title: Protein kinase C (PKC)eta-mediated PKC mu activation modulates ERK and JNK signal pathways.
abstract: Protein kinase C (PKC), a family of lipid-activated serine kinases, is involved in multiple functions in the regulation of growth control. The PKC-related isoform PKC mu/PKD has been implicated in mitogenic signal cascades because of the activation of p42/p44 MAPK leading to Elk1-mediated gene transcription, and PKC mu/PKD has been shown to be activated via a PKC-dependent pathway. By using confocal analyses, we demonstrate here that PKC mu partially colocalizes with PKC eta in different cell types. Colocalization depends on the presence of the PKC mu pleckstrin homology domain. Coexpression of constitutively active PKC eta with PKC mu leads to a significant enhancement of the PKC mu substrate phosphorylation capacity as a result of an increased phosphorylation of the activation loop Ser(738/742) of PKC mu, whereas Ser(910) autophosphorylation remains unaffected. In vitro phosphorylation experiments show that PKC eta directly phosphorylates PKC mu on activation loop serines. Consequently, the p42 MAPK cascade is triggered leading to an increase in reporter gene activity driven by a serum-responsive element in HEK293 cells. At the same time, PKC eta-mediated JNK activation is reduced, providing evidence for a mutual regulation of PKC mu/PKC eta affecting different arms of the p38/ERK/JNK pathways. Our data provide evidence for the sequential involvement of selective PKC isoforms in kinase cascades and identify the relevant domains in PKC mu for interaction with and activation by PKC eta as pleckstrin homology domain and activation loop.
authors.affiliation: Fraunhofer Institute for Interfacial Engineering, Nobelstrasse 12, University of Stuttgart, Allmandring 31, 70569 Stuttgart, Germany.
authors.forename: Ilona
authors.initials: I
authors.lastname: Brändlin
authors.forename: Susanne
authors.initials: S
authors.lastname: Hübner
authors.forename: Tim
authors.initials: T
authors.lastname: Eiseler
authors.forename: Marina
authors.initials: M
authors.lastname: Martinez-Moya
authors.forename: Andreas
authors.initials: A
authors.lastname: Horschinek
authors.forename: Angelika
authors.initials: A
authors.lastname: Hausser
authors.forename: Gisela
authors.initials: G
authors.lastname: Link
authors.forename: Steffen
authors.initials: S
authors.lastname: Rupp
authors.forename: Peter
authors.initials: P
authors.lastname: Storz
authors.forename: Klaus
authors.initials: K
authors.lastname: Pfizenmaier
authors.forename: Franz-Josef
authors.initials: FJ
authors.lastname: Johannes
mesh_terms: D001943:Breast Neoplasms; D002460:Cell Line; D017931:DNA Primers; D004789:Enzyme Activation; D005260:Female; D017930:Genes, Reporter; D005982:Glutathione Transferase / Q000235:genetics; D049452:Green Fluorescent Proteins; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D019169:Jurkat Cells; D008164:Luminescent Proteins / Q000235:genetics; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014162:Transfection
chemical_list: D017931:DNA Primers; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D005982:Glutathione Transferase; C119190:protein kinase C nu; C089212:protein kinase D; D011493:Protein Kinase C; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases