title: Small G proteins Rac1 and Ras regulate serine/threonine protein phosphatase 5 (PP5)·extracellular signal-regulated kinase (ERK) complexes involved in the feedback regulation of Raf1.
abstract: Serine/threonine protein phosphatase 5 (PP5, PPP5C) is known to interact with the chaperonin heat shock protein 90 (HSP90) and is involved in the regulation of multiple cellular signaling cascades that control diverse cellular processes, such as cell growth, differentiation, proliferation, motility, and apoptosis. Here, we identify PP5 in stable complexes with extracellular signal-regulated kinases (ERKs). Studies using mutant proteins reveal that the formation of PP5·ERK1 and PP5·ERK2 complexes partially depends on HSP90 binding to PP5 but does not require PP5 or ERK1/2 activity. However, PP5 and ERK activity regulates the phosphorylation state of Raf1 kinase, an upstream activator of ERK signaling. Whereas expression of constitutively active Rac1 promotes the assembly of PP5·ERK1/2 complexes, acute activation of ERK1/2 fails to influence the phosphatase-kinase interaction. Introduction of oncogenic HRas (HRas(V12)) has no effect on PP5-ERK1 binding but selectively decreases the interaction of PP5 with ERK2, in a manner that is independent of PP5 and MAPK/ERK kinase (MEK) activity, yet paradoxically requires ERK2 activity. Additional studies conducted with oncogenic variants of KRas4B reveal that KRas(L61), but not KRas(V12), also decreases the PP5-ERK2 interaction. The expression of wild type HRas or KRas proteins fails to reduce PP5-ERK2 binding, indicating that the effect is specific to HRas(V12) and KRas(L61) gain-of-function mutations. These findings reveal a novel, differential responsiveness of PP5-ERK1 and PP5-ERK2 interactions to select oncogenic Ras variants and also support a role for PP5·ERK complexes in regulating the feedback phosphorylation of PP5-associated Raf1.
authors.affiliation: From the Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-6600.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Mazalouskas
authors.forename: Raquel
authors.initials: R
authors.lastname: Godoy-Ruiz
authors.forename: David J
authors.initials: DJ
authors.lastname: Weber
authors.forename: Danna B
authors.initials: DB
authors.lastname: Zimmer
authors.forename: Richard E
authors.initials: RE
authors.lastname: Honkanen
authors.forename: Brian E
authors.initials: BE
authors.lastname: Wadzinski
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D002417:Cattle; D002460:Cell Line; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism*; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D006023:Glycoproteins; C117307:KRAS protein, human; D009097:Multienzyme Complexes; D011518:Proto-Oncogene Proteins; C107953:RAC1 protein, human; C021240:tissue-factor-pathway inhibitor 2; D019908:Proto-Oncogene Proteins c-raf; D048049:Extracellular Signal-Regulated MAP Kinases; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras); D020830:rac1 GTP-Binding Protein; D018631:ras Proteins
keywords: ERK; Feedback Phosphorylation; MAP Kinases (MAPKs); MEK; PP5; Rac; Raf; Ras; S100 Proteins; Small G Protein