Abstract 5670: Phospho-PEA-15 sensitizes ovarian cancer cells to paclitaxel by impairing the microtubule-destabilizing effect of SCLIP
Authors: Xie Xuemei , Bartholomeusz Chandra , Kazansky Anna , Ahmed Ahmed A. , Diao Lixia , Baggerly Keith A. , Hortobagyi Gabriel N. , Ueno Naoto T. 
Published: August 2012

Abstract
Paclitaxel is a standard chemotherapeutic agent for ovarian cancer. Resistance of ovarian cancer cells to the drug has been a major obstacle in clinical practice. Thus, alternative approaches are needed to conquer the resistance. PEA-15 (phosphoprotein enriched in astrocytes-15 kDa) regulates cell proliferation and apoptosis. It is phosphorylated at S104 and S116 by Akt, PKC and CaMKII. PEA-15's functions are phosphorylation dependent. Although PEA-15 is known to mediate chemoresistance in breast cancer, the effect of PEA-15 phosphorylation status on chemosensitivity remains unknown. We hypothesized that phospho-PEA-15 (pPEA-15) enhances sensitivity of ovarian cancer cells to paclitaxel. To test our hypothesis, we silenced PEA-15 expression in HEY and OVTOKO cells using siRNA and observed a 14% reduction in apoptosis after paclitaxel exposure. To further determine if PEA-15 phosphorylation contributes to chemosensitivity, we generated SKOV3.ip1-vector (control), SKOV3.ip1-AA (AA, phosphoinhibitory at S104 and S116) and SKOV3.ip1-DD (DD, phosphomimetic at S104 and S116) stable ovarian cancer cells. Compared to the control, DD cells showed a 15% reduction in cell viability (P&lt;0.01), a 92% inhibition in anchorage-independent growth (P&lt;0.001), and a 15% increase in apoptosis after paclitaxel treatment. In contrast, AA cells had a 10% increase in cell viability (P&lt;0.01) and a 20% decrease in apoptosis. These results indicate that pPEA-15 sensitizes ovarian cancer cells to paclitaxel. cDNA microarray analysis revealed that SCLIP, a microtubule (MT)-destabilizing phosphoprotein, was involved in pPEA-15-mediated chemosensitization. The level of SCLIP was 8.5-fold higher at mRNA and 1.6-fold higher at protein in untreated DD cells than in the control and AA cells. Interestingly, exposure to paclitaxel resulted in a 2-fold reduction in SCLIP's protein level and a dramatic increase in its phosphorylation level in DD cells. No similar changes were observed in the control and AA cells. Further, compared to the control and AA cells, higher levels of acetylated and detyrosinated α-tubulin were detected in DD cells exposed to paclitaxel, indicating that MTs are highly stabilized in treated DD cells. These results suggest that reduced expression and increased phosphorylation of SCLIP impair its MT-destabilizing effect, thereby enhancing paclitaxel sensitivity in DD cells. We demonstrate that pPEA-15 mediates chemosensitization in ovarian cancer cells by impairing the MT-destabilizing effect of SCLIP. Our findings highlight the importance of pPEA-15 as a promising target for improving the efficacy of paclitaxel-based chemotherapy in ovarian cancer. Further studies will be conducted to determine: 1) the association between pPEA-15 and SCLIP, and 2) the in vivo effectiveness of pPEA-15 in improving the therapeutic efficacy of paclitaxel in an ovarian xenograft mouse model.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5670. doi:1538-7445.AM2012-5670