Regulation of Hypoxia-inducible Factor 1α (HIF-1α) by Lysophosphatidic Acid Is Dependent on Interplay between p53 and Kruppel-like Factor 5

Hypoxia-inducible factor 1 alpha (HIF-1 alpha) and p53 are pivotal regulators of tumor growth. Lysophosphatidic acid (LPA) is a lipid mediator that functions as a mitogen by acting through LPA receptors. We have shown previously that LPA stimulates HIF-1 alpha expression in colon cancer cells. To determine the mechanism of HIF-1 alpha induction by LPA, we compared the effect of LPA on HIF-1 alpha in several colon cancer cell lines. LPA transcriptionally induced HIF-1 alpha in colon cancer cells. HIF-1 alpha induction was observed in cells expressing WT p53, where LPA decreased p53 expression. However, LPA failed to induce HIF-1 alpha when the p53 gene was mutated. A decrease in p53 expression was dependent on induction of p53-specific E3 ubiquitin ligase Mdm2 by LPA. Kruppel-like factor 5 (KLF5) is an effector of LPA-induced proliferation of colon cancer cells. Because HIF-1 alpha was necessary for LPA-induced growth of colon cancer cells, we determined the relationship between KLF5 and HIF-1 alpha by a loss-of-function approach. Silencing of KLF5 inhibited LPA-induced HIF-1 alpha induction, suggesting that KLF5 is an upstream regulator of HIF-1 alpha. KLF5 and p53 binding to the Hif1 alpha promoter was assessed by ChIP assay. LPA increased the occupancy of the Hif1 alpha promoter by KLF5, while decreasing p53 binding. Transfection of HCT116 cells with KLF5 or p53 attenuated the binding of the other transcription factor. These results identify KLF5 as a transactivator of HIF-1 alpha and show that LPA regulates HIF-1 alpha by dynamically modulating its interaction with KLF5 and p53.