c-Myc is a transcription factor belonging to the bHLH (basic Helix Loop Helix)-Leucine Zipper family.

It is activated upon various mitogenic signals such as Wnt, Shh and EGF. Through its bHLH domain it can bind to DNA, while the Leucine Zipper domain allows the dimerisation with its partner Max. On one hand, c-Myc can bind to special consensus sequences on the DNA called E-boxes and thus activate a first set of target genes. On the other hand, it can also repress a second set of target genes, those normally controlled by the Miz-1 protein. It does so by binding Miz-1 and thus displacing the p300 co-activator .

By modifying the expression of its target genes, c-Myc activation leads to numerous biological functions. The first to be discovered was its capability to drive cellular proliferation , but it also plays a very important role in regulating cellular growth , apoptosis, differentiation and stem cell self-renewal . c-myc is a very strong proto-oncogene and it is very often found to be upregulated in many types of cancers.