title: Identification of the atypical MAPK Erk3 as a novel substrate for p21-activated kinase (Pak) activity.
abstract: The class I p21-activated kinases (Pak1-3) regulate many essential biological processes, including cytoskeletal rearrangement, cell cycle progression, apoptosis, and cellular transformation. Although many Pak substrates, including elements of MAPK signaling cascades, have been identified, it is likely that additional substrates remain to be discovered. Identification of such substrates, and determination of the consequences of their phosphorylation, is essential for a better understanding of class I Pak activity. To identify novel class I Pak substrates, we used recombinant Pak2 to screen high density protein microarrays. This approach identified the atypical MAPK Erk3 as a potential Pak2 substrate. Solution-based in vitro kinase assays using recombinant Erk3 confirmed the protein microarray results, and phospho-specific antisera identified serine 189, within the Erk3 activation loop, as a site directly phosphorylated by Pak2 in vitro. Erk3 protein is known to shuttle between the cytoplasm and the nucleus, and we showed that selective inhibition of class I Pak kinase activity in cells promoted increased nuclear accumulation of Erk3. Pak inhibition in cells additionally reduced the extent of Ser(189) phosphorylation and inhibited the formation of Erk3-Prak complexes. Collectively, our results identify the Erk3 protein as a novel class I Pak substrate and further suggest a role for Pak kinase activity in atypical MAPK signaling.
authors.affiliation: Division of Biology and Molecular, Cellular, and Developmental Biology Program, Kansas State University, Manhattan, Kansas 66506, USA.
authors.forename: Alina
authors.initials: A
authors.lastname: De la Mota-Peynado
authors.forename: Jonathan
authors.initials: J
authors.lastname: Chernoff
authors.forename: Alexander
authors.initials: A
authors.lastname: Beeser
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000201:enzymology / Q000235:genetics; D003593:Cytoplasm / Q000201:enzymology / Q000235:genetics; D006801:Humans; D020935:MAP Kinase Signaling System / Q000502:physiology; D048053:Mitogen-Activated Protein Kinase 6 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000502:physiology; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018411:Spodoptera; D013379:Substrate Specificity / Q000502:physiology; D054462:p21-Activated Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D011994:Recombinant Proteins; C515907:PAK2 protein, human; D054462:p21-Activated Kinases; D048053:Mitogen-Activated Protein Kinase 6