A highly conserved tyrosine of Tim-3 is phosphorylated upon stimulation by its ligand galectin-9.
Tim-3 is a member of the TIM family of proteins (T-cell immunoglobulin mucin) involved in the regulation of CD4+ T-cells. Tim-3 is a T(H)1-specific type 1 membrane protein and regulates T(H)1 proliferation and the development of tolerance. Binding of galectin-9 to the extracellular domain of Tim-3 results in apoptosis of T(H)1 cells, but the intracellular pathways involved in the regulatory function of Tim-3 are unknown. Unlike Tim-1, which is expressed in renal epithelia and cancer, Tim-3 has not been described in cells other than neuronal or T-cells. Using RT-PCR we demonstrate that Tim-3 is expressed in malignant and non-malignant epithelial tissues. We have cloned Tim-3 from an immortalized liver cell carcinoma line and identified a highly conserved tyrosine in the intracellular tail of Tim-3 (Y265). We demonstrate that Y265 is specifically phosphorylated in vivo by the interleukin inducible T cell kinase (ITK), a kinase which is located in close proximity of the TIM genes on the allergy susceptibility locus 5q33.3. Stimulation of Tim-3 by its ligand galectin-9 results in increased phosphorylation of Y265, suggesting that this tyrosine residue plays an important role in downstream signalling events regulating T-cell fate. Given the role of TIM proteins in autoimmunity and cancer, the conserved SH2 binding domain surrounding Y265 could represent a possible target site for pharmacological intervention.
van de Weyer
Philipp S
PS
Department of Nephrology, University Medical Center, D-79106 Freiburg, Germany.
Muehlfeit
Michael
M
Klose
Christoph
C
Bonventre
Joseph V
JV
Walz
Gerd
G
Kuehn
E Wolfgang
EW
D000595:Amino Acid Sequence; D045744:Cell Line, Tumor; D004848:Epithelium / Q000378:metabolism; D037161:Galectins / Q000502:physiology*; D000072597:Hepatitis A Virus Cellular Receptor 2; D006801:Humans; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D009369:Neoplasms / Q000378:metabolism; D009928:Organ Specificity; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011991:Receptors, Virus / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism*; D018909:src Homology Domains
D037161:Galectins; C448908:HAVCR2 protein, human; D000072597:Hepatitis A Virus Cellular Receptor 2; C105032:LGALS9 protein, human; D008565:Membrane Proteins; D011991:Receptors, Virus; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; C080813:emt protein-tyrosine kinase