Inhibitor of Growth 4 (ING4) is a positive regulator of rRNA synthesis

Duc-Anh Trinh,Ryutaro Shirakawa,Hisanori Horiuchi,Natsumi Sakata,Kota Goto,Tomohiro Kimura

doi:10.1038/s41598-019-53767-1

Abstract

Ribosome biogenesis is essential for maintaining basic cellular activities although its mechanism is not fully understood. Inhibitor of growth 4 (ING4) is a member of ING family while its cellular functions remain controversial. Here, we identified several nucleolar proteins as novel ING4 interacting proteins. ING4 localized in the nucleus with strong accumulation in the nucleolus through its plant homeodomain, which is known to interact with histone trimethylated H3K4, commonly present in the promoter of active genes. ING4 deficient cells exhibited slower proliferation and the alteration in nucleolar structure with reduced rRNA transcription, which was rescued by exogenous expression of GFP-ING4 to the similar levels of wild type cells. In the ING4 deficient cells, histone H3K9 acetylation and the key rRNA transcription factor UBF at the promoter of rDNA were reduced, both of which were also recovered by exogenous GFP-ING4 expression. Thus, ING4 could positively regulate rRNA transcription through modulation of histone modifications at the rDNA promoter.

Highlights

Inhibitor of Growth (ING) protein family is composed of 5 members, which share a highly conserved homologous plant-homeodomain (PHD) at their C-terminus
Among the Inhibitor of growth 4 (ING4)-associated proteins identified, several nucleolar proteins such as nucleolar and coiled-body phosphoprotein 1 (NOLC1) that is known important in ribosomal RNA (rRNA) transcription19, 1Department of Oral Cancer Therapeutics, Graduate School of Dentistry, Tohoku University, Sendai, Japan. 2Department of Molecular and Cellular Biology, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan. 3Present address: Research Center for Molecular Genetics, Institute for Promotion of Medical Science Research, Yamagata University Faculty of Medicine, Yamagata, Yamagata, Japan. *email: hisanori.horiuchi.e8@ tohoku.ac.jp www.nature.com/scientificreports/
Www.nature.com/scientificreports nucleolar GTP-binding protein 2 (GNL2) that is important in the rRNA assembly and export[20], G Protein nucleolar 3 (GNL3) that is important in rRNA processing[21], nucleolar GTP-binding protein 1 (NGB1) and nucleolin (NCL), a critical regulator of rRNA transcription[22,23], were included (Fig. 1A)

Summary

Introduction

Inhibitor of Growth (ING) protein family is composed of 5 members, which share a highly conserved homologous plant-homeodomain (PHD) at their C-terminus. ING1, the prototype member of ING family, has first been demonstrated to inhibit cell proliferation[3]. As for the function of ING4 in cell proliferation, both positive and negative regulations have so far been reported. ING4 has been reported to bind and activate p53, resulting in induction of p21 tumor suppressor and inhibition of cell proliferation[10,11]. Upstream binding factor (UBF) is considered the most prominent transcription factor because its binding to the rDNA promoter is critical for recruitment of the pre-initiation complex and Pol I activity[16,17,18]. We identified several nucleolar proteins as novel ING4 binding proteins, and demonstrated that ING4 promoted cell proliferation and rRNA synthesis through modulating histone modifications at rDNA promoters

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Conclusion