Ng D C, Carlsen R C, Walsh D A
Department of Biological Chemistry, School of Medicine, University of California, Davis, CA 95616, USA.
Biochem J. 1997 Aug 1;325 ( Pt 3)(Pt 3):793-800. doi: 10.1042/bj3250793.
Neural influences on the co-ordination of expression of the multiple subunits of skeletal muscle phosphorylase kinase and their assembly to form the holoenzyme complex, alpha4beta4gamma4delta4, have been examined during denervation and re-innervation of adult skeletal muscle and during neonatal muscle development. Denervation of the tibialis anterior and extensor digitorum longus muscles of the rat hindlimb was associated with a rapid decline in the mRNA for the gamma subunit, and an abrupt decrease in gamma-subunit protein. The levels of the alpha- and beta-subunit proteins in the denervated muscles also declined rapidly, their time course of reduction being similar to that for the gamma-subunit protein, but they did not decrease to the same extent. In contrast with the rapid decline in gamma-subunit mRNA upon denervation, alpha- and beta-subunit mRNAs stayed at control innervated levels for approx. 8-10 days, but then decreased rapidly. Their decline coincided very closely with the onset of re-innervation. Re-innervation of the denervated muscles, which occurs rapidly and uniformly after the sciatic nerve crush injury, produced an eventual slow and prolonged recovery of the mRNA for all three subunits and parallel increases in each of the subunit proteins. A similar co-ordinated increase of both subunit mRNA and subunit proteins of the phosphorylase kinase holoenzyme was observed during neonatal muscle development, during the period when the muscles were attaining their adult pattern of motor activity. The phosphorylase kinase holoenzyme remains in a non-activated form during all of these physiological changes, as is compatible with the presence of the full complement of the regulatory subunits. These data are consistent with a model whereby the transcriptional and translational expression of phosphorylase kinase gamma subunit occurs only with concomitant expression of the alpha and beta subunits. This would ensure that free and unregulated, activated gamma subunit alone, which would give rise to unregulated glycogenolysis, is not produced. The data also suggest that control of phosphorylase kinase subunit expression and the formation of the holoenzyme in skeletal muscle is provided by the motor nerve, probably through imposed levels or patterns of muscle activity.
在成年骨骼肌去神经支配和重新支配过程以及新生儿肌肉发育过程中，研究了神经对骨骼肌磷酸化酶激酶多个亚基表达协调及其组装形成全酶复合物α4β4γ4δ4的影响。大鼠后肢胫前肌和趾长伸肌去神经支配与γ亚基mRNA迅速下降以及γ亚基蛋白突然减少有关。去神经支配肌肉中α和β亚基蛋白水平也迅速下降，其减少的时间进程与γ亚基蛋白相似，但下降程度不同。与去神经支配后γ亚基mRNA迅速下降相反，α和β亚基mRNA在约8 - 10天内保持在对照神经支配水平，但随后迅速下降。它们的下降与重新支配的开始非常吻合。坐骨神经挤压损伤后迅速且均匀发生的去神经支配肌肉的重新支配，最终使所有三个亚基的mRNA缓慢而持久地恢复，并且每个亚基蛋白平行增加。在新生儿肌肉发育期间，即肌肉达到其成年运动活动模式的时期，观察到磷酸化酶激酶全酶的亚基mRNA和亚基蛋白有类似的协调增加。在所有这些生理变化过程中，磷酸化酶激酶全酶保持非激活形式，这与调节亚基的完整互补存在相一致。这些数据与一个模型一致，即磷酸化酶激酶γ亚基的转录和翻译表达仅与α和β亚基的伴随表达同时发生。这将确保不会产生单独的、自由且不受调节的激活γ亚基，否则会导致不受调节的糖原分解。数据还表明，骨骼肌中磷酸化酶激酶亚基表达的控制和全酶的形成可能由运动神经提供，可能是通过施加的肌肉活动水平或模式。
