AJP - Endocrinology and Metabolism, Vol 263, Issue 2 E205-E209, Copyright © 1992 by American Physiological Society
PDGF induces tyrosine phosphorylation in osteoblast-like cells: relevance to mitogenesis
G. Davidai, A. Lee, I. Schvartz and E. Hazum
Division of Biology, Glaxo Research Institute, Research Triangle Park, North Carolina 27709.
We have studied the association between protein tyrosine phosphorylation
and the mitogenic effect induced by platelet-derived growth factor (PDGF)
in the osteoblast-like cell line MC3T3-E1. PDGF caused a dose-dependent
increase in [3H]thymidine incorporation in MC3T3-E1 cells, reaching a
plateau at 10 ng/ml. Vanadate, a potent phosphatase inhibitor, induced a
twofold increase in thymidine incorporation. The combination of vanadate
and PDGF resulted in a dose-dependent synergistic effect on thymidine
incorporation. Genistein, a tyrosine kinase inhibitor, inhibited in a
dose-related manner (2-20 microM) the mitogenic effect induced by either
PDGF or the combination of vanadate and PDGF. These observations suggest
that tyrosine kinases are involved in mediating the mitogenic effect of
PDGF in these cells. PDGF treatment of MC3T3-E1 cells and subsequent
immunoblotting with antiphosphotyrosine antibodies resulted in a marked
phosphorylation of the PDGF receptor. Vanadate had a lesser effect on PDGF
receptor phosphorylation, but given together with PDGF it induced a
significant increase in the intensity of receptor phosphorylation.
Preincubation with genistein abrogated these effects. Taken together, these
findings indicate a direct correlation between thymidine incorporation and
tyrosine phosphorylation in MC3T3-E1 cells and suggest that tyrosine
phosphorylation plays a role in PDGF-induced mitogenic activity in
osteoblast-like cells.
