Hypoxia up-regulates vascular endothelial growth factor in U-87 MG cells: involvement of TRPC1

Canonical Transient Receptor Potential (TRPC) channels play important roles in diverse physiological processes. The contribution of TRPC channels to up-regulate VEGF expression under hypoxic conditions was studied in a malignant glioma cell line, U-87 MG cells. Up-regulation of VEGF gene expression by hypoxia was markedly suppressed by a TRPC channel blocker. RT-PCR showed that U-87 MG cells expressed four TRPC isoforms in normoxia: TRPC1, 3, 4, and 5. In addition, the expression of TRPC3, 4, and 5 decreased greatly under hypoxia exposure in U-87 MG cells. In contrast, TRPC1 expression was unchanged. These results suggest TRPC channels were involved in hypoxia-induced VEGF expression, and compared with other TRPC isoforms, TRPC1 might play a different role in this process. Furthermore, we determined the function of TRPC1 by RNAi. Two different siRNAs against TRPC1 largely inhibited hypoxia-induced up-regulation of VEGF mRNA and protein levels. However, overexpression of TRPC3 or 5 neither enhanced hypoxia-induced VEGF expression, nor prevented it. Taken together, our present data suggest that TRPC1, but not TRPC3 or 5, is involved in hypoxia-induced VEGF expression in U-87 MG cells.