OBJECTIVE:
Vasodilator-stimulated phosphoprotein (VASP) was identified as a
substrate for cGMP-dependent
protein kinase (PKG) and cAMP-dependent
protein kinase (PKA). It is preferentially
phosphorylated at serine239 by PKG, whereas serine157 is a preferred
phosphorylation site for PKA. In addition, serine157 is
phosphorylated by PKC in response to serum. We have investigated the effects of VASP and VASP
phosphorylation at serine157 and serine239 on
smooth muscle cell (SMC) proliferation and
nitric oxide (NO)-mediated
growth inhibition. METHODS AND RESULTS:
Aortic SMCs
derived from VASP-deficient
mice were transduced with
retroviral vectors encoding either
wild-type VASP or VASP
mutants (S157A-VASP and S239A-VASP), in which serine157 and serine239, respectively, were replaced by a nonphosphorylatable
amino acid,
alanine. Expression of wt-VASP and S239A-VASP significantly increased proliferation, whereas expression of S157A-VASP was
inhibitory. Expression of S239A-VASP rendered SMCs less sensitive to
growth inhibition by the NO donor,
S-nitroso-n-acetylpenicillamine, when compared with cells expressing wt-VASP. Similar effects were observed in cultured rat SMCs in which wt-VASP, S157A-VASP, and S239A-VASP were expressed. CONCLUSIONS: Our data suggest that VASP
phosphorylation at serine157 is required for the growth-stimulatory effect of VASP in SMCs, whereas VASP
phosphorylation at serine239 is involved in the growth
inhibitory effects of NO on SMCs.
