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Enhanced MET signaling in mouse epidermis activates EGFR and initiates squamous carcinogenesis

ABSTRACT: MET expression is elevated in a majority of human skin cancers but its contributions to pathogenesis have not been evaluated. In a mouse model of constitutive overexpression of HGF (MT-HGF), the incidence of squamous cell skin tumors induced by initiation with 7,12-dimethylbenz(a)anthracene (DMBA) followed by exposure to 12-O-tetradecanoyl-phorbol-13-acetate (TPA) is increased fivefold over control groups. Half of these tumors carry Hras1 or Kras mutations. Without DMBA initiation, tumors also erupt on MT-HGF mouse skin but only when TPA promotion is enhanced by crossing these mice with mice overexpressing cutaneous PKCα. None of these tumors have Ras mutations. In culture, MT-HGF keratinocytes share identical MET mediated phenotypic and biochemical features with wildtype keratinocytes transformed by oncogenic RAS. In both cell types, these common features of initiated keratinocytes arise from autocrine activation of EGFR through elevated expression and release of EGFR ligands. Inhibition of EGFR ablates the initiated signature of MT-HGF keratinocytes in vitro and causes regression of MT-HGF induced tumors in vivo. Global gene expression data indicate that MT-HGF and RAS transformed keratinocytes share largely an identical profile of over 5000 mRNAs. Gene ontology analysis reveals the most affected concordant signature is enriched for functions relevant to tissue development and response to wounding, accompanied by cytokine and growth factor activity, and peptidase and endopeptidase activity previously not linked to initiated keratinocytes. Furthermore, gene co-expression analysis in skin cancer patients revealed a core RAS/MET co-expression network considerably activated in pre cancerous and cancerous lesions. Thus MET activation though EGFR contributes to human cutaneous cancers, and inhibitors could be efficacious in advanced lesions such as those seen in transplant recipient patients. In this dataset with provide gene expression data from primary mouse keratinocytes in culture.

ORGANISM(S): Mus musculus

PROVIDER: GSE58671 | GEO | 2016/06/21

SECONDARY ACCESSION(S): PRJNA253134

REPOSITORIES: GEO

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Project description:MET, the receptor for hepatocyte growth factor (HGF), is involved in wide variety of biological events and its aberrant activation is implicated in the pathogenesis of cancer. Especially, MET signaling is associated with resistance to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs), key drugs in therapy of non-small cell lung cancer. MET has 11 potential N-glycosylation sites, however, the site-specific roles of N-glycans have not been elucidated. Here, we report that N-glycans regulate proteolytic processing of MET and HGF induced MET signaling, site specifically. N-glycosylation inhibitors suppressed processing and trafficking of endogenous MET in H1975 and EBC-1 lung cancer cells and exogenous MET in CHO cells. We purified the recombinant extracellular domain of human MET and determined the site-specific N-glycan structures and occupancy using nanoflow liquid chromatography-electrospray ionization mass spectrometry. The results indicated that most sites were fully glycosylated and the dominant population were complex-type which were rich in sialic acids and core fucoses. To examine the effects of N-glycan deletion of MET, we prepared endogenous-MET-knockout Flp-In CHO cells and transfected with series of N-glycan deletion mutants of MET. It was found that several N-glycans are implicated in processing of MET. It was also suggested that the N-glycans of -subunit of MET positively regulate HGF signaling, and the N-glycans of β-subunit negatively regulate HGF signaling. In all-N-glycan deletion mutant, processing and signaling were significantly suppressed. It was observed that the cell proliferation rate was suppressed in all-N-glycan deletion mutant, although the cell surface expression levels of MET were not completely diminished. We examined the HGF biding affinity for the recombinant extracellular domain of MET and found that peptide N-glycosidase F treatment did not affect the ligand binding affinity. It was suggested that N-glycans of MET affect the status and the function of the receptor site-specifically.

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Enhanced MET signaling in mouse epidermis activates EGFR and initiates squamous carcinogenesis

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