Phorbol ester-induced G1 phase arrest selectively mediated by protein kinase Cdelta-dependent induction of p21.
Although protein kinase C (PKC) has been widely implicated in the positive and negative control of proliferation, the underlying cell cycle mechanisms regulated by individual PKC isozymes are only partially understood. In this report, we show that PKCdelta mediates phorbol ester-induced G1 arrest in lung adenocarcinoma cells and establish an essential role for this novel PKC in controlling the expression of the cell cycle inhibitor p21. Activation of PKC with phorbol 12-myristate 13-acetate (PMA) in early G1 phase impaired progression of lung adenocarcinoma cells into S phase, an effect that was completely abolished by specific depletion of PKCdelta, but not PKCalpha. Although the PKC effect was unrelated to the inhibition of cyclin D1 expression, PKC activation significantly up-regulated p21 and down-regulated Rb hyperphosphorylation and cyclin A expression. Elevations in p21 mRNA and protein by PMA were mediated by PKCdelta but not PKCalpha. Studies using luciferase reporters also revealed an essential role for PKCdelta in the PMA-induced inhibition of Rb-dependent cyclin A promoter activity. Finally, we showed that the cell cycle inhibitory effect of PKCdelta is greatly attenuated by RNA interference-mediated knock-down of p21. Our results identify a novel link between PKCdelta and G1 arrest via p21 up-regulation and highlight the complexities in the downstream effectors of PKC isozymes in the context of cell cycle progression and proliferation.
Nakagawa
Motonori
M
Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6160, USA.
Oliva
Jose Luis
JL
Kothapalli
Devashish
D
Fournier
Alaina
A
Assoian
Richard K
RK
Kazanietz
Marcelo G
MG
D000230:Adenocarcinoma / Q000473:pathology; D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology; D049109:Cell Proliferation; D019925:Cyclin A / Q000096:biosynthesis; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis* / Q000502:physiology; D015536:Down-Regulation; D016193:G1 Phase / Q000187:drug effects*; D006801:Humans; D007527:Isoenzymes; D008175:Lung Neoplasms / Q000473:pathology; D010703:Phorbol Esters / Q000494:pharmacology*; D010766:Phosphorylation; D051745:Protein Kinase C-delta / Q000378:metabolism*; D034622:RNA Interference; D012333:RNA, Messenger / Q000032:analysis; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
C493956:CDKN1A protein, human; D019925:Cyclin A; D050759:Cyclin-Dependent Kinase Inhibitor p21; D007527:Isoenzymes; D010703:Phorbol Esters; D012333:RNA, Messenger; D051745:Protein Kinase C-delta