Abstract 4502: Heat shock protein 47 maintains cancer cell survival through its inhibitory effect on ER stress sensor IRE1alpha activity

Abstract

Abstract Background and aims: Heat shock protein 47 (HSP47) is a collagen-specific chaperone and is expressed in fibroblasts and stromal cells that constitutively produce and secrete several types of collagens. In a tumor microenvironment, HSP47 is also highly expressed in cancer-associated fibroblasts, involving in the tumorigenesis through construction of the extracellular matrix. Intriguingly, HSP47 is expressed in cancer cells in which almost no collagen is synthesized, and its expression has been reported to be associated with malignant grade of gliomas and poor prognosis of breast cancer. However, the functional significance of HSP47 in cancer cells remains unclear. Thus, the purpose of the present study was to clarify the molecular mechanism by which HSP47 maintains cancer cell survival and to explore the possibility of HSP47 becoming a therapeutic target for tumors. Methods: Expression of HSP47, collagen type I and collagen type IV mRNAs and proteins was examined in 13 human cancer cell lines by real-time PCR and western blotting. After transfection of colorectal cancer cells with HSP47 siRNA, cell proliferation, morphological features and apoptosis were examined by flow cytometric analysis, transmission electron microscopy and western blotting. To determine whether silencing of HSP47 expression suppresses tumorigenicity, an HSP47 siRNA-liposome complex was intratumorally injected in colorectal tumor-bearing Balb/c nu/nu mice. Results: HSP47 mRNA and protein, but not collagen type I and collagen type IV, were expressed in 13 human cancer cell lines. Silencing of HSP47 in colorectal cancer cells markedly caused apoptosis. Electron microscopic analysis revealed that dilation of the endoplasmic reticulum (ER) in colorectal cancer cells was induced by silencing of HSP47, similar to that evoked by ER stress. Furthermore, activation of the ER stress sensor inositol-requiring protein 1alpha (IRE1alpha)/apoptosis signal-regulating kinase 1/Jun-N-terminal kinase signaling pathway was responsible for apoptosis of colorectal cancer cells by silencing of HSP47. Immunoprecipitation of HSP47 and IRE1alpha showed that HSP47 forms a complex with IRE1alpha in colorectal cancer cells under a basal condition. Persistent activation of IRE1alpha by silencing of HSP47 triggered an increase in reactive oxygen species in colorectal cancer cells followed by activation of the other ER stress sensors PKR-like ER kinase and activating transcription factor 6alpha, resulting in activation of the subsequent apoptosis-associated signaling pathway. Finally, treatment of colorectal cancer cell-bearing mice with HSP47 siRNA resulted in complete regression of colorectal tumors. Conclusion: These results suggest that HSP47 sustains cancer cell survival through its inhibitory effect on IRE1alpha activity and that targeted disruption of HSP47 might become a therapeutic modality for tumors. Citation Format: Akihiro Yoneda, Norio Takei, Kaori Sawada, Marina Kosaka, Kenjiro Minomi, Yasuaki Tamura. Heat shock protein 47 maintains cancer cell survival through its inhibitory effect on ER stress sensor IRE1alpha activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4502. doi:10.1158/1538-7445.AM2017-4502