ras-induced neuronal differentiation of PC12 cells: possible involvement of fos and jun

Rat pheochromocytoma PC12 cells differentiate to sympathetic neuron-like cells upon treatment with nerve growth factor (NGF). The ras and src transforming proteins also induce PC12 neuronal differentiation and are likely to involve the protein kinase C signal transduction pathway. Using a number of ras mutants, we have established that the domains of oncogenic ras protein responsible for PC12 differentiation overlap those required for cellular transformation. All of the ras mutants that induced neuronal differentiation also activated c-fos transcription through the dyad symmetry element (DSE). Transforming ras protein activated an intracellular signal pathway, which led to the induction of 12-O-tetradecanoyl phorbol-13-acetate-responsive elements; activation was enhanced by coexpression of the proto-oncogene jun (encoding AP-1) and was further augmented by fos. Nuclear extracts from ras-infected PC12 cells showed an increased AP-1 DNA-binding activity. Transcriptional activation by ras was independent of the cyclic AMP-dependent pathway of signal transduction. We propose a possible involvement of fos and jun in ras-induced differentiation.