The cellular oxygen tension regulates expression of the endoplasmic oxidoreductase ERO1‐Lα

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Abstract
The formation of disulfide bonds in the endoplasmic reticulum requires protein disulfide isomerase (PDI) and endoplasmic reticulum oxidoreductin 1 (ERO1) that reoxidizes PDI. We report here that the expression of the rat, mouse and human homologues of ERO1‐Like protein α but not of the isoform ERO1‐Lβ are stimulated by hypoxia in rats vivo and in rat, mouse and human cell cultures. The temporal pattern of hypoxic ERO1‐Lα induction is very similar to that of genes triggered by the hypoxia inducible transcription factor (HIF‐1) and is characteristically mimicked by cobalt and by deferoxamine, but is absent in cells with a defective aryl hydrocarbon receptor translocator (ARNT, HIF‐1β). We speculate from these findings that the expression of ERO1‐Lα is probably regulated via the HIF‐pathway and thus belongs to the family of classic oxygen regulated genes. Activation of the unfolded protein response (UPR) by tunicamycin, on the other hand, strongly induced ERO1‐Lβ and more moderately ERO1‐Lα expression. The expression of the two ERO1‐L isoforms therefore appears to be differently regulated, in the way that ERO1‐Lα expression is mainly controlled by the cellular oxygen tension, whilst ERO1‐Lβ is triggered mainly by UPR. The physiological meaning of the oxygen regulation of ERO1‐Lα expression likely is to maintain the transfer rate of oxidizing equivalents to PDI in situations of an altered cellular redox state induced by changes of the cellular oxygen tension.