Kawabe Jun-ichi, Okumura Satoshi, Lee Ming-Chih, Sadoshima Junichi, Ishikawa Yoshihiro
Department of Cell Biology and Molecular Medicine, New Jersey Medical Scchool, University of Medicine and Dentistry of New Jeresy, Newark 07101-1709, USA.
Am J Physiol Heart Circ Physiol. 2004 May;286(5):H1845-52. doi: 10.1152/ajpheart.00593.2003.
Mechanical stress contributes to vascular disease related to hypertension. Activation of ERK is key to mediating cellular proliferation and vascular remodeling in response to stretch stress. However, the mechanism by which stretch mediates ERK activation in the vascular tissue is still unclear. Caveolin, a major component of a flasklike invaginated caveolae, acts as an adaptor protein for an integrin-mediated signaling pathway. We found that cyclic stretch transiently induced translocation of caveolin from caveolae to noncaveolar membrane sites in vascular smooth muscle cells (VSMCs). This translocation of caveolin was determined by detergent solubility, sucrose gradient fractionation, and immunocytochemistry. Cyclic stretch induced ERK activation; the activity peaked at 5 min (the early phase), decreased gradually, but persisted up to 120 min (the late phase). Disruption of caveolae by methyl-beta-cyclodextrin, decreasing the caveolar caveolin and accumulating the noncaveolar caveolin, enhanced ERK activation in both the early and late phases. When endogenous caveolins were downregulated, however, the late-phase ERK activation was subsided completely. Caveolin, which was translocated to noncaveolar sites in response to stretch, is associated with beta1-integrins as well as with Fyn and Shc, components required for ERK activation. Taken together, caveolin in caveolae may keep ERK inactive, but when caveolin is translocated to noncaveolar sites in response to stretch stress, caveolin mediates stretch-induced ERK activation through an association with beta1-integrins/Fyn/Shc. We suggest that stretch-induced translocation of caveolin to noncaveolar sites plays an important role in mediating stretch-induced ERK activation in VSMCs.
机械应力会导致与高血压相关的血管疾病。ERK的激活是介导细胞增殖和血管重塑以应对拉伸应力的关键。然而，拉伸在血管组织中介导ERK激活的机制仍不清楚。小窝蛋白是烧瓶状内陷小窝的主要成分，作为整合素介导的信号通路的衔接蛋白发挥作用。我们发现，周期性拉伸可短暂诱导小窝蛋白在血管平滑肌细胞（VSMC）中从小窝转移至非小窝膜位点。小窝蛋白的这种转移通过去污剂溶解性、蔗糖密度梯度分级分离和免疫细胞化学来确定。周期性拉伸诱导ERK激活；活性在5分钟时达到峰值（早期阶段），随后逐渐下降，但在120分钟内一直持续存在（晚期阶段）。用甲基-β-环糊精破坏小窝，减少小窝内的小窝蛋白并积累非小窝内的小窝蛋白，可增强早期和晚期阶段的ERK激活。然而，当内源性小窝蛋白下调时，晚期ERK激活则完全消退。响应拉伸转移至非小窝位点的小窝蛋白与β1整合素以及ERK激活所需的成分Fyn和Shc相关联。综上所述，小窝内的小窝蛋白可能使ERK保持无活性，但当小窝蛋白响应拉伸应力转移至非小窝位点时，小窝蛋白通过与β1整合素/Fyn/Shc结合介导拉伸诱导的ERK激活。我们认为，拉伸诱导的小窝蛋白向非小窝位点的转移在介导VSMC中拉伸诱导的ERK激活中起重要作用。
