CUTTING EDGE - THE B-CELL SURFACE PROTEIN CD72 RECRUITS THE TYROSINE PHOSPHATASE SHP-1 UPON TYROSINE PHOSPHORYLATION

Activation signals of lymphocytes are negatively regulated by the memb rane molecules carrying the immunoreceptor tyrosine-based inhibition m otif (ITIM), Upon tyrosine phosphorylation, ITIMs recruit SH2-containi ng phosphatases such as SHP-1, resulting in down-modulation of cell ac tivation. We showed that the cytoplasmic domain of the CD72 molecule c arries an ITIM and is associated in vitro with SHP-1 upon tyrosine pho sphorylation, Moreover, cross-linking of B cell Ag receptor (BCR) enha nces both tyrosine phosphorylation of CD72 and association of CD72 wit h SHP-1 in B cell line WEHI-231, These results indicate that CD72 recr uits SHP-1 upon tyrosine phosphorylation induced by BCR signaling, sug gesting that CD72 is a negative regulator of BCR signaling.