RACK1 Regulates Src Activity on Apoptosis of Vascular Smooth Muscle Cells Induced by Cyclic Strain

Abstract

Mechanical cyclic strain (CS) is an important regulator of apoptosis of vascular smooth muscle cells (VSMCs), which are involved in vascular remodeling during hypertension. However, its mechanism is still unclear. Using FX-4000T Strain Unit, VSMCs from rat aorta were exposed to CS in vitro with defined parameters, the static, 5%-CS and 15%-CS, for 6, 12 and 24 h, at a constant frequency of 1.25 Hz, respectively. Then cellular apoptosis were analyzed by expression of caspase-3 using western blotting and TUNEL assay using a confocal microscope. The expression of receptor of activated C kinase (RACK1) and phosphorylations of Src and Akt, were detected by western blotting. It revealed that after 24-h-application, 5%-CS significantly repressed VSMC apoptosis and RACK1 expression in comparison with the static and 15%-CS. The phosphorylations of Src on Tyr416 residue were repressed in 5%-CS, compared with the static and 15%-CS, treated for 12 and 24 h. However, phosphorylations of Src on the other residue, Tyr527, were not changed. Compared with 15%-CS, activations of Akt were decreased in VSMCs treated with 5%-CS for 6 and 12 h, but not in 24 h. Using RACK1 target siRNA transfection, the expressions of RACK1 were markedly repressed, while the apoptosis of VSMCs and activation of Src were decreased, but the activation of Akt was increased. The results suggested that CS might modulate VSMC apoptosis via regulating the expression of RACK1 and the subsequent phosphorylation of Tyr416 residue on Src.