Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan, United States of America.
PLoS One. 2013 Jun 11;8(6):e66029. doi: 10.1371/journal.pone.0066029. Print 2013.
RhoA and Rac1 have been implicated in the mechanism of CCK-induced amylase secretion from pancreatic acini. In all cell types studied to date, inactive Rho GTPases are present in the cytosol bound to the guanine nucleotide dissociation inhibitor RhoGDI. Here, we identified the switch mechanism regulating RhoGDI1-Rho GTPase dissociation and RhoA translocation upon CCK stimulation in pancreatic acini. We found that both Gα13 and PKC, independently, regulate CCK-induced RhoA translocation and that the PKC isoform involved is PKCα. Both RhoGDI1 and RhoGDI3, but not RhoGDI2, are expressed in pancreatic acini. Cytosolic RhoA and Rac1 are associated with RhoGDI1, and CCK-stimulated PKCα activation releases the complex. Overexpression of RhoGDI1, by binding RhoA, inhibits its activation, and thereby, CCK-induced apical amylase secretion. RhoA translocation is also inhibited by RhoGDI1. Inactive Rac1 influences CCK-induced RhoA activation by preventing RhoGDI1 from binding RhoA. By mutational analysis we found that CCK-induced PKCα phosphorylation on RhoGDI1 at Ser96 releases RhoA and Rac1 from RhoGDI1 to facilitate Rho GTPases signaling.
RhoA 和 Rac1 被认为参与了 CCK 诱导胰腺腺泡淀粉酶分泌的机制。在迄今为止研究的所有细胞类型中，无活性的 Rho GTPases 存在于细胞质中，与鸟嘌呤核苷酸解离抑制剂 RhoGDI 结合。在这里，我们确定了调节 RhoGDI1-Rho GTPase 解离和 CCK 刺激下 RhoA 易位的开关机制在胰腺腺泡中。我们发现，Gα13 和 PKC 均可独立调节 CCK 诱导的 RhoA 易位，涉及的 PKC 同工型是 PKCα。RhoGDI1 和 RhoGDI3，但不是 RhoGDI2，在胰腺腺泡中表达。细胞质中的 RhoA 和 Rac1 与 RhoGDI1 相关，CCK 刺激的 PKCα 激活释放该复合物。通过与 RhoA 结合，RhoGDI1 的过表达抑制其激活，从而抑制 CCK 诱导的顶端淀粉酶分泌。RhoA 易位也被 RhoGDI1 抑制。无活性的 Rac1 通过阻止 RhoGDI1 与 RhoA 结合，影响 CCK 诱导的 RhoA 激活。通过突变分析，我们发现 CCK 诱导的 RhoGDI1 上的 PKCα 磷酸化 Ser96 释放 RhoA 和 Rac1 从 RhoGDI1 以促进 Rho GTPases 信号。
