Ia binding ligands and cAMP stimulate nuclear translocation of PKC in B lymphocytes

Selective effects of cholera toxin on the activation of mouse B cells by different polyclonal activators

Murine B cells were stimulated in vitro with anti-immunoglobulin (Ig) antibodies, lipopolysaccharide, or with various combinations of phorbol dibutyrate and ionomycin. Very low concentrations (ca. 10(-14) M) of cholera toxin inhibited anti-Ig-stimulated DNA synthesis, while the response to LPS was only abrogated by 2 X 10(4)-10(5)-fold greater concentrations of the toxin. Earlier responses in anti-Ig-stimulated B cells, such as increases in Ia antigen levels, were not affected by the toxin. Protein kinase C-activating phorbol esters, together with Ca2+ ionophores, are believed to stimulate DNA synthesis in lymphocytes by mimicking the two second messengers resulting from ligation of the antigen receptors. However, concentrations of cholera toxin which totally abolish anti-Ig-induced B cell proliferation significantly enhanced DNA and RNA synthesis induced by phorbol dibutyrate plus ionomycin. The results are discussed in terms of possible effects of cholera toxin on guanine nucleotide-binding (G) proteins controlling receptor coupling to second messenger-generating systems in B cells.

Antibody-induced cAMP accumulation in splenocytes from athymic nude mice

Products from the hydrolysis of phosphatidylinositol 4,5-bisphosphate (IP3) can increase and/or potentiate cAMP accumulation in a variety of cells. Antibody to surface immunoglobulins activates IP3 hydrolysis in B-lymphocytes. In this study we have examined whether anti-Ig also stimulated and/or potentiated increases in the cAMP levels of splenocytes from athymic nude mice. Furthermore, since TPA potentiates anti-Ig-induced DNA synthesis and cAMP modulates DNA synthesis, the effects of TPA on any anti-Ig-induced changes in cAMP were also studied. Antibody (25 micrograms/ml) stimulated a rapid ris in cAMP which increased from 250 fmol/10(6) cells to 400 fmol/10(6) cells within 1 min and then subsided to 310 fmol/10(6) cells by 10 min. TPA (96 nM) suppressed the anti-Ig-induced cAMP accumulation at 1 min by 60%, but potentiated the forskolin (114 microM)-induced rise by 151%. Two other activators of protein kinase C, dioctanoylglycerol (5 microM), and anti-Ig (25 micrograms/ml), also potentiated the forskolin response by 198% and 52%, respectively. These results suggest that modulation of the adenylate cyclase system by anti-Ig may act in concert with cytokines and/or prostaglandins secreted by other lymphoid cells to define the state of proliferation or differentiation in B-cells.