Cell Growth & Differentiation, Vol 6, Issue 1 39-49, Copyright © 1995 by American Association of Cancer Research

ARTICLES

In vivo and in vitro serine/threonine phosphorylations of epidermal growth factor receptor upon entry into the cell cycle

I Pillay and SV Sharma
Department of Microbiology and Immunology, University of Tennessee/Memphis 38163.

Protein phosphorylation and dephosphorylation is one of the main mechanisms of cell cycle regulation. This study examines the modulation of epidermal growth factor receptor phosphorylation as cells emerge from quiescence and enter the S phase of the cell cycle. The epidermal growth factor receptor is phosphorylated primarily on serine and threonine, but not on tyrosine residues, in an S phase-dependent fashion, as determined by phosphoamino acid analysis and anti-phosphotyrosine immunoblotting. These phosphorylations occur both in vitro and in vivo and are ligand independent. Some of the sites that are phosphorylated in vitro also appear to be phosphorylated in vivo, as determined by two-dimensional tryptic phosphopeptide analysis. At least one of the in vivo phosphorylation sites is phosphorylated by mitogen-activated protein kinase. Although the mechanism for this ligand-independent phosphorylation is not known, its correlation with emergence from quiescence and entry into the cell cycle suggests that the phosphorylation of epidermal growth factor receptor on serine and threonine residues may have heretofore unknown role(s) in cell cycle entry and progression.

This article has been cited by other articles:

				N. Kiyokawa, E. K. Lee, D. Karunagaran, S.-Y. Lin, and M.-C. Hung Mitosis-specific Negative Regulation of Epidermal Growth Factor Receptor, Triggered by a Decrease in Ligand Binding and Dimerization, Can Be Overcome by Overexpression of Receptor J. Biol. Chem., July 25, 1997; 272(30): 18656 - 18665. [Abstract] [Full Text] [PDF]