Altered signal transduction secondary to surface IgM cross-linking on B-chronic lymphocytic leukemia cells. Differential activation of the phosphatidylinositol-specific phospholipase C.
To further study the mechanisms by which surface Ig triggering activates the inositol phospholipid signaling pathway, we have used B cells from chronic lymphocytic leukemia patients which, as previously described, display two patterns of response upon sIg cross-linking: in one group this cross-linking induces an inositol phosphate release, an intracellular free Ca2+ concentration elevation and a subsequent cell proliferation; in a second group none of these events occur although there is an increased class II Ag expression following anti-mu stimulation as in the first group. We have been able to demonstrate that the phosphatidyl inositol specific phospholipase C (PI-PLC) can be activated in permeabilized B cells from the first group by direct stimulation, with GPT gamma S, of a guanine nucleotide binding (G) protein. In addition, since anti-mu + GTP gamma S stimulate an increased inositol phosphate production in these cells, this suggests that surface Ig cross-linking activates PI-PLC via a G protein. However, in cells from the second group no inositol phosphate is released after GTP gamma S stimulation although PI-PLC can be directly activated by high Ca2+ concentrations. This reflects in these cells, an interruption of the signaling cascade sIg/G protein/PI-PLC at the level of the G protein or at the G protein/PI-PLC coupling. In cells from both groups PMA treatment, which is known to alter phosphatidyl inositol metabolism in B cells, completely inhibits PI-PLC activation even by high Ca2+ concentrations. These studies show that the phosphatidyl inositol-dependent signaling cascade after surface Ig triggering can be altered at different levels in B cells.
Hivroz
C
C
Laboratory of Immunochemistry and Immunopathology, INSERM U. 108, Paris, France.
Gény
B
B
Brouet
J C
JC
Grillot-Courvalin
C
C
D001402:B-Lymphocytes / Q000502:physiology*; D002051:Burkitt Lymphoma / Q000503:physiopathology*; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000502:physiology; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006681:HLA-D Antigens / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism; D008213:Lymphocyte Activation; D010703:Phorbol Esters / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism; D011940:Receptor Aggregation; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D015398:Signal Transduction; D013873:Thionucleotides / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism*
D006681:HLA-D Antigens; D007295:Inositol Phosphates; D010703:Phorbol Esters; D010716:Phosphatidylinositols; D011947:Receptors, Antigen, B-Cell; D013873:Thionucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins