Molecular regulation of adipocyte differentiation.

Significant advances have been made recently toward understanding the molecular events that regulate adipocyte differentiation. In vitro models of adipogenesis, such as the 3T3-L1 and F-442A preadipocyte cell lines have proven to be an invaluable resource in elucidating mechanisms of adipocyte differentiation. Subject to modulation by hormonal, dietary, and genetic influences, the differentiation program now appears to be distinctly controlled through the coordinate regulation of transcription factors that predominantly include members of the C/EBP and PPAR families. Increased understanding of these critical factors and how they are regulated will provide insights into adipose tissue development as well as treatment of obesity.

Developmental profile of homeobox gene expression during 3T3-L1 adipogenesis.

The homeobox family of proteins are transcription factors are known to be important during the differentiation of a variety of mammalian tissues, however, expression of the genes encoding homeobox proteins during adipogenesis or in adipose tissue has not been described. To investigate whether members of the homeobox gene family are expressed and regulated during adipocyte differentiation, RNA was isolated from 3T3-L1 preadipocyte cells during the hormonal induced differentiation of this cell line into adipocytes. A reverse transcriptase-polymerase chain reaction strategy using degenerate oligonucleotide primers complementary to the highly conserved homeodomain resulted in the identification of 10 different homeobox genes expressed during 3T3-L1 adipogenesis. One of the clones appears to be unique and 9 of the clones represented known members of the homeobox gene family. Examination of the relative mRNA levels encoding these proteins by ribonuclease protection assay during adipocyte differentiation revealed that 3 members, Hox a4, Hox a7, and Hox d4, are regulated as a function of adipocyte development. Further examination of RNA isolated from murine retroperitoneal adipose tissue revealed that these three regulated homeobox mRNAs are expressed in vivo. Combined, these results suggest that members of the homeobox gene family may serve an important role during the differentiation of adipocytes.

Improved gene transfer into human lymphocytes using retroviruses with the gibbon ape leukemia virus envelope.

Gene-modified lymphocytes have a potential role in the therapy of cancer, infectious diseases, and genetic disorders of the immune system. Current gene therapy protocols involving gene transfer into lymphocytes utilize retroviruses with amphotropic envelope proteins. However, transduction efficiencies in lymphocytes using these viruses are relatively low. A potential strategy to improve gene transfer efficiency is the utilization of alternative retroviral envelopes that target unique receptors on the cell surface. One such alternative retroviral envelope, the gibbon ape leukemia virus (GALV) envelope, targets a distinct surface receptor (GLVR-1) that is 60% homologous but not cross-reactive to the amphotropic receptor (GLVR-2/RAM-1). Understanding the relationship between receptor expression and transduction efficiency is important for designing new strategies to improve gene transfer. Therefore, we compared GLVR-1 and GLVR-2 mRNA levels in lymphocytes and found that GLVR-1 was expressed 8- to 19-fold higher than GLVR-2. We then analyzed whether this enhanced expression of GLVR-1 correlated with increased infectivity of lymphocytes by retroviral vectors that utilize the GALV envelope compared to those that use the amphotropic envelope. We evaluated retroviral vectors packaged with either PA317 or PG13, which express the amphotropic and GALV envelopes, respectively. Lymphocyte transduction with PG13-packaged vectors was 4- to 18-fold higher than that with PA317-packaged vectors. These findings suggest that receptor expression level is an important factor in retroviral-target interactions and that gene transfer into human T lymphocytes should be performed with retroviruses that use the GALV envelope as opposed to retroviruses that use the amphotropic envelope.

In vivo antitumor activity of T cells redirected with chimeric antibody/T-cell receptor genes.

In an effort to broaden the applicability of adoptive cellular immunotherapy toward nonmelanoma cancers, we have designed chimeric antibody/T-cell receptor genes composed of the variable domains from mAbs joined to T-cell receptor-signaling chains. We have demonstrated that T cells retrovirally transduced with these genes can recognize antibody-defined antigens and that this recognition leads to T-cell activation, specific lysis, and cytokine release. In this study, we have examined the in vivo activity of murine T cells transduced with a chimeric receptor gene (MOv-gamma) derived from the mAb MOv18, which binds to a folate-binding protein overexpressed on most human ovarian adenocarcinomas. Nude mice that were given i.p. implants of human ovarian cancer (IGROV) cells were treated 3 days later with i.p. murine tumor-infiltrating lymphocytes (TIL) derived from an unrelated tumor. Mice treated with MOv-gamma-transduced TIL (MOv-TIL) had significantly increased survival compared to mice treated with saline only, nontransduced TIL, or TIL transduced with a control anti-trinitrophenyl chimeric receptor gene (TNP-TIL). In another model, C57BL/6 mice were given i.v. injections of a syngeneic methylcholanthrene-induced sarcoma transduced with the folate-binding protein (FBP) gene. Three days later, mice were treated i.v. with various transduced murine TIL (derived from an unrelated tumor), followed by low-dose systemic interleukin 2. Eleven days after tumor injection, mice were sacrificed, and lung metastases were counted. In multiple experiments, mice receiving MOv-TIL had significantly fewer lung metastases than did mice treated with interleukin 2 alone, nontransduced TIL, or TNP-TIL. These studies indicate that T cells can be gene modified to react in vivo against tumor antigens, defined by mAbs. This approach is potentially applicable to a number of neoplastic and infectious diseases and may allow adoptive immunotherapy against types of cancer not previously amenable to cellular immunotherapy.

Interleukin-2-transduced lymphocytes grow in an autocrine fashion and remain responsive to antigen.

The maintenance of T lymphocytes in vivo after adoptive transfer for immunotherapy requires the systemic administration of interleukin-2 (IL-2), but prolonged administration of IL-2 is associated with substantial toxicity. The constitutive production of IL-2 by T cells may be an alternative method to prolong T-cell survival and potentially augment antitumor responses. To study the effects of constitutive production of IL-2 on the growth and antigen reactivity of a murine T cell, the sperm-whale myoglobin (SWM) specific T-cell line 14.1 was retrovirally transduced with the cDNA for IL-2. Cells that were transduced with vectors without an internal promoter were able to proliferate in the absence of exogenously added IL-2, and to grow in an autocrine fashion. These vectors used an internal ribosomal entry site (IRES) to allow translation of the neomycin phosphotransferase (neor) gene. In contrast, the cells transduced with an IL-2 vector in which the neor gene was under the transcriptional control of an internal SV-40 promoter failed to proliferate or grow in the absence of exogenously added IL-2. The proliferation of the cells growing without IL-2 could be inhibited with antibodies to the IL-2 receptor or to human IL-2, indicating that they were still IL-2 dependent. Despite their autocrine growth, no tumor formation was observed in syngeneic mice injected subcutaneously with the transduced cells, and the cells retained their antigen reactivity and specificity. These results suggest that autocrine growth of T cells for therapy will not interfere with effector function.

Characterization of cytochrome P450 2E1 induction in a rat hepatoma FGC-4 cell model by ethanol.

The hepatic microsomal ethanol-oxidizing system (MEOS) has been well characterized as an important pathway in ethanol metabolism. Cytochrome P450 2E1 (CYP 2E1), the principal component of MEOS, is ethanol inducible and has been implicated in hepatotoxicity associated with alcohol abuse and exposure to organic solvents. Results of chronic in vivo experiments have shown that ethanol induction of hepatic CYP 2E1 occurs by a two-step mechanism. The first step of induction is associated with low blood alcohol concentrations (BACs) and appears to be post-transcriptional, whereas high BACs observed in step-two induction are associated with increased CYP 2E1 gene transcription. The mechanisms underlying these induction steps are under intense investigation. Progress in this area has been limited due to lack of hepatic cell culture models that express CYP 2E1. We report here an in vitro tissue culture cell model, the FGC-4 hepatoma cell line, that exhibits basal levels of CYP 2E1 apoprotein that are inducible by ethanol treatment. Total cellular RNA and microsomal fractions were isolated from control or ethanol-treated confluent cells, and CYP 2E1 mRNA and apoprotein levels were characterized by northern blot or immunoblot analysis, respectively. Initial experiments on isolated microsomes revealed detectable levels of CYP 2E1 apoprotein in control cells that were induced 5-fold in cells treated with 100 mM ethanol for 24 hr. Concentration-response experiments demonstrated that the maximal 24-hr induction in CYP 2E1 apoprotein level was 5-fold and was attained at a concentration of 10 mM ethanol. Interestingly, while the steady-state mRNA levels encoding CYP 2E1 were detectable, they remained unchanged in identically treated cells. Furthermore, there was no observed increase in CYP 2E1 mRNA levels in an extended time course to 72 hr or at higher alcohol concentrations (up to 1500 mM), providing preliminary evidence that the induction is post-transcriptional. The time course of CYP 2E1 apoprotein induction by exposure to 100 mM ethanol demonstrated maximal induction at 8 hr. Measurement of CYP 2E1 apoprotein levels after removal of ethanol from pretreated cells demonstrated the half-life of the apoprotein to be 12.7 hr, in good agreement with previous reports using primary hepatocytes. The half-life of the induced protein after ethanol removal in the presence of cyclohexamide (10 micrograms/mL) was biphasic with a rapid 1.8 hr first phase followed by a slower 44.7 hr second phase.(ABSTRACT TRUNCATED AT 400 WORDS)

Upregulation of tumor necrosis factor-alpha production by retrovirally transduced human tumor-infiltrating lymphocytes using trans-retinoic acid.

The ability of retinoic acid (RA) to upregulate gene expression in human tumor-infiltrating lymphocytes (TIL) transduced with a Moloney murine leukemia virus containing the cDNA encoding tumor necrosis factor (TNF) has been studied. TNF production was increased approximately twofold after treatment with RA. This increase was dose dependent and corresponded to a rise in the level of LTR-driven mRNA measured by Northern analysis. RA did not appreciably increase transcription by the SV40 promoter or increase endogenous TNF production. The effect lasted for 3-6 days following withdrawal of RA. These studies indicate that RA can upregulate LTR-driven gene expression in TIL cells bearing retroviral vectors and may thus be of use in studies of the gene therapy of cancer.

Lysis of ovarian cancer cells by human lymphocytes redirected with a chimeric gene composed of an antibody variable region and the Fc receptor gamma chain.

To expand the spectrum of recognition of effector lymphocytes and to redirect them towards predefined targets, we have altered the specificity of human tumor-infiltrating lymphocytes (TIL) through stable modification with chimeric receptor genes consisting of single-chain antibody variable regions linked to the gamma subunit common to the immunoglobulin (Ig)G and IgE Fc receptors. Using either hapten or ovarian carcinoma-specific monoclonal antibodies, we constructed chimeric receptor genes and retrovirally introduced them into CD8+ TIL. Redirected TIL specifically lysed trinitrophenyl-labeled Daudi or a human ovarian carcinoma cell line (IGROV-1), and secreted granulocyte/macrophage colony-stimulating factor upon stimulation with the appropriate antigen. This strategy may allow new approaches towards the adoptive immunotherapy of cancer in humans.

Functional and molecular characterization of tumor-infiltrating lymphocytes transduced with tumor necrosis factor-alpha cDNA for the gene therapy of cancer in humans.

TNF is effective in causing the regression of selected murine tumors when administered at high concentrations. Therapeutic levels in humans cannot be obtained systemically, however, because of dose-limiting toxicity. The development of immunotherapy with IL-2 and tumor-infiltrating lymphocytes (TIL), which can accumulate at tumor sites in some patients, and of efficient retroviral techniques for gene transfer into eukaryotic cells has allowed new therapeutic approaches using TNF. We have retrovirally transduced human TIL with the gene for TNF in an attempt to deliver high concentrations of TNF to the tumor site without dose-limiting systemic toxicity. Successful gene insertion was confirmed by Southern hybridization in 16 of 16 transduced and selected TIL cultures from 15 different patients, with an estimated 28 to 93% transduced cells within each culture. Transduced selected TIL cultures produced greater amounts of TNF, compared with nontransduced controls, in 11 of 16 cultures evaluated. However, overall production of TNF was > 30-fold lower, compared with a transduced and highly selected tumor cell line control (MEL-TNF). In addition, steady state levels of vector-derived transcript in nine of 10 transduced selected TIL cultures were < 14% of the amount seen in the MEL-TNF control line. In an attempt to increase TNF production, TIL were transduced with a mutated form of TNF containing the IFN-gamma signal peptide in place of the transmembranous region, to enhance secretion into the endoplasmic reticulum. By using this vector, TNF production increased by an average of fivefold. These studies demonstrate that TIL can be genetically modified to express and secrete a protein for use in targeted cancer therapy but that partial expression blockades exist that prevent maximal cytokine production by introduced genes in TIL.