Analysis of Fos protein complexes and Fos-related antigens by high-resolution two-dimensional gel electrophoresis.

Protein complexes containing the c-fos protein (Fos) and (Fos)-related antigens were isolated from serum-stimulated fibroblasts and from nerve growth factor plus benzodiazepine-treated pheochromocytoma (PC12) cells, and investigated by high-resolution two-dimensional gel electrophoresis. The results show that Fos is complexed with a basic 39-kDa protein (p39) in fibroblasts, and primarily with an acidic 40-kDa protein (p40) in PC12 cells. Whole cells lysates from both cell types contain p40, suggesting that the interaction of Fos and other cellular proteins is dependent on the differentiated state of the cell. In addition to p39 and p40, a heterogeneous population of polypeptides of approximately 48 kDa are present in Fos complexes isolated from non-denatured extracts of either cell type. These proteins may represent a minor class of Fos-binding proteins. Analysis of extracts prepared under denaturing conditions using antisera raised against a Fos peptide (amino acids 127-152) reveals a series of Fos-related antigens. These antigens are induced, some with a slower kinetics than Fos, in fibroblasts and PC12 cells. Thus, c-fos may represent a marker for a family of genes, some of which are antigenically related, that are part of an early cellular transcriptional response to diverse extracellular stimuli.