Regulation of yeast fatty acid desaturase in response to iron deficiency

Abstract

Unsaturated fatty acids (UFA) are essential components of phospholipids that greatly contribute to the biophysical properties of cellular membranes. Biosynthesis of UFAs relies on a conserved family of iron-dependent fatty acid desaturases, whose representative in the model yeast Saccharomyces cerevisiae is Ole1. OLE1 expression is tightly regulated to adapt UFA biosynthesis and lipid bilayer properties to changes in temperature, and in UFA or oxygen availability. Despite iron deficiency being the most extended nutritional disorder worldwide, very little is known about the mechanisms and the biological relevance of fatty acid desaturases regulation in response to iron starvation. In this report, we show that endoplasmic reticulum-anchored transcription factor Mga2 activates OLE1 transcription in response to nutritional and genetic iron deficiencies. Cells lacking MGA2 display low UFA levels and do not grow under iron-limited conditions, unless UFAs are supplemented or OLE1 is overexpressed. The proteasome, E3 ubiquitin ligase Rsp5 and the Cdc48 complex are required for OLE1 activation during iron depletion. Interestingly, Mga2 also activates the transcription of its own mRNA in response to iron deficiency, hypoxia, low temperature and low UFAs. MGA2 up-regulation contributes to increase OLE1 expression in these situations. These results reveal the mechanism of OLE1 regulation when iron is scarce and identify the MGA2 auto-regulation as a potential activation strategy in multiple stresses.

Iron Regulatory Mechanisms in Saccharomyces cerevisiae

“…The activation of the RTG response during iron deficiency may provide sufficient α-ketoglutarate as a nitrogen donor for biosynthetic processes. Moreover, a decrease in the activity of the iron-dependent Δ9 fatty acid desaturase Ole1 in iron-deficient conditions causes a drop in the levels of unsaturated fatty acids (UFAs) that releases the endoplasmic reticulum (ER)-anchored Mga2 transcription factor and activates the transcription of OLE1 ( Romero et al, 2018a ; Figure 2 ). UFA regulation of Mga2 is essential for growth in iron-depleted conditions ( Romero et al, 2018a ; Jorda et al, 2020 ).…”

“…Moreover, a decrease in the activity of the iron-dependent Δ9 fatty acid desaturase Ole1 in iron-deficient conditions causes a drop in the levels of unsaturated fatty acids (UFAs) that releases the endoplasmic reticulum (ER)-anchored Mga2 transcription factor and activates the transcription of OLE1 ( Romero et al, 2018a ; Figure 2 ). UFA regulation of Mga2 is essential for growth in iron-depleted conditions ( Romero et al, 2018a ; Jorda et al, 2020 ). In fact, the levels of UFAs have been reported to be crucial for the Aft1-dependent activation of the iron regulon, although no mechanistic clues have been provided yet ( Jorda et al, 2020 ).…”

A genome-wide transcriptional study reveals that iron deficiency inhibits the yeast TORC1 pathway

“…For instance, the mRNA levels of CTH2 mRNA increased 17-fold after 3 hours of iron deprivation (Supplementary Data S2). Cluster 4 also contained the Mga2dependent transcriptional induction reported for the OLE1 fatty acid desaturase in response to iron limitation [24]. Interestingly, cluster 2 contained genes whose RA decrease was more pronounced than its drop in TR, suggesting a significant contribution of mRNA decay to its regulation ( Figure 3).…”

“…Since Sch9 protein is around 100 KDa, a chemical fragmentation of Sch9-HA protein was performed with NTCB (2-nitro-5-thiocyanatobenzoic acid), which cyanylates cysteine residues that under alkaline conditions are followed by chain cleavage at the modified residues. Chromatin immunoprecipitation (ChIP) assays were performed to determine RNA Pol II binding to Rtg1-regulated gene promoters as described [24]. Cell extracts for ChIP were incubated with Dynabeads Pan Mouse IgG (Invitrogen), previously bound to a monoclonal mouse anti-Rpb1 antibody (clone 8WG16, Covance), and DNA was purified with the High Pure PCR Product Purification Kit (Roche).…”

“…SPOT camera (Diagnostic Instruments). β-Galactosidase activity was measured as previously described [24]. Total intracellular iron levels were determined as previously described [25].…”