Inhibition of endogenous Sp1 protein decreased the Brg-1-mediated transcriptional activation of the SPARC gene. 4T1 cells were respectively transfected with siRNA control (-) or siRNAs specific for Sp1 (+). 24 hrs after transfection, the luciferase reporter construct pREP4-SP-luc was co-transfected with Brg-1 expression plasmid or empty plasmid (control) into 4T1 cells. Cell lysates were prepared 48 hrs after the second transfection. (A) The luciferase activity was analyzed. The data shown (mean ± SEM) are the averages of three independent experiments performed in triplicate. (B) Protein expression levels of Sp1, Brg-1 and β-actin (internal control) in transfected 4T1 cells were assessed using Western blot analysis. The illustrated result is a representative of three independent experiments.