# Novel roles for USP36 in ribosome biogenesis

> **NIH NIH R01** · OREGON HEALTH & SCIENCE UNIVERSITY · 2020 · $305,717

## Abstract

Project Summary
Ribosome biogenesis, a complex cellular process for making the ribosome in the nucleolus, is essential for
normal cell growth and proliferation. Defects in ribosome biogenesis are associated with a group of diseases
called ribosomopathies. Thus, it is crucial to understand how ribosome biogenesis is properly regulated during
normal cell homeostasis. It has been shown that SUMOylation plays a key role in ribosome biogenesis in the
nucleolus, including rRNA synthesis and processing, ribosome subunit assembly, maturation and nuclear
export. Yet, a SUMO ligase (E3) mediating nucleolar SUMOylation has not been identified. We recently
discovered that the deubiquitinating enzyme USP36 is a novel nucleolar SUMO E3. Overexpression of USP36
promotes SUMOylation, mainly in the nucleolus, whereas knockdown of USP36 drastically reduces the levels
of SUMOylation in cells. We show that USP36 directly binds to Ubc9 (SUMO E2) and SUMO, and possesses
SUMO E3 activity in vitro in reconstituted systems, demonstrating that USP36 is a novel bona fide SUMO E3.
The SUMO E3 activity is mapped to an N-terminal region (amino acids 120-300). We further found that USP36
mediates the SUMOylation of Nop58 and Nhp2, components of the box C/D and box H/ACA small nucleolar
ribonucleoprotein (snoRNP) complexes, respectively, and regulates their binding to snoRNAs. Together, these
data lead to a novel hypothesis that USP36 functions as a crucial SUMO E3 mediating nucleolar
SUMOylation and thus being critical for ribosome biogenesis. To gain further insight into the role of USP36 in
the regulation of nucleolar SUMOylation and ribosome biogenesis, we will investigate the molecular and
biochemical mechanisms underlying the SUMO E3 activity of USP36 in Aim 1, including how the N-terminal
SUMO E3 domain contributes to USP36's SUMO E3 activity, how USP36 promotes poly-SUMO chain
formation and SUMO transfer to substrates, and how its SUMO E3 and Dub activity are determined. We will
then elucidate the nucleolar functions of USP36 as a SUMO E3 in snoRNP and ribosome biogenesis in Aim 2,
including whether USP36 regulates snoRNP and ribosome biogenesis-related protein group SUMOylation,
whether it regulates rRNA modifications and rRNA processing, and whether it also regulates ribosome subunit
maturation and nuclear export. Finally, we will elucidate whether USP36's nucleolar SUMO E3 activity is critical
for cell growth and proliferation as well as tissue homeostasis and regeneration in vivo using inducible USP36
knockout mice models in Aim 3. Achieving these goals will provide critical insight into how USP36 properly
regulates SUMOylation in the nucleolus and how it regulates ribosome biogenesis.

## Key facts

- **NIH application ID:** 9978841
- **Project number:** 5R01GM130604-02
- **Recipient organization:** OREGON HEALTH & SCIENCE UNIVERSITY
- **Principal Investigator:** Mu-Shui Dai
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $305,717
- **Award type:** 5
- **Project period:** 2019-07-16 → 2023-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9978841

## Citation

> US National Institutes of Health, RePORTER application 9978841, Novel roles for USP36 in ribosome biogenesis (5R01GM130604-02). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9978841. Licensed CC0.

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