Sustained activation of protein kinase C downregulates nuclear factor-kappaB signaling by dissociation of IKK-gamma and Hsp90 complex in human colonic epithelial cells.
Activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate (PMA) triggers cellular signals that lead to the activation of the transcription factor NF-kappaB (nuclear factor kappaB) in various cell types. In addition to NF-kappaB activation by short-time PMA treatment, here we report that the prolonged exposure of human colonic cancer epithelial cells treated with PMA can also lead to a persistent inhibition of NF-kappaB activation. PMA selectively causes the degradation of IkappaB kinases (IKKs) including IKK-gamma and IKK-beta, and subsequent inhibition of tumor necrosis factor (TNF) induced IKK and NF-kappaB activation in human colon cancer cell line HCT-116, but not in other gastrointestinal tract cells. The use of Ro-318220 and GO-6983, general PKC inhibitors as well as MG-132, a proteasome-specific inhibitor, abrogated PMA-induced degradation of IKK-gamma and recovered the activation of IKK by TNF, suggesting that IKK complex is predominantly degraded by the proteasome pathway in a PKC-dependent manner. We also found that IKK-gamma strongly associates with heat shock protein 90 (Hsp90) in HCT-116 cells, and that this interaction was dramatically reduced after exposure to PMA. Furthermore, high levels of Hsp90 expression and enhanced association with IKK were observed in human colon cancer tissues. Taken together, these results suggest that long-term activation of PKC by PMA inhibits NF-kappaB system in case of colon cancer cells by disrupting the interaction of IKK-gamma with Hsp90, which may represent a novel regulatory mechanism of PKC-dependent cellular differentiation and limited proliferation of colonic epithelial cells.
Park
Kyeong Ah
KA
Department of Pharmacology, Cancer Research Institute, College of Medicine, Chungnam National University, 6 Munhwa-dong, Jung-gu, Daejeon 301-131, Korea.
Byun
Hee Sun
HS
Won
Minho
M
Yang
Keum-Jin
KJ
Shin
Sanghee
S
Piao
Longzhen
L
Kim
Jin Man
JM
Yoon
Wan-Hee
WH
Junn
Eunsung
E
Park
Jongsun
J
Seok
Jeong Ho
JH
Hur
Gang Min
GM
D015153:Blotting, Western; D016923:Cell Death; D002478:Cells, Cultured; D003106:Colon / Q000187:drug effects / Q000378:metabolism*; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism*; D007124:Immunoenzyme Techniques; D047468:Immunoprecipitation; D007668:Kidney / Q000187:drug effects / Q000378:metabolism; D008156:Luciferases; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D009369:Neoplasms / Q000378:metabolism / Q000473:pathology; D011493:Protein Kinase C / Q000378:metabolism*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D018841:HSP90 Heat-Shock Proteins; D016328:NF-kappa B; D008156:Luciferases; D051550:I-kappa B Kinase; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate