title: Differential activation of stress-responsive signalling proteins associated with altered loading in a rat skeletal muscle.
abstract: Skeletal muscle undergoes a significant reduction in tension upon unloading. To explore intracellular signalling mechanisms underlying this phenomenon, we investigated twitch tension, the ratio of actin/myosin filaments, and activities of key signalling molecules in rat soleus muscle during a 3-week hindlimb suspension and 2-week reloading. Twitch tension and myofilament ratio (actin/myosin) gradually decreased during unloading but progressively recovered to initial levels during reloading. To study the involvement of stress-responsive signalling proteins during these changes, the activities of protein kinase C alpha (PKCalpha) and three mitogen-activated protein kinases (MAPKs)--c-Jun NH2-terminal kinase (JNK), extracellular signal-regulated protein kinase (ERK), and p38 MAPK--were examined using immunoblotting and immune complex kinase assays. PKCalpha phosphorylation correlated positively with the tension (Pearson's r = 0.97, P < 0.001) and the myofilament ratio (r = 0.83, P < 0.01) over the entire unloading and reloading period. Treatment of the soleus muscle with a PKC activator resulted in a similar paralleled increment in both PKCalpha phosphorylation and the alpha-sarcomeric actin expression. The three MAPKs differed in the pattern of activation in that JNK activity peaked only for the first hours of reloading, whereas ERK and p38 MAPK activities remained elevated during reloading. These results suggest that PKCalpha may play a pivotal role in converting loading stress to intracellular changes in contractile proteins that determine muscle tension. Differential activation of MAPKs may also help alleviate muscle damage, modulate energy transport and/or regulate the expression of contractile proteins upon altered loading.
authors.affiliation: Department of Life Science, College of Liberal Arts and Science, Yonsei University, Wonju, Republic of Korea. ichoi@dragon.yonsei.ac.kr
authors.forename: Inho
authors.initials: I
authors.lastname: Choi
authors.forename: Kisoo
authors.initials: K
authors.lastname: Lee
authors.forename: Myungjoo
authors.initials: M
authors.lastname: Kim
authors.forename: Moonyong
authors.initials: M
authors.lastname: Lee
authors.forename: Kyoungsook
authors.initials: K
authors.lastname: Park
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D001835:Body Weight / Q000502:physiology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism*; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008854:Microscopy, Electron; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism*; D009210:Myofibrils / Q000378:metabolism; D009218:Myosins / Q000378:metabolism; D010766:Phosphorylation; D020033:Protein Isoforms / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D000199:Actins; D006360:Heat-Shock Proteins; D020033:Protein Isoforms; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D009218:Myosins