Phosphatase UBLCP1 controls proteasome assembly.

Shuangwu Sun,Xia Lin,Sisi Liu,Tao Tao,Chuang Sun,Xin-Hua Feng,Wang Zeng,Zhengmao Zhang

doi:10.1098/rsob.170042

Abstract

Ubiquitin-like domain-containing C-terminal domain phosphatase 1 (UBLCP1), an FCP/SCP phosphatase family member, was identified as the first proteasome phosphatase. UBLCP1 binds to proteasome subunit Rpn1 and dephosphorylates the proteasome in vitro. However, it is still unclear which proteasome subunit(s) are the bona fide substrate(s) of UBLCP1 and the precise mechanism for proteasome regulation remains elusive. Here, we show that UBLCP1 selectively binds to the 19S regulatory particle (RP) through its interaction with Rpn1, but not the 20S core particle (CP) or the 26S proteasome holoenzyme. In the RP, UBLCP1 dephosphorylates the subunit Rpt1, impairs its ATPase activity, and consequently disrupts the 26S proteasome assembly, yet it has no effects on the RP assembly from precursor complexes. The Rpn1-binding and phosphatase activities of UBLCP1 are essential for its function on Rpt1 dephosphorylation and proteasome activity both in vivo and in vitro. Our study establishes the essential role of the UBLCP1/Rpn1/Rpt1 complex in regulating proteasome assembly.

Highlights

The ubiquitin proteasome system (UPS) plays a key role in maintaining cellular proteostasis [1]
We independently found the interaction of Ubiquitin-like domain-containing C-terminal domain phosphatase 1 (UBLCP1), a member of the small C-terminal domain phosphatases (SCPs) family, with the proteasome
We found that pre-incubation with recombinant glutathione S-transferase (GST)-UBLCP1 disabled regulatory particles (RP) to bind and activate core particle (CP), while RP pretreated with phosphatase-dead GST-DDAA retained its ability to activate CP in degradation of artificial substrate Suc-LLVY-AMC

Summary

Introduction

The ubiquitin proteasome system (UPS) plays a key role in maintaining cellular proteostasis [1]. Aberrant proteostasis may lead to cell dysfunction and diseases such as cancer and neurodegenerative disorders. A functional 26S proteasome comprises a barrel-shaped 20S core particle (CP) [1,2] and one or two 19S regulatory particles (RP) capping at the ends [2,3]. Poly-ubiquitinated protein substrates are first recognized by RP through ubiquitin receptors or ubiquitin shuttle receptors in the RP [2,5,6]. RP is responsible for substrate unfolding and CP a-ring gate opening in an ATPdependent manner [9 –11]. The substrates committed to degradation will be translocated into the hydrolytic chamber of the CP for degradation

Methods

Results

Conclusion