Association of tyrosine phosphorylation of gtpase activating
protein with mitogenic action of serotonin.
Lee, Sheu-Ling, Wei-Wei Wang, and Barry L. Fanburg.
Pulmonary and Critical Care Division, Department of Medicine, New
England Medical Center/Tufts University School of Medicine, Boston,
Massachusetts 02111
APStracts 3:0237C, 1996.
We have previously shown that serotonin (5-HT) induces both
hyperplasia and hypertrophy of pulmonary artery smooth muscle cells
(SMC) but not of endothelial cells (EC) through its high affinity
uptake. The present studies demonstrate rapid enhancement by 5-HT of
Tyr-phosphorylation (Tyr-p) of proteins, including p120, that also
occurs in SMC but not in EC. The p120 protein was identified as
GTPase activating protein (GAP) by immunoprecipitation. Its
phosphorylation occurred within minutes and preceded other events
associated with 5-HT-induced mitogenesis. Tyrosine kinase (TK) and 5
-HT uptake inhibitors and 8-BrcAMP blocked both the 5-HT induced-DNA
synthesis and Tyr-p of GAP. Vanadate elevated DNA synthesis and Tyr-p
of GAP of both control and 5-HT-treated cells. 5-HT failed to alter
Tyr-p of GAP in cellular homogenates, as opposed to intact cells. In
the presence of IBMX, 5-HT inhibited cellular growth, presumably
through its action on 5-HT1A or 5-HT4 receptors and elevation of
cAMP, but this was not associated with an alteration of Tyr-p of GAP.
Similarly, a 5-HT1 or 5-HT2 receptor agonist failed to stimulate Tyr
-p or DNA synthesis of SMC. Stimulation of cellular proliferation and
enlargement produced by 1 _M 5-HT was totally abolished by TK
inhibitors that did not affect 5-HT uptake. These data indicate that
Tyr-phosphorylation of GAP may act as an intermediate signal in 5-HT
-induced mitogenesis of SMC that requires cellular internalization of
5-HT rather than its action on a membrane receptor.
Received 26 December 1995; accepted in final form 8 July 1996.
APS Manuscript Number C760-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996