title: Activation loop phosphorylation of ERK3/ERK4 by group I p21-activated kinases (PAKs) defines a novel PAK-ERK3/4-MAPK-activated protein kinase 5 signaling pathway.
abstract: Classical mitogen-activated protein (MAP) kinases are activated by dual phosphorylation of the Thr-Xxx-Tyr motif in their activation loop, which is catalyzed by members of the MAP kinase kinase family. The atypical MAP kinases extracellular signal-regulated kinase 3 (ERK3) and ERK4 contain a single phospho-acceptor site in this segment and are not substrates of MAP kinase kinases. Previous studies have shown that ERK3 and ERK4 are phosphorylated on activation loop residue Ser-189/Ser-186, resulting in their catalytic activation. However, the identity of the protein kinase mediating this regulatory event has remained elusive. We have used an unbiased biochemical purification approach to isolate the kinase activity responsible for ERK3 Ser-189 phosphorylation. Here, we report the identification of group I p21-activated kinases (PAKs) as ERK3/ERK4 activation loop kinases. We show that group I PAKs phosphorylate ERK3 and ERK4 on Ser-189 and Ser-186, respectively, both in vitro and in vivo, and that expression of activated Rac1 augments this response. Reciprocally, silencing of PAK1/2/3 expression by RNA interference (RNAi) completely abolishes Rac1-induced Ser-189 phosphorylation of ERK3. Importantly, we demonstrate that PAK-mediated phosphorylation of ERK3/ERK4 results in their enzymatic activation and in downstream activation of MAP kinase-activated protein kinase 5 (MK5) in vivo. Our results reveal that group I PAKs act as upstream activators of ERK3 and ERK4 and unravel a novel PAK-ERK3/ERK4-MK5 signaling pathway.
authors.affiliation: Institut de Recherche en Immunologie et Cancérologie, Université de Montréal, Montreal, Quebec H3C 3J7, Canada.
authors.forename: Paul
authors.initials: P
authors.lastname: Déléris
authors.forename: Matthias
authors.initials: M
authors.lastname: Trost
authors.forename: Ivan
authors.initials: I
authors.lastname: Topisirovic
authors.forename: Pierre-Luc
authors.initials: PL
authors.lastname: Tanguay
authors.forename: Katherine L B
authors.initials: KL
authors.lastname: Borden
authors.forename: Pierre
authors.initials: P
authors.lastname: Thibault
authors.forename: Sylvain
authors.initials: S
authors.lastname: Meloche
mesh_terms: D004789:Enzyme Activation / Q000502:physiology; D020536:Enzyme Activators / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000502:physiology*; D048053:Mitogen-Activated Protein Kinase 6 / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D054462:p21-Activated Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D020536:Enzyme Activators; D047908:Intracellular Signaling Peptides and Proteins; C111049:MAP-kinase-activated kinase 5; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D048053:Mitogen-Activated Protein Kinase 6