Tumor growth is the orchestration of various oncogenes and tumor suppressors, and the regulation of these genes offers a rational therapeutic approach to cancer treatment. In this study, we found a new regulator of tumor growth, phosphatidylinositol 4-kinase type II alpha (PI4KII alpha), the mechanism of which is involved in angiogenesis and hypoxia-inducible factor HIF-1 alpha regulation. Results obtained from a human cancer tissue microarray showed that PI4KII alpha protein expression increases markedly in seven types of cancers compared with normal tissues. Suppression of PI4KII alpha leads to retarded tumor growth in nude mice. Downregulation of PI4KII alpha in cancer cells eliminates tumor cell-induced endothelial cell tubulogenesis and migration, and results in impaired angiogenesis. Further investigation showed that PI4KII alpha can directly regulate HIF-1 alpha expression and that the expression of these two proteins is correlated in vivo. At the same time, downregulation of PI4KII alpha markedly reduces HER-2 autophosphorylation, and PI4KII alpha specifically triggers HIF-1 alpha accumulation through a phosphatidylinositol 3-kinase (PI3K)- and extracellular signal-regulated protein kinase (ERK)-dependent pathway, suggesting that PI4KII alpha may regulate HIF-1 alpha through the HER-2/PI3K, ERK cascade. In summary, we discovered a pivotal role for PI4KII alpha in the regulation of tumor growth. Our results shed new light on understanding the novel functions of PI4KII alpha in cancer and suggest that PI4KII alpha may be a promising specific target for tumor therapy. Oncogene (2010) 29, 2550 - 2559; doi:10.1038/onc.2010.14; published online 15 February 2010