cancers Article HGF/MET Axis Induces Tumor Secretion of Tenascin-C and Promotes Stromal Rewiring in Pancreatic Cancer Chiara Modica 1 , Martina Olivero 1,2 , Francesca Zuppini 1,2 , Melissa Milan 1 , Cristina Basilico 1, * and Elisa Vigna 1,2, *   Citation: Modica, C.; Olivero, M.; Zuppini, F.; Milan, M.; Basilico, C.; Vigna, E. HGF/MET Axis Induces Tumor Secretion of Tenascin-C and Promotes Stromal Rewiring in Pancreatic Cancer. Cancers 2021, 13, 3519. https://doi.org/10.3390/ cancers13143519 Academic Editor: Guido Eibl Received: 30 April 2021 Accepted: 10 July 2021 Published: 14 July 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Candiolo Cancer Institute, FPO-IRCCS, 10060 Candiolo, Italy; modicachiara89@gmail.com (C.M.); martina.olivero@ircc.it (M.O.); francesca.zuppini@unito.it (F.Z.); melissa.milan@ircc.it (M.M.) 2 Department of Oncology, University of Turin, 10060 Candiolo, Italy * Correspondence: cribasilico@gmail.com (C.B.); elisa.vigna@ircc.it (E.V.); Tel.: +39-011-993-3228 (C.B. & E.V.) Simple Summary: It has been previously shown that activation of the MET receptor by its ligand, the hepatocyte growth factor (HGF), modulates the tumor-stroma cross-talk in models of pancreatic cancer. We now wish to cast light on the molecular mechanisms by which this ligand/receptor pair sustains the interaction between cancer cells and the tumor microenviroment. To this end, we compared data obtained by large-scale analysis of gene expression in pancreatic cancer cells grown in the presence of HGF versus cells grown in the presence of HGF and treated with specific inhibitors of HGF/MET signaling. By clustering differentially expressed genes according to functional groups, we identified candidate genes involved in the process. Among these, tenascin C was selected due to its activity in sustaining the malignant phenotype. Our results highlight a new role for tenascin C, which could represent the operative arm through which MET promotes activation of the stromal compartment in pancreatic cancer. Abstract: Pancreatic ductal adenocarcinoma is an aggressive tumor characterized by the presence of an abundant stromal compartment contributing significantly to the malignant phenotype. Pancreatic stellate cells are peculiar fibroblasts present in the stroma and represent the predominant source of extracellular matrix proteins, pro-inflammatory cytokines, and growth factors, including hepatocyte growth factor (HGF). Exploiting a co-culture system of human pancreatic stellate cells and cancer cells, we demonstrated that fibroblast activation was reduced upon HGF/MET axis inhibition. To unveil the signaling pathways sustaining stroma modulation orchestrated by MET activation in the tumor, we analyzed the gene expression profile in pancreatic cancer cells stimulated with HGF and treated with HGF/MET inhibitors. Transcriptome analysis showed that, among all the genes modulated by HGF, a subset of 125 genes was restored to the basal level following treatment with the inhibitors. By examining these genes via ingenuity pathway analysis, tenascin C emerged as a promising candidate linking MET signaling and tumor microenvironment. MET-dependent tenascin C modulation in pancreatic cancer cells was validated at RNA and protein levels both in vitro and in vivo. In conclusion, this work identifies tenascin C as a gene modulated by MET activation, suggesting a role in MET-mediated tumor-stroma interplay occurring during pancreatic tumor progression. Keywords: pancreatic ductal adenocarcinoma; tumor microenvironment; hepatocyte growth factor; MET oncogene; tenascin C; metastasis 1. Introduction Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer and is characterized by highly aggressive behavior [1]. According to the PDAC progression model, invasive adenocarcinoma arises from a well-defined duct lesion, called a pancreatic intraepithelial neoplasia, which evolves into a malignant adenocarcinoma Cancers 2021, 13, 3519. https://doi.org/10.3390/cancers13143519 https://www.mdpi.com/journal/cancers