Increased expression of PHD3 represses the HIF-1 signaling pathway and contributes to poor neovascularization in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is known as one of the most malignant potential diseases with poor neovascularization. By comparing PDAC to hepatocellular carcinoma (HCC), which is well vascularized, we investigated the mechanisms and tumor biological significance of the poor neovascularization in PDAC. Surgical specimens from primary PDAC and HCC patients were immunohistologically stained to detect the expressions of CD105, CD44, HIF-1 alpha, PHD3, and Siah2. We also used two PDAC and two HCC cell lines to compare the expressions of HIF-1 alpha, PHD3, and CD44, as well as the production of VEGF in hypoxic condition. The role of PHD3 in regulating HIF-1 alpha expression was further confirmed by siRNA knockdown in a PDAC cell line that highly expressed PHD3. There were significantly fewer microvessels but more cancer stem cells in PDAC specimens compared to HCC specimens. The expression of CD105 was reversely related to the expression of CD44 in PDAC and HCC specimens. PDAC specimens also showed higher expressions of PHD3 but lower expressions of HIF-1 alpha. Similarly, the expression of PHD3 was observed clearly in PDAC cell lines, but was almost completely negative in HCC cell lines. Hypoxic stimulation clearly enhanced HIF-1 alpha expression and VEGF secretion in both HCC cell lines, but did not significantly change in PDAC cell lines. The knockdown of PHD3 in PDAC cells restored the hypoxic-induced HIF-1 alpha expression, which accordingly stimulated the cells' VEGF secretion. The enhanced expression of PHD3 might likely contribute to the poor neovascularization and affect the biological characterization in PDAC cancer cells.