Caldesmon Regulate The Mobility of Tumor Cells by Mediating The Actin Cytoskeleton Stability
钙调蛋白结合蛋白通过调节细胞骨架稳定性影响肿瘤细胞运动能力

Light chain (l-CaD) is an important actin binding protein, presents almost all types of vertebrate cells. In vitro studies showed that l-CaD can bind to G-actin to accelerate the polymerization of the G-actin into F-actin and stabilize the formed F-actin. Upon phosphorylation, the l-CaD will disassociate from the F-acin to facilitate its disassembly into G-actin. In order to explore whether the l-CaD mediate the cell mobility by its effect on cytoskeleton, Human breast cancer cell line MCF-7 was chosen as experimental model in which the expression level of l-CaD is very low. By transfection, wild type l-CaD and its phosphorylation mutant (A1234-CaD unphosphorylatable CaD; D1234-CaD phosphorylated CaD) were force-expressed in MCF-7 cells. First, the effect of the l-CaD on cytoskeleton structure was tested by confocal images; and then the transwell assay was performed to address the influence of l-CaD on cell migration activities; Furthermore, the cell contractility and cell detachment which are sub-steps of cell migration were addressed by Fourier-Transform traction microscopy on single cell level and trypsin stimulation respectively. The results showed that l-CaD had significant effect on cytoskeleton structure of MCF-7 cells. The unphosphorylated l-CaD concentrated on cytoskeleton, increased its intensity which generated more cell contractility and inhibited the response of the cells to the trypsin stimulation. Because of the stabilization effect on cytoskeleton by unphosphorylated l-CaD, the rearrangement of the cytoskeleton was inhibited which resulted in the decrease of the cell migration activities; The phosphorylated l-CaD has very low affinity to the cytoskeleton, so its effect on cell mobility was not significant compared to the controlled cells. Taken together, upon phosphorylation, the l-CaD acted like a "protein switch", it will mediate the cell mobility by its effect on cytoskeleton disassembly and rearrangement.