Liu Rong, Hossain M Moazzem, Chen Xuequn, Jin Jian-Ping
Department of Physiology, Wayne State University School of Medicine , Detroit, Michigan 48201, United States.
Biochemistry. 2017 Oct 17;56(41):5526-5538. doi: 10.1021/acs.biochem.7b00794. Epub 2017 Sep 27.
SM22α, also named transgelin, is an actin filament-associated protein in smooth muscle and fibroblasts. Three decades after its discovery, the biological function of SM22α remains under investigation. Here we report a novel finding that the expression and degradation of SM22α/transgelin are regulated by mechanical tension. Following a mass spectrometry identification of SM22α degradation in isolated and tension-unloaded mouse aorta, we developed specific monoclonal antibodies to study the regulation of SM22α in human fetal lung myofibroblast line MRC-5 and primary cultures of neonatal mouse skin fibroblasts. The level of SM22α is positively related to the mechanical tension in the cytoskeleton produced by the myosin II motor in response to the stiffness of the culture matrix. Quantitative reverse transcription polymerase chain reaction demonstrated that the expression of SM22α is regulated at the transcriptional level. This mechanical regulation resembles that of calponin 2, another actin filament-associated protein. Immunofluorescent staining co-localized SM22α with F-actin, myosin, and calponin 2 in mouse skin fibroblasts. The close phylogenetic relationship between SM22α and the calponin family supports that SM22α is a calponin-like regulatory protein. The level of SM22α is decreased in skin fibroblasts isolated from calponin 2 knockout mice, suggesting interrelated regulation and function of the two proteins. On the other hand, SM22α expression was maximized at a matrix stiffness higher than that for calponin 2 in the same cell type, indicating differentiated regulation and tension responsiveness. The novel mechanoregulation of SM22α/transgelin lays the groundwork for understanding its cellular functions.
SM22α，也称为转胶蛋白，是平滑肌和成纤维细胞中一种与肌动蛋白丝相关的蛋白质。在其被发现三十年后，SM22α的生物学功能仍在研究中。在此我们报告一项新发现，即SM22α/转胶蛋白的表达和降解受机械张力调节。在通过质谱鉴定了分离的、无张力负荷的小鼠主动脉中SM22α的降解后，我们开发了特异性单克隆抗体，以研究人胎儿肺成肌纤维细胞系MRC-5和新生小鼠皮肤成纤维细胞原代培养物中SM22α的调节情况。SM22α的水平与肌球蛋白II马达响应培养基质硬度而在细胞骨架中产生的机械张力呈正相关。定量逆转录聚合酶链反应表明，SM22α的表达在转录水平受到调节。这种机械调节类似于另一种与肌动蛋白丝相关的蛋白质——钙调蛋白2的调节。免疫荧光染色显示，在小鼠皮肤成纤维细胞中，SM22α与F-肌动蛋白、肌球蛋白和钙调蛋白2共定位。SM22α与钙调蛋白家族之间密切的系统发育关系支持SM22α是一种类钙调蛋白调节蛋白。从钙调蛋白2基因敲除小鼠分离的皮肤成纤维细胞中，SM22α的水平降低，表明这两种蛋白质的调节和功能相互关联。另一方面，在相同细胞类型中，当基质硬度高于钙调蛋白2时，SM22α的表达达到最大值，表明存在分化调节和张力反应性。SM22α/转胶蛋白的这种新的机械调节为理解其细胞功能奠定了基础。
