Transmembrane signaling through B cell MHC class II molecules: anti-Ia antibodies induce protein kinase C translocation to the nuclear fraction

Among receptors of immunologic importance, antigen receptors on B cells (mIg) and T cells (Ti/T3), as well as receptors for IL 2 and IL 3, appear to utilize a transmembrane signal transduction mechanism that involves protein kinase C (PKC) translocation from the cytosol to the plasma membrane. Here we report evidence that B cell surface type II major histocompatibility molecules (I-A and I-E) can act as signal transducing molecules, as evidenced by the ability of soluble ligands that bind these molecules to stimulate rapid translocation (less than 2 min) of cytosolic PKC. This phenomenon differs qualitatively from translocation induced by anti-Ig antibodies and all other ligands thus far studied, in involving an apparent translocation of protein kinase C to the nucleus. Data suggest that I-A/E molecules may play an active role in T cell-dependent B cell activation. They also provide an explanation for the previously observed suppressive effects of soluble I-A and I-E binding ligands on B cell activation in demonstrating that these ligands (anti-IA/E) deplete the cytosolic reservoir of PKC normally translocated to the plasma membrane after anti-Ig or LPS stimulation.

Transmembrane signaling through B cell MHC class II molecules: anti-Ia antibodies induce protein kinase C translocation to the nuclear fraction

Among receptors of immunologic importance, antigen receptors on B cells (mIg) and T cells (Ti/T3), as well as receptors for IL 2 and IL 3, appear to utilize a transmembrane signal transduction mechanism that involves protein kinase C (PKC) translocation from the cytosol to the plasma membrane. Here we report evidence that B cell surface type II major histocompatibility molecules (I-A and I-E) can act as signal transducing molecules, as evidenced by the ability of soluble ligands that bind these molecules to stimulate rapid translocation (less than 2 min) of cytosolic PKC. This phenomenon differs qualitatively from translocation induced by anti-Ig antibodies and all other ligands thus far studied, in involving an apparent translocation of protein kinase C to the nucleus. Data suggest that I-A/E molecules may play an active role in T cell-dependent B cell activation. They also provide an explanation for the previously observed suppressive effects of soluble I-A and I-E binding ligands on B cell activation in demonstrating that these ligands (anti-IA/E) deplete the cytosolic reservoir of PKC normally translocated to the plasma membrane after anti-Ig or LPS stimulation.

[Clinical observation on the changes in plasma cyclic nucleotides in patients with leukemia before and after treatment and their relation to cell-mediated immunity]

Level of plasma cyclic nucleotides was determined in 47 normal subjects and 63 patients with leukemia. Follow-up was carried out in 20 of these patients. The relation between the level of cyclic nucleotides and cell-mediated immunity was studied.

THE RESULTS

There was no significant difference in cyclic adenosine monophosphate (cAMP) between the normal subjects and leukemic patients, whereas cyclic guanosine monophosphate (cGMP) level was markedly elevated and cAMP/cGMP ratio was obviously reduced in the untreated and unrelieved patients. There was no significant difference in the various types of leukemia. In patients with complete remission (CR) after treatment, their cyclic nucleotides were similar to those in normal subjects, but they remained abnormal in patients without clinical remission after treatment. In CR patients treated regularly for half a year, the cGMP level when first diagnosed was lower than that of patients who died soon or were unrelieved. Plasma cGMP level was negatively correlated to E-rosette forming cell (E-RFC) and cAMP/cGMP ratio was positively correlated to E-RFC. These results suggest that the plasma cGMP be used as additional parameter to monitor the treatment response and prognosis. Reduced E-RFC in leukemia may be related to the elevated cGMP and/or lowered cAMP/cGMP ratio.

Translocation of protein kinase C during membrane immunoglobulin-mediated transmembrane signaling in B lymphocytes

Previous studies have implicated a role for protein kinase C (PKC) in transmembrane signal transduction by B cell surface immunoglobulin (Ig). Specifically, the pharmacologic PKC activator phorbol myristate acetate mimics the biologic effects of mIg cross-linking ligands, and cross-linking of membrane Ig (mIg) induces polyphosphoinositide hydrolysis generating diacylglycerol, a potent activator of PKC. Studies described here additionally implicate PKC in mIg-mediated signaling by demonstrating rapid translocation of activatable PKC (PKCa) from cytosol to Triton-soluble membrane fractions after cross-linking of cell surface IgM or IgD. This response, which is also induced by phorbol myristate acetate and lipolysaccharide, is detectable within 1 min of mIg cross-linking and is followed within 4 min by additional translocation of PKCa to a Triton-insoluble particulate compartment. The ability of dbcAMP plus theophylline to inhibit polyphosphoinositide hydrolysis, PKCa translocation, and the B cell's subsequent biological response suggests that these events may be causally related.

Translocation of protein kinase C during membrane immunoglobulin-mediated transmembrane signaling in B lymphocytes

Previous studies have implicated a role for protein kinase C (PKC) in transmembrane signal transduction by B cell surface immunoglobulin (Ig). Specifically, the pharmacologic PKC activator phorbol myristate acetate mimics the biologic effects of mIg cross-linking ligands, and cross-linking of membrane Ig (mIg) induces polyphosphoinositide hydrolysis generating diacylglycerol, a potent activator of PKC. Studies described here additionally implicate PKC in mIg-mediated signaling by demonstrating rapid translocation of activatable PKC (PKCa) from cytosol to Triton-soluble membrane fractions after cross-linking of cell surface IgM or IgD. This response, which is also induced by phorbol myristate acetate and lipolysaccharide, is detectable within 1 min of mIg cross-linking and is followed within 4 min by additional translocation of PKCa to a Triton-insoluble particulate compartment. The ability of dbcAMP plus theophylline to inhibit polyphosphoinositide hydrolysis, PKCa translocation, and the B cell's subsequent biological response suggests that these events may be causally related.

[Radioimmunoassay of the antitumor drug--methotrexate (MTX)]

The specific efficient anti-MTX antibody was obtained from the rabbits immunized with an artificial antigen produced by condensing MTX and bovine serum albumin in water-soluble carbodi-imide. The affinity constant (Ka) of the antibody is 1.8 X 10(9) L/mol. The rapid, sensitive and specific radioimmunoassay was developed with the tritium-labeled MTX as the tracer and the dextran-coated charcoal as the separating reagent. The concentration of MTX was measured within 1.5 hours and the lowest detectable level was 0.1 ng using only 10 microliter of serum or other biological fluids. Folic acid and its derivatives, hormones and other chemotherapy drugs have no influence on this assay. The method has an acceptable accuracy and precision: the recovery is 96.5%; the coefficients of variation (CV) within and between assay are 8% and 14%. The method is successful for the monitor of the MTX concentration in patient's plasma and study of its metabolism and pharmacokinetics.