C/EBPalpha-dependent induction of glutathione S-transferase zeta/maleylacetoacetate isomerase (GSTzeta/MAAI) expression during the differentiation of mouse fibroblasts into adipocytes.

Western blot analysis of 3T3-L1 adipocyte proteins using an anti-C/EBPalpha antibody detected a 24kD polypeptide in addition to the expected 42 and 30kD isoforms of C/EBPalpha. Mass spectrometric sequencing of the protein following its purification by HPLC and preparative 2D gel electrophoresis identified it as glutathione S-transferase zeta/maleylacetoacetate isomerase (GSTzeta/MAAI). Expression of GSTzeta/MAAI mRNA and protein was induced during the terminal phase of adipogenesis in 3T3-L1 preadipocytes. Ectopic expression of PPARgamma2 in NIH-3T3 fibroblasts exposed to insulin and troglitazone-induced perilipin production, but was incapable of activating GSTzeta/MAAI unless C/EBPalpha was also expressed. Similarly, ectopic expression of C/EBPalpha in PPARgamma +/- or PPARgamma -/- MEFs demonstrated that the C/EBPalpha-dependent induction of GSTzeta/MAAI production was dependent on expression of endogenous PPARgamma. These data suggest a role for GSTzeta/MAAI in mature adipocytes that may be responsive to the thiazolidinedione class of insulin sensitizing PPARgamma ligands.