title: Adaptor SKAP-55 binds p21 activating exchange factor RasGRP1 and negatively regulates the p21-ERK pathway in T-cells.
abstract: While the adaptor SKAP-55 mediates LFA-1 adhesion on T-cells, it is not known whether the adaptor regulates other aspects of signaling. SKAP-55 could potentially act as a node to coordinate the modulation of adhesion with downstream signaling. In this regard, the GTPase p21(ras) and the extracellular signal-regulated kinase (ERK) pathway play central roles in T-cell function. In this study, we report that SKAP-55 has opposing effects on adhesion and the activation of the p21(ras) -ERK pathway in T-cells. SKAP-55 deficient primary T-cells showed a defect in LFA-1 adhesion concurrent with the hyper-activation of the ERK pathway relative to wild-type cells. RNAi knock down (KD) of SKAP-55 in T-cell lines also showed an increase in p21(ras) activation, while over-expression of SKAP-55 inhibited activation of ERK and its transcriptional target ELK. Three observations implicated the p21(ras) activating exchange factor RasGRP1 in the process. Firstly, SKAP-55 bound to RasGRP1 via its C-terminus, while secondly, the loss of binding abrogated SKAP-55 inhibition of ERK and ELK activation. Thirdly, SKAP-55-/- primary T-cells showed an increased presence of RasGRP1 in the trans-Golgi network (TGN) following TCR activation, the site where p21(ras) becomes activated. Our findings indicate that SKAP-55 has a dual role in regulating p21(ras)-ERK pathway via RasGRP1, as a possible mechanism to restrict activation during T-cell adhesion.
authors.affiliation: Cell Signalling Section, Department of Pathology, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Helga
authors.initials: H
authors.lastname: Schneider
authors.forename: Hongyan
authors.initials: H
authors.lastname: Wang
authors.forename: Monika
authors.initials: M
authors.lastname: Raab
authors.forename: Elke
authors.initials: E
authors.lastname: Valk
authors.forename: Xin
authors.initials: X
authors.lastname: Smith
authors.forename: Matt
authors.initials: M
authors.lastname: Lovatt
authors.forename: Zhonglin
authors.initials: Z
authors.lastname: Wu
authors.forename: Braudel
authors.initials: B
authors.lastname: Maqueira-Iglesias
authors.forename: Klaus
authors.initials: K
authors.lastname: Strebhardt
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Rudd
mesh_terms: D000818:Animals; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism*; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D015151:Immunoblotting; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000378:metabolism*; D014158:Transcription, Genetic; D050807:ets-Domain Protein Elk-1 / Q000235:genetics* / Q000378:metabolism; D021601:trans-Golgi Network
chemical_list: D048049:Extracellular Signal-Regulated MAP Kinases; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; D010750:Phosphoproteins; D016283:Proto-Oncogene Proteins p21(ras); D050807:ets-Domain Protein Elk-1; C494113:Elk1 protein, mouse; C112278:Rasgrp1 protein, mouse; C514255:SKAP1 protein, mouse