DEF-1, a Novel Src SH3 Binding Protein That Promotes Adipogenesis in Fibroblastic Cell Lines

Abstract

The Src homology 3 (SH3) motif is found in numerous signal transduction proteins involved in cellular growth and differentiation. We have purified and cloned a novel protein, DEF-1 (differentiation-enhancing factor), from bovine brain by using a Src SH3 affinity column. Ectopic expression of DEF-1 in fibroblasts resulted in the differentiation of a significant fraction of the culture into adipocytes. This phenotype appears to be related to the induction of the transcription factor peroxisome proliferator-activated receptor γ (PPARγ), since DEF-1 NIH 3T3 cells demonstrated augmented levels of PPARγ mRNA and, when treated with activating PPARγ ligands, efficient induction of differentiation. Further evidence for a role for DEF-1 in adipogenesis was provided by heightened expression of DEF-1 mRNA in adipose tissue isolated from obese and diabetes mice compared to that in tissue isolated from wild-type mice. However, DEF-1 mRNA was detected in multiple tissues, suggesting that the signal transduction pathway(s) in which DEF-1 is involved is not limited to adipogenesis. These results suggest that DEF-1 is an important component of a signal transduction process that is involved in the differentiation of fibroblasts and possibly of other types of cells.

ACKNOWLEDGMENTS

We are indebted to A. Gashler, J. Chan, I. Aksoy, C. Furman, W. Haser, and A. Yamakawa for advice, helpful discussions, and contributions of unpublished data. We are grateful to W. S. Lane, R. Robinson, V. Bailey, J. Neveu, T. Addona, and E. Spooner of the Harvard Microchemistry Facility for their expertise in the HPLC, mass spectrometry, and peptide sequencing. We also thank the members of the Dana-Farber core facility for performing all the DNA sequencing described.

This work was supported by an NIH postdoctoral fellowship to F.J.K. (CA09134) and NIH grants to B.M.S. (R37DK31405) and T.M.R. (CA43803).