Functional role of STRAP in colorectal cancer metastasis and in chemoresistance

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Project Summary/Abstract Despite the high rate of recurrence following therapy in colorectal cancer (CRC) and relatively rapid pace of cancer stem-like cell research in solid tumors, researches are impeded due to limited knowledge of the CRC epithelial stem cell hierarchy and complex heterogeneity of the disease. Recent evidences suggest that colorectal tumors comprise a small fraction of cancer stem-like cells that seed the tumor bulk and may be responsible for metastasis, resistance to therapy, and tumor recurrence. Others (Buess et al., 2004) and we (Halder et al, 2006) have shown that STRAP (Serine Threonine Kinase Receptor Associated Protein) is significantly upregulated in colorectal carcinomas including metastases, and upregulation of STRAP in CRC patients contributes to worse survival with chemotherapy, suggesting its potential contribution to the aggressive disease and chemoresistance. Therefore, understanding the functional role of STRAP in CRC metastasis, in the maintenance of cancer stem-like cells, and in chemoresistance is very crucial. We identified the novel WD-domain containing protein called STRAP that binds with both TGF-ß receptor complex and Smad7, and inhibits TGF-ß signaling. We have shown that STRAP is upregulated in several cancers, induces epithelial-to-mesenchymal (EMT) transition (Kashikar et al, 2010), and promotes cell growth and tumorigenicity in vitro in a TGF-ß-independent manner (Halder et al, 2006). Our preliminary data suggest that STRAP regulates the expression of MMPs, and Wnt/ß-catenin and Notch signaling. To determine the role of STRAP in vivo, we have recently generated Strap knock out mice, which is embryonic lethal at 9.5 dpc. Azoxymethane treatment of the Strap heterozygous mice produces fewer and smaller tumors when compared with wild type mice. To study the effect of STRAP in an organ specific manner, we have also generated conditional knock out mice using the Cre-lox approach. Therefore, little is known about the TGF-ß- independent role of STRAP in intestinal cancer metastasis and chemoresistance. Based on the background information and our preliminary results, we have formulated the following hypotheses: Upregulation of STRAP in colorectal cancer plays an active role in metastasis and its functional interaction with Wnt/ß-catenin and Notch pathway is involved in colon cancer stem-like cell self-renewal and chemoresistance. The following Specific Aims are proposed to test these hypotheses: Aim 1: Determine the mechanism of how STRAP contributes to colorectal cancer metastasis. Aim 2: Determine the role of STRAP in the maintenance and self- renewal of colon cancer stem-like cells. Aim 3: Determine the role of STRAP in regulating chemoresistance of colorectal cancer. Impact: Despite the development of treatment regimens, metastasis remains the most critical determinant of survival, as median survival for patients with metastatic colorectal cancer is 5 months among veterans. Moreover, drug resistance and relapse of cancers are the other two critical survival-influencing factors of CRC. Completion of the proposed aims will uncover the novel function of STRAP in CRC metastasis, stem-like cell self-renewal, and drug resistance. The outcome of this project will provide strong translational potential to develop therapeutics by targeting STRAP for this un-targetable aggressive disease. This basic and preclinical biomedical research will include two priority research areas of specific interest to BLR&D, risky behavior related to smoking and women's health (RFA# BX-16-001).