTRs correlates with their transactivational activity. In the present study, we demonstrate that the endogenous FeLV LTRs do not generate LTR-specific RNA transcripts in the feline embryo fibroblast cell line AH927. Furthermore, infection of AH927 cells by an exogenous FeLV subgroup A virus did not induce production of such LTR-specific transcripts from the endogenous proviral genomes, although the LTR-specific transcripts from the exogenous virus were readily detected. Finally, LTR-specific transcripts were not generated in BALB/3T3 cells transiently transfected with isolated CFE-6 LTR, in contrast to transfections with LTRs from exogenous viruses. Our data thus suggest that the inability of endogenous FeLV LTRs in gene transactivation is not due to cell line specificity or presence of any upstream inhibitory cis-acting element. Endogenous, nonleukemogenic FeLV LTRs, therefore, do not transactivate cellular gene expression, and this property appears to be specific to exogenous, leukemogenic FeLVs.

Differential pathogenicity of two feline leukemia virus subgroup A molecular clones, pFRA and pF6A.

F6A, a molecular clone of subgroup A feline leukemia virus (FeLV) is considered to be highly infectious but weakly pathogenic. In recent studies with a closely related subgroup A molecular clone, FRA, we demonstrated high pathogenicity and a strong propensity to undergo recombination with endogenous FeLV (enFeLV), leading to a high frequency of transition from subgroup A to A/B. The present study was undertaken to identify mechanisms of FeLV pathogenesis that might become evident by comparing the two closely related molecular clones. F6A was shown to have an infectivity similar to that of FRA when delivered as a provirus. Virus load and antibody responses were also similar, although F6A-infected cats consistently carried higher virus loads than FRA-infected cats. However, F6A-infected cats were slower to undergo de novo recombination with enFeLV and showed slower progression to disease than FRA-infected cats. Tumors collected from nine pF6A- or pFRA-inoculated cats expressed lymphocyte markers for T cells (seven tumors) and B cells (one tumor), and non-T/B cells (one tumor). One cat with an A-to-A/C conversion developed erythrocyte hypoplasia. Genomic mapping of recombinants from pF6A- and pFRA-inoculated cats revealed similar crossover sites, suggesting that the genomic makeup of the recombinants did not contribute to increased progression to neoplastic disease. From these studies, the mechanism most likely to account for the pathologic differences between F6A and FRA is the lower propensity for F6A to undergo de novo recombination with enFeLV in vivo. A lower recombination rate is predicted to slow the transition from subgroup A to A/B and slow the progression to disease.

A novel association between the human heat shock transcription factor 1 (HSF1) and prostate adenocarcinoma.

A search for differentially expressed genes in a pair of nonmetastatic (PC-3) versus metastatic variant (PC-3M) human prostate carcinoma cell lines led to identification of the human heat shock factor (HSF1) as an overexpressed gene product in PC-3M cells. Analysis of primary prostate cancer specimens indicated that HSF1 is generally up-regulated in most of the malignant prostate epithelial cells relative to the normal prostate cells. Among the known effectors of HSF1 action, constitutive levels of HSP70 and HSP90 are not significantly altered by the naturally elevated expression of HSF1 as in PC-3M cells or by transduced overexpression of HSF1 in PC-3 cells. The basal levels of HSP27 in both cases are, however, consistently increased by two- to threefold. With respect to response to heat shock, high basal concentration of HSP90 is not further enhanced in these cells, and HSP70 is up-regulated irrespective of HSF1 level. Heat shock, however, causes an increase in HSP27 when HSF1 is up-regulated, except when the expression of HSF1 is already too high. These results document for the first time that HSF1 is overexpressed in human prostate cancer cells, at least one consequence of which in the prostate cancer cell lines tested is stimulation of both basal and stress-induced expression of HSP27, an important factor in cell growth, differentiation, or apoptosis.

A novel truncated env gene isolated from a feline leukemia virus-induced thymic lymphosarcoma.

We PCR amplified the exogenous feline leukemia virus (FeLV)-related env gene species from lymphosarcomas induced by intradermally administered plasmid DNA of either the prototype FeLV, subgroup A molecular clone, F6A, or a new molecular clone, FeLV-A, Rickard strain (FRA). Of the nine tumors examined, six showed the presence of deleted env species of variable sizes in the tumor DNA. One env mutant, which was detected in a FRA-induced thymic lymphosarcoma, had a large internal deletion beginning from almost the N-terminal surface glycoprotein (SU) up to the middle region of the transmembrane (TM) protein of the env gene. The deduced polypeptide of this truncated env (tenv) retained the complete signal peptide and seven amino acids of the N-terminal mature SU of FRA env gene, followed by eight amino acids from the frameshift in the TM region. To study the biological function of tenv, we used a murine retrovirus vector to produce amphotropic virions. Infection of feline fibroblasts (H927), human fibrosarcoma cells (HT1080), or human B-lymphoma cells (Raji) led to pronounced cytotoxicity, while the tenv virus did not induce significant cytotoxicity to feline T-lymphoma cells (3201B) or human T-lymphoma cells (CEM). Together, these results convincingly demonstrated that the genetic events that led to truncation in the env gene occurred de novo in FeLV lymphomagenesis and that such a product, tenv could induce cytotoxicity to fibroblastic and B-lymphoid cells but not to T-lymphoid tumor cells. This type of selective toxicity might be potentially important in the development of the neoplastic disease.

Suppression of prostate carcinoma cell invasion by expression of antisense L-plastin gene.

Based on the finding that gene expression for the actin-bundling protein L-plastin is inducible by androgen and that L-plastin is overexpressed in malignant epithelium of the prostate, we examined the functional consequences of L-plastin down-regulation in prostate carcinoma cell lines by both transfection and retroviral infection. We constructed retroviral vectors to express two different regions of the L-plastin gene, a 1713-bp 3'-coding portion and a 163-bp 5'-untranslated region, both in antisense orientation. Introduction of either constructs into prostate carcinoma cell lines, PC-3 and its isogenic but metastatic variant PC-3M cells, reduced the growth rates of both cell lines. In vitro invasion and motility of PC-3 and PC-3M cells were drastically suppressed (approximately 10-fold) by the expression of the antisense constructs. Evidence was obtained to indicate that L-plastin protein levels were indeed decreased by the antisense expression. The antisense construct for the 5'-untranslated region with the most unique sequence for the L-plastin gene was more effective in down-regulation efficiency compared with the larger antisense construct in the coding region, which maintains homology to other members of the plastin gene family. Cells infected with the 163-bp antisense virus, which were also tested in a nude mouse diaphragm invasion model, showed suppression of in vivo invasion of both PC-3 and PC-3M cells. These results suggested that overexpression of L-plastin might be functionally involved in prostate cancer invasion and metastasis, and raised the possibility that L-plastin gene-specific antisense delivery could potentially be a useful approach to interfere with prostate cancer progression in vivo.

Recombinant feline leukemia virus (FeLV) variants establish a limited infection with altered cell tropism in specific-pathogen-free cats in the absence of FeLV subgroup A helper virus.

Feline leukemia virus subgroup B (FeLV-B) is commonly associated with feline lymphosarcoma and arises through recombination between endogenous retroviral elements inherited in the cat genome and corresponding regions of the envelope (env) gene from FeLV subgroup A (FeLV-A). In vivo infectivity for FeLV-B is thought to be inefficient in the absence of FeLV-A. Proposed FeLV-A helper functions include enhanced replication efficiency, immune evasion, and replication rescue for defective FeLV-B virions. In vitro analysis of the recombinant FeLV-B-like viruses (rFeLVs) employed in this study confirmed these viruses were replication competent prior to their use in an in vivo study without FeLV-A helper virus. Eight specific-pathogen-free kittens were inoculated with the rFeLVs alone. Subsequent hematology and histology results were within normal limits, however, in the absence of detectable viremia, virus expression, or significant seroconversion, rFeLV proviral DNA was detected in bone marrow tissue of 4/4 (100%) cats at 45 weeks postinoculation (pi), indicating these rFeLVs established a limited but persistent infection in the absence of FeLV-A. Altered cell tropism was also noted. Focal infection was seen in T-cell areas of the splenic follicles in 3/4 (75%) rFeLV-infected cats analyzed, while an FeLV-A-infected cat showed focal infection in B-cell areas of the splenic follicles. Nucleotide sequence analysis of the surface glycoprotein portion of the rFeLV env gene amplified from bone marrow tissue collected at 45 weeks pi showed no sequence alterations from the original rFeLV inocula.

Pathogenicity induced by feline leukemia virus, Rickard strain, subgroup A plasmid DNA (pFRA).

A new provirus clone of feline leukemia virus (FeLV), which we named FeLV-A (Rickard) or FRA, was characterized with respect to viral interference group, host range, complete genome sequence, and in vivo pathogenicity in specific-pathogen-free newborn cats. The in vitro studies indicated the virus to be an ecotropic subgroup A FeLV with 98% nucleotide sequence homology to another FeLV-A clone (F6A/61E), which had also been fully sequenced previously. Since subgroup B polytropic FeLVs (FeLV-B) are known to arise via recombination between ecotropic FeLV-A and endogenous FeLV (enFeLV) env elements, the in vivo studies were conducted by direct intradermal inoculation of the FRA plasmid DNA so as to eliminate the possibility of coinoculation of any FeLV-B which may be present in the inoculum prepared by propagating FeLV-A in feline cell cultures. The following observations were made from the in vivo experiments: (i) subgroup conversion from FeLV-A to FeLV-A and FeLV-B, as determined by the interference assay, appeared to occur in plasma between 10 and 16 weeks postinoculation (p.i.); (ii) FeLV-B-like recombinants (rFeLVs), however, could be detected in DNA isolated from buffy coats and bone marrow by PCR as early as 1 to 2 weeks p.i.; (iii) while a mixture of rFeLV species containing various amounts of N-terminal substitution of the endogenous FeLV-derived env sequences were detected at 8 weeks p.i., rFeLV species harboring relatively greater amounts of such substitution appeared to predominate at later infection time points; (iv) the deduced amino acid sequence of rFeLV clones manifested striking similarity to natural FeLV-B isolates, within the mid-SU region of the env sequenced in this work; and (v) four of the five cats, which were kept for determination of tumor incidence, developed thymic lymphosarcomas within 28 to 55 weeks p.i., with all tumor DNAs harboring both FeLV-A and rFeLV proviruses. These results provide direct evidence for how FeLV-B species evolve in vivo from FeLV-A and present a new experimental approach for efficient induction of thymic tumors in cats, which should be useful for the study of retroviral lymphomagenesis in this outbred species.

In vivo evolution and selection of recombinant feline leukemia virus species.

Ecotropic feline leukemia viruses subgroup A (FeLV-A) is known to recombine with endogenous FeLV (enFeLV) env elements yielding polytropic FeLV-B viruses. However, scattered nucleotide differences exist between enFeLV env elements and corresponding sequences of exogenous FeLV-B isolates. To address this disparity, we examined recombinant FeLV (rFeLV) viruses obtained from three experimentally-induced feline thymic tumors, along with rFeLVs derived from one naturally-occurring thymic tumor. Two of the three experimental cats were challenged with a FeLV-A/Rickard preparation, while one cat received this FeLV-A along with a mixture of in vitro-generated rFeLVs. The FeLV-A/Rickard preparation employed in this study was shown to be free of detectable rFeLVs since no recombinant products were observed in this preparation following nested PCR analyses. For each of the four tumor DNAs, nucleotide sequence analysis was performed on multiple clones of rFeLV-specific PCR products derived from the surface glycoprotein (SU) portion of the recombinant proviral env gene. Relative to the parental enFeLV sequence used to generate the rFeLVs, a total of 19 nucleotide differences were found scattered within the SU region of the env gene in these in vivo-derived rFeLV clones. Most interestingly, this set of 19 differences led to complete sequence identity with natural FeLV-B isolates. Our results indicate these differences are present early in the in vivo evolution of recombinant viruses, suggesting that rFeLVs harboring these differences are strongly selected. We also present evidence indicating an in vivo selection pattern exists for specific recombinant species containing relatively greater amounts of enFeLV-derived SU sequence. This in vivo selection process appears to be gradual, occurring over the infection timecourse, yielding rFeLV species which have recombination structural motifs similar to those seen in natural FeLV-B isolates.

Downregulation of human FGF8 activity by antisense constructs in murine fibroblastic and human prostatic carcinoma cell systems.

Previously, we described cloning of three alternatively spliced mRNA forms of human FGF8, a, b, and e, of which the b form is the major expressed species in both normal and tumor prostatic epithelial cells. In this report, we describe construction and overexpression of sense and antisense sequences of either the full length FGF8b coding region (215-amino acids or 215aa), 103aa N-terminal part or a smaller N-terminal region (34aa), each including the 23aa putative signal peptide domain, via a retrovirus system. While the morphologic transforming activities of the sense 215aa and 103aa constructs were similar in NIH3T3 cells, 103aa displayed reduced soft agar clonogenic activity. The 34aa construct was practically inert in these assays, although its expression could mimic the ability of 215aa or 103aa in conferring cell growth under reduced serum condition. Overexpression of any of the three constructs in antisense orientation, however, was similarly effective in reversing the morphology and anchorage-independent growth property of FGF8b-transfected NIH3T3 cells. The expression of the antisense 215aa construct significantly reduced the growth rate of the human prostatic carcinoma DU145 cells and inhibited their soft agar clonogenic activity and in vivo tumorigenicity in nude mice. Taken together, these results identify N-terminal portions of FGF8 protein isoform for having the domains necessary for one or more of the biologic effects examined, and suggest that low levels of FGF8 expressed in prostatic epithelial cells may contribute significantly to their growth and tumorigenic properties.

Retrovirus receptor PiT-1 of the Felis catus.

We isolated a cDNA encoding a feline homolog of human PiT-1, a sodium-dependent phosphate symporter which is utilized by gibbon ape leukemia virus (GALV) as a receptor for entry into host cells. The overall homology between the human and feline receptors is 92 and 93% at the nucleotide and deduced amino acid levels, respectively. Hydropathy analyses implied ten potential membrane spanning regions and, in analogy to human and murine homologs, five extracellular and four intracellular loops. Strikingly, the amino acid sequence of the fourth extracellular loop, which is critical for GALV surface glycoprotein binding, has complete identity between the human and feline PiT-1s, while the mouse PiT-1, non-functional for GALV entry, is quite divergent. Ectopic expression of the feline PiT-1 in guinea pig cells, which are non-permissive to feline leukemia virus (FeLV), subgroup B virus, conferred susceptibility to FeLV-B infection confirming the functional ability of the cloned product to serve as a receptor for a natural retrovirus of the homologous species.

p53 protein and gene alterations in pathological stage C prostate carcinoma.

PURPOSE: We determined the extent of p53 immunoreactivity in pathological stage C prostate cancer as well as its correlation to tumor grade, substage, recurrence and proliferation rate. To define better the temporal relationship of p53 nuclear reactivity in prostate cancer p53 immunoreactivity was evaluated in all associated prostatic intraepithelial neoplasia lesions. MATERIALS AND METHODS: Using immunohistochemistry p53 status and proliferation rate were determined in 96 tumors from patients with pathological stage C prostate cancer. Single strand conformational polymorphism in exons 5 to 8 was used in a subset of specimens to assess the association of p53 nuclear accumulation with mutations in the p53 gene. RESULTS: p53 Nuclear reactivity was demonstrated in 10 tumors (10.4%), including 6 with high and 4 with low level nuclear reactivity. Of the tumors 86 (89.6%) had no evidence of p53 immunoreactivity. Each of the 6 tumors with high level p53 reactivity had associated areas of prostatic intraepithelial neoplasia that also showed p53 nuclear reactivity. Furthermore, pathological stage C substage (C1, 2 or 3) was significantly associated with p53 nuclear reactivity (p = 0.04). Proliferation rates were correlated with p53 nuclear reactivity (p = 0.09), while there was no association with tumor grade or recurrence. p53 Gene alterations were noted in 2 of the 3 p53 positive tumors versus no alterations in the p53 gene of 3 p53 negative tumors. CONCLUSIONS: p53 Nuclear accumulation is uncommon in pathological stage C prostate cancer and its presence in premalignant prostatic intraepithelial neoplasia lesions suggests that it may be an early event in a subset of prostate cancers.