Troglitazone induces p27Kip1-associated cell-cycle arrest through down-regulating Skp2 in human hepatoma cells.
Increasing evidence has confirmed that ligands for peroxisome proliferator-activated receptor gamma (PPARgamma) exhibit antitumoral effects through inhibition of cell proliferation and induction of cell differentiation in several malignant neoplasms. Recently, we have documented the accumulation of a cyclin-dependent kinase inhibitor, p27(Kip1), as well as an unexpected accumulation in cyclin E in G1-arrested human hepatoma cells treated with the PPARgamma ligand troglitazone. Simultaneous accumulations in both p27(Kip1) and cyclin E are known to be characteristic phenotypes in cells derived from mice lacking Skp2, an F-box protein component of the SCF ubiquitin-ligase complex. Thus, the aim of the present study was to assess whether Skp2 might be involved in the down-regulation of p27(Kip1) in troglitazone-treated human hepatoma cells. A striking decrease in Skp2 expression and a reciprocal increase in p27(Kip1) expression were found in troglitazone-treated hepatoma cells but not in those cells treated with other PPARgamma ligands such as pioglitazone and ciglitazone. Quantitative real-time RT-PCR analysis showed that troglitazone down-regulated Skp2 at the mRNA levels. Consistently, ectopic overexpression in Skp2 brought resistance to troglitazone, resulting in a decreased population of arrested cells at the G1 phase compared with that in the mock-transfected cells. In surgically resected hepatocellular carcinoma (HCC) tissue, an increased expression in Skp2 was found in both the moderately differentiated HCCs and the poorly differentiated HCCs. In conclusion, troglitazone attenuated Skp2 expression, thereby promoting p27(Kip1) accumulation in human hepatoma cells. This therapeutic potential of the ligand may lead to new cell-cycle-based antitumor strategies for advanced HCCs.
Koga
Hironori
H
Second Department of Medicine and Research Center for Innovative Cancer Therapy, Kurume University, Japan. hirokoga@med.kurume-u.ac.jp
Harada
Masaru
M
Ohtsubo
Motoaki
M
Shishido
Shoichiro
S
Kumemura
Hiroto
H
Hanada
Shinichiro
S
Taniguchi
Eitaro
E
Yamashita
Katsumi
K
Kumashiro
Ryukichi
R
Ueno
Takato
T
Sata
Michio
M
D000970:Antineoplastic Agents / Q000494:pharmacology*; D042846:CDC2-CDC28 Kinases; D006528:Carcinoma, Hepatocellular; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D002839:Chromans / Q000494:pharmacology*; D019927:Cyclin E / Q000235:genetics / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D016193:G1 Phase / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008113:Liver Neoplasms; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D044786:S-Phase Kinase-Associated Proteins; D013844:Thiazoles / Q000494:pharmacology*; D045162:Thiazolidinediones; D000077288:Troglitazone; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism
D000970:Antineoplastic Agents; C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D002839:Chromans; D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D012333:RNA, Messenger; D044786:S-Phase Kinase-Associated Proteins; D013844:Thiazoles; D045162:Thiazolidinediones; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D000077288:Troglitazone