Differential regulation of mRNAs encoding protein kinase C isoenzymes in activated human B cells.

Stimulation of human B cells via HLA class II antigens leads to an increase of PKC activity as a consequence of a transcriptional upregulation of the PKC. Extending previous data, other known B-cell activators, which include anti-IgM, SAC, and TSST1, are shown here to increase the cytosolic PKC activity significantly. Human B cells express significant mRNA levels of the PKC alpha, beta, delta, epsilon, and zeta species while the gamma species is consistently absent. The levels of PKC alpha and epsilon mRNA are increased by exposure to a nonmitogenic anti-IgM antibody in a lymphoblastoid B-cell line while PKC beta and delta mRNA are instead downregulated by this agent. An anti-HLA class II antibody (D1.12) induced an increase of PKC alpha, beta, and delta mRNA. A time study of PKC mRNA levels in anti-IgM-treated cells showed that the accumulation of the PKC alpha mRNA precedes the increase of PKC enzymatic activity. Moreover, PKC beta mRNA decreased following treatment with SAC while, on the contrary, it increased following TPA, anti-HLA class II (1.35) mAb, or mitogenic anti-IgM treatment. Our results underline the complexity of signal transduction via the PKC pathway by revealing that the PKC isoforms are differentially regulated and are in keeping with the idea that they may have distinct physiologic roles in human B cells.

Bacterial superantigen signaling via HLA class II on human B lymphocytes.

Staphylococcus enterotoxins and toxic shock syndrome toxin-1 (TSST-1) are members of the family of staphylococcal exoproteins (SE) which binds specifically to HLA class II molecules and certain V beta T cell receptor phenotypes. These bacterial products have been termed "superantigens" due to their capacity to stimulate a greater proportion of T lymphocytes than peptide antigens without a requirement for antigen processing. The SE stimulate monocytes to secrete IL-1 and TNF-alpha and affect B lymphocyte proliferation in response to anti-human IgM and Ig production by PBMC. The current study concerns the transmission of signals in human B lymphocytes following fixation of TSST-1. Activation of both PLC and PKC are observed while intracellular calcium levels remain unchanged. Levels of HLA class II mRNA were increased suggesting that a pathway leading to activation was triggered. This study therefore identifies some of the second messengers involved after SE fixation on HLA class II molecules and suggests that the signals transmitted via class II antigens as well as those via the TCR may have a role in the physiological responses to bacterial superantigens.

[Demonstration of transcriptional regulation of protein kinase C by class II anti-HLA antibodies in human CA cells of the lymphoblastoid line]. / Mise en évidence d'une régulation transcriptionnelle de la protéine kinase C (PKC) exercée par les anticorps anti-HLA de classe II dans les cellules de la lignée lymphoblastoïde humaine CA.

HLA class II antigens are involved in signal transduction in B lymphocytes. We have previously reported that the ligation of HLA class II antigens in B cells results in an increase of cytosolic and membrane PKC activity [3]. Unlike TPA, no translocation of the cytosolic PKC was observed following anti HLA class II antibody treatment. However, an increase of both PKC activity (cytosolic and membrane) and quantity was observed. These effects are completely abolished by actinomycin D treatment. Northern blot analysis and PCR reaction revealed that anti HLA class II antibodies induce an increase of the PKC beta level which is significant after 20 minutes of stimulation and rose to a maximum after 60 minutes. Taken together, our results show that anti HLA class II antibodies exert a transcriptional regulation of PKC in human B lymphocytes.

Effect of prostaglandin E2 on agonist-stimulated cAMP accumulation in the distal convoluted tubule isolated from the rabbit kidney.

The effects of calcitonin, vasoactive intestinal peptide (VIP), parathyroid hormone (PTH) and isoprenaline on intracellular cAMP accumulation were determined in the distal tubule (DCT) microdissected from collagenase-treated rabbit kidney. In DCTb (the initial "bright" portion) calcitonin (10 ng/ml) elicited a highly reproducible response 203.7 +/- 19.1 fmol cAMP mm-1 4 min-1 (SE,N = 13) whereas VIP-induced cAMP accumulation was less and more variable from one experiment to another (1 microM, 97.2 +/- 17.8 fmol mm-1 4 min-1, SE, N = 12). When used in combination, these two agonists were non-additive, indicating stimulation of a single pool of cAMP in DCTb. In DCTg, ("granular") which consists of at least two cell types, PTH (100 nM) elicited a marked, reproducible accumulation of cAMP (154.3 +/- 27.0 fmol mm-1 4 min-1; SE, N = 5). Isoprenaline (1 microM) and VIP (1 microM) induced much smaller increases in cAMP levels 20.9 +/- 2.7 and 29.4 +/- 4.1 fmol mm-1 4 min-1 (SE, N = 5) respectively, and, when used in combination, were non-additive, demonstrating that VIP and isoprenaline are active on the same cell type. In DCTb, prostaglandin E2 (PGE2) inhibited both calcitonin- and VIP-stimulated cAMP accumulation (calcitonin 57.8 +/- 2.7% inhibition, SE, N = 16; VIP, 80.6 +/- 2.1% inhibition, SE, N = 5). The EC50 values for calcitonin were 1.21 +/- 0.33 ng/ml and 1.83 +/- 0.25 ng/ml (SD, N = 3) in the absence and presence of PGE2 (300 nM) respectively with an IC50 for PGE2 of 26.3 +/- 6.3 nM (SE, N = 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Protein kinase C (PKC) activation via human leucocyte antigen class II molecules. A novel regulation of PKC activity.

Analysis of intracellular localization of protein kinase C (PKC) in a lymphoblastoid B cell line shows that anti-human leucocyte antigen (HLA) class II antibodies induce an increase of cytosolic and membrane PKC activities. This phenomenon is both time- and dose-dependent. The maximal PKC activation was observed after exposure to 12.5 micrograms/ml antibody for 30 to 45 min. Unlike TPA, no translocation of the cytosolic PKC was observed at any time following exposure to the anti-HLA class II antibodies. We observed a good correlation between the [3H]phorbol dibutyrate binding activity and the enzymatic activity of PKC. Using a panel of antibodies specific for the HLA class II isotypes (DP, DQ, DR), we demonstrated that PKC activation via HLA class II molecules is not restricted to one isotype. We also showed by Western blot analysis that the increased PKC activity correlates with a quantitative increase of PKC. The increase of PKC activity induced by anti-HLA class II antibodies was completely abolished by the treatment with actinomycin D, a transcriptional inhibitor, or cycloheximide, a translational inhibitor. Finally, Northern blot analysis revealed that anti-HLA class II antibodies induce an increase of the PKC alpha and PKC beta mRNAs levels which are significant after 20 min of stimulation and rose to a maximum after 60 min. In summary, our results show that increased PKC activity induced by HLA class II antibody is regulated at the transcriptional level.

Signal transduction in B lymphocytes.

We have examined the activity and intracellular compartmentalization of protein kinase C (PKC) following activation of human B lymphocytes by anti-human leukocyte antigen (HLA) class II antibodies. 12-O-Tetradecanoylphorbol 13-acetate (TPA) treatment increased membrane-associated PKC (between five and nine times greater than the control value) and decreased cytosolic PKC (between 70% and 100% of the control value). In contrast, anti-class II antibodies induce an activation of PKC which results either in an increase of cytosolic activity or membrane-bound activity without redistribution of cytosolic PKC. The effect of TPA and HLA class II molecules on total PKC activity was comparable: when TPA induced an increase of total PKC activity so did HLA class II molecules and when TPA did not, HLA class II molecules did not. Measurement on SDS PAGE of histone phosphorylation confirmed the above results of PKC activity. Taken together, our results suggest that PKC might be implicated in HLA class II-induced B lymphocyte activation.

Effect of PGE2 and alpha-adrenergic agonists on AVP-dependent cAMP levels in rabbit and rat CCT.

The effect of prostaglandins and alpha-adrenergic agonists on arginine vasopressin-induced adenosine 3',5'-cyclic monophosphate (cAMP) production was investigated in microdissected rat and rabbit cortical collecting tubules (CCT) incubated in vitro. In rabbit CCT, addition to all media of a prostaglandin synthesis inhibitor increased this production; exogenous prostaglandin E2 (PGE2) induced a reproducible dose-dependent inhibition of cAMP accumulation. Maximal inhibition (mean: 57.5%) was observed with 0.3 microM PGE2, and threshold inhibition was observed with concentrations ranging from 3 to 10 nM PGE2. Inhibition of cAMP levels in rabbit CCT was also obtained with 0.3 microM PGF2 alpha (mean inhibition: 44.3%) but not with alpha-adrenergic agonists studied under the same conditions. The opposite was observed in rat CCT studied in parallel: the alpha-agonists inhibited cAMP production by up to 80%, but PGE2 had no effect.