title: Protein kinase G type Ialpha activity in human ovarian cancer cells significantly contributes to enhanced Src activation and DNA synthesis/cell proliferation.
abstract: Previously, we showed that basal activity of nitric oxide (NO)/cyclic GMP (cGMP)/protein kinase G (PKG) signaling pathway protects against spontaneous apoptosis and confers resistance to cisplatin-induced apoptosis in human ovarian cancer cells. The present study determines whether basal PKG kinase activity regulates Src family kinase (SFK) activity and proliferation in these cells. PKG-Ialpha was identified as predominant isoform in both OV2008 (cisplatin-sensitive, wild-type p53) and A2780cp (cisplatin-resistant, mutated p53) ovarian cancer cells. In both cell lines, ODQ (inhibitor of endogenous NO-induced cGMP biosynthesis), DT-2 (highly specific inhibitor of PKG-Ialpha kinase activity), and PKG-Ialpha knockdown (using small interfering RNA) caused concentration-dependent inhibition of DNA synthesis (assessed by bromodeoxyuridine incorporation), indicating an important role of basal cGMP/PKG-Ialpha kinase activity in promoting cell proliferation. DNA synthesis in OV2008 cells was dependent on SFK activity, determined using highly selective SFK inhibitor, 4-(4'-phenoxyanilino)-6,7-dimethoxyquinazoline (SKI-1). Studies using DT-2 and PKG-Ialpha small interfering RNA revealed that SFK activity was dependent on PKG-Ialpha kinase activity. Furthermore, SFK activity contributed to endogenous tyrosine phosphorylation of PKG-Ialpha in OV2008 and A2780cp cells. In vitro coincubation of recombinant human c-Src and PKG-Ialpha resulted in c-Src-mediated tyrosine phosphorylation of PKG-Ialpha and enhanced c-Src autophosphorylation/activation, suggesting that human c-Src directly tyrosine phosphorylates PKG-Ialpha and the c-Src/PKG-Ialpha interaction enhances Src kinase activity. Epidermal growth factor-induced stimulation of SFK activity in OV2008 cells increased PKG-Ialpha kinase activity (indicated by Ser(239) phosphorylation of the PKG substrate vasodilator-stimulated phosphoprotein), which was blocked by both SKI-1 and SU6656. The data suggest an important role of Src/PKG-Ialpha interaction in promoting DNA synthesis/cell proliferation in human ovarian cancer cells. The NO/cGMP/PKG-Ialpha signaling pathway may provide a novel therapeutic target for disrupting ovarian cancer cell proliferation.
authors.affiliation: Nevada Cancer Institute, Las Vegas, Nevada.
authors.forename: Elaine L
authors.initials: EL
authors.lastname: Leung
authors.forename: Janica C
authors.initials: JC
authors.lastname: Wong
authors.forename: Mary G
authors.initials: MG
authors.lastname: Johlfs
authors.forename: Benjamin K
authors.initials: BK
authors.lastname: Tsang
authors.forename: Ronald R
authors.initials: RR
authors.lastname: Fiscus
mesh_terms: D000081247:CSK Tyrosine-Protein Kinase; D002277:Carcinoma / Q000201:enzymology* / Q000235:genetics; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D006152:Cyclic GMP / Q000378:metabolism; D062965:Cyclic GMP-Dependent Protein Kinase Type I; D017869:Cyclic GMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D004261:DNA Replication / Q000235:genetics*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D006801:Humans; D009569:Nitric Oxide / Q000378:metabolism; D010051:Ovarian Neoplasms / Q000201:enzymology* / Q000235:genetics; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D019061:src-Family Kinases
chemical_list: D004791:Enzyme Inhibitors; D009569:Nitric Oxide; D004815:Epidermal Growth Factor; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; C000631346:CSK protein, human; D062965:Cyclic GMP-Dependent Protein Kinase Type I; D017869:Cyclic GMP-Dependent Protein Kinases; C569718:PRKG1 protein, human; D006152:Cyclic GMP