Divergent Insulin and Platelet-derived Growth Factor Regulation of Focal Adhesion Kinase (pp125) Tyrosine Phosphorylation, and Rearrangement of Actin Stress Fibers

doi:10.1074/jbc.270.17.10199

Divergent Insulin and Platelet-derived Growth Factor Regulation of Focal Adhesion Kinase (pp125) Tyrosine Phosphorylation, and Rearrangement of Actin Stress Fibers (*)

From the (1)

** To whom correspondence should be addressed:
Dept. of Physiology and Biophysics, The University of Iowa, Iowa City, IA 52242
.

Abstract

Insulin treatment of Chinese hamster ovary cells expressing high levels of the human insulin receptor resulted in the tyrosine dephosphorylation of the 125-kDa focal adhesion kinase (pp125). The decrease in pp125 tyrosine phosphorylation paralleled a decrease in the cellular content of actin stress fibers, and these changes were independent of the extracellular matrix on which the cells were grown. The reduction in both pp125 tyrosine phosphorylation and actin stress fibers occurred in an insulin concentration-dependent manner, with significant effects at approximately 0.3 nM and a maximal effect at 3 nM. However, in the continuous presence of insulin, the decreases in the tyrosine phosphorylation state of pp125 and actin stress fiber content were transient. Maximal reduction of pp125 tyrosine phosphorylation was observed following 15 min of insulin treatment, with a return to unstimulated control levels by 60 min. Similarly, actin stress fiber content was maximally reduced by 15 min of insulin treatment and fully recovered by 60 min. In contrast to insulin, platelet-derived growth factor stimulation increased actin stress fiber content and enhanced pp125 tyrosine phosphorylation. These data demonstrate a novel signaling role for insulin in inducing the tyrosine dephosphorylation of pp125 and a concomitant reorganization of actin stress fibers, which underlies at least one aspect of signaling divergence between the insulin and platelet-derived growth factor receptor tyrosine kinases.

Footnotes

↵^§ Recipient of a research fellowship training award from The University of Iowa Cardiovascular Center.
↵^¶ Contributed equally to this study.
↵* This work was supported by research Grants DK33823 and DK25295 from the National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

pp125

125-kDa focal adhesion kinase

PDGF

platelet-derived growth factor

CHO/IR

Chinese Hamster ovary cells expressing the human insulin receptor

SH2

Src homology 2 domain

PBS

phosphate-buffered saline; TRITC-phalloidin; car-boxytetramethylrhodamine isothiocyanate-conjugated phalloidin

FITC-phalloidin

fluorescein isothiocyanate-conjugated phalloidin.