Abstract LB-282: Loss of PTP-PEST Promotes Tumor Invasion, Apoptosis Resistance and Activation of STAT3 in Metastatic Colon Cancer.

Abstract The transcription factor STAT3 is hyperactivated by phosphorylation on Y705 in over 75% of metastatic colon cancers and is associated with EMT, cancer stem cells, survival and chemoresistance. However, the mechanisms of STAT3 inactivation are not well-defined. Here, we identified the protein tyrosine phosphatase, PTP-PEST, as a novel negative regulator of STAT3 in colon carcinoma cells. Using lentiviral-mediated shRNA silencing of PTP-PEST in HCT116 colon carcinoma cells, we show that PTP-PEST knockdown enhances activation of STAT3. Whereas STAT3 is activated by cell attachment to collagen in control cells expressing non-targeting shRNA, PTP-PEST knockdown leads to constitutive, anchorage-independent STAT3 activity. Silencing of PTP-PEST enhances anchorage-independent survival in soft agar, tumor sphere growth and matrigel invasion in vitro. Consistent with increased invasion and survival, PTP-PEST knockdown cells showed enhanced expression of STAT3 target genes, MMP2 and mcl-1. Significantly, PTP-PEST knockdown enhanced apoptosis resistance in three-dimensional matrigel cultures in response to the chemotherapy drug, 5-fluorouracil (5-FU). PTP-PEST knockdown cells treated with 5-FU in 3-D matrigel spheroid cultures showed increased cell viability, reduced caspase-3 activation and enhanced activation of STAT3 relative to non-targeting controls. Furthermore, in subcutaneous nude mouse xenografts, although overall tumor growth was not affected by PTP-PEST knockdown, immunohistochemistry showed reduced caspase-3 and elevated P-STAT3 levels in these tumors. Intrasplenic injection of PTP-PEST knockdown cells in athymic nude mice resulted in enhanced metastatic potential as assessed by quantitative PCR for human DNA content in mouse liver. Finally, reduced PTP-PEST expression correlates with metastasis in clinical specimens from colon cancer patients. Taken together, these findings suggest that down-regulation of PTP-PEST in colon cancer may promote metastasis through increased invasion and apoptosis resistance, mediated, in part, by enhanced activation of STAT3. Citation Format: Rosario Espejo, Yowjiun Jeng, Camille Johnson, Russ Carmical, Allan Brasier, Celia Chao, Sarita K. Sastry. Loss of PTP-PEST promotes tumor invasion, apoptosis resistance and activation of STAT3 in metastatic colon cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-282. doi:10.1158/1538-7445.AM2013-LB-282