Regulation of vascular endothelial growth factor transcription by endothelial PAS domain protein 1 (EPAS1) and possible involvement of EPAS1 in the angiogenesis of renal cell carcinoma

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Abstract
BACKGROUND Endothelial PAS domain protein 1 (EPAS1) is a basic helix‐loop‐helix/PAS domain transcription factor that expressed most abundantly in highly vascularized organs. The authors examined the effect of transfection of EPAS1 cDNA on the endogenous expression of vascular endothelial growth factor (VEGF) in the 293 Tet‐Off cell line and the possible involvement of EPAS1 in the angiogenesis of renal cell carcinoma (RCC). METHODS Complete cDNA of EPAS1 was cloned and transfected to cells from the 293 Tet‐Off fetal kidney cell line, in which the expression of EPAS1 can be inhibited by doxycycline. The subsequent changes in expression pattern of VEGF and transferrin receptor (TfR), a target gene of hypoxia‐inducible factor 1α (HIF‐1α), were examined by semiquantitative reverse transcription‐polymerase chain reaction (RT‐PCR) and enzyme‐linked immunosorbent assay. In addition, expression of EPAS1, HIF‐1α, and VEGF were analyzed by semiquantitative RT‐PCR in five RCC cell lines and in 13 RCC tissue samples. In situ hybridization was performed on 7 of the 13 RCC tissue samples. RESULTS Endogenous VEGF was increased significantly by the introduction of EPAS1 cDNA at both the mRNA level and the protein level. With the inhibition of EPAS1 by doxycycline treatment, the expression of VEGF was significantly decreased accordingly, whereas the expression of TfR was not affected. EPAS1 was detected in all of the RCC cell lines examined. In RCC tissue samples, EPAS1 mRNA and VEGF mRNA were increased significantly in tumor tissues compared with normal adjacent kidney tissues. In situ hybridization showed that EPAS1 and VEGF were coexpressed topographically in tumor tissues. CONCLUSIONS These results suggest that endogenous VEGF can be up‐regulated transcriptionally by EPAS1, and EPAS1 may be involved in the angiogenesis of RCC. Cancer 2001;91:1429–36. © 2001 American Cancer Society.