Abstract 4956: Hsp27 negatively affects Hippo tumor suppressor pathway to regulate cell survival in cancer
Authors: Vahid Sepideh , Thaper Daksh , Zoubeidi Amina 
Published: August 2015

Introduction: Heat shock protein 27 (Hsp27) is a molecular chaperone highly and uniformly expressed in treatment resistant cancers like castrate resistant prostate cancer (CRPC). Hsp27 regulates activity of several oncogenic pathways and its levels correlate with aggressive tumor behaviour, drug resistance and tumor growth. Similarly, dysregulation of the Hippo tumor suppressor pathway, which restricts organ size and cell proliferation, occurs in many types of cancers. In healthy cells, activation of the Hippo pathway results in phosphorylation and cytoplasmic retention of two transcriptional co-activators YAP and TAZ, whereas in cancer YAP/TAZ are free to translocate to the nucleus and increase cell proliferation by promoting the activities of certain transcriptional factors including TEAD1. Inactivation of the Hippo pathway correlates with poor patient outcome and progression of tumors as well as an increase in migration, invasion and metastatic potential of cancer cells. Therefore it is of great importance to establish the correlation between Hsp27 and the Hippo pathway to further discover suitable targets in the treatment of metastatic malignancies.

Methods: Hsp27 gain and loss of function experiments were done on 3 different cancer cell lines and the functional effects on every step of the pathway were monitored via Western blots and Immunofluorescence. Activity of YAP/TAZ after Hsp27 gain and loss of function was monitored by conducting qRT-PCR on TEAD target genes. Transcriptional activity of TEAD1 was also examined using a TEAD-dependent Luciferase reporter construct. Co-immunoprecipitation assay was conducted to analyze protein interactions in the absence/presence of Hsp27. Pathway activity in prostate cancer will be assessed by immunohistochemistry staining of core components of the pathway in patients’ tissue samples.

Results: Our preliminary findings indicate that Hsp27 negatively affects the Hippo pathway. We found that targeting Hsp27 using siRNA in the PC3 (prostate cancer), A549 (lung cancer) and MDA-MB-453 (triple negative breast cancer) leads to increased cytoplasmic retention of p-YAP compared to control siRNA treated cells. Moreover, using immunofluorescence, we observed reduced nuclear translocation of the YAP/TAZ as well as sequestration of these components with cytoplasmic 14-3-3 proteins in siRNA treated PC3 cells. Furthermore inhibition of Hsp27 in prostate and lung tumour cells resulted in suppression of TEAD transcriptional activity analyzed by qRT-PCR and luciferase assay. Hsp27 over-expression experiments yielded opposite results compared to knockdown.

Conclusion: Hsp27 overexpression contributes to inactivation of Hippo pathway. Targeting Hsp27 leads to inactivation of YAP and TAZ onco-proteins affecting cancer cell survival.

Impact: Our data further supports the significance of targeting Hsp27 as a treatment option in cancers, especially metastatic malignancies like CRPC.

Citation Format: Sepideh Vahid, Daksh Thaper, Amina Zoubeidi. Hsp27 negatively affects Hippo tumor suppressor pathway to regulate cell survival in cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4956. doi:10.1158/1538-7445.AM2015-4956