Carcinogenesis Advance Access originally published online on January 23, 2009
Carcinogenesis 2009 30(4):671-681; doi:10.1093/carcin/bgp027
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The prolyl isomerase Pin1 interacts with a ribosomal protein S6 kinase to enhance insulin-induced AP-1 activity and cellular transformation
College of Pharmacy, Chosun University, Gwangju 501-759, South Korea
1 Hormel Institute, University of Minnesota, Austin, MN 55912, USA
* To whom correspondence should be addressed. Tel: +82 62 230 6379; Fax: +82 62 230 6379; Email: chs{at}chosun.ac.kr
Phosphorylation of proteins on serine or threonine residues that immediately precede proline (pSer/Thr-Pro) is specifically catalyzed by the peptidyl-prolyl cis–trans isomerase Pin1 and is a central signaling mechanism in cell proliferation and transformation. Although Pin1 is frequently overexpressed in hepatocellular carcinoma (HCC), the molecular mechanism of Pin1 in HCC has not been completely elucidated. Here, we show that Pin1 interacts with p70S6K in vitro and ex vivo. Overexpression of Pin1 resulted in enhanced p70S6K phosphorylation induced by insulin in SK-HEP-1 cells. In contrast, Pin1–/– mouse embryonic fibroblasts (MEFs) exhibited significantly decreased insulin-induced p70S6K phosphorylation compared with Pin1+/+ MEFs. Furthermore, Pin1 enhanced the insulin-induced extracellular signal-regulated protein kinase (ERK)1/2 phosphorylation through its interaction with p70S6K, whereas the inhibition of p70S6K activity by rapamycin suppressed insulin-induced ERK1/2 phosphorylation in SK-HEP-1 cells. Hence, Pin1 affected activator protein-1 activity through p70S6K-ERK1/2 signaling in SK-HEP-1 cells. Most importantly, Pin1-overexpressing JB6 Cl41 cells enhanced neoplastic cell transformation promoted by insulin much more than green fluorescent protein-overexpressing JB6 Cl41 control cells. These results imply that Pin1 amplifies insulin signaling in hepatocarcinoma cells through its interaction with p70S6K, suggesting that Pin1 plays an important role in insulin-induced tumorigenesis and is a potential therapeutic target in hepatocarcinoma.
Abbreviations: AP-1, activator protein-1; DMEM, Dulbecco's modified Eagle medium; ERK, extracellular signal-regulated protein kinase; FBS, fetal bovine serum; GFP, green fluorescent protein; GSK3, glycogen synthase kinase 3; HCC, hepatocellular carcinoma; HRP, horseradish peroxidase; MEF, mouse embryonic fibroblast; MEK, mitogen-activated protein kinase kinase; mTOR, mammalian target of rapamycin; PI3K, phosphatidyl-inositide-3-OH-kinase; siRNA, small interfering RNA; WT, wild type
These authors contributed equally to this work. Received October 7, 2008; revised January 7, 2009; accepted January 16, 2009.
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