Identification and Characterization of a Low Oxygen Response Element Involved in the Hypoxic Induction of a Family ofSaccharomyces cerevisiae Genes

Abstract

An organism's ability to respond to changes in oxygen tension depends in large part on alterations in gene expression. The oxygen sensing and signaling mechanisms in eukaryotic cells are not fully understood. To further define these processes, we have studied the ⌬9 fatty acid desaturase gene OLE1 in Saccharomyces cerevisiae. We have confirmed previous data showing that the expression of OLE1 mRNA is increased in hypoxia and in the presence of certain transition metals. OLE1 expression was also increased in the presence of the iron chelator 1,10-phenanthroline. A 142-base pair (bp) region 3 to the previously identified fatty acid response element was identified as critical for the induction of OLE1 in response to these stimuli using OLE1 promoter-lacZ reporter constructs. Electromobility shift assays confirmed the presence of an inducible band shift in response to hypoxia and cobalt. Mutational analysis defined the nonameric sequence ACTCAACAA as necessary for transactivation. A 20-base pair oligonucleotide containing this nonamer confers up-regulation by hypoxia and inhibition by unsaturated fatty acids when placed upstream of a heterologous promoter in a lacZ reporter construct. Additional yeast genes were identified which respond to hypoxia and cobalt in a manner similar to OLE1. A number of mammalian genes are also up-regulated by hypoxia, cobalt, nickel, and iron chelators. Hence, the identification of a family of yeast genes regulated in a similar manner has implications for understanding oxygen sensing and signaling in eukaryotes.

A dual signalling pathway for the hypoxic expression of lipid genes, dependent on the glucose sensor Rag4, is revealed by the analysis of the KlMGA2 gene in Kluyveromyces lactis

“…In S. cerevisiae, the fatty acid desaturase gene OLE1 is induced by hypoxia (Kwast et al, 1999) and is a consolidated target gene of Mga2 (Kwast et al, 1999;Jiang et al, 2001;Vasconcelles et al, 2001). We identified ORF KLLA0C05566g as the orthologue gene of OLE1 in K. lactis and named it KlOLE1.…”

Dosage-dependent functions of fatty acid desaturase Ole1p in growth and morphogenesis of Candida albicans

“…A deletion analysis of the OLE1 promoter identified a 111 bp fatty acid-regulated region (FAR) which is essential for transcription activation and repression by unsaturated fatty acids (Choi et al, 1996). In addition, the low oxygen response promoter element (LORE) mediates oxygen repression of OLE1 (Nakagawa et al, 2001;Vasconcelles et al, 2001). Two genes encoding components of fatty acid transporters, FAA1 and FAA4, were found to be essential for unsaturated fatty acidrepression of OLE1 via FAR sequences (Faergeman et al, 2001).…”

The Membrane Proteins, Spt23p and Mga2p, Play Distinct Roles in the Activation of Saccharomyces cerevisiae OLE1 Gene Expression

“…It can activate and confer fatty acid-mediated repression on a foreign gene when placed upstream of the Saccharomyces CYC1 basal promoter elements. We have also identified a second low oxygen response element (LORE) that is positioned ϳ200 bases downstream from the FAR element (7). That element acts with the FAR element to strongly activate transcription in response to hypoxic conditions and on induction by cobalt, which is thought to interfere with an unidentified oxygen sensor.…”

“…The unsaturated fatty acid products of Ole1p compose 75-80% of the fatty acyl groups in membrane lipids, and the regulation of its activity plays a dominant role in governing the composition and physical properties of membranes in growing cells. Expression of the OLE1 gene is regulated by a number of physiological and nutritional controls, including nutrient fatty acids (3-6) and molecular oxygen (7)(8)(9). We have shown previously that unsaturated fatty acids exhibit strong repressive effects on OLE1 expression at the levels of transcription (6) and mRNA stability (5).…”