PHD3 inhibits colon cancer cell metastasis through the occludin-p38 pathway

Prolyl hydroxylase 3 (PHD3) hydroxylates HIF in the presence of oxygen, leading to HIF degradation. PHD3 inhibits tumorigenesis. However, the underlying mechanism is not well understood. Herein, we demonstrate that PHD3 inhibits the metastasis of colon cancer cells through the occludin-p38 MAPK pathway independent of its hydroxylase activity. We found that PHD3 inhibited colon cancer cell metastasis in the presence of the PHD inhibitor DMOG, and prolyl hydroxylase-deficient PHD3 (H196A) suppressed cell metastasis as well. PHD3 controls the stability of the tight junction protein occludin in a hydroxylase-independent manner. We found that PHD3-inhibited colon cancer cell metastasis was rescued by knockdown of occludin and that occludin acted as a negative regulator of cell metastasis, implying that PHD3 suppresses metastasis through occludin. Furthermore, we found that knockdown of occludin induced phosphorylation of p38 MAPK, and the p38 inhibitor SB203580 impeded cell migration and invasion induced by occludin knockdown, indicating that occludin functions through p38. Moreover, we found that knockdown of occludin enhanced and overexpression of occludin decreased the expression of MKK3/6, the upstream kinase of p38. Our results suggest that PHD3 inhibits the metastasis of colon cancer cells through the occludin-p38 pathway independent of its hydroxylase activity. The findings reveal a previously undiscovered mechanism underlying the regulation of cancer cell metastasis by PHD3 and highlight a noncanonical hydroxylase-independent function of PHD3 in the suppression of cancer cells.