The transcription factor Fos-related antigen 1 is induced by thiazolidinediones during differentiation of 3T3-L1 cells

Thiazolidinediones (TZDs) are a new class of compounds that improve the insulin sensitivity in patients with non-insulin-dependent diabetes mellitus (NIDDM) as well as in rodent models of NIDDM. These compounds act as high-affinity ligands for a member of the nuclear hormone receptor superfamily PPAR gamma, which has been shown to play an important role in adipocyte differentiation. The strong correlation between the antidiabetic activity of TZDs and their ability to activate PPAR gamma has led to suggestions that PPAR gamma or downstream regulated genes mediate the effects of TZDs. To identify novel genes that potentially mediate the effects of TZDs, we have isolated genes that are differentially expressed during thiazolidinedione-stimulated differentiation of 3T3-L1 cells. Using mRNA differential display, we have compared 3T3-L1 cells treated to differentiate in the presence of BRL49653 with untreated 3T3-L1 cells and identified Fos-related antigen 1 (Fra-1), a member of the Fos protein family, as a novel molecular target for BRL49653 action in 3T3-L1 cells. Analysis of all members of the Fos-Jun family of transcription factors showed that Fra-1 was the only member that was specifically up-regulated by BRL49653. The only other member of the Fos-Jun family expressed in differentiated 3T3-L1 cells was JunD and a complex of Fra-1 and JunD was formed on a consensus AP-1 binding element in differentiated 3T3-L1 cells, suggesting that the complex of Fra-1 and JunD may play a role in the stimulation of the differentiation process of 3T3-L1 cells observed after treatment of the cells with insulin sensitizers.