mdm-2 gene amplification in 3T3-L1 preadipocytes

In this study the regulation of the murine double minute-2 (mdm-2) gene was examined in NIH 3T3-L1 preadipocytes. The 3T3-L1 cell line, under proper c onditions, has the capacity to differentiate from fibroblasts into adipocyt es [15]. A recent report demonstrated that mdm-2 overexpression could block myogenesis [12]. While examining the regulation of the mdm-2 gene during a dipogenesis, it was discovered that 3T3-L1 cells possess a 36-fold elevatio n of mdm-2 mRNA relative to A31 cells, another immortalized Balb/c 3T3 fibr oblast cell line that lacks the capacity to differentiate. Based on Souther n blot analysis, the increase in mdm-2 mRNA was the result of a mdm-2 gene amplification. The level of Mdm-2 protein in undifferentiated 3T3-L1 cells was elevated relative to A31 fibroblasts and resulted from translation of m RNA transcripts initiating from the p53-independent P1 promoter. We also ex amined how mdm-2 and p53 levels changed as undifferentiated fibroblasts con verted to adipocytes. While mdm-2 mRNA levels remained elevated, p53 mRNA, protein, and DNA-binding activity decreased. These results suggest that adi pogenesis is unaffected by elevated Mdm-2 levels and that the overexpressio n of mdm-2 mRNA is predominantly p53 independent.