Summary for Project 4 led by Research Project Leader Katie Ryan, PhD Lung cancer is one of the most common cancer types and claims the lives of more Arkansans than any other cancer. Most lung cancers metastasize, which leads to poor prognosis. Studying mechanisms that drive metastatic potential is key to unlocking new strategies for the treatment of this deadly form of cancer. The major goal of this COBRE Research Project is to investigate the role of a non-canonical Rho GTPase, Rnd3, as a mediator of lung cancer metastasis. Rnd3 has been proposed as an independent marker for lung cancer-related survival. Our data show patients with lung adenocarcinoma expressing low levels of Rnd3 have significantly higher survival probability rates compared to those with high levels of Rnd3. Yet, the impact of Rnd3 on the molecular features of lung cancer remain obscure. We found that suppressing Rnd3 expression in lung adenocarcinoma cells decreased cell migration and invasion, two hallmarks of metastasis. We then made the exciting discovery that Rnd3 regulation of both cell migration and invasion occurs independently of ROCK1 signaling, one of the best-studied regulators of Rnd3 activity. Our findings support the idea that Rnd3 is regulated by a novel pathway in lung cancer. Rnd3 is not regulated by the canonical Rho GTPase cycle. Rather, this non- canonical GTPase is regulated at the transcriptional level and by post-translational modifications (PTMs) that affect Rnd3 localization, stability, and protein–protein interactions. The molecular features of Rnd3 regulation are understudied and not well defined. The central hypothesis for this COBRE project is that Rnd3 regulation in lung cancer occurs through a ROCK1-independent mechanism that alters both the phosphorylation status and localization of Rnd3, resulting in increased metastatic potential in vitro and in vivo. To test this hypothesis, we will pursue the following Specific Aims: (Aim 1) elucidate ROCK1-independent regulation of Rnd3 in lung cancer, (Aim 2) delineate the roles of PTMs as determinants of Rnd3 function in lung cancer, and (Aim 3) investigate in vivo the role of Rnd3 in mediating lung cancer metastasis. The proposed work is significant because lung cancer is the major cause of cancer death in the US, and metastasis is a key driver of this outcome. The proposed research aligns with the scientific theme of the Center for Molecular Interactions in Cancer (CMIC). The COBRE support will help establish my independent research program by providing mentoring and access to Research Cores that are critical to identifying the molecular basis of Rnd3-mediated control of metastatic potential in lung cancer.