Ubiquitin-Binding Protein CG5445 Suppresses Aggregation and Cytotoxicity of Amyotrophic Lateral Sclerosis-Linked TDP-43 in Drosophila

Abstract

Ubiquitin-mediated protein degradation plays essential roles in proteostasis and is involved in the pathogenesis of neurodegenerative diseases in which ubiquitin-positive aberrant proteins accumulate. However, how such aberrant proteins are processed inside cells has not been fully explored. Here, we show that the product of , a previously uncharacterized gene, prevents the accumulation of aggregate-prone ubiquitinated proteins. We found that ubiquitin conjugates were associated with CG5445, the knockdown of which caused the accumulation of detergent-insoluble ubiquitinated proteins. Furthermore, CG5445 rescued eye degeneration caused by the amyotrophic lateral sclerosis (ALS)-linked mutant TAR DNA-binding protein of 43 kDa (TDP-43), which often forms ubiquitin-positive aggregates in cells through the capacity of CG5445 to bind to ubiquitin chains. Biochemically, CG5445 inhibited the accumulation of insoluble forms and promoted their clearance. Our results demonstrate a new possible mechanism by which cells maintain ubiquitinated aggregation-prone proteins in a soluble form to decrease their cytotoxicity until they are degraded.

The N Termini of TAR DNA-Binding Protein 43 (TDP43) C-Terminal Fragments Influence Degradation, Aggregation Propensity, and Morphology

“…4A and B ). A number of proteins have been reported to play a role in TDP43 clearance ( 65 , 78 – 80 ). Recently, the β4-strand of the RRM2 domain of human TDP43 was shown to harbor a degradation signal recognized by the VHL/ElonginB/C/Cul2/Rbx1 complex ( 80 ).…”

Specific Modification of Aged Proteasomes Revealed by Tag-Exchangeable Knock-In Mice

“…Antibodies. The antibodies against Rpn1 to -3, Rpn6 to -8, Rpn10, Rpn13, Rpt1 to -6, ␣2, ␤3, Uch37, Usp14, Txnl1, HHR23b, and PA28␥ were described previously (62)(63)(64)(65)(66)(67). Polyclonal antibodies against Rpn5, Rpn9, Rpn11, EGFP, and HaloTag were raised in rabbits by using recombinant proteins of human Rpn5 (residues 1 to 161), human Rpn9 (full length), human Rpn11 (residues 171 to 287), EGFP (full length), and HaloTag (full length), respectively.…”

Amyotrophic Lateral Sclerosis Genes in Drosophila melanogaster

“…This indicates that the level of TDP-43 must be tightly regulated throughout life. GOF experiments also revealed that excess of TBPH or TDP-43 is highly toxic in muscles [ 270 , 306 , 307 ], glial cells [ 270 , 307 , 309 , 325 , 326 ], and in the eye [ 266 , 274 , 289 , 290 , 292 , 293 , 302 , 303 , 304 , 306 , 307 , 310 , 312 , 314 , 315 , 316 , 317 , 318 , 319 , 320 , 324 , 327 , 328 , 329 , 330 , 331 , 332 , 333 , 334 ]. Moreover, it was reported that TBPH or TDP-43 overexpression induces cell death, as was shown in motoneurons [ 266 , 289 , 290 , 301 ], glial cells [ 309 , 326 ], mushroom bodies [ 265 , 290 ], and in the eye.…”

“…This may explain some discrepancies between different GOF studies ( Table 9 and Table 10 ). Several phenotypes induced by TBPH /TDP-43 GOF, such as eye degeneration and climbing defects, show age-dependent progression [ 265 , 275 , 289 , 290 , 293 , 305 , 307 , 308 , 309 , 311 , 312 , 314 , 315 , 316 , 318 , 320 , 321 , 324 , 325 , 330 , 331 , 332 , 333 , 334 ]. As TBPH expression decreased with aging [ 338 ], one may speculate that reduced endogenous TBPH levels exacerbate GOF effects without excluding that phenotype aggravation may be due to continuous abnormal accumulation of TBPH /TDP-43.…”

“…Additionally, dUBPY silencing enhanced the age-dependent eye degeneration induced by TDP-43 expression [ 332 ]. Another study found that the TDP-43 M337V -induced eye degeneration was suppressed or enhanced by GOF and LOF of CG5445 gene, respectively [ 334 ]. CG5445 encodes a protein that interacts with ubiquitinated proteins and promotes their degradation [ 334 ].…”