Erk3

Extracellular signal-regulated kinase 3 (Erk3) is a member of the mitogen-activated protein (MAP) kinase family of serine/threonine kinases. Together with Erk4, it defines a distinct subfamily of MAP kinases that is found exclusively in vertebrates. Little is known about the biological function of Erk3 and its cellular targets. Recent work has shown that Erk3 interacts with and activates the MAP kinase–activated protein kinase MK5, suggesting a physiological relationship between the two protein kinases. Overexpression of stabilized forms of Erk3 in immortalized fibroblasts inhibits S-phase entry, indicating that Erk3 may act as a negative regulator of cell-cycle progression in certain cellular contexts. It remains to be determined whether Erk3 regulates cell proliferation under physiological conditions.