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Tyrosine phosphatase SHP-2 binding to CTLA-4: absence of direct YVKM/YFIP motif recognition

H Schneider1, C E Rudd

  • 1Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, USA.

Biochemical and Biophysical Research Communications
|March 1, 2000
PubMed

Insights

Cytotoxic T-Lymphocyte-Associated protein 4 (CTLA-4) signaling remains unclear. This study found that phosphorylated CTLA-4 tyrosines do not directly bind to the phosphatase SHP-2, suggesting an indirect interaction in T-cells.

Area of Science:

  • Immunology
  • Molecular Biology
  • Cell Signaling

Background:

  • Cytotoxic T-Lymphocyte-Associated protein 4 (CTLA-4) is a key regulator of T-cell activation and proliferation.
  • The precise intracellular signaling mechanisms by which CTLA-4 exerts its inhibitory functions are not fully understood.
  • CTLA-4 is known to interact with phosphatidylinositol 3-kinase (PI3K) and the phosphatase SHP-2.

Purpose of the Study:

  • To investigate the direct binding interaction between phosphorylated CTLA-4 and the SH2 domains of SHP-2.
  • To elucidate the role of specific tyrosine phosphorylation sites on CTLA-4 in mediating SHP-2 association.
  • To clarify the nature of the CTLA-4 and SHP-2 interaction in T-cells.

Main Methods:

  • Utilized in vitro binding assays with wild-type and mutant SHP-2 constructs (including isolated SH2 domains).
  • Investigated binding to phosphorylated CTLA-4 tyrosine motifs (YVKM and YFIP).
  • Confirmed CTLA-4 and SHP-2 association in murine T-cells.

Main Results:

  • Phosphorylation of CTLA-4 tyrosines at YVKM and YFIP motifs did not facilitate direct binding of SHP-2 SH2 domains.
  • Neither single nor tandem SHP-2 SH2 domains bound to the phosphorylated CTLA-4 motifs.
  • SHP-2 association with CTLA-4 was confirmed in T-cells, but appears to be an indirect event.

Conclusions:

  • The phosphorylated YVKM and YFIP motifs on CTLA-4 are unlikely to be direct binding sites for SHP-2.
  • The observed association between CTLA-4 and SHP-2 in T-cells is likely mediated indirectly, potentially involving PI3K.
  • Further research is needed to fully delineate the indirect signaling pathways connecting CTLA-4 and SHP-2.

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