Myeloid translocation gene-16 co-repressor promotes degradation of hypoxia-inducible factor 1.

Parveen Kumar,Ram Ajore,Urban Gullberg,Inge Olsson,Sonia Rocha

doi:10.1371/journal.pone.0123725

Abstract

The myeloid translocation gene 16 (MTG16) co-repressor down regulates expression of multiple glycolytic genes, which are targets of the hypoxia-inducible factor 1 (HIF1) heterodimer transcription factor that is composed of oxygen-regulated labile HIF1α and stable HIF1β subunits. For this reason, we investigated whether MTG16 might regulate HIF1 negatively contributing to inhibition of glycolysis and stimulation of mitochondrial respiration. A doxycycline Tet-On system was used to control levels of MTG16 in B-lymphoblastic Raji cells. Results from co-association studies revealed MTG16 to interact with HIF1α. The co-association required intact N-terminal MTG16 residues including Nervy Homology Region 1 (NHR1). Furthermore, electrophoretic mobility shift assays demonstrated an association of MTG16 with hypoxia response elements (HREs) in PFKFB3, PFKFB4 and PDK1 promoters in-vitro. Results from chromatin immunoprecipitation assays revealed co-occupancy of these and other glycolytic gene promoters by HIF1α, HIF1β and MTG16 in agreement with possible involvement of these proteins in regulation of glycolytic target genes. In addition, MTG16 interacted with prolyl hydroxylase D2 and promoted ubiquitination and proteasomal degradation of HIF1α. Our findings broaden the area of MTG co-repressor functions and reveal MTG16 to be part of a protein complex that controls the levels of HIF1α.

Highlights

Co-repressors modulate gene expression by controlling activities of transcription factor complexes
We demonstrate that the myeloid translocation gene 16 (MTG16) corepressor is an opposing regulator of hypoxia-inducible factor 1 (HIF1) by serving as a HIF1α-interacting protein with an amplifying effect on HIF1α hydroxylation and proteasomal degradation
The relevance of MTG16-mediated reduction of HIF1α observed under the non-hypoxic conditions may be questioned, as HIF1α was much lower than in the cells exposed to hypoxia

Summary

Introduction

Co-repressors modulate gene expression by controlling activities of transcription factor complexes. Restoration/elevation of the myeloid translocation gene 16 (MTG16) corepressor inhibited expression of key genes of glucose metabolism, which diminished glycolysis, stimulated mitochondrial respiration and decreased cell cycle activity [1]. The conserved MTG co-repressor gene family with similarity to Nervy in Drosophila accommodates MTG8 (or eight-twenty one, ETO) and MTG-related protein-1 (MTGR1) [2]. MTG16 is the most highly expressed isoform in hematopoietic stem/progenitor, erythroid, megakaryocytic, and B cells [3,4]. All MTG genes are targets of chromosomal translocations in leukemia as fusion partners to the gene encoding the transcription factor AML1 [5,6,7,8,9,10]. PLOS ONE | DOI:10.1371/journal.pone.0123725 May 14, 2015

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