Germ cell nuclear factor relieves cAMP-response element modulator τ-mediated activation of the testis-specific promoter of human mitochondrial glycerol-3-phosphate dehydrogenase

Abstract

Mitochondrial glycerol-3-phosphate dehydrogenase (mGPDH) is an essential component of the glycerol phosphate shuttle that transfers reduction equivalents from the cytosol into the mitochondrion. Within the testis, immunohisiological analysis localized human mG-PDH to late spermatids and to the midpiece of spermatozoa. The expression of human mGPDH is regulated by two somatic promoters, and here, we describe a third testis-specific promoter of human mGPDH. The usage of this testis-specific promoter correlates with the expression of a shortened mGPDH transcript of ∼2.4 kb in length, which is solely detectable from testicular RNA. Within the testis-specific promoter, we detected a cAMP-response element (CRE) site at -51, which binds the testis-specific transcriptional activator CRE modulator τ (CREMτ) in electrophoretic mobility shift assays. This recognition site overlaps with a nuclear receptor binding half-site at -49, which binds the testis-specific transcriptional repressor germ cell nuclear factor (GCNF). Both factors compete for binding to the same DNA response element. Ectopic expression of CREMτ in HepG2 cells activated a promoter-driven luciferase construct in transient transfection experiments. Additional cotransfection of GCNF relieved this activity, suggesting a down-regulation of CREMτ-mediated activation by GCNF. This effect was preserved by introducing the CRE/nuclear receptor-binding element into a heterologous promoter context. Our data suggest a down-regulation of CREMτ-mediated gene expression by GCNF, which might be a general regulation mechanism for several postmeiotically expressed genes with a temporal expression peak during early spermatid development.