Non-small cell lung carcinoma (NSCLC) is promoted by the increased activities of several small GTPases, including K-Ras4B, Rap1A, Rap1B, RhoC, and Rac1. SmgGDS is an unusual guanine nucleotide exchange factor that activates many of these small GTPases, and thus may promote NSCLC development or progression. We report here that SmgGDS protein levels are elevated in NSCLC tumors, compared with normal lung tissue from the same patients or from individuals without cancer. To characterize SmgGDS functions in NSCLC, we tested the effects of silencing SmgGDS expression by transfecting cultured NSCLC cells with SmgGDS small interfering RNA (siRNA). Cells with silenced SmgGDS expression form fewer colonies in soft agar, do not proliferate in culture due to an arrest in G1 phase, and exhibit disrupted myosin organization and reduced cell migration. The transcriptional activity of NF-κB in NSCLC cells is diminished by transfecting the cells with SmgGDS siRNA, and enhanced by transfecting the cells with a cDNA encoding SmgGDS. Because RhoA is a major substrate for SmgGDS, we investigated whether diminished RhoA expression mimics the effects of diminished SmgGDS expression. Silencing RhoA expression with RhoA siRNA disrupts myosin organization, but only moderately decreases cell proliferation and does not inhibit migration. Our finding that the aggressive NSCLC phenotype is more effectively suppressed by silencing SmgGDS than by silencing RhoA is consistent with the ability of SmgGDS to regulate multiple small GTPases in addition to RhoA. These results demonstrate that SmgGDS promotes the malignant NSCLC phenotype and is an intriguing therapeutic target in NSCLC.
This work was supported by National Institutes of Health Grant GM069700, American Heart Association Grant 0355759U, Advancing a Healthier Wisconsin, and the Cancer Center of the Medical College of Wisconsin. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
