Simple SummaryThe MET receptor and its ligand Hepatocyte Growth Factor (HGF) sustain cell proliferation, survival, motility, and invasion. Several pieces of evidence suggest that these biological activities support the metastatic potential of transformed cells. Cancer cell dissemination is sustained by cell-autonomous (executed by cancer cells) and non-cell-autonomous (executed by cells composing the tumor microenvironment) functions. To define the role of the HGF/MET axis in this complex process, we genetically knocked out theMETgene in cancer cells that were not dependent on MET signaling for their growth. In this way, we exclusively evaluated the relevance of the HGF/MET axis in prompting cell-autonomous activities (MET signaling in tumor microenvironment cells is maintained intact) independently of their intrinsic ability to proliferate (that is sustained by different oncogenic drivers). Our results proved that HGF/MET axis plays a crucial role in directing cell-autonomous functions regulating cancer cell dissemination, supporting a possible use of MET inhibitors in metastatic cancers.AbstractCancer cell dissemination is sustained by cell-autonomous and non-cell-autonomous functions. To disentangle the role of HGF (Hepatocyte Growth Factor) and MET ligand/receptor axis in this complex process, we genetically knocked out the MET gene in cancer cells in which MET is not the oncogenic driver. In this way, we evaluated the contribution of the HGF/MET axis to cancer cell dissemination independently of its direct activities in cells of the tumor microenvironment. The lack of MET expression in MET−/−cells has been proved by molecular characterization. From a functional point of view, HGF stimulation of MET−/−cancer cells was ineffective in eliciting intracellular signaling and in sustaining biological functions predictive of malignancy in vitro (i.e., anchorage-independent growth, invasion, and survival in the absence of matrix adhesion). Cancer cell dissemination was assessed in vivo, evaluating: (i) the ability of MET−/−lung carcinoma cells to colonize the lungs following intravenous injection and (ii) the spontaneous dissemination to distant organs of MET−/−pancreatic carcinoma cells upon orthotopic injection. In both experimental models, MET ablation affects the time of onset, the number, and the size of metastatic lesions. These results define a crucial contribution of the HGF/MET axis to cell-autonomous functions driving the metastatic process.