Transcriptional activation by the Myc oncoprotein.

The Myc transcription factor functions as a downstream effector of most mitogenic signals. Myc is synthesized rapidly in response to extracellular mitogenic signals, and blocking Myc induction abolishes or at least severely attenuates any mitogenic response. Furthermore, ectopic Myc expression can often bypass the requirement for extracellular signals for entry into S phase. Thus, the Myc transcription factor is both necessary and in many ways sufficient to promote the growth of diverse cell types. Given this potent biological activity, it is not surprising that mutations in the myc gene are among the most frequent in human and animal cancers. Understanding the molecular basis of Myc function has been a central issue in the fields of cancer biology and signal transduction for 20 years.