Analysis of activation mechanisms of Rho and RhoGEFs as a new molecular target for lung cancer therapy.

Rho GTP酶在多种细胞功能的调控中起着重要作用。越来越多的证据表明，RhoA的过度表达有助于人类癌症的发展。然而，RhoA的激活状态在癌细胞中的定义并不明确。在这项研究中，我们检测了RhoA及其上游激活物RhoGEF在不同肺癌细胞中的表达水平和激活状态。此外，我们还分析了RhoA在这些细胞中的激活机制，以寻找治疗肺癌的新的分子靶点。我们发现，RhoA在各种肺癌细胞中都被激活，而不受其表达水平的影响。尤其是在小细胞肺癌(SCLC)细胞中，RhoA的激活状态高于其表达水平。接下来，我们首次检测了三个含有RhoGEF的Rgl结构域：p115Rhogef、LARG和PDZ-Rhogef在这些癌细胞中作为RhoA直接激活剂的候选基因的表达水平。我们发现LARG在所有类型的肺癌细胞中都有强烈的表达，提示LARG在肺癌发病机制中的重要作用。最后，我们利用广谱G-α受体拮抗剂和最近报道的G-GPC-Q选择性抑制剂，剖析了小细胞肺癌细胞表面受体到Rho的信号通路。我们发现，小细胞肺癌细胞中RhoA的高激活状态主要依赖于神经内分泌肽自分泌系统，该系统通过Gα12将GPCRa偶联到RhoA上。这些结果表明，抑制这一信号通路可能成为肺癌靶向治疗的新策略。

Rho GTPases play an essential role in the control of various cellular functions. Accumulating evidence suggests that RhoA overexpression contributes to human cancer development. However, the activation states of RhoA are poorly defined in cancer cells. In this study, we examined both the expression levels and the activation states of RhoA and its upstream activator, RhoGEFs, in various lung cancer cells. Additionally, we analyzed the mechanisms of RhoA activation in these cells to search for new molecular targets for lung cancer treatment. We found that RhoA is activated in various lung cancer cells independent of its expression levels. Especially, the activation status of RhoA is higher comparing to its expression levels in small cell lung cancer (SCLC) cells. Next, we measured the expression levels of three RGL-domain containing RhoGEFs: p115RhoGEF, LARG, and PDZ-RhoGEF, as a candidate for direct activator of RhoA in these cancer cells for the first time. We found that LARG is strongly expressed in all types of lung cancer cells, suggesting the importance of LARG in lung cancer pathogenesis. Finally, we dissected the signaling pathway from cell surface receptor to Rho in SCLC cells using broad-spectrum GPCR antagonist and recently reported Gαq-selective inhibitor. We found that the high activation state of RhoA in SCLC cells mainly depends on a neuroendocrine peptide autocrine system which signals through Gα12 coupled GPCR to RhoA. These results suggest that inhibition of this signaling pathway will be the possible new strategies for targeted lung cancer therapy.