RTL8 promotes nuclear localization of UBQLN2 to subnuclear compartments associated with protein quality control

Harihar Milaganur Mohan, Hanna Trzeciakiewicz, Amit Pithadia, Emily V. Crowley, Regina Pacitto, Nathaniel Safren, Bryce Trotter, Chengxin Zhang, Xiaogen Zhou, Yang Zhang, Venkatesha Basrur, Henry L. Paulson*, Lisa M. Sharkey*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


The brain-expressed ubiquilins (UBQLNs) 1, 2 and 4 are a family of ubiquitin adaptor proteins that participate broadly in protein quality control (PQC) pathways, including the ubiquitin proteasome system (UPS). One family member, UBQLN2, has been implicated in numerous neurodegenerative diseases including ALS/FTD. UBQLN2 typically resides in the cytoplasm but in disease can translocate to the nucleus, as in Huntington’s disease where it promotes the clearance of mutant Huntingtin. How UBQLN2 translocates to the nucleus and clears aberrant nuclear proteins, however, is not well understood. In a mass spectrometry screen to discover UBQLN2 interactors, we identified a family of small (13 kDa), highly homologous uncharacterized proteins, RTL8, and confirmed the interaction between UBQLN2 and RTL8 both in vitro using recombinant proteins and in vivo using mouse brain tissue. Under endogenous and overexpressed conditions, RTL8 localizes to nucleoli. When co-expressed with UBQLN2, RTL8 promotes nuclear translocation of UBQLN2. RTL8 also facilitates UBQLN2’s nuclear translocation during heat shock. UBQLN2 and RTL8 colocalize within ubiquitin-enriched subnuclear structures containing PQC components. The robust effect of RTL8 on the nuclear translocation and subnuclear localization of UBQLN2 does not extend to the other brain-expressed ubiquilins, UBQLN1 and UBQLN4. Moreover, compared to UBQLN1 and UBQLN4, UBQLN2 preferentially stabilizes RTL8 levels in human cell lines and in mouse brain, supporting functional heterogeneity among UBQLNs. As a novel UBQLN2 interactor that recruits UBQLN2 to specific nuclear compartments, RTL8 may regulate UBQLN2 function in nuclear protein quality control.

Original languageEnglish (US)
Article number176
JournalCellular and Molecular Life Sciences
Issue number3
StatePublished - Mar 2022


  • Nuclear protein quality control
  • RTL8
  • UBQLN2
  • Ubiquilin
  • Ubiquitin proteasome system

ASJC Scopus subject areas

  • Cellular and Molecular Neuroscience
  • Molecular Medicine
  • Molecular Biology
  • Cell Biology
  • Pharmacology


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