Role of growth factors and their receptors in the control of normal cell proliferation and cancer.

Polypeptide growth factors modulate proliferation of nontransformed cells in vivo and in vitro, while cancer appears to reflect an alteration of growth-regulatory mechanisms found in normal cells. Some provocative clues for understanding the cellular biochemical events involved in growth regulation have come from the study of transforming retroviral oncogenes. Some of these oncogenes encode proteins similar to those implicated in growth factor-mediated growth control. Of particular interest is the study of growth factor receptors present on the cell surface, which are cellular homologs of members of the largest class of oncogenes, the tyrosine kinases. It is likely that the study of the interplay of growth factors, and the molecular basis of pleiotropic effects elicited by growth factors, will help to explain how growth factor-signaling pathways affect gene expression and cell division in normal and transformed states.