title: Truncated MEK1 is required for transient activation of MAPK signalling in G2 phase cells.
abstract: The primary endpoint of signalling through the canonical Raf-MEK-ERK MAP kinase cascade is ERK activation. Here we report a novel signalling outcome for this pathway. Activation of the MAP kinase pathway by growth factors or phorbol esters during G2 phase results in only transient activations of ERK and p90RSK, then suppression to below control levels. A small peak of ERK and p90RSK activation in early G2 phase cells was identified, and inhibition of this delayed entry into mitosis. The previously identified, proteolytically cleaved form of MEK1 termed tMEK (truncated MEK1), is also induced with G2 phase MAPK pathway activation. We demonstrate that addition of recombinant mutants of MEK1 with an N-terminal truncation similar to that of tMEK also inhibited ERK and p90RSK activations and delayed progression into mitosis. Only catalytically inactive forms of tMEK were capable of these effects, but surprisingly, phosphorylation on the activating Ser218/222 sites was also required. A lack of MEK1 or ability to accumulate tMEK resulted in the absence of the feedback inhibition of ERK and p90RSK activations. tMEK is a novel output from the canonical MAP kinase signalling pathway, acting in a MAPK signalling-regulated dominant negative manner to inhibit ERK and p90RSK activations, acting as a dampening mechanism to reduce the magnitude or duration of MAPK pathway signalling in G2/M phase.
authors.affiliation: The University of Queensland Diamantina Institute, Princess Alexandra Hospital, Brisbane, Queensland, Australia.
authors.forename: Tanya
authors.initials: T
authors.lastname: Pike
authors.forename: Charlotte
authors.initials: C
authors.lastname: Widberg
authors.forename: Andrew
authors.initials: A
authors.lastname: Goodall
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Payne
authors.forename: Nichole
authors.initials: N
authors.lastname: Giles
authors.forename: John
authors.initials: J
authors.lastname: Hancock
authors.forename: Brian
authors.initials: B
authors.lastname: Gabrielli
mesh_terms: D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D016195:G2 Phase; D006367:HeLa Cells; D006801:Humans; D059566:M Phase Cell Cycle Checkpoints; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism; D015398:Signal Transduction; D059008:Time-Lapse Imaging
chemical_list: D034741:RNA, Small Interfering; D011994:Recombinant Proteins; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1