Introduction: The peptidyl prolyl cis/trans isomerase 1 (PIN1) binds the specific motif comprising a phosphorylated serine or threonine residue preceding a proline (pSer/Thr-Pro) in proteins. PIN1 catalyses isomerisation of the prolyl peptide bond, and subsequently induces conformational changes in the substrates and modulates their functions. Through this mechanism, PIN1 is involved in many cellular events, including cell cycle progression, cell proliferation and cell transformation. Our previous work has revealed that PIN1 is over-expressed in hepatocellular carcinomas (HCC) and enhances hepatocarinogenesis. In this study, we investigated the role of the interaction between PIN1 and Survivin, an inhibitor of apoptosis protein (IAP), in tumorigenesis.

Methods and Results: By co-immunoprecipitation experiments, we found that PIN1 interacted with Survivin via the phosphorylated Thr34-pro motif in Survivin. We then further investigated the effects of PIN1 on the anti-apoptotic function of Survivin using flow cytometry by staining the cells with Annexin V and 7-AAD. Both caspase-9 and caspase-3 activities were also detected by flow cytometry. Through these experiments, over-expression of PIN1 in cervical carcinoma HeLa and human nontumorigenic liver MIHA cells were found to suppress the apoptotic response induced by staurosporine through inactivation of caspase-9 and caspase-3. However, the expression of the PIN1 mutants that are catalytically inactive or defective for protein-binding activity did not result in an inhibition of apoptosis. Likewise, the targeted inhibition of PIN1 by small interfering RNA in HeLa and human hepatoma PLC/PRF/5 cells enhanced the apoptotic response induced by staurosporine through caspase-9 and caspase-3 activation. In addition, down-regulation of Survivin by small interfering RNA in PIN1 over-expressing cells abolished the anti-apoptotic effect induced by PIN1, suggesting that the inhibition of apoptosis is mediated through the PIN1-Survivin interaction.

Conclusion: Since phosphorylation of Thr34 in Survivin suppresses pro-caspase-9 activation by increasing the binding between Survivin and pro-caspase-9, our results suggest that PIN1 may further regulate the anti-apoptotic role of Survivin through modulation of its binding to pro-caspase-9.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1212.

©2010 American Association for Cancer Research
2010