Yin Xingping, Choudhury Monideepa, Bag Jnanankur
University of Guelph, Department of Molecular Biology and Genetics, Guelph, ON, Canada.
FEBS Lett. 2002 Apr 24;517(1-3):45-9. doi: 10.1016/s0014-5793(02)02574-7.
The check-points that maintain stoichiometric synthesis of muscle proteins were examined by misexpression of slow troponin C (sTnC) in mouse C2 myotubes. The sTnC mRNA was overexpressed in myotubes by transfecting these cells with a plasmid construct containing the constitutive CMV promoter-driven sTnC cDNA. An approximately four-fold increase of sTnC mRNA level in the transfected cells was observed. However, the increased mRNA level did not produce a corresponding increase of the sTnC polypeptide level in transfected cells. Only a modest 1.5-fold increase of the sTnC polypeptide level in the transfected cells was observed. The excess sTnC polypeptide in transfected cells was found in the soluble form which was not complexed with other thin filament proteins. The difference between the increase of sTnC mRNA and the polypeptide levels in transfected cells was not due to inefficient translation of the overexpressed sTnC mRNA. Analyses of the stability of the sTnC polypeptide in the thin filament and in the unassembled soluble forms showed that the excess soluble sTnC polypeptide was degraded more rapidly than the sTnC polypeptide of the thin filament. Analyses of the mRNA and polypeptide levels of several thin filament complements showed no effect of overexpression of the sTnC mRNA.
通过在小鼠C2肌管中错误表达慢肌钙蛋白C（sTnC）来研究维持肌肉蛋白化学计量合成的检查点。通过用含有组成型巨细胞病毒（CMV）启动子驱动的sTnC cDNA的质粒构建体转染这些细胞，使sTnC mRNA在肌管中过表达。在转染细胞中观察到sTnC mRNA水平增加了约四倍。然而，增加的mRNA水平并未导致转染细胞中sTnC多肽水平相应增加。在转染细胞中仅观察到sTnC多肽水平适度增加了1.5倍。转染细胞中过量的sTnC多肽以可溶形式存在，未与其他细肌丝蛋白形成复合物。转染细胞中sTnC mRNA增加与多肽水平之间的差异并非由于过表达的sTnC mRNA翻译效率低下所致。对细肌丝中sTnC多肽和未组装可溶形式的稳定性分析表明，过量的可溶sTnC多肽比细肌丝中的sTnC多肽降解得更快。对几种细肌丝成分的mRNA和多肽水平分析表明，sTnC mRNA过表达没有影响。
