CSN-5, a Component of the COP9 Signalosome Complex, Regulates the Levels of UNC-96 and UNC-98, Two Components of M-lines in Caenorhabditis elegans Muscle

• Authors: Rachel K. Miller, Emory University; Hiroshi Qadota, Emory University; Thomas J. Stark, Emory University; Kristina B. Mercer, Emory University; Tesheka S. Wortham, Emory University; Akwasi Anyanful, Emory University; Guy Benian, Emory University
• Journal Title: Molecular Biology of the Cell
• Volume: Volume 20, Number 15
• Publisher: American Society for Cell Biology | 2009-08-01, Pages 3608-3616
• Type of Work: Article | Final Publisher PDF
• Publisher DOI: http://doi.org/10.1091/mbc.E09-03-0208
• Subjects: Health Sciences, Pathology; Biology, Molecular; Biology, Cell

Abstract

In Caenorhabditis elegans two M-line proteins, UNC-98 and UNC-96, are involved in myofibril assembly and/or maintenance, especially myosin thick filaments. We found that CSN-5, a component of the COP9 signalosome complex, binds to UNC-98 and -96 using the yeast two-hybrid method. These interactions were confirmed by biochemical methods. The CSN-5 protein contains a Mov34 domain. Although one other COP9 signalosome component, CSN-6, also has a Mov34 domain, CSN-6 did not interact with UNC-98 or -96. Anti-CSN-5 antibody colocalized with paramyosin at A-bands in wild type and colocalized with abnormal accumulations of paramyosin found in unc-98, -96, and -15 (encodes paramyosin) mutants. Double knockdown of csn-5 and -6 could slightly suppress the unc-96 mutant phenotype. In the double knockdown of csn-5 and -6, the levels of UNC-98 protein were increased and the levels of UNC-96 protein levels were slightly reduced, suggesting that CSN-5 promotes the degradation of UNC-98 and that CSN-5 stabilizes UNC-96. In unc-15 and unc-96 mutants, CSN-5 protein was reduced, implying the existence of feed back regulation from myofibril proteins to CSN-5 protein levels. Taken together, we found that CSN-5 functions in muscle cells to regulate UNC-98 and -96, two M-line proteins.