MAPK1 and polycystic kidney disease: HNF-1β controls cellular proliferation and tubule formation by regulating the expression of a number of kidney-specific genes, including polycystic kidney and hepatic disease 1 (PKHD1), uromodulin (UMOD) and suppressor of cytokine signaling-3 (SOCS3) expression and the signal transducer and activator of transcription 3 (STAT3)/mitogen-activated protein kinase 1 (MAPK1, Erk) activation cascade (77).