SHP-1 regulates Fcγ receptor–mediated phagocytosis and the activation of RAC

Abstract

Fcγ receptor–mediated phagocytosis is a complex process involving the activation of protein tyrosine kinases, events that are potentially down-regulated by protein tyrosine phosphatases. We used the J774A.1 macrophage cell line to examine the roles played by the protein tyrosine phosphatase SHP-1 in the negative regulation of Fcγ receptor–mediated phagocytosis. Stimulation with sensitized sheep red blood cells (sRBCs) induced tyrosine phosphorylation of CBL and association of CBL with CRKL. These events were completely or partially abrogated by PP1 or the heterologous expression of dominant-negative SYK, respectively. Heterologous expression of wild-type but not catalytically inactive SHP-1 also completely abrogated the phagocytosis of IgG-sensitized sRBCs. Most notably, overexpressed SHP-1 associates with CBL and this association led to CBL dephosphorylation, loss of the CBL-CRKL interaction, and the suppression of Rac activation. These data represent the first direct evidence that SHP-1 is involved in the regulation of Fcγ receptor–mediated phagocytosis and suggest that activating signals mediated by SRC family kinases SYK, CBL, phosphatidyl inositol-3 (PI-3) kinase, and Rac are directly opposed by inhibitory signals through SHP-1.

ITIM-dependent endocytosis of CD33-related Siglecs: role of intracellular domain, tyrosine phosphorylation, and the tyrosine phosphatases, Shp1 and Shp2

“…Additional studies will be required to identify the full repertoire of proteins that bind to CD33 and similar immunoreceptors and address the functions of these interactions. All of these SH2 domain-containing proteins have been implicated to play a direct or indirect role in endocytosis, for example, by interaction with immunoreceptor tyrosinebased activation motif (ITAM)-containing Fc␥Rs [26,50,51], by recruiting growth factor receptor-bound protein 2 and linkage to clathrin-mediated endocytosis pathways or Cbl family proteins [41,42], or by acting as a guanine nucleotide exchange factor of dynamin-1 [52]. However, CrkL and PLC-␥1 favored binding to the C-terminal, ITIM-like motif, which is relatively less important for endocytosis [14], and Shp1, Shp2, and Syk bound preferentially to the proximal ITIM of CD33, which is more important for endocytosis [14].…”

Macrophages of multiple sclerosis patients display deficient SHP-1 expression and enhanced inflammatory phenotype

“…Once macrophages enter the CNS, the SHP-1-deficiency can contribute to enhanced Fc-g receptor-mediated myelin phagocytosis in the presence of antibodies and complement. 12,[109][110][111] These hypotheses indicate a two-step process in which SHP-1-deficiency in macrophages is a precondition to tissue-specific inflammation triggered by a CNS-specific inflammatory signal. The latter is consistent with a recent mouse study in which SHP-1 deficiency alone does not result in inflammatory disease but rather establishes a permissive state in which microbial infection triggers inflammation and autoimmunity.…”

The coordination of signaling during Fc receptor-mediated phagocytosis

“…Syk signaling is required for efficient phosphorylation of the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI-3K) [14], which activates the PI-3K catalytic subunit p110␤ [15], generating PI-3,4,5-trisphosphate [PI(3,4,5)P 3 ] from PI-4,5bisphosphate [PI(4,5)P 2 ] in the membrane near the receptor complex. Other proteins recruited to the FcR complex include the protein phosphatase Src homology 2 (SH2)-containing tyrosine phosphatase-1 [16,17], Gab2 [18], SH2 domain-containing leukocyte phosphoprotein of 76 kDa [19], Cbl, Nck [20], and the 5Ј PI phosphatase, SH2 domain-containing inositol phosphatase 1 (SHIP-1) [17,21].…”