Occupancy of the B cell specific glycoprotein, CD72 results in the activation of src family tyrosine kinases, phospholipase-γ activation and calcium mobilization. CD72 does not contain ITAM motifs like B cell receptor (BCR) complex to recruit tyrosine kinases and does not activate syk. Hence, we examined whether CD72 signaling involved the CD19 coreceptor and its associated phosphatidylinositol 3-kinase (PI 3-K). Two specific inhibitors of PI 3-K, wortmannin and LY294002 inhibited CD72 as well as BCR stimulated B cell proliferation. CD72 ligation induced CD19 tyrosine phosphorylation and caused an increased association of PI 3-K with CD19 as well as its lipid kinase activity. A prominent increase in the tyrosine phosphorylation of CD21 and CD35 was observed in BCR but not CD72 stimulated cells. Independent cross-linking or cocross-linking of CD72 and CD19 failed to induce tyrosine phosphorylation of syk suggesting that under these conditions also, CD72 signaling was independent of syk activation. A stimulation-dependent physical association between CD19 and CD72 was seen in CD72 ligated cells providing a possible mechanism by which CD72 may recruit CD19 and influence activation of CD19-associated PI 3-K. B lymphocytes from CD19-/- mice were defective in CD72 but not BCR induced proliferation, suggesting the importance of PI 3-K activation and CD19 signaling events for CD72 mediated B cell activation.
|頁（從 - 到）||A918|
|出版狀態||Published - 1998 三月 20|
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