Binding of transcription factor activating protein 2 γ on the 5′-proximal promoter region of human porcine endogenous retrovirus subgroup A receptor 2/GPR172B

Nakaya Y, Shimode S, Kobayashi T, Imakawa K, Miyazawa T. Binding of transcription factor activating protein 2γ on the 5′‐proximal promoter region of human porcine endogenous retrovirus subgroup A receptor 2/GPR172B. Xenotransplantation 2012; 19: 177–185. © 2012 John Wiley & Sons A/S. : Background: Xenotransplantation is one of the solutions for the shortage of organ donors, and pigs have been considered to be the most suitable animal donors. Specific pathogen‐free pigs are utilized in the xenotransplantation; however, pigs have infectious gammaretroviruses, named porcine endogenous retroviruses (PERVs) in their genome. Of them, PERV‐A and PERV‐B can infect human cells in vitro and potentially induce diseases like other gammaretroviruses. The human cellular receptors for PERV‐A were identified and named human PERV‐A receptor (HuPAR)‐1 and HuPAR‐2 (also called as GPR172A and GPR172B, respectively). We have recently reported that HuPAR‐2 expression was regulated by epigenetic modification and preferentially expressed in placenta. However, the detailed mechanisms of HuPAR‐2 expression have not been fully characterized. In this study, we analyzed molecular mechanisms associated with HuPAR‐2 transcription through the identification of transcription factors that bind to the promoter region of HuPAR‐2. Methods: In situ hybridization was performed to identify the cells expressing HuPAR‐2 in placental tissues. Transcriptional activities were measured by dual‐luciferase reporter assay using serial deletion mutants of HuPAR‐2 5′‐flanking region. To identify the transcription factors bound to the promoter region, in silico analysis, electrophoresis mobility shift assay, and chromatin immunoprecipitation assay were conducted. The effect of the transcription factor transcription factor activator protein (TFAP)‐2γ on the promoter activities was investigated by overexpression of the factor. Results: We identified that HuPAR‐2 was specifically expressed in villous trophoblast cells. We also identified that a region spanning from −126 to −32 had proximal promoter activities and TFAP‐2γ bound to a region spanning from −58 to −35 in vitro and in vivo. The overexpression of TFAP‐2γ also augmented the proximal promoter activity. Conclusion: We demonstrated that TFAP‐2γ is one of the transcription factors involved in the HuPAR‐2 expression in human villous trophoblast cells. By studying transcriptional factors involved in the expression of HuPAR‐2, we may find a clue to contr