Positive and negative regulation of a sterol biosynthetic gene (ERG3) in the post‐squalene portion of the yeast ergosterol pathway

Abstract

Regulation of sterol biosynthesis in the terminal portion of the pathway represents an efficient mechanism by which the cell can control the production of sterol without disturbing the production of other essential mevaionate pathway products. We demonstrate that mutations affecting early and late steps in sterol homeostasis modulate the expression of the ERG3 gene: a late step in sterol biosynthesis in yeast. Expression of ERG3 is increased in response to a mutation in the major isoform of HMG CoA reductase which catalyzes the rate-limiting step of sterol biosynthesis. Likewise, mutations in non-auxotrophic ergosterol biosynthetic genes downstream of squalene production (erg2, erg3, erg4, ergS, and ergO') result in an up-regulation of ERG3 expression. Deletion analysis of the ERG3 promoter identified two upstream activation sequences: UAS1, which when deleted reduces ERG3 gene expression 3-4-fuld but maintains sterol regulation and UAS2, which when deleted further reduces ERG3 expression and abolishes sterol regulation. The recent isolation of two yeast genes responsible for the esterification of intracellular sterol (ARE1 and ARE2) has enabled us to directly analyze the relationship between sterol esterification and de novo biosynthesis. Our results demonstrate that the absence of sterol esterification leads to a decrease in total intracellular sterol and ERG3 is a target of this negative regulation.

Structural and Biochemical Properties of Lipid Particles from the Yeast Saccharomyces cerevisiae

“…In contrast, changes in the sterol composition of TM DGA1 ϩ and TM LRO1 ϩ cannot be attributed to substrate specificities of (missing) SE synthases but rather to a feedback regulation to the sterol biosynthetic pathway. This view is in line with data reported by ArthingtonSkaggs et al (39) showing that lack of Are1p or Are2p downregulated Erg3p. This down-regulation may be the reason for the accumulation of ergosta-7-enol and ergosta-7,22-dienol (Fig.…”

“…TM DGA1 ϩ and TM LRO1 ϩ , which lacked sterol esterification, accumulated ergosta-7,22-dienol and ergosta-7-enol at the expense of other sterol precursors. This effect may be explained by down-regulation of Erg3p as reported previously by Arthington-Skaggs et al (39) and will be discussed FIGURE 2. Activities of neutral lipid-synthesizing enzymes in vitro.…”

“…Effect of sterol esterification on sterol biosynthesis. Lack of sterol esterification down-regulates Erg3p (39), which causes a decreased amount of ergosta-5,7,22,24-tetraenol and an increased amount of ergosta-7-enol and ergosta-7,22-dienol. This effect may pave the way for an alternative pathway of episterol conversion by Erg4p and Erg5p to ergosterol.…”

Synthesis of Novel Lipids in Saccharomyces cerevisiae by Heterologous Expression of an Unspecific Bacterial Acyltransferase

“…The relatively low ASAT activity in yeast might be the reason that WS/DGAT was unable to restore steryl ester synthesis in S. cerevisiae H1246. Another reason might be a lower intracellular concentration of sterols in the mutant, since it has been shown that down-regulation of sterol biosynthesis occurred in mutants defective in ARE1 and ARE2 (3,37). However, the sterol content in S. cerevisiae H1246 was not determined in this study.…”

SUT1 is a putative Zn[II]2Cys6‐transcription factor whose upregulation enhances both sterol uptake and synthesis in aerobically growing Saccharomyces cerevisiae cells

“…This may be because ergosterol itself was able to exert feedback regulation at different steps of the pathway. Indeed, the expression of ERG3, for example, was shown to be dependent on the endogenous ergosterol level [45]. A proposed hypothesis to explain the deregulation of the pathway could be that SUT1 overexpression might result in the upregulation of HMG2 which is normally repressed in aerobiosis and is less sensitive to retro-inhibition by ergosterol than HMG1 [46].…”