Regulation of p57KIP2 and tumorigenesis by the prolyl hydroxylase PHD3 in renal cell carcinoma

Abstract

Prolyl hydroxylase domain-containing protein 3 (PHD3) is one of enzymes catalyzing proline-hydroxylation of hypoxia inducible factor (HIF)-α subunits, which is key regulatory event of HIF activity. In renal cell carcinoma (RCC) tissues, PHD3 is commonly expressed at markedly higher level than surrounding normal tissue. PHD3 is one of the target genes, of which the expressions are induced by HIFs. Because high level of HIF activities is known to play a crucial role in tumorigenesis of RCC, the control of PHD3 by HIFs is simply expected to be negative feedback loop. However, PHD3 shows strong tumorigenenic effects in RCC by itself. The forced expression of PHD3 in Caki-1, where PHD3 is expressed at low level, stimulated the proliferation and led to tumor formation in xenographed nude mice. The knocking-down of PHD3 in A498 and 768-O RCC cell lines, where PHD3 is highly expressed, severely inhibited the cell-cycle progression and the proliferation. A498 tumors formed in xenographed nude mice were effectively shrinked by single injection of lentivirus expressing shRNA for PHD3. When the conditional expression system of shRNA for PHD3 was introduced to A498 cells, the xenographed tumors are completed disappeared by administration of doxycycline. The expression of p57KIP2 is characteristically reduced in RCC tissues, and proved to be related with high expression of PHD3 in present study. The p57 promotor reporter assay revealed that PHD3 strongly suppressed p57 transcription. The suppression of p57KIP2 expression by PHD3 might be involved in renal cell tumorigenesis in part.