VEGF upregulates VEGF receptor-2 on human outer root sheath cells and stimulates proliferation through ERK pathway.

Vascular endothelial growth factor (VEGF) is a key regulator of physiological and pathological angiogenesis. The biological effects of VEGF are mediated by receptor tyrosine kinases. VEGF receptor-2, the primary receptor for VEGF, is thought to mediate most functional effects. In this study, we examined the expression and roles of VEGF receptor-2 on human outer root sheath cells (ORS). The expression of VEGFR-2 was determined at mRNA and protein levels by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot. Localization of VEGFR-2 in ORS cells was detected by immunofluorescence. The effect of VEGF on ORS cell proliferation was determined by MTT assays. Our data showed the expression of VEGFR-2 on ORS cells at both mRNA and protein levels. Immunostaining for VEGFR-2 demonstrated strong signal on cultured ORS cells. Exogenous VEGF(165) stimulated proliferation of ORS cells and upregulated expression of VEGFR-2 in a dose-dependent manner. Moreover, VEGF(165) induced phosphorylation of VEGFR-2, PLC-γ1, PKC-α, MEK, and p44/42 MAPK (ERK1/2) in a time-dependent manner. Taken together, human ORS cells express functional VEGF receptor-2 and exogenous VEGF(165) upregulates expression of VEGFR-2 and stimulates proliferation of ORS cells via VEGFR-2 mediated ERK signaling pathway.