SOK1 is a member of the germinal center kinase (GCK-III) subfamily but little is known about it, particularly with respect to its role in signal transduction pathways relative to tumor metastasis. By stably transfecting SOK1 siRNA into the MCF-7 breast cancer cell line we found that SOK1 promotes the migration of MCF-7 cells, as determined using wound-healing and Boyden chamber assays. However, cell proliferation assays revealed that silencing SOK1 had no effect on cell growth relative to the normal cells. Silencing SOK1 also had an effect on the expression and phosphorylation status of a number of proteins in MCF-7 cells, including FAK and GM130, whereby a decrease in SOK1 led to an increase in the expression of these proteins. (C) 2011 Elsevier Inc. All rights reserved.