Activation of protein kinase G Increases the expression of p21CIP1, p27KIP1, and histidine triad protein 1 through Sp1.
The anticancer role of cyclic guanosine 3',5'-monophosphate (cGMP)-dependent protein kinase G (PKG) has become of considerable interest, but the underlying mechanisms are not fully established. In this study, we examined the effects of activation of PKG on the expression of three tumor suppressor proteins in human SW480 colon cancer cells. Our results revealed that treatment with cell permeable cGMP derivatives, or the cGMP phosphodiesterase inhibitor sulindac sulfone (exisulind, aptosyn, hereafter called exisulind) led to increased expression of the tumor suppressor proteins p21(CIP1), p27(KIP1), and Histidine triad protein 1 (HINT1), and their corresponding mRNAs. Overexpression of PKG Ibeta also caused increased expression of the p21(CIP1), p27(KIP1), and HINT1 proteins. Both the p21(CIP1) and p27(KIP1) promoters contain Sp1 binding sites and they were activated by PKG in luciferase reporter assays. Specific Sp1 sites in the p21 and p27 promoters were sufficient to mediate PKG-induced luciferase reporter activity, suggesting an interaction between Sp1 and PKG. Indeed, we found that PKG can phosphorylate Sp1 on serine residue(s) and this resulted in transcriptional activation of Sp1. Knockdown of Sp1 expression with siRNA inhibited the increased expression of p21(CIP1), p27(KIP1), and HINT1 induced by the cGMP derivative 8-pCPT-cGMP in SW480 cells. These novel effects of PKG activation on the expression of three tumor suppressor genes may explain, at least in part, the anticancer effects of activation of PKG. They also provide a rationale for further developing activators of PKG for the prevention and treatment of cancer.
Cen
Bo
B
Herbert Irving Comprehensive Cancer Center, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA.
Deguchi
Atsuko
A
Weinstein
I Bernard
IB
D001665:Binding Sites; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism* / Q000502:physiology*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics* / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004789:Enzyme Activation / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics* / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D016329:Sp1 Transcription Factor / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
C493956:CDKN1A protein, human; C436291:CDKN1B protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; C063306:HINT1 protein, human; D047908:Intracellular Signaling Peptides and Proteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D016329:Sp1 Transcription Factor; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017869:Cyclic GMP-Dependent Protein Kinases