THOC5, a member of the mRNA export complex, contributes to processing of a subset of wingless/integrated (Wnt) target mRNAs and integrity of the gut epithelial barrier

Shashank Saran,Doan Dh Tran,Teruko Tamura,Himpriya Chopra,Robert Klopfleisch,Andrea Hoffmann,Alexandra Koch,Lutz Wiehlmann,Oliver Pabst,Patricia Moran-Losada,Sabine Klebba-Färber

doi:10.1186/1471-2121-14-51

Shashank Saran, Doan Dh Tran + Show 9 more

Open Access

https://doi.org/10.1186/1471-2121-14-51

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Abstract

BackgroundTHO (Suppressors of the transcriptional defects of hpr1 delta by overexpression) complex 5 (THOC5), an mRNA export protein, is involved in the expression of only 1% of all genes. Using an interferon inducible knockout mouse system, we have previously shown that THOC5 is an essential element in the maintenance of hematopoietic stem cells and cytokine-mediated hematopoiesis in adult mice. Here we interrogate THOC5 function in cell differentiation beyond the hematopoietic system and study pathological changes caused by THOC5 deficiency.ResultsTo examine whether THOC5 plays a role in general differentiation processes, we generated tamoxifen inducible THOC5 knockout mice. We show here that the depletion of THOC5 impaired not only hematopoietic differentiation, but also differentiation and self renewal of the gut epithelium. Depletion of the THOC5 gene did not cause pathological alterations in liver or kidney.We further show that THOC5 is indispensable for processing of mRNAs induced by Wnt (wingless/integrated) signaling which play key roles in epithelial cell differentiation/proliferation. A subset of Wnt target mRNAs, SRY-box containing gene 9 (Sox9), and achaete-scute complex homolog 2 (Ascl2), but not Fibronectin 1 (Fn1), were down-regulated in THOC5 knockout intestinal cells. The down-regulated Wnt target mRNAs were able to bind to THOC5. Furthermore, pathological alterations in the gastrointestinal tract induced translocation of intestinal bacteria and caused sepsis in mice. The bacteria translocation may cause Toll-like receptor activation. We identified one of the Toll-like receptor inducible genes, prostaglandin-endoperoxidase synthase 2 (Ptgs2 or COX2) transcript as THOC5 target mRNA.ConclusionTHOC5 is indispensable for processing of only a subset of mRNAs, but plays a key role in processing of mRNAs inducible by Wnt signals. Furthermore, THOC5 is dispensable for general mRNA export in terminally differentiated organs, indicating that multiple mRNA export pathways exist. These data imply that THOC5 may be a useful tool for studying intestinal stem cells, for modifying the differentiation processes and for cancer therapy.

Highlights

THO (Suppressors of the transcriptional defects of hpr1 delta by overexpression) complex 5 (THOC5), an mRNA export protein, is involved in the expression of only 1% of all genes
We have previously shown that THOC5 is a substrate for several tyrosine kinases such as macrophage-colony stimulating factor (M-CSF, or CSF-1) receptor, Fms [9], and various leukemogenic tyrosine kinases, such as BcrAbl, translocation-ets-leukemia (TEL)-platelet derived growth factor (PDGF) receptor, or nucleophosmin (NPM)-anaplastic lymphoma kinase (ALK) [10,11]
We examined whether THOC5 plays a role in processing of wingless/ integrated (Wnt) target mRNAs, SRY-box containing gene 9 (Sox9) or achaete-scute complex homolog 2 (Ascl2)

Summary

Introduction

THO (Suppressors of the transcriptional defects of hpr delta by overexpression) complex 5 (THOC5), an mRNA export protein, is involved in the expression of only 1% of all genes. The THO complex, which is a sub-member of TREX (transcription/export), was originally identified in Saccharomyces cerevisiae as a five protein complex (Tho2p, Hpr1p, Mft1p, Thp2p, and Tex1) [1,2,3,4,5,6] that plays a role in transcriptional elongation, nuclear RNA export and genome stability In higher eukaryotes such as Drosophila melanogaster [7] or humans [8], three proteins, (THOC1/ hHpr1/p84, THOC2/hRlr, and THOC3) and three additional unique proteins were identified, namely THOC5/ Fms interacting protein (FMIP) [9], THOC6 and THOC7, as members of the THO complex. We recently examined THOC5 dependent mRNAs in monocytes/macrophages In this system only 99 genes were down-regulated upon depletion of THOC5 [17]. Depletion of THOC5 does not affect bulk poly (A) + RNA export [18] and it has been recently shown that the knockdown of THOC5 in Hela cells leads to down-regulation of 289 genes [19]

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