AARS1 and cancer: However, given that catecholamines can stimulate all nine AR subtypes and, in the presence of propranolol, can activate not only subtypes of α-ARs but also β3-ARs, which may produce effects opposite to those of β1 and β2-AR stimulation [13], the relative role of each β-AR subtypes in regulating cancer cell proliferation, as well as their contribution to the antiproliferative action of α-ARs on B16F10 cells, remain to be clarified.