VEGF Receptor 1 (VEGFR1, Flt1) and VEGFR2 (KDR/ Flk1) are expressed on the cell surface of the human GBSCs. VEGFR2 appears to mediate almost all of the known cellular responses to VEGF.
Collectively, we hypothesize that VEGF can promote the proliferation of GBSCs through VEGFR2 under both normoxic and hypoxic conditions.
Upon replating at one cell per well, GBSCs spheres formed from single CD133+ cells, usually reaching to a size of 40-60 cells in approximately 2 weeks (Figure 1(a)).
GBSCs spheres were found to express brain tumor stem cell markers, CD133 and nestin, which were examined by immunofluorescence (Figures 1(b) and 1(c)).
VEGF Promotes GBSCs Proliferation through VEGFR2 but Not VEGFR1.
Regardless of various concentrations VEGF treatment, hypoxia alone increased proliferation rate of GBSCs. Exogenous VEGF promoted the proliferation of GBSCs in a dose-dependent manner.
Our results showed that Ki8751 did not inhibit GBSCs proliferation when no exogenous VEGF was added.
VEGFR2 Signaling but Not VEGFR1 Signaling Is Involved in GBSCs Proliferation.
Contrary to VEGFR2 inhibitor, VEGFR1 antibody increased the phosphorylated level of VEGFR2 when GbSCs were treated with high concentration of VEGF, whereas VEGFR1 antibody did not enhance the VEGFR2 phosphorylation level when VEGF concentration was decreased to 100 ng/mL (Figure 3(c)), indicating that VEGFR1 has a negative feedback effect on VEGFR2 when cells were exposed to higher concentration of VEGF.
Recent evidence suggests that GBSCs may be important for the initiation, propagation, and recurrence of glioblastoma, and hence GBSCs are now emerging as critical therapeutic targets .
Multiple treatment modalities have targeted VEGF and VEGFRs due to their significant roles in regulating angiogenic processes and GBSCs proliferation.
GBSCs were isolated from primary human brain tumor patient specimens.