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

To understand the function of B cell antigen receptor (BCR)-relatedcomplex on pre-B cells (pre-BCR, V_preB5/µ heavy chain/lg-/lg-ß),we examined pre-BCR- and BCR-mediated signaling events in humanand mouse pre-B (Nalm-6, 697, NFS-5), Immature B (lgM⁺ Daudi,WEH1–231) and mature B (lgM⁺;lgD⁺ BALL1) cell lines. Antl-µcross-linking induced tyrosine phosphorylation of the cytoplasmicproteins In each cell type, but did not induce a detectableCa²⁺ mobilization response in pre-B cells. While the pre-B cellsexpressed Syk protein at levels similar to those found In Bcell lines, pre-BCR cross-linkage did not Induce phosphorylationof Syk tyrosine residues. Different protein kinase C Isozymeswere expressed by pre-B (PKC-), Immature B (PKC- and -ß)and mature B (PKC-ß) cell lines. Anti-µ cross-linkingInduced PKC translocatlon from the cytosolic to the membranecompartment In Immature and mature B cells, but did not havethis effect In a pre-B cell line. Antl-µ cross-linkinginduced tyrosine phosphorytation of the p85 and p110 subunitsof phophatldylinositol 3-kinase (PI3-kinase) In both pre-B andB cell lines, but the pre-BCR induced PI3-kinase activationwas Syk independent. Ligation of the pre-BCR complex thus triggersa characteristic signaling pattern In pre-B cells.