Abstract 4445: RhoA is required for lung adenocarcinoma progression but is dispensable for K-Ras-induced tumor initiation
Authors: Zandvakili Inuk , Zheng Yi 
Published: May 2015

Abstract
K-Ras is a prolific driver of lung tumorigenesis, yet it has eluded direct pharmaceutical inhibition to date. Here we test an alternative inhibition strategy by targeting RhoA, the prototypic member of the Rho family of GTPases and a downstream functional mediator of K-Ras signaling. Rho GTPases are signal transduction proteins that control cell shape, motility and proliferation. Given these roles, it is unsurprising that Rho proteins have been implicated in multiple stages of cancer progression. In fact, RhoA protein and activity levels are increased in lung, gastric, pancreatic and colon cancers. In vitro studies by us and others have found that K-Ras-driven lung adenocarcinoma cells are exquisitely sensitive to shRNA mediated RhoA inhibition, and demonstrate decreased proliferation, migration, invasion and anchorage-independent growth. Despite these findings, no genetic studies demonstrating RhoA involvement in tumorigenesis have been carried out to date. Thus, we generated a murine lung cancer model by crossing the widely used Lox-Stop-Lox KRasG12D transgenic mouse with RhoAflox/flox mice. Simultaneous deletion of RhoA and activation of K-Ras is achieved by either endotracheal administration of Adeno-Cre virus or by transgenic expression of CCSP-Cre; a lung specific Clara cell secretory protein promoter driven Cre. We found that Adeno-Cre administration to RhoAflox/flox mice not only led to the growth of RhoA-null tumors, but that surprisingly these mice had more and larger tumors as compared to wild type controls. These results indicate that RhoA is not essential for K-Ras-driven tumor formation. However, RhoAflox/flox RhoC-/- mice administered Adeno-Cre virus displayed fewer and smaller tumors, suggesting that K-Ras-driven tumorigenesis requires either RhoA or RhoC signaling. In contrast, CCSP-Cre driven tumors grow unabated regardless of RhoA status. Given the stark contrast between our in vivo and in vitro studies, we are testing the hypothesis that during the natural course of lung adenocarcinoma progression, cells grow reliant on RhoA signaling and may be susceptible to pharmaceutical RhoA inhibition. On the other hand, murine tumors initiated in the absence of RhoA may upregulate compensatory pathways downstream of K-Ras, paradoxically increasing tumor growth. While RhoA represents a valid target for suppressing K-Ras driven tumor cell proliferation and invasion, neither RhoA nor RhoC is essential for K-Ras-driven tumorigenesis. Moreover, our findings suggest that there is selective pressure within tumors after RhoA loss resulting not only in compensation between Rho-family members but also complex compensatory signaling leading to a paradoxical increase in tumor formation.
Citation Format: Inuk Zandvakili, Yi Zheng. RhoA is required for lung adenocarcinoma progression but is dispensable for K-Ras-induced tumor initiation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4445. doi:10.1158/1538-7445.AM2014-4445