sq-23377 and mezerein

In order to examine the role of phosphatidylinositol bisphosphate (PIP2) hydrolysis in B cell activation, we studied the effect of various classes of protein kinase C (PKC) activators on anti-Ig-mediated B cell stimulation. Anti-Ig-stimulated PIP2 hydrolysis, elevations in [Ca2+]i, and induction of DNA synthesis were inhibited by PMA (a phorbol ester) as previously reported. In contrast, indolactam (an alkaloid PKC activator) inhibited PIP2 hydrolysis and elevations in [Ca2+]i, but stimulated rather than inhibited cellular proliferation. In order to examine whether the binding avidity of the PKC activators to PKC played a role in determining their activity to stimulate or inhibit B cell activation, we studied two other PKC activators, bryostatin and mezerein. Again, both inhibited anti-Ig mediated PIP2 hydrolysis and elevations in [Ca2+]i, whereas only the former inhibited induction of DNA synthesis. These data suggest that a) high levels of PIP2 hydrolysis and elevations in [Ca2+]i are not essential for anti-Ig-mediated induction of B cell DNA synthesis and b) activation of PKC may induce both stimulatory and inhibitory pathways of B cell activation, and whether stimulation or inhibition of cell activation is observed may depend on the combined intensity of these two signals.

Topics: Animals; Antibodies, Anti-Idiotypic; B-Lymphocytes; Bryostatins; Calcium; Diterpenes; Enzyme Activation; Immunoglobulin delta-Chains; In Vitro Techniques; Indoles; Ionomycin; Lactams; Lactones; Lymphocyte Activation; Macrolides; Mice; Mice, Inbred DBA; Phosphatidylinositol 4,5-Diphosphate; Phosphatidylinositols; Protein Kinase C; Receptors, Antigen, B-Cell; Signal Transduction; Terpenes

In a previous paper we have shown that the calcium ionophores, A23187 and ionomycin, induce a morphological differentiation of cultured astrocytes to a process-bearing form. As A23187 is known to induce the turnover of inositol phospholipids in astrocytes, and this response is dependent on extracellular calcium, we examined the morphological effects of exposure of cells to protein kinase C activators. 1,2-Dioctanoyl-sn-glycerol, mezerein and various phorbol esters are shown to result in no alteration in the morphology of cultured astrocytes. The results suggest that the morphological response of cultured astrocytes to calcium ionophores is not dependent on activation of protein kinase C.

Topics: Animals; Astrocytes; Bucladesine; Cells, Cultured; Cerebral Cortex; Diglycerides; Diterpenes; Ethers; Glycerides; Ionomycin; Phorbol Esters; Protein Kinase C; Rats; Terpenes

The effects of divalent ionophores (A23187 and ionomycin), Ca2+ channel agonist (BAY K 8644), and protein kinase C (C-kinase) activators [phorbol 12-myristate 13-acetate (PMA), mezerein] on bovine tracheal smooth muscle contraction were investigated. A23187 (5 microM) and ionomycin (0.5 microM) produced a prompt but transient contraction. C-kinase activators either produced no effect--e.g., PMA at 200 nM--or produced a rise in tension that was slow in onset but then gradually increased--e.g., mezerein at 400 nM. In contrast, ionophores and C-kinase activators, in combination, acted synergistically to produce a prompt and sustained contractile response that is reminiscent of that observed in response to carbachol, a cholinergic agonist. In addition, BAY K 8644 (20 nM), which has a minimal effect on tension by itself, could significantly enhance contraction induced by C-kinase activators. The contraction induced by all of these agents was quickly reversed either by removal of extracellular Ca2+ or upon addition of forskolin, an activator of adenylate cyclase. A similar reversal of carbachol-induced contraction by forskolin was observed with carbachol-induced contraction. These findings strongly suggest that C-kinase plays an important role in mediating tracheal smooth muscle contraction.

Topics: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Animals; Calcimycin; Calcium; Cattle; Colforsin; Diterpenes; Drug Synergism; Enzyme Activation; Ethers; In Vitro Techniques; Ionomycin; Muscle Contraction; Muscle, Smooth; Nifedipine; Protein Kinase C; Terpenes; Tetradecanoylphorbol Acetate; Trachea

We have used phorbol esters, such as 12-O-tetradecanoyl phorbol 13-acetate (TPA), to study the actions of protein kinase C (a TPA receptor) on cytosolic free Ca2+ concentrations [( Ca2+]i) and hormone secretion in rat pituitary cells (GH cells), and to elucidate the role of diacylglycerol (a protein kinase C activator) in thyrotropin-releasing hormone (TRH) action. TPA had a dual action on [Ca2+]i, inducing a stimulatory phase from 300 (basal) to 420 nM, which was interrupted in 30-60 s by an inhibitory phase which transiently lowered [Ca2+]i to 240 nM and rose in 3-10 min to yield the stimulatory phase. TPA-mediated changes in [Ca2+]i were induced by other phorbol esters and mezerein but not by phorbol or activators of kinases different from protein kinase C. Both phases of TPA action on [Ca2+]i were abolished by 5-min pretreatment with ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) (1.33 mM) or Ca2+ channel antagonists (verapamil or nifedipine). TPA also enhanced the rate of sustained hormone secretion without inducing a burst of hormone release (unlike TRH). Also, stimulation of secretion by TPA was not inhibited by Ca2+ channel antagonists and was resistant (10%) to EGTA. Simultaneous addition of TPA with the ionophore ionomycin (100 nM) reconstituted a TRH-like spike, nadir and plateau of [Ca2+]i. Ionomycin generated the spike in [Ca2+]i by releasing TRH-sensitive Ca2+ stores, while TPA induced the nadir (inhibitory phase), and a nifedipine/verapamil-sensitive plateau of [Ca2+]i (stimulatory phase). Concurrent (but not separate) addition of ionomycin and TPA also reconstituted a TRH-like burst of hormone secretion. These and previous results indicate that activation of protein kinase C by TPA or diacylglycerol (which is elevated by TRH) and a simultaneous spike in [Ca2+]i are required for burst secretion. Diacylglycerol may also mediate the TRH-induced nadir and plateau of [Ca2+]i; the latter process contributes to Ca2+-dependent stimulation of steady secretion by TRH.

Topics: Animals; Anti-Bacterial Agents; Caenorhabditis elegans Proteins; Calcium; Carrier Proteins; Cells, Cultured; Cytosol; Diterpenes; Egtazic Acid; Epidermal Growth Factor; Ethers; Insulin; Ionomycin; Phorbols; Pituitary Gland; Potassium; Protein Kinase C; Protein Kinases; Rats; Receptors, Drug; Receptors, Immunologic; Terpenes; Tetradecanoylphorbol Acetate; Thyrotropin-Releasing Hormone