Price L S, Norman J C, Ridley A J, Koffer A
Physiology Department, University College London, UK.
Curr Biol. 1995 Jan 1;5(1):68-73. doi: 10.1016/s0960-9822(95)00018-2.
Regulated secretion by mast cells is known to be controlled by GTP-binding proteins, but the proteins involved have not been identified. Rac and Rho, two small GTPases related to the oncoprotein Ras, mediate transmission of signals from cell-surface receptors to the actin cytoskeleton. In rat mast cells, both Rac and Rho participate in effecting the centripetal redistribution of filamentous actin that is observed after stimulation of the cells. Rho is responsible for polymerization of actin filaments in the cell interior, whereas Rac is required for the entrapment in the interior of filaments released from the cortex. Such cytoskeletal changes could be important in control of the exocytotic process, so we examined whether Rac and Rho also play a role in regulated secretion by mast cells.
We show that the constitutively active mutant proteins, V14RhoA and V12Rac1, enhance regulated secretion from permeabilized mast cells by increasing the proportion of cells that are competent to respond to stimulation. In addition, inhibition of endogenous Rac and Rho activity using inhibitors, N17Rac1 and C3 transferase, respectively, reduces the secretory response of mast cells to stimuli.
These results provide direct evidence that, in mast cells, both Rac and Rho are components of the signalling pathway that leads to secretion.
已知肥大细胞的调节性分泌受GTP结合蛋白控制，但相关蛋白尚未确定。Rac和Rho是与癌蛋白Ras相关的两种小GTP酶，介导从细胞表面受体到肌动蛋白细胞骨架的信号传递。在大鼠肥大细胞中，Rac和Rho均参与细胞受刺激后观察到的丝状肌动蛋白向心再分布的过程。Rho负责细胞内肌动蛋白丝的聚合，而Rac则是使从皮质释放的肌动蛋白丝被困在细胞内所必需的。这种细胞骨架变化在控制胞吐过程中可能很重要，因此我们研究了Rac和Rho是否也在肥大细胞的调节性分泌中发挥作用。
我们发现，组成型活性突变蛋白V14RhoA和V12Rac1通过增加有能力响应刺激的细胞比例，增强了通透肥大细胞的调节性分泌。此外，分别使用抑制剂N17Rac1和C3转移酶抑制内源性Rac和Rho活性，可降低肥大细胞对刺激的分泌反应。
这些结果提供了直接证据，表明在肥大细胞中，Rac和Rho都是导致分泌的信号通路的组成部分。
