No abstract

The CCAAT/enhancer-binding protein ot (C/EBPa) has been implicated in the regulation of adipoblast differentiation. In this study we investigate the potential of C/EBPot to promote the adipogenic program in a variety of fibroblastic cells. Transduction of the C/EBPc~ gene into eight mouse fibroblastic cell lines by retroviruses and DNA transfection generates adipocyte colonies at variable frequencies. The most dramatic results are obtained with NIH-3T3 cells, in which the percentage of G418-resistant colonies that exhibit the adipocyte morphology is reproducibly >50% when the C/EBPc~ gene is transduced by retroviruses. The ability to promote the adipogenic program requires the potent transcriptional activation domain of C/EBPa and is not observed with C/EBPI3. Paradoxically, in spite of its antimitogenic effects, clonal cell lines that stably express high amounts of C/EBPa can readily be generated. Stable expression of C/EBPot in BALB/c-3T3 cells dramatically enhances their ability to terminally differentiate into adipocytes. The results demonstrate that C/EBPa can efficiently promote the adipogenic program in a variety of mouse fibroblastic cells, including those that have little or no spontaneous capacity to undergo adipogenesis.

An environment of high glucose concentration stimulates the synthesis of extracellular matrix (ECM) in mesangial cell (MC) cultures. This may result from a similar increase in intracellular glucose concentration. We theorized that increased uptake, rather than glucose concentration per se is the major determinant of exaggerated ECM formation. To test this, we compared the effects of 35 mM glucose on ECM synthesis in normal MCs with those of 8 mM glucose in the same cells overexpressing the glucose transporter GLUT1 (MCGT1). Increasing medium glucose from 8 to 35 mM caused normal MCs to increase total collagen synthesis and catabolism, with a net 81-90% increase in accumulation. MCs transduced with the human GLUT] gene (MCGT1) grown in 8 mM glucose had a 10-fold greater GLUT1 protein expression and a 1.9, 2.1, and 2.5-fold increase in cell myo-inositol, lactate production, and cell sorbitol content, respectively, as compared to control MCs transduced with bacterial f8-galactosidase (MCLacZ). MCGT1 also demonstrated increased glucose uptake (5-fold) and increased net utilization (43-fold), and greater synthesis of individual ECM components than MCLacZ. In addition, total collagen synthesis and catabolism were also enhanced with a net collagen accumulation 111-118% greater than controls. Thus, glucose transport activity is an important modulator of ECM formation by MCs; the presence of high extracellular glucose concentrations is not necessarily required for the stimulation of matrix synthesis. (J.

Two obstacles limiting the efficacy of nearly all cancer gene therapy trials are low gene transduction efficiencies and the lack of tumor specificity. Recently, a replication-competent, E1B-attenuated adenovirus (ONYX-015) was developed that could overcome these limitations, because it was capable of efficiently and selectively destroying tumor cells lacking functional p53. In an attempt to improve both the efficacy and safety of this approach, we constructed a similar adenovirus (FGR) containing a cytosine deaminase (CD)/herpes simplex virus type-1 thymidine kinase (HSV-1 TK) fusion gene, thereby allowing for the utilization of double-suicide gene therapy, which has previously been demonstrated to produce significant antitumor effects and potentiate the therapeutic effects of radiation. The FGR virus exhibited the same tumor cell specificity and replication kinetics as the ONYX-015 virus in vitro. Importantly, both the CD/5-FC and HSV-1 TK/GCV suicide gene systems markedly enhanced the tumor cell-specific cytopathic effect of the virus, and, as expected, sensitized tumor cells to radiation. By contrast, neither the FGR virus nor either suicide gene system showed significant toxicity to normal human cells. Both suicide gene systems could be used to suppress viral replication effectively, thereby providing a means to control viral spread. The results support the thesis that the three-pronged approach of viral therapy, suicide gene therapy, and radiotherapy may represent a powerful and safe means of selectively destroying tumor cells in vivo.

3T3-L1 adipoblasts that express large amounts of c-Myc cannot terminally differentiate, raising the possibility that Myc inhibits the expression of genes that promote adipogenesis. The CCAAT/enhancer binding protein (C/EBP alpha) is induced during 3T3-L1 adipogenesis when cells commit to the differentiation pathway. Transfection of 3T3-L1 adipoblasts with the gene that encodes C/EBP alpha caused overt expression of the adipocyte morphology. Expression of Myc prohibited the normal induction of C/EBP alpha and prevented adipogenesis. Enforced expression of C/EBP alpha overcame the Myc-induced block to differentiation. These results provide a molecular basis for the regulation of adipogenesis and implicate Myc and C/EBP alpha as pivotal controlling elements.