Interleukin-6 Signaling in Colorectal Cancer Progression---The Causal Roles of Epithelial- and Endothelial-to-Mesenchymal Transition

Cancer is an increasingly prevalent health problem around the world. The difficulties in cancer treatment are attributed to the metastatic spread of tumor cells, which is the leading cause of cancer mortality. The tumor vascular system including endothelial cells (ECs) is crucial in the activation of angiogenesis and tumor metastasis. Recent studies have indicated that ECs also contribute to tumor progression through the endothelial-to-mesenchymal transition (EndMT), a unique source of cancer associated fibroblast (CAF). In addition, the aberrant activation of epithelial-to-mesenchymal transition (EMT) has also been implicated in the enhanced metastasis. Growing evidence suggest that inflammation promotes EndMT and EMT. A crucial mediator of the tumor-promoting effects of inflammation is interleukin-6 (IL-6). Elevated serum IL-6 has been associated with advanced stages, metastasis and decreased survival of colorectal cancer patients. However, the molecular mechanisms underlying these associations remain to be fully defined. In our preliminary studies, we noted that treatment of HCT116 colorectal cancer cells with IL-6 results in EMT, as evidenced by induction of the mesenchymal markers vimentin, snail, slug and repression of the epithelial marker E-cadherin. IL-6 also increased a-smooth muscle actin (aSMA) and decreased endothelial marker CD31 and Vascular-Endothelial (VE)-Cadherin in human umbilical vascular endothelial cells (HUVECs), suggesting that IL-6 induced EndMT. IL-65s actions on EMT were attenuated in the presence of STAT3 siRNA or PP2, a Src signaling inhibitor. Moreover, IL-6 increased Src and STAT3 phosphorylation in HCT116 and HUVECs. These results suggested that IL-6 signaling may modulate EndMT and EMT that leads to colorectal cancer metastasis. This project aimed to explore the Src-related signaling mechanisms that contribute to IL-6-induced EndMT in HUVECs and EMT in colorectal cancer cells. We will also establish xenograft animal model to characterize the causal role of IL-6-induced EndMT and EMT in tumor metastasis. The central hypothesis of this project is that IL-6 induces EMT in colorectal cancer cells and promotes EndMT in HUVECs via Src signaling, leading to enhanced colorectal cancer progression. Results derived from this proposal may greatly broaden our insight into the understanding of IL-6 associated EndMT and colorectal cancer cell EMT. It will also aid in future development of new IL-6 signaling-targeting strategies in the treatment of colorectal cancer. The hypotheses and specific aims are described below: Specific Aim 1: To investigate the role of Src signaling cascade in IL-6-induced EndMT and EMT in HUVECs and colorectal cancer cells Hypothesis 1: IL-6-induced EndMT in HUVECs and EMT in colorectal cancer cells are mediated by Src signaling cascade Specific Aim 2: To characterize selected transcription factors such as STAT3, Snail, Slug and/or Twist required for IL-6-Src cascade leading to EndMT or EMT Hypothesis 2: Activation of the IL-6-Src cascade causes STAT3, Snail, Slug and/or Twist activation and consequently EndMT or EMT Specific Aim 3: To confirm in vivo that IL-6-induced EndMT and EMT contribute to colorectal cancer progression in xenograft murine models Hypothesis 3: IL-6-induced EndMT and EMT enhances colorectal cancer metastasis andprogression