title: Protein phosphatase 2A suppresses MAP kinase signalling and ectopic protein expression.
abstract: Signalling by MAP kinase was examined in COS-7 cells by transiently expressing a transcription reporter system plus epitope-tagged protein phosphatase 2A catalytic subunit [(HA)3-PP2Ac]. Transactivation of a luciferase gene by GAL4-Elk-1 in serum-stimulated cells was reduced 20-fold by co-expression of wild type (HA)3-PP2Ac. This reduction of MAP kinase signalling required specific type-2A phosphatase activity, because the effects were not mimicked by co-expression of either a mutated, inactive (HA)3-PP2Ac or wild-type PP1Cdelta. Expression of (HA)3-PP2Ac was severely restricted by its own activity because 3-fold more inactive (HA)3-PP2Ac was produced. In a different assay the kinase activity of FLAG-ERK2 was 4-fold lower when co-transfected with (HA)3-PP2Ac, compared to controls. Unexpectedly, mRNA of the reporter constructs were nearly eliminated by even low level expression of (HA)3-PP2Ac in either COS7 or HEK293 cells. The results show that PP2A activity is strictly regulated and can be a limiting factor in ectopic expression of various proteins.
authors.affiliation: Center for Cell Signalling, University of Virginia, Charlottesville 22908, USA.
authors.forename: H
authors.initials: H
authors.lastname: Chung
authors.forename: D L
authors.initials: DL
authors.lastname: Brautigan
mesh_terms: D016475:3T3 Cells; D000818:Animals; D019556:COS Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002461:Cell Line, Transformed; D004789:Enzyme Activation; D015870:Gene Expression; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D010749:Phosphoprotein Phosphatases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D014176:Protein Biosynthesis; D054648:Protein Phosphatase 2; D012333:RNA, Messenger; D011994:Recombinant Proteins / Q000096:biosynthesis; D015398:Signal Transduction
chemical_list: D012333:RNA, Messenger; D011994:Recombinant Proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2