Triggering aggresome formation. Dissecting aggresome-targeting and aggregation signals in synphilin 1.
Abnormal polypeptides that escape proteasome-dependent degradation and aggregate in cytosol can be transported via microtubules to an aggresome, a recently discovered organelle where aggregated proteins are stored or degraded by autophagy. We used synphilin 1, a protein implicated in Parkinson disease, as a model to study mechanisms of aggresome formation. When expressed in naïve HEK293 cells, synphilin 1 forms multiple small highly mobile aggregates. However, proteasome or Hsp90 inhibition rapidly triggered their translocation into the aggresome, and surprisingly, this response was independent on the expression level of synphilin 1. Therefore, aggresome formation, but not aggregation of synphilin 1, represents a special cellular response to a failure of the proteasome/chaperone machinery. Importantly, translocation to aggresomes required a special aggresome-targeting signal within the sequence of synphilin 1, an ankyrin-like repeat domain. On the other hand, formation of multiple small aggregates required an entirely different segment within synphilin 1, indicating that aggregation and aggresome formation determinants can be separated genetically. Furthermore, substitution of the ankyrin-like repeat in synphilin 1 with an aggresome-targeting signal from huntingtin was sufficient for aggresome formation upon inhibition of the proteasome. Analogously, attachment of the ankyrin-like repeat to a huntingtin fragment lacking its aggresome-targeting signal promoted its transport to aggresomes. These findings indicate the existence of transferable signals that target aggregation-prone polypeptides to aggresomes.
Zaarur
Nava
N
Department of Biochemistry, Boston University Medical School, Boston, Massachusetts 02118.
Meriin
Anatoli B
AB
Department of Biochemistry, Boston University Medical School, Boston, Massachusetts 02118.
Gabai
Vladimir L
VL
Department of Biochemistry, Boston University Medical School, Boston, Massachusetts 02118.
Sherman
Michael Y
MY
Department of Biochemistry, Boston University Medical School, Boston, Massachusetts 02118. Electronic address: sherma1@bu.edu.
D020816:Amino Acid Motifs / Q000235:genetics; D001343:Autophagy / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism*; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D000071058:Huntingtin Protein; D008870:Microtubules / Q000235:genetics / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010300:Parkinson Disease / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000235:genetics; D021381:Protein Transport / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics
D002352:Carrier Proteins; D018841:HSP90 Heat-Shock Proteins; C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D021382:Protein Sorting Signals; C118958:SNCAIP protein, human; D046988:Proteasome Endopeptidase Complex