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Roberts, J. E.

Publications and source records attributed to Roberts, J. E..

2 recordsLinked to original sources
bioRxiv2025

UBQLN2 facilitates degradation of the retrotransposon protein PEG10 via UBE3A activity

Ubiquilins are a family of extrinsic ubiquitin receptors that are thought to facilitate protein degradation by shuttling proteins to the proteasome. However, the defining characteristics of Ubiquilin clients, and the steps of Ubiquilin-mediated degradation, have been elusive. Previously, we showed Ubiquilin 2 (UBQLN2) regulates the proteasomal degradation of PEG10, a unique virus-like protein which comes in two forms: a gag protein which is not regulated by UBQLN2, and a gag-pol protein which is dependent on UBQLN2. Here, we refine the model of Ubiquilin activity through the UBQLN2-mediated degradation of PEG10. UBQLN2 binding did not ensure degradation, and was independent of client ubiquitination, though ubiquitination of key lysine residues was necessary for gag-pol proteolysis. Ubiquitination was dependent on the E3 ubiquitin ligase UBE3A, which was surprisingly unable to regulate gag-pol in the absence of UBQLN2. Together, we have established a stepwise model of UBQLN2-mediated degradation that represents a new perspective on Ubiquilin function. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=183 SRC="FIGDIR/small/646022v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@21f763org.highwire.dtl.DTLVardef@1f88cdborg.highwire.dtl.DTLVardef@e79156org.highwire.dtl.DTLVardef@f6d6ce_HPS_FORMAT_FIGEXP M_FIG Graphical abstract: Working model of UBQLN2 and UBE3A-mediated degradation of PEG10 gag-pol. In an apparent first step, UBQLN2 binds both PEG10 gag and gag-pol through STI1:gag-dominated interactions, independent of PEG10 ubiquitination. Either concurrently or immediately thereafter, UBQLN2 binds to UBE3A through interactions facilitated by UBA:AZUL domain binding, though other protein domains contribute to this interaction as well. UBE3A and other unknown E3 ligases contribute to the ubiquitination of gag-pol on lysine residues of both the gag and pol regions, which is necessary for proteasomal degradation. The proteasome also interacts with UBQLN2:UBE3A:PEG10, likely through UBL domain interactions with the regulatory cap. Inhibition of E1 ubiquitin activation through TAK243, UBE3A activity with siRNA, or proteasomal degradation with Bortezomib all interfere with UBQLN2-mediated PEG10 degradation. C_FIG

cell biology↗
bioRxiv2022

UBQLN2 restrains the domesticated retrotransposon PEG10 to maintain neuronal health in ALS

Amyotrophic Lateral Sclerosis (ALS) is a fatal, neurodegenerative disease characterized by progressive motor neuron dysfunction and loss. A portion of ALS is caused by mutation of the proteasome shuttle factor Ubiquilin 2 (UBQLN2), but the molecular pathway leading from UBQLN2 dysfunction to disease remains unclear. Here, we demonstrate a function of UBQLN2 in regulating activity of the domesticated gag-pol retrotransposon paternally expressed gene 10 (PEG10) in human cells and tissues. In cells, the PEG10 gag-pol protein cleaves itself in a mechanism reminiscent of retrotransposon self-processing to generate a liberated nucleocapsid fragment, which uniquely localizes to the nucleus and changes expression of genes involved in axon remodeling. In spinal cord tissue from ALS patients, PEG10 gag-pol is elevated compared to healthy controls. These findings implicate the retrotransposon-like activity of PEG10 as a contributing mechanism in ALS through regulation of gene expression, and restraint of PEG10 as a primary function of UBQLN2.

cell biology↗