Characterization of a brain-enriched chaperone, MRJ, that inhibits Huntingtin aggregation and toxicity independently.

Molecular chaperones are involved in a wide range of cellular events, such as protein folding and oligomeric protein complex assembly. DnaK- and DnaJ-like proteins are the two major classes of molecular chaperones in mammals. Recent studies have shown that DnaJ-like family proteins can inhibit polyglutamine aggregation, a hallmark of many neurodegenerative diseases, including Huntington's disease (HD). Although most DnaJ-like proteins studied are ubiquitously expressed, some have restricted expression, so it is possible that some specific chaperones may affect polyglutamine aggregation in specific neurons. In this report, we describe the isolation of a DnaJ-like protein MRJ and the characterization of its chaperone activity. Tissue distribution studies showed that MRJ is highly enriched in the central nervous system. In an in vitro cell model of HD, overexpressed MRJ effectively suppressed polyglutamine-dependent protein aggregation, caspase activity, and cellular toxicity. Collectively, these results suggest that MRJ has a relevant functional role in neurons.