RESUMEN
BACKGROUND: Spermatic cord torsion can lead to testis ischemia (I) and subsequent ischemia-reperfusion (I/R) causing germ cell-specific apoptosis. Previously, we demonstrated that the hypoxia-inducible factor-1 (HIF-1) transcription factor, a key regulator of physiological responses to hypoxia, is abundant in Leydig cells in normoxic and ischemic testes. We hypothesize that testicular HIF-1 activates the expression of antiapoptotic target genes to protect Leydig cells from apoptosis. In silico analysis of testis genes containing a consensus hypoxia response element (HRE, 5'-RCGTG-3') identified myeloid cell leukemia-1 (Mcl-1) as a potential HIF-1 target gene. The purpose of this study was to determine whether HIF-1 shows DNA-binding activity in normoxic and ischemic testes and whether Mcl-1 is a target gene of testicular HIF-1. METHODS: The testicular HIF-1 DNA-binding capacity was analyzed in vitro using a quantitative enzyme-linked immunosorbent assay (ELISA) and electrophoretic mobility shift assays (EMSA). MCL-1 protein expression was evaluated by immunoblot analysis and immunohistochemistry. The binding of testicular HIF-1 to the Mcl-1 gene was examined via chromatin immunoprecipitation (ChIP) analysis. RESULTS: The ELISA and EMSA assays demonstrated that testicular HIF-1 from normoxic and ischemic testes binds DNA equally strongly, suggesting physiological roles for HIF-1 in the normoxic testis, unlike most tissues in which HIF-1 is degraded under normoxic conditions and is only activated by hypoxia. MCL-1 protein was determined to be abundant in both normoxic and ischemic testes and expressed in Leydig cells. In a pattern identical to that of HIF-1 expression, the steady-state levels of MCL-1 were not significantly affected by I or I/R and MCL-1 co-localized with HIF-1α in Leydig cells. Chromatin immunoprecipitation (ChIP) analysis using a HIF-1 antibody revealed sequences enriched for the Mcl-1 promoter. CONCLUSIONS: The results demonstrated that, unlike what is observed in most tissues, HIF-1 displays DNA-binding activity in both normoxic and ischemic testes, and Mcl-1 may be a key target gene of testicular HIF-1 with potential roles in the antiapoptotic protection of Leydig cells.