title: Identification of a novel lipid raft-targeting motif in Src homology 2-containing phosphatase 1.
abstract: The tyrosine phosphatase Src homology 2-containing phosphatase 1 (SHP-1) is a key negative regulator of TCR-mediated signaling. Previous studies have shown that in T cells a fraction of SHP-1 constitutively localizes to membrane microdomains, commonly referred to as lipid rafts. Although this localization of SHP-1 is required for its functional regulation of T cell activation events, how SHP-1 is targeted to the lipid rafts was unclear. In this study, we identify a novel, six-amino acid, lipid raft-targeting motif within the C terminus of SHP-1 based on several biochemical and functional observations. First, mutations of this motif in the context of full-length SHP-1 result in the loss of lipid raft localization of SHP-1. Second, this motif alone restores raft localization when fused to a mutant of SHP-1 (SHP-1 DeltaC) that fails to localize to rafts. Third, a peptide encompassing the 6-mer motif directly binds to phospholipids whereas a mutation of this motif abolishes lipid binding. Fourth, whereas full-length SHP-1 potently inhibits TCR-induced tyrosine phosphorylation of specific proteins, expression of a SHP-1-carrying mutation within the 6-mer motif does not. Additionally, although SHP-1 DeltaC was functionally inactive, the addition of the 6-mer motif restored its functionality in inhibiting TCR-induced tyrosine phosphorylation. Finally, this 6-mer mediated targeting of SHP-1 lipid rafts was essential for the function of this phosphatase in regulating IL-2 production downstream of TCR. Taken together, these data define a novel 6-mer motif within SHP-1 that is necessary and sufficient for lipid raft localization and for the function of SHP-1 as a negative regulator of TCR signaling.
authors.affiliation: Department of Microbiology, University of Virginia Health System, Charlottesville, VA 22908, USA.
authors.forename: Mohan
authors.initials: M
authors.lastname: Sankarshanan
authors.forename: Zhong
authors.initials: Z
authors.lastname: Ma
authors.forename: Tessy
authors.initials: T
authors.lastname: Iype
authors.forename: Ulrike
authors.initials: U
authors.lastname: Lorenz
mesh_terms: D000409:Alanine / Q000235:genetics; D020816:Amino Acid Motifs / Q000235:genetics; D000818:Animals; D002460:Cell Line; D015536:Down-Regulation / Q000235:genetics / Q000276:immunology; D006801:Humans; D019169:Jurkat Cells; D021962:Membrane Microdomains / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D051379:Mice; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D054645:Protein Phosphatase 1; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6 / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D011948:Receptors, Antigen, T-Cell / Q000037:antagonists & inhibitors / Q000502:physiology; D017384:Sequence Deletion; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D018909:src Homology Domains / Q000235:genetics
chemical_list: D010446:Peptide Fragments; D011948:Receptors, Antigen, T-Cell; D054645:Protein Phosphatase 1; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D000409:Alanine