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Vol. 299, Issue 2, 583-592, November 2001
Cell Pathways, Inc., Horsham, Pennsylvania (L.L., H.L., T.U., M.L.,
M.D., G.S., R.P., W.J.T.); and Department of Pharmacology, College of
Medicine, University of South Alabama, Mobile, Alabama (W.J.T.)
These studies report on the activation and induction of cGMP-dependent
protein kinase (PKG) by exisulind and analogs and test the hypothesis
that PKG is involved in the induction of apoptosis in colon tumor
cells. Exisulind and analogs are proapoptotic drugs developed as
inhibitors of cGMP phosphodiesterase gene families 5 and 2 that
have been shown to sustain increased cGMP in SW480 and HT29 cells. At
concentrations that induced apoptosis, both exisulind and CP461
increased PKG activity in SW480 cell supernatants. PKG activation was
dose-dependent and sustained. Activation of PKG by exisulind and
analogs was also seen in the colon tumor cell lines HT29, T84, and
HCT116. The guanylyl cyclase activators YC-1 and guanylin increased PKG
activity secondary to increased cellular cGMP and induced apoptosis in
colon tumor cells. Exisulind and CP461 had no direct effect on purified
PKG activity or on basal and stimulated PKG activity from cell
supernatants. An additional effect of exisulind after 8 h of drug
treatment was a dose-dependent increase of PKG I
protein expression.
-Catenin, a potential new substrate for PKG, whose regulation
influences apoptosis, was phosphorylated by PKG in vitro.
32P-labeled cells treated with exisulind showed
increased phosphorylation of
-catenin. These data indicate that
exisulind and analogs activate and induce PKG, resulting in increased
phosphorylation of
-catenin and enhanced apoptosis to promote colon
tumor cell death.
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