C/EBPα-dependent induction of glutathione S-transferase ζ/maleylacetoacetate isomerase (GSTζ/MAAI) expression during the differentiation of mouse fibroblasts into adipocytes

Western blot analysis of 3T3-L1 adipocyte proteins using an anti-C/EBPα antibody detected a 24 kD polypeptide in addition to the expected 42 and 30 kD isoforms of C/EBPα. Mass spectrometric sequencing of the protein following its purification by HPLC and preparative 2D gel electrophoresis identified it as glutathione S-transferase ζ/maleylacetoacetate isomerase (GSTζ/MAAI). Expression of GSTζ/MAAI mRNA and protein was induced during the terminal phase of adipogenesis in 3T3-L1 preadipocytes. Ectopic expression of PPARγ2 in NIH-3T3 fibroblasts exposed to insulin and troglitazone-induced perilipin production, but was incapable of activating GSTζ/MAAI unless C/EBPα was also expressed. Similarly, ectopic expression of C/EBPα in PPARγ +/− or PPARγ −/− MEFs demonstrated that the C/EBPα-dependent induction of GSTζ/MAAI production was dependent on expression of endogenous PPARγ. These data suggest a role for GSTζ/MAAI in mature adipocytes that may be responsive to the thiazolidinedione class of insulin sensitizing PPARγ ligands.