MYC and pheochromocytoma: MYC requires its basic helix-loop-helix leucine zipper (bHLHLZ) dimerization partner MAX for its transcriptional and oncogenic activities [1,2,4,76] however, a rat pheochromocytoma cell line (PC-12) does not express MAX mRNA or protein, yet retains a transcriptionally functional MYC protein [77,78].