Histidine domain-containing protein tyrosine phosphatase (HD-PTP) is a putative phosphatase that has been shown to affect the signaling and downregulation of certain receptor tyrosine kinases. To investigate if HD-PTP affects platelet-derived growth factor receptor β (PDGFRβ) signaling, we employed the overexpression of HA-tagged HD-PTP, as well as siRNA-mediated and lentivirus shRNA-mediated silencing of HD-PTP in NIH3T3 cells. We found that HD-PTP was recruited to the PDGFRβ in a ligand-dependent manner. Depletion of HD-PTP resulted in an inability of PDGF-BB to promote tyrosine phosphorylation of the ubiquitin ligases c-Cbl and Cbl-b, with a concomitant missorting and reduction of the degradation of activated PDGFRβ. In contrast, ligand-induced internalization of PDGFRβ was unaffected by HD-PTP silencing. Furthermore, the levels of STAM and Hrs of the ESCRT0 machinery were decreased, and immunofluorescence staining showed that in HD-PTP-depleted cells, PDGFRβ accumulated in large aberrant intracellular structures. After the reduction of HD-PTP expression, an NIH3T3-derived cell line that has autocrine PDGF-BB signaling (sis-3T3) showed increased ability of anchorage-independent growth. However, exogenously added PDGF-BB promoted efficient additional colony formation in control cells, but was not able to do so in HD-PTP-depleted cells. Furthermore, cells depleted of HD-PTP migrated faster than control cells. In summary, HD-PTP affects the intracellular sorting of activated PDGFRβ and the migration, proliferation and tumorigenicity of cells stimulated by PDGF.
Keywords: Cbl-b; ESCRT; HD-PTP; PDGFRβ; PLCγ; STAT3; Ubiquitination; c-Cbl.
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