Xiang, Xiaoyu

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<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<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<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.

Platelet-derived growth factor (PDGF) and transforming growth factor-β (TGF-β) signaling are required for hepatic stellate cell (HSC) activation under pathological conditions such as liver metastatic tumor growth. These two signaling pathways are functionally divergent; PDGF signaling promotes proliferation and migration of HSCs, and TGF-β induces transdifferentiation of quiescent HSCs into myofibroblasts. Although PDGF signaling is implicated in TGF-β-mediated epithelial mesenchymal transition of tumor cells, the role of PDGF receptors in TGF-β activation of HSCs has not been investigated. Here we report that PDGF receptor-α (PDGFR-α) is required for TGF-β signaling of cultured human HSCs although HSCs express both PDGF-α and -β receptors. PDGFR-α knockdown inhibits TGF-β-induced phosphorylation and nuclear accumulation of SMAD2 with no influence on AKT or ERK phosphorylation associated with noncanonical TGF-β signaling. PDGFR-α knockdown suppresses TGF-β receptor I (TβRI) but increases TβRII gene transcription. At the protein level, PDGFR-α is recruited to TβRI/TβRII complexes by TGF-β stimulation. PDGFR-α knockdown blocks TGF-β-mediated internalization of TβRII and induces accumulation of TβRII at the plasma membrane, thereby inhibiting TGF-β phosphorylation of SMAD2. Functionally, knockdown of PDGFR-α reduces paracrine effects of HSCs on colorectal cancer cell proliferation and migration in vitro. In mice and patients, colorectal cancer cell invasion of the liver induces upregulation of PDGFR-α of HSCs. In summary, our finding that PDGFR-α knockdown inhibits SMAD-dependent TGF-β signaling by repressing TβRI transcriptionally and blocking endocytosis of TGF-β receptors highlights a convergence of PDGF and TGF-β signaling for HSC activation and PDGFR-α as a therapeutic target for liver metastasis and other settings of HSC activation.

Liver microenvironment is a critical determinant for development and progression of liver metastasis. Under transforming growth factor beta (TGF‐β) stimulation, hepatic stellate cells (HSCs), which are liver‐specific pericytes, transdifferentiate into tumor‐associated myofibroblasts that promote tumor implantation (TI) and growth in the liver. However, the regulation of this HSC activation process remains poorly understood. In this study, we tested whether vasodilator‐stimulated phosphoprotein (VASP) of HSCs regulated the TGF‐β‐mediated HSC activation process and tumor growth. In both an experimental liver metastasis mouse model and cancer patients, colorectal cancer cells reaching liver sinusoids induced up‐regulation of VASP and alpha‐smooth muscle actin (α‐SMA) in adjacent HSCs. VASP knockdown in HSCs inhibited TGF‐β‐mediated myofibroblastic activation of HSCs, TI, and growth in mice. Mechanistically, VASP formed protein complexes with TGF‐β receptor II (TβRII) and Rab11, a Ras‐like small GTPase and key regulator of recycling endosomes. VASP knockdown impaired Rab11 activity and Rab11‐dependent targeting of TβRII to the plasma membrane, thereby desensitizing HSCs to TGF‐β1 stimulation. Conclusions: Our study demonstrates a requirement of VASP for TGF‐β‐mediated HSC activation in the tumor microenvironment by regulating Rab11‐dependent recycling of TβRII to the plasma membrane. VASP and its effector, Rab11, in the tumor microenvironment thus present therapeutic targets for reducing TI and metastatic growth in the liver. (Hepatology 2015;61:361–374)