Hypoxia induces the expression of a 43-kDa protein (PROXY-1) in normal andmalignant cells

This study was designed to determine the expression of cellular factors tha t may participate in phenotypic changes that occur under conditions of hypo xia. Using the RT-PCR differential display method, we isolated a cDNA fragm ent corresponding to a gene whose expression was induced in trophoblast and breast carcinoma cells cultured under 1 or 2% oxygen vs 4% oxygen or highe r. This gene encodes a 43-kDa protein initially identified in homocysteine- treated endothelial cells and later shown to be upregulated in various huma n and mouse cell types (termed RTP, Drg1, Cap43, rit42, Ndr1), Herein we re fer to this gene product as PROXY-1, for Protein Regulated by OXYgen-1. Ele vated mRNA and protein levels were first observed ill cells cultured in 1% oxygen for 8 h, Although PROXY-1 mRNA levels returned to near-control value s within 2 h of reexposure to 20% oxygen, protein levels remained high 72 h after reexposure to 20% oxygen. Treatment of cells with hypoxia mimics suc h as cobalt or iron chelators also increased PROXY-1 expression. Moreover, presence of 30% carbon monoxide in the hypoxic atmosphere abrogated the upr egulation of PROXY-1 expression. These findings suggest that hypoxia upregu lates PROXY-1 levels through a heme protein-dependent pathway and that asse ssment of PROXY-1 expression may be of potential use in evaluating tissue h ypoxia, (C) 2000 Academic Press.