WNK2 and obesity due to melanocortin 4 receptor deficiency: Notably, ERK signaling is activated in the livers of several murine models of obesity (12), and blockade of this interorgan system by expression of a dominant-negative mutant of mitogen-activated protein kinase/ERK kinase-1 (d/nMEK), pharmacological deafferentation of the splanchnic nerve, or dissection of the vagus was each shown to suppress the obesity-induced increases in β cells (5).