Abstract 1633: Vasodilator-stimulated phosphoprotein promotes β1-integrin-FAK-YAP1/TAZ signaling axis that is required for liver metastasis of GI cancer
Authors: Xiang Xiaoyu , Piao Jinhua , Muthusamy Selvaraj , Wang Lei , Deng Yibin , Huang Shengbing , Urrutia Raul , Lai Jinping , Kang Ningling 
Published: July 2016

Abstract
Introduction: Liver metastasis of pancreatic or colorectal tumors is a major cause of cancer-related death worldwide. When cancer cells reach the liver parenchyma and make a direct contact with the surrounding extracellular matrix (ECM), β1-integrin-FAK signaling is activated allowing the cells attach, migration, and proliferate. Thus, the β1-integrin-FAK signaling axis is key for cancer cells to colonize the liver. However, mechanisms governing β1-integrin activation and how this pathway promotes liver metastasis remain incompletely understood. Aim: We sought to test the hypothesis that vasodilator-stimulated phosphoprotein (VASP), an actin binding protein, regulates the β1-integrin-FAK signaling axis, thereby, promoting liver metastasis of GI cancer. Methods: We employed lentiviruses encoding different VASP shRNAs to knockdown (KD) VASP in human GI cancer cells. We used a Matrigel-based 3-dimensional (3D) cell culture model and intrasplenic tumor injection mouse model to assess the role of VASP for cancer cells in vitro and in vivo. Immunofluorescence (IF) was used to study localization of VASP and active β1-integrin (using Huts-4 antibody), and Western blot analysis (WB) was used to quantitate protein levels of active β1-integrin and YAP1/TAZ. Additionally, we performed VASP immunohistochemistry (IHC) to analyze VASP immunoreactivity in 116 colorectal or pancreatic adenocarcinomas of patients. Results: In the Matrigel-based 3D-culture model, a single cancer cell gave arise to a 3D-cancer spheroid after being cultured for 6-8 days. Using KM12L4, HCT116, or HT29 colorectal cancer cells, and L3.6 or MIA PaCa-1 pancreatic cancer cells, we found that VASP KD reduced the sizes of the 3D-cancer spheroids grown on Matrigel (P&lt;0.05 by t-test for each cell line). IF and WB show that VASP KD reduced levels of Huts-4 (active β1-integrin) in KM12L4, HCT116 colorectal cancer cells and in L3.6, MIA PaCa-1 pancreatic cancer cells. VASP KD also reduced the protein levels of P-FAK and YAP1/TAZ in the 4 cell lines tested. Additionally, YAP1/TAZ protein levels were reduced by PF-228, a FAK inhibitor that blocks the β1-integrin-FAK signaling. In the intrasplenic tumor implanation mouse model, VASP KD suppressed liver metastasis of GI cancer as well as reduced Huts-4 and YAP1 signals of their liver metastases in mice (P&lt;0.05 by t-test). IHC of patient's samples reveals that VASP protein levels were upregulated in cancer cells in 81% of colorectal tumors (51/63) and pancreatic tumors (43/53), with higher VASP levels being associated with liver metastasis of colorectal cancer (P&lt;0.01 by Fisher exact test). Conclusions: VASP promotes ECM-mediated β1-integrin-FAK-YAP1/TAZ signaling axis of GI cancer. We propose that VASP and the β1-integrin-FAK-YAP1/TAZ signaling axis represent potential new therapeutic targets for liver metastasis of pancreatic or colorectal cancer.
Citation Format: Xiaoyu Xiang, Jinhua Piao, Selvaraj Muthusamy, Lei Wang, Yibin Deng, Shengbing Huang, Raul Urrutia, Jinping Lai, Ningling Kang. Vasodilator-stimulated phosphoprotein promotes β1-integrin-FAK-YAP1/TAZ signaling axis that is required for liver metastasis of GI cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1633.