PolyQ‐expanded huntingtin and ataxin‐3 sequester ubiquitin adaptors hHR23B and UBQLN2 into aggregates via conjugated ubiquitin

Abstract

The components of ubiquitin (Ub)-proteasome system, such as Ub, Ub adaptors, or proteasome subunits, are commonly accumulated with the aggregated proteins in inclusions, but how protein aggregates sequester Ub-related proteins remains elusive. Using N-terminal huntingtin (Htt-N552) and ataxin (Atx)-3 as model proteins, we investigated the molecular mechanism underlying sequestration of Ub adaptors by polyQ-expanded proteins. We found that polyQ-expanded Htt-N552 and Atx-3 sequester endogenous Ub adaptors, human RAD23 homolog B (hHR23B) and ubiquilin (UBQLN)-2, into inclusions. This sequestration effect is dependent on the UBA domains of Ub adaptors and the conjugated Ub of the aggregated proteins. Moreover, polyQ-expanded Htt-N552 and Atx-3 reduce the protein level of xeroderma pigmentosum group C (XPC) by sequestration of hHR23B, suggesting that this process may cut down the available quantity of hHR23B and thus affect its normal function in stabilizing XPC. Our findings demonstrate that polyQ-expanded proteins sequester Ub adaptors or other Ub-related proteins into aggregates or inclusions through ubiquitination of the pathogenic proteins. This study may also provide a common mechanism for the formation of Ub-positive inclusions in cells.-Yang, H., Yue, H.-W., He, W.-T., Hong, J.-Y., Jiang, L.-L., Hu, H.-Y. PolyQ-expanded huntingtin and ataxin-3 sequester ubiquitin adaptors hHR23B and UBQLN2 into aggregates via conjugated ubiquitin.

Inclusion bodies formed by polyglutamine and poly(glycine-alanine) are enriched with distinct proteomes but converge in proteins that are risk factors for disease and involved in protein degradation

“…Four of these proteins (all except Dnajb1) form a robust protein-protein interaction network with a significant gene ontology enrichment for clathrin coat assembly (GO:0048268; FDR of 0.0031) suggestive that this mechanism is involved in polyQ aggregation. Clint1 and Ubqln2 were previously shown to colocalize to polyQ inclusions, supporting this conclusion [47, 59]. An interesting note with respect to mechanism is that UBQLN2 targets ubiquitinated substrates for degradation in ERAD and autophagy [60].…”

Immiscible inclusion bodies formed by polyglutamine and poly(glycine-alanine) are enriched with distinct proteomes but converge in proteins that are risk factors for disease and involved in protein degradation

“…Clint1 and Ubqln2 were previously shown to colocalize to polyQ inclusions, supporting this conclusion [54,74]. An interesting note with respect to mechanism is that UBQLN2 targets ubiquitinated substrates for degradation in ERAD and autophagy [75].…”

Domain interactions reveal auto-inhibition of the deubiquitinating enzyme USP19 and its activation by HSP90 in the modulation of huntingtin aggregation

“…The CS2-domian mutants, including D288A, D288N, Y290A, K292A, H300A, Y302A and R367A were constructed by site-directed mutagenesis. For construction of the eukaryotic expression plasmid, USP19_b and its mutants were cloned into the eukaryotic expression vector HA-pcDNA3.0 [20]; and Htt-N552 100Q was cloned into FLAG-pcDNA3.1 [25]. All the expression plasmids used and the primers for cloning are listed in Supplementary Table S2.…”