Keywords: adenosine receptor, breast cancer, cholera toxin, G protein-coupled receptor, protein isoprenylation, protein kinase A (PKA), Ras-related protein 1 (Rap1), b-adrenergic receptor Abbreviations: Adenosine 2B Receptor (A 2 BR), b-adrenergic receptor (bAR), Bay 60-6583 (Bay), Cholera toxin (Ctx), half time (T 1/2 ), Isoproterenol (Iso), G protein-coupled receptors (GPCR), Phosphate buffered saline (PBS), Protein kinase A (PKA), Propranolol (Prop).A greater understanding of the molecular basis of breast cancer metastasis will lead to identification of novel therapeutic targets and better treatments. Rap1B is a small GTPase that suppresses the metastasis of breast cancer cells by increasing cell-cell adhesion. In breast cancer, a decrease in Rap1B prenylation and subsequent loss of Rap1B at the plasma membrane decreases cell-cell adhesion and increases cell scattering, which promotes the metastatic phenotype. Protein kinase A (PKA) was recently found to phosphorylate Rap1B and inhibit its prenylation. PKA is activated by G protein-coupled receptors (GPCR) that stimulate Ga s . In this study, we investigated whether the general Ga s activator, cholera toxin, and agonists of the b-adrenergic receptor (bAR), which is a Ga s -coupled GPCR, promote Rap1B phosphorylation and inhibit its prenylation. We show here that cholera toxin and bAR activation phosphorylate Rap1B and inhibit its prenylation and membrane localization, reducing cell-cell adhesion and promoting cell scattering. Furthermore, we report that breast cancer cell migration is decreased by the FDA-approved b-blocker, propranolol. Pharmacological targeting of GPCRs, especially those such as the bAR that are regulated by FDA-approved drugs, to increase cell adhesion and decrease cell scattering could provide a promising therapeutic approach to reduce breast cancer metastasis.