The pathway connecting m2 receptors to the nucleus involves small GTP-binding proteins acting on divergent MAP kinase cascades.

Abstract m1 and m2 receptors are traditionally linked to tissue specific functions performed by fully differentiated cells. However, these receptors have been also implicated in growth stimulation. The mechanisms whereby these receptors regulate proliferative signaling pathways are still poorly understood. Furthermore, pharmacological evidence suggest that many growth promoting agents act on G i coupled receptors, but there is no formal proof that induction of DNA-synthesis results from decreased intracellular levels of cAMP. In our laboratory, we have used the expression of m1 and m2 receptors as a model for studying proliferative signaling through G protein-coupled receptors. Currently available evidence suggest that these receptors signal to distinct members of the MAP kinase superfamily, MAP kinase and JNK, through βγ subunits of heterotrimeric G proteins acting, respectively, on a Ras and Rac1 dependent pathway.