A dominant-negative isoform of hypoxia-inducible factor-1 alpha specifically expressed in human testis.
Spermatogenesis in the seminiferous tubuli of the testis occurs under a high proliferation rate, suggesting considerable oxygen consumption. Because of the lack of blood vessels, the oxygen partial pressure in the lumen of these tubuli is very low. We previously identified a testis isoform of the hypoxia-inducible factor (HIF)-1alpha in ... the mouse, termed mHIF-1alphaI.1. Here, we demonstrate that expression of mHIF-1alphaI.1 increases during puberty, further demonstrating its gene induction in postmeiotic germ cells. Using 5'-rapid amplification of cDNA ends, we identified a novel HIF-1alpha isoform in the human testis, called hHIF-1alphaTe. Like mHIF-1alphaI.1, hHIF-1alphaTe mRNA is derived from an alternative promoter-first exon combination, but with a different genomic organization and a different nucleotide sequence. Reverse transcription-polymerase chain reaction analysis confirmed that hHIF-1alphaTe is exclusively expressed in the testis. As determined by immunofluorescence of ejaculated sperm cells, HIF-1alpha protein is mainly localized in the postacrosomal head and in the midpiece of spermatozoa. Though overlapping with mitochondrial localization in human and mouse spermatozoa, neither hHIF-1alphaTe nor hHIF-1alpha associated with mitochondria. In contrast with the ubiquitously expressed HIF-1alpha protein and the mouse testis-specific mHIF-1alphaI.1 isoform, the hHIF-1alphaTe mRNA sequence predicts a protein with an N-terminal truncation of the DNA-binding domain. As shown by yeast two-hybrid assays, hHIF-1alphaTe still formed heterodimeric complexes with HIF-1beta. However, hHIF-1alphaTe was incapable of forming a DNA-binding HIF-1 complex. Overexpression of exogenous hHIF-1alphaTe resulted in the inhibition of the endogenous HIF-1 transcriptional activity, demonstrating that the testis-specific hHIF-1alphaTe isoform is a dominant-negative regulator of normal HIF-1 activity.
Mesh Terms:
Aging, Animals, Base Sequence, DNA, DNA-Binding Proteins, Gene Amplification, Genes, Dominant, Humans, Hypoxia-Inducible Factor 1, Hypoxia-Inducible Factor 1, alpha Subunit, Male, Mice, Molecular Sequence Data, Nuclear Proteins, Protein Isoforms, RNA, Messenger, Spermatozoa, Testis, Transcription Factors
Aging, Animals, Base Sequence, DNA, DNA-Binding Proteins, Gene Amplification, Genes, Dominant, Humans, Hypoxia-Inducible Factor 1, Hypoxia-Inducible Factor 1, alpha Subunit, Male, Mice, Molecular Sequence Data, Nuclear Proteins, Protein Isoforms, RNA, Messenger, Spermatozoa, Testis, Transcription Factors
Biol. Reprod.
Date: Jul. 01, 2004
PubMed ID: 15031145
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