Isolation of a hypoxia-induced cDNA with homology to the mammalian growth-related protein p23

Abstract

Hypoxia leads to a cellular stress reaction and can induce transcription of immediate early genes, such as c-fos. We have generated a differential cDNA cloning strategy to isolate further hypoxia-induced genes. We report on the identification and characterization of a novel transcript (cDNA clone pSH16), which is inducible 12-fold in HeLa cells after 50 min of exposure to hypoxia. Sequence analysis revealed a hybrid transcript with high homology to the mammalian growth-related protein p23 mRNA fused to mitochondrial 16S rRNA. Complete homology was found for the coding region, whereas the 3'-untranslated part of the hypoxia-induced p23 sequence was elongated and carried an ATTTA box and a second consensus poly(A) signal in addition. The functional integrity of the pSH16 mRNA was verified by cell-free translation. Hypoxia induced the expression of both fusion partners, p23 and 16S rRNA, separately. In contrast to the hypoxia-induced expression in HeLa cells, we found constitutive high-level expression in breast and cervix tissue. No further upregulation of p23 transcripts was detectable in primary tumors of the breast and cervix. These data provide first evidence for a hypoxia-induced upregulation of the mammalian growth-related protein p23, which might be relevant for understanding of the physiology of hypoxic conditions in tumors.