C-MYC DOES NOT REQUIRE MAX FOR TRANSCRIPTIONAL ACTIVITY IN PC-12 CELLS

The c-Myc proto-oncogene is a basic helix-loop-helix leucine zipper (b /HLH/LZ) protein that participates in cellular growth and differentiat ion. The expression of c-Myc mRNA is rapidly induced by nerve growth f actor (NGF) and epidermal growth factor (EGF) in PC-12 pheochromocytom a cells. In most cell types, c-Myc forms a sequence-specific DNA bindi ng complex with the stable, constitutively expressed Max. This complex can function as a transcriptional regulator. We show here that the ex pression of Max mRNA or protein was not detected in PC-12 cells. Never theless, treatment of PC-12 cells with NGF and serum caused an increas e in the expression of the c-Myc protein and the transcription of a re porter gene linked to the Myc/Max DNA binding site. Transcription from the same reporter gene is stimulated by overexpression of c-Myc. Thes e results suggest that c-Myc protein functions as a transcriptional re gulator in PC-12 cells despite the lack of Max protein. Therefore, Myc /Max complexes may not be an absolute requirement for Myc-dependent ge ne expression. (C) 1994 Academic Press, Inc.