The ubiquitin ligase CHIP/STUB1 targets mutant keratins for degradation.
Keratin (K) intermediate filament proteins form cytoskeletal scaffolds in epithelia, the disruption of which leads to a large number of human disorders. KRT5 or KRT14 mutations cause epidermolysis bullosa simplex (EBS). The considerable intra- and interfamilial variability in EBS suggests modifying loci, most of which are unknown. In many human disorders, chaperones and the ubiquitin-proteasome system have been found to modify disease severity, thereby providing novel therapy targets. Here, we demonstrate upregulation of stress-induced Hsp70 and Hsp90 in two EBS models, namely, in neonatal K5(-/-) mice and upon proteasome inhibition in cells that stably express the disease-causing mutation K14-p.Arg125Cys, both harboring keratin aggregates. Furthermore, proteasome inhibition caused nuclear translocation of pHSF-1 and an increase in K14-p.Arg125Cys-positive aggregates in cells. Overexpression of the chaperone-associated ubiquitin ligase CHIP/STUB1 strongly reduced keratin aggregates through increased degradation of mutant K14. Using CHIP-p.Met1_Ala142del (DeltaTPR-CHIP), we demonstrated the involvement of Hsc70 and Hsp70 in mutant keratin degradation. Our data uncover common principles between EBS and other protein misfolding disorders, revealing that aggregation-prone keratins are targeted by components of the chaperone machinery. Thus, modulation of the chaperone machinery using small molecules may represent a novel therapeutic strategy for dominant EBS, allowing reformation of an intact keratin cytoskeleton.
Löffek
Stefanie
S
Institute of Biochemistry and Molecular Biology, University of Bonn, Nussallee 11, Bonn, Germany. loeffek@ibmb.uni-bonn.de
Wöll
Stefan
S
Höhfeld
Jörg
J
Leube
Rudolf E
RE
Has
Cristina
C
Bruckner-Tuderman
Leena
L
Magin
Thomas M
TM
D000818:Animals; D045744:Cell Line, Tumor; D016110:Epidermolysis Bullosa Simplex / Q000378:metabolism / Q000473:pathology; D050883:HSC70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D007633:Keratins / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D018832:Molecular Chaperones / Q000378:metabolism; D050505:Mutant Proteins / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D011499:Protein Processing, Post-Translational; D020836:Protein Structure, Quaternary; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
D050883:HSC70 Heat-Shock Proteins; D018832:Molecular Chaperones; D050505:Mutant Proteins; D061988:Proteasome Inhibitors; D007633:Keratins; C467728:STUB1 protein, human; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex