SKAP55 modulates T cell antigen receptor-induced activation of the Ras-Erk-AP1 pathway by binding RasGRP1.
Src kinase-associated phosphoprotein of 55 kDa (SKAP55) is an adapter protein with an N-terminal region, a pleckstrin homology domain, a linker with tyrosine phosphorylation sites, and a C-terminal Src homology 3 domain. We report that overexpression of SKAP55 disrupts signaling from the TCR to the Ras-Erk-AP-1 pathway and transcription of the IL-2 gene in primary human T cells and in Jurkat T leukemia cells. In contrast, moderate overexpression of SKAP55 increased TCR-dependent AP-1 transcriptional activity, suggesting that high-level SKAP55 overexpression interfered with the assembly of functional signaling complexes required for TCR coupling to the Ras pathway. In support of this view, knock-down of SKAP55 by RNA interference resulted in decreased reporter gene activation and decreased ERK phosphorylation. In contrast, TCR-induced NF-kappaB activation was not affected. Since constitutively active forms of Ras or Raf-1 overcame the inhibitory effects of SKAP55 overexpression, we searched for a mechanism upstream of Ras and found that SKAP55 co-immunoprecipitated with the Ras activator RasGRP1. The binding of RasGRP1 to SKAP55 required the C-terminus of SKAP55 and was enhanced by tyrosine phosphorylation of SKAP55. These results suggest that SKAP55 modulates signal transduction from the TCR to Ras by binding to RasGRP1.
Kosco
Karena A
KA
Program on Inflammatory Disease Research, Infectious and Inflammatory Disease Center, The Burnham Institute for Medical Research, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA. karenakosco@yahoo.com
Cerignoli
Fabio
F
Williams
Scott
S
Abraham
Robert T
RT
Mustelin
Tomas
T
D002460:Cell Line; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D020868:Gene Silencing; D017930:Genes, Reporter; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D010750:Phosphoproteins / Q000737:chemistry / Q000172:deficiency / Q000378:metabolism*; D011485:Protein Binding; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000201:enzymology; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism*
D004268:DNA-Binding Proteins; D020662:Guanine Nucleotide Exchange Factors; D010750:Phosphoproteins; C491790:RASGRP1 protein, human; D011948:Receptors, Antigen, T-Cell; C108336:SKAP1 protein, human; D018808:Transcription Factor AP-1; D048049:Extracellular Signal-Regulated MAP Kinases; D018631:ras Proteins