Cross-linking of B cell antigen receptor-related structure of pre-B cell lines induces tyrosine phosphorylation of p85 and p110 subunits and activation of phosphatidylinositol 3-kinase

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Abstract
To understand the function of B cell antigen receptor (BCR)-related complex on pre-B cells (pre-BCR, VpreB5/μ heavy chain/lg-α/lg-β), we examined pre-BCR- and BCR-mediated signaling events in human and mouse pre-B (Nalm-6, 697, NFS-5), Immature B (lgM+ Daudi, WEH1–231) and mature B (lgM+;lgD+ BALL1) cell lines. Antl-μ cross-linking induced tyrosine phosphorylation of the cytoplasmic proteins In each cell type, but did not induce a detectable Ca2+ mobilization response in pre-B cells. While the pre-B cells expressed Syk protein at levels similar to those found In B cell lines, pre-BCR cross-linkage did not Induce phosphorylation of Syk tyrosine residues. Different protein kinase C Isozymes were expressed by pre-B (PKC-α), Immature B (PKC-α and -β) and mature B (PKC-β) cell lines. Anti-μ cross-linking Induced PKC translocatlon from the cytosolic to the membrane compartment In Immature and mature B cells, but did not have this effect In a pre-B cell line. Antl-μ cross-linking induced tyrosine phosphorytation of the p85 and p110 subunits of phophatldylinositol 3-kinase (PI3-kinase) In both pre-B and B cell lines, but the pre-BCR induced PI3-kinase activation was Syk independent. Ligation of the pre-BCR complex thus triggers a characteristic signaling pattern In pre-B cells.

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