Troglitazone induces p27Kip1-associated cell-cycle arrest through down-regulating Skp2 in human hepatoma cells

Abstract

Increasing evidence has confirmed that ligands for peroxisome proliferator-activated receptor ␥ (PPAR␥) 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 PPAR␥ 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 troglitazonetreated hepatoma cells but not in those cells treated with other PPAR␥ ligands such as pioglitazone and ciglitazone. Quantitative real-time RT-PCR analysis showed that troglitazone downregulated 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.

Prognostic significance of the F‐box protein Skp2 expression in diffuse large B‐cell lymphoma

“…Taken together, re-evaluation of the prognostic significance for p27 expression in malignant neoplasms may be required, paying close attention to its subcellular localization. Although this study included relatively a small number of patients with DLBCL, the results provided deep insights into a new cell-cycle-based strategy for the treatment of DLBCL by precisely targeting Skp2 [29]. …”

CITED2 is a novel direct effector of peroxisome proliferator‐activated receptor γ in suppressing hepatocellular carcinoma cell growth

“…Hep3B cells (80% confluent) were exposed to 100 lM rosiglitazone for various times (3,8,12, or 24 hours). The PPARc/DNA binding activity in nuclear extract was measured using an enzyme-linked immunosorbent assay (ELISA)-based assay (Cayman Chemical, Ann Arbor, Mich).…”

“…6 We and others previously showed that rosiglitazone, a thiazolidinedione-class drug, inhibited hepatocarcinogenesis in vitro and in vivo by inducing cell apoptosis and cell cycle arrest. [7][8][9] However, the PPARc regulatory network and its molecular targets in liver cancer remain largely unknown. In this study, we identified the PPARc downstream targets relevant to carcinogenesis, by using oligonucleotide microarray and gene ontology analysis.…”

Anaphase-promoting complex-dependent proteolysis of cell cycle regulators and genomic instability of cancer cells

“…Skp2 expression is also affected by treatment with retinoic acid, thus altering the ability of p27 to be ubiquitinated (Nakamura et al, 2003). Troglitazone belongs to a group of ligands for peroxisome proliferator-activated receptor gamma (PPARgamma) (Koga et al, 2003). Its antitumoral effects in human hepatoma cells are also due to a decreased gene expression of Skp2 at the mRNA level, leading to the accumulation of p27 (Koga et al, 2003).…”

“…Troglitazone belongs to a group of ligands for peroxisome proliferator-activated receptor gamma (PPARgamma) (Koga et al, 2003). Its antitumoral effects in human hepatoma cells are also due to a decreased gene expression of Skp2 at the mRNA level, leading to the accumulation of p27 (Koga et al, 2003). Targeting the APC by specific inhibitors of the multiple subunits is another very promising approach for a more specific cancer therapy and subject of ongoing research.…”