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The ubiquitin ligase Ozz decreases the replacement rate of embryonic myosin in myofibrils

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Title: The ubiquitin ligase Ozz decreases the replacement rate of embryonic myosin in myofibrils
Authors: Ichimura, Emi Browse this author
Ojima, Koichi Browse this author
Muroya, Susumu Browse this author
Suzuki, Takahiro Browse this author
Kobayashi, Ken Browse this author →KAKEN DB
Nishimura, Takanori Browse this author →KAKEN DB
Keywords: myofibril
skeletal muscle
thick filament
ubiquitin ligase
ubiquitin-proteasome system
Issue Date: Sep-2021
Publisher: John Wiley & Sons
Journal Title: Physiological reports
Volume: 9
Issue: 17
Start Page: e15003
Publisher DOI: 10.14814/phy2.15003
Abstract: Myosin, the most abundant myofibrillar protein in skeletal muscle, functions as a motor protein in muscle contraction. Myosin polymerizes into the thick filaments in the sarcomere where approximately 50% of embryonic myosin (Myh3) are replaced within 3 h (Ojima K, Ichimura E, Yasukawa Y, Wakamatsu J, Nishimura T, Am J Physiol Cell Physiol 309: C669-C679, 2015). The sarcomere structure including the thick filament is maintained by a balance between protein biosynthesis and degradation. However, the involvement of a protein degradation system in the myosin replacement process remains unclear. Here, we show that the muscle-specific ubiquitin ligase Ozz regulates replacement rate of Myh3. To examine the direct effect of Ozz on myosin replacement, eGFP-Myh3 replacement rate was measured in myotubes overexpressing Ozz by fluorescence recovery after photobleaching. Ozz overexpression significantly decreased the replacement rate of eGFP-Myh3 in the myofibrils, whereas it had no effect on other myosin isoforms. It is likely that ectopic Ozz promoted myosin degradation through increment of ubiquitinated myosin, and decreased myosin supply for replacement, thereby reducing myosin replacement rate. Intriguingly, treatment with a proteasome inhibitor MG132 also decreased myosin replacement rate, although MG132 enhanced the accumulation of ubiquitinated myosin in the cytosol where replaceable myosin is pooled, suggesting that ubiquitinated myosin is not replaced by myosin in the myofibril. Collectively, our findings showed that Myh3 replacement rate was reduced in the presence of overexpressed Ozz probably through enhanced ubiquitination and degradation of Myh3 by Ozz.
Type: article
Appears in Collections:農学院・農学研究院 (Graduate School of Agriculture / Faculty of Agriculture) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

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