Mediator Subunit Gal11p/MED15 Is Required for Fatty Acid-dependent Gene Activation by Yeast Transcription Factor Oaf1p

Jitendra K Thakur,Haribabu Arthanari,Fajun Yang,Katherine H Chau,Gerhard Wagner,Anders M Näär

doi:10.1074/jbc.m808263200

Jitendra K Thakur, Haribabu Arthanari + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m808263200

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Abstract

The yeast zinc cluster transcription factor Oaf1p activates transcription of target genes in response to direct binding of fatty acids in a manner analogous to the vertebrate nuclear receptor peroxisome proliferator-activated receptoralpha (PPARalpha). PPARs and other metazoan nuclear receptors productively engage several distinct LXXLL motif-containing co-activators, including p160 family members and the TRAP220/MED1 subunit of the Mediator co-activator, to promote ligand-dependent gene activation. Yeast, however, does not appear to harbor LXXLL motif co-activators, and the mechanism of fatty acid-dependent gene activation by the yeast PPARalpha analog Oaf1p is unknown. Here we show that the yeast Mediator subunit Gal11p/MED15 and its activator-targeted KIX domain plays a critical role in fatty acid-dependent transcriptional regulation of fatty acid beta-oxidation and peroxisomal genes by Oaf1p and for the ability of yeast to utilize fatty acids as a sole carbon source. Moreover, structural studies by NMR spectroscopy reveal that the Oaf1p activation domain interacts with the Gal11p/MED15 KIX domain in a manner similar to the yeast zinc cluster family member and xenobiotic receptor Pdr1p, revealing that the Gal11p/MED15 KIX domain is a key target of several ligand-dependent transcription factors in yeast. Together with previous work showing that the Caenorhabditis elegans Gal11p/MED15 homolog MDT-15 plays a critical role in regulation of fatty acid metabolism by the nematode PPAR-like nuclear receptor NHR-49, the findings presented here provide evidence for an ancient and essential role of a Mediator co-activator subunit in regulation of fatty acid metabolism by nuclear receptor-like transcription factors in eukaryotes.

Highlights

Vertebrate nuclear receptors, including PPARs, stimulate expression of target genes by recruiting different classes of transcription co-activators, including Mediator, a large co-activator complex conserved from yeast to human [5]
We first tested whether fatty acids and peroxisome proliferators/non-steroidal anti-inflammatory drugs (NSAIDs) interact with a C-terminal fragment of Oaf1p harboring the fatty acid-binding domain [4]
Our findings suggest that binding of peroxisome proliferators cannot relieve intramolecular inhibitory contacts that prevent the Oaf1p activation domain from interacting with the Gal11p/MED15 KIX domain, explaining why these drugs are incapable of effectively inducing transcription of Oaf1p target genes

Summary

Introduction

Vertebrate nuclear receptors, including PPARs, stimulate expression of target genes by recruiting different classes of transcription co-activators, including Mediator, a large co-activator complex conserved from yeast to human [5]. Together with the finding by others that gene activation by the Caenorhabditis elegans PPAR␣-like nuclear receptor NHR-49 requires the Gal11p/MED15 homolog MDT-15 [9], these studies suggest that targeting of the Gal11p/ MED15 KIX domain is a conserved transactivation mechanism shared by members of the fungal ligand-dependent zinc cluster transcription factor family and metazoan nuclear receptors.

Results

Conclusion