Cross-linkage of Ly-6A/E induces Ca2+ translocation in the absence of phosphatidylinositol turnover and mediates proliferation of normal murine B lymphocytes.
Ly-6A/E is a phosphatidylinositol (PI)-linked membrane protein whose expression is induced or upregulated on normal murine T and B cells by IFN-gamma. Cross-linkage of Ly-6A/E expressed on normal murine T cells stimulates Ca2+ translocation, and in the presence of a protein kinase C (PKC) activator, lymphokine secretion, and cellular proliferation. Utilizing an anti-Ly-6A/E mAb, we studied the effect of cross-linking Ly-6A/E on IFN-gamma-treated resting B cells, for Ca2+ translocation, PI turnover, and cellular proliferation. Since these events are known to be stimulated by cross-linkage of B cell membrane (m)Ig, we compared the changes mediated through these respective membrane proteins. We show that cross-linkage of B cell Ly-6A/E stimulates a large, rapid, and sustained increase in the concentration of intracellular free calcium ([Ca2+]i) comparable in magnitude, though somewhat delayed, relative to that observed after cross-linking of mIg. Cross-linkage of B cell Ly-6A/E does not, however, stimulate detectable PI turnover, in contrast to PI turnover induced by ligation of mIg. Both the Ly-6A/E- and mIg-mediated increase in [Ca2+]i occur through mobilization of internal Ca2+ stores as well as entry of Ca2+ into the cell from the extracellular compartment. Ly-6A/E-mediated Ca2+ translocation appears to be under the regulation of PKC in that short term pretreatment of B cells with the PKC activator, PMA, inhibits the Ly-6A/E- as well as the mIg-mediated increase in [Ca2+]i, whereas prolonged exposure to PMA, under conditions that lead to depletion of PKC, results in an augmentation in Ca2+ translocation after ligation of either Ly-6A/E or mIg. Co-capping studies indicate that Ly-6A/E and mIg cap independently in the B cell membrane, thus suggesting that the Ly-6A/E-induced effects on Ca2+ translocation are not mediated through simultaneous modulation of mIg. Anti-Ly6A/E, by itself, does not stimulate an increase in [3H]thymidine incorporation by IFN-gamma-treated resting B cells, but induces a striking increase in the presence of PMA. By contrast, anti-Ig by itself stimulates significant increases in [3H]thymidine incorporation that is inhibited by PMA. Thus, Ly-6A/E is a potent mediator of B cell activation that may use a signal transduction system in quiescent B cells that is distinct from that of the Ag receptor.
Snapper
C M
CM
Department of Pathology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814.
Yamada
H
H
Mond
J J
JJ
June
C H
CH
D000818:Animals; D000950:Antigens, Ly / Q000032:analysis / Q000502:physiology*; D001402:B-Lymphocytes / Q000276:immunology*; D002118:Calcium / Q000378:metabolism*; D007072:Immunoglobulin D / Q000502:physiology; D007371:Interferon-gamma / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000187:drug effects*; D008674:Metals, Rare Earth / Q000494:pharmacology; D051379:Mice; D008806:Mice, Inbred AKR; D008807:Mice, Inbred BALB C; D010716:Phosphatidylinositols / Q000378:metabolism*; D011493:Protein Kinase C / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D000950:Antigens, Ly; D007072:Immunoglobulin D; D008674:Metals, Rare Earth; D010716:Phosphatidylinositols; D007371:Interferon-gamma; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium