Treatment of rabbit neutrophils with phorbol esters results in increased ADP-ribosylation catalyzed by pertussis toxin and inhibition of the GTPase stimulated by fMet-Leu-Phe

Uncoupling of ATP-induced inositol phosphate formation and Ca(2+) mobilization by phorbol ester in canine cultured tracheal epithelial cells

The regulation of the increase in inositol phosphates (IPs) production and intracellular Ca(2+) concentration ([Ca(2+)](i)) by protein kinase C (PKC) was investigated in canine cultured tracheal epithelial cells (TECs). Pretreatment of TECs with phorbol 12-myristate 13-acetate (PMA, 1 microM) for 30 min attenuated the ATP- and UTP-induced IPs formation and Ca(2+) mobilization. The concentrations of PMA that gave half-maximal (EC(50)) inhibition of ATP- and UTP-induced IPs accumulation and an increase in [Ca(2+)](i) were 5-10 and 4-12 nM, respectively. Prior treatment of TECs with staurosporine (1 microM), a PKC inhibitor, partially inhibited the ability of PMA to attenuate ATP- and UTP-induced responses, suggesting that the inhibitory effect of PMA is mediated through the activation of PKC. Furthermore, analysis of cell extracts by Western blotting with antibodies against different PKC isozymes revealed that TECs expressed PKC-alpha, -betaI, -betaII, -gamma, -delta, -epsilon, -theta, and -zeta. With PMA treatment of the cells for various times, translocation of PKC-alpha, -betaI, -betaII, -gamma, -delta, -epsilon, and -theta from the cytosol to the membrane was seen after 5- and 30-min and 2- and 4-h treatment. However, 6-h treatment caused a partial down-regulation of these PKC isozymes. PKC-zeta was not significantly translocated and down-regulated at any of the times tested. In conclusion, these results suggest that activation of PKC may inhibit the phosphoinositide (PI) hydrolysis and consequently attenuate the [Ca(2+)](i) increase or inhibit independently both responses to ATP and UTP. The translocation of PKC-alpha, -betaI, -betaII, -delta, -epsilon, -gamma, and -theta induced by PMA caused an attenuation of ATP- and UTP-induced IPs accumulation and Ca(2+) mobilization in TECs.

Inhibition of bradykinin-induced phosphoinositide hydrolysis and Ca2+ mobilisation by phorbol ester in rat cultured vascular smooth muscle cells

Regulation of the increase in inositol phosphate (IP) production and intracellular Ca2+ concentration ([Ca2+]i by protein kinase C (PKC) was investigated in cultured rat vascular smooth muscle cells (VSMCs). Pretreatment of VSMCs with phorbol 12-myristate 14-acetate (PMA, 1 microM) for 30 min almost abolished the BK-induced IP formation and Ca2+ mobilisation. This inhibition was reduced after incubating the cells with PMA for 4 h, and within 24 h the BK-induced responses were greater than those of control cells. The concentrations of PMA giving a half-maximal (pEC50) and maximal inhibition of BK induced an increase in [Ca2+]i, were 7.8 +/- 0.3 M and 1 microM, n = 8, respectively. Prior treatment of VSMCs with staurosporine (1 microM), a PKC inhibitor, inhibited the ability of PMA to attenuate BK-induced responses, suggesting that the inhibitory effect of PMA is mediated through the activation of PKC. Paralleling the effect of PMA on the BK-induced IP formation and Ca2+ mobilisation, the translocation and downregulation of PKC isozymes were determined by Western blotting with antibodies against different PKC isozymes. The results revealed that treatment of the cells with PMA for various times, translocation of PKC-alpha, betaI, betaII, delta, epsilon, and zeta isozymes from the cytosol to the membrane were seen after 5 min, 30 min, 2 h, and 4 h of treatment. However, 24-h treatment caused a partial downregulation of these PKC isozymes in both fractions. Treatment of VSMCs with 1 microM PMA for either 1 or 24 h did not significantly change the K(D) and Bmax of the BK receptor for binding (control: K(D) = 1.7 +/- 0.2 nM; Bmax = 47.3 +/- 4.4 fmol/mg protein), indicating that BK receptors are not a site for the inhibitory effect of PMA on BK-induced responses. In conclusion, these results demonstrate that translocation of PKC-alpha, betaI, betaII, delta, epsilon, and zeta induced by PMA caused an attenuation of BK-induced IPs accumulation and Ca2+ mobilisation in VSMCs.

Regulation of 5-hydroxytryptamine-induced signal transduction in canine cultured aorta smooth muscle cells by phorbol ester

Regulation of the increase in inositol phosphates (IPs) production and intracellular Ca2+ concentration ([Ca2+]i) by protein kinase C (PKC) was investigated in cultured canine aorta smooth muscle cells (ASMCs). Stimulation of ASMCs by 5-hydroxytryptamine (5-HT) led to IPs formation and caused an initial transient [Ca2+]i peak followed by a sustained elevation of [Ca2+]i in a concentration-dependent manner. Pretreatment of ASMCs with phorbol 12-myristate 13-acetate (PMA) for 30 min almost abolished the 5-HT-induced IPs formation and Ca2+ mobilization. This inhibition was reduced after long-term incubating the cells with PMA. Prior treatment of ASMCs with staurosporine or GF109203X, PKC inhibitors, inhibited the ability of PMA to attenuate 5-HT-induced responses, suggesting that the inhibitory effect of PMA is mediated through the activation of PKC. In parallel with the effect of PMA on the 5-HT-induced IP formation and Ca2+ mobilization, the translocation and down-regulation of PKC isozymes were determined by Western blotting with antibodies against different PKC isozymes. The results revealed that treatment of ASMCs with PMA for various times, translocation of PKC-alpha, betaI, betaII, delta, epsilon, theta, and zeta isozymes from the cytosol to the membrane was seen after 5-min, 30-min, 2-h, and 4-h treatment. However, 24-h treatment caused a partial down-regulation of these PKC isozymes. In conclusion, these results demonstrate that translocation of PKC-alpha, betaI, betaII, delta, epsilon, theta, and zeta induced by PMA caused an attenuation of 5-HT-induced IPs accumulation and Ca2+ mobilization in ASMCs.

Uncoupling of bradykinin-induced phosphoinositide hydrolysis and Ca2+ mobilization by phorbol ester in canine cultured tracheal epithelial cells

1. Regulation of the increase in inositol phosphates (IPs) production and intracellular Ca2+ concentration ([Ca2+]i by protein kinase C (PKC) was investigated in canine cultured tracheal epithelial cells (TECs). Stimulation of TECs by bradykinin (BK) led to IPs formation and caused an initial transient [Ca2+]i peak in a concentration-dependent manner. 2. Pretreatment of TECs with phorbol 12-myristate 13-acetate (PMA, 1 microM) for 30 min attenuated the BK-induced IPs formation and Ca2+ mobilization. The maximal inhibition occurred after incubating the cells with PMA for 2 h. 3. The concentrations of PMA that gave half-maximal (pEC50) inhibition of BK-induced IPs accumulation and an increase in [Ca2+]i were 7.07 M and 7.11 M, respectively. Inactive phorbol ester, 4alpha-phorbol 12,13-didecanoate at 1 microM, did not inhibit these responses. Prior treatment of TECs with staurosporine (1 microM), a PKC inhibitor, inhibited the ability of PMA to attenuate BK-induced responses, suggesting that the inhibitory effect of PMA is mediated through the activation of PKC. 4. In parallel with the effect of PMA on the BK-induced IPs formation and Ca2+ mobilization, the translocation and down-regulation of PKC isozymes were determined. Analysis of cell extracts by Western blotting with antibodies against different PKC isozymes revealed that TECs expressed PKC-alpha, betaI, betaII, gamma, delta, epsilon, theta and zeta. With PMA treatment of the cells for various times, translocation of PKC-alpha, betaI, betaII, gamma, delta, epsilon and theta from cytosol to the membrane was seen after 5 min, 30 min, 2 h, and 4 h treatment. However, 6 h treatment caused a partial down-regulation of these PKC isozymes. PKC-zeta was not significantly translocated and down-regulated at any of the times tested. 5. Treatment of TECs with 1 microM PMA for either 30 min or 6 h did not significantly change the KD, and Bmax receptor for BK binding (control: KD=1.7+/-0.3 nM; Bmax=50.5+/-4.9 fmol/mg protein), indicating that BK receptors are not a site for the inhibitory effect of PMA on BK-induced responses. 6. In conclusion, these results suggest that activation of PKC may inhibit the phosphoinositide hydrolysis and consequently attenuate the [Ca2+]i increase or inhibit independently both responses to BK. The translocation of pKC-alpha, betaI, betaII, delta, epsilon, gamma, and theta induced by PMA caused an attenuation of BK-induced IPs accumulation and Ca2+ mobilization in TECs.

Inhibition of 5-hydroxytryptamine-induced phosphoinositide hydrolysis and Ca2+ mobilization in canine cultured tracheal smooth muscle cells by phorbol ester

1. Regulation of the increase in inositol-1,4,5-trisphosphate (IP3) production and intracellular Ca2+ concentration ([Ca2+]i by protein kinase C (PKC) was investigated in canine cultured tracheal smooth muscle cells (TSMCs). Stimulation of TSMCs by 5-hydroxytryptamine (5-HT) caused an initial transient [Ca2+]i peak followed by a sustained elevation of [Ca2+]i in a concentration-dependent manner. 2. Pretreatment of TSMCs with phorbol 12-myristate 13-acetate (PMA, 1 microM) for 30 min blocked the 5-HT-induced IP3 formation and Ca2+ mobilization. This inhibition was reduced after the cells had been incubated with PMA for 8 h, and within 48 h the 5-HT-induced Ca2+ mobilization reached the same extent as control cells. 3. The concentration of PMA that gave half-maximal inhibition of 5-HT-induced increase in [Ca2+]i was 4 nM. Pretreatment of TSMCs with staurosporine (1 microM) of GF109203X (0.1 microM), PKC inhibitors, inhibited the ability of PMA to attenuate 5-HT-induced responses, suggesting that the inhibitory effect of PMA was mediated through the activation of PKC. 4. In parallel with the effect of PMA on 5-HT-induced IP3 formation and Ca2+ mobilization, the translocation and down-regulation of PKC isozymes were determined by Western blot analysis in TSMCs. Analysis of cell extracts by Western blotting with antibodies against different PKC isozymes revealed that TSMCs expressed PKC-alpha, beta I, beta II, delta, epsilon, theta and zeta. With PMA treatment of the cells for various times, translocation of PKC-alpha, beta I, beta II, delta, epsilon, and theta from the cytosol to the membrane was seen after 5 min, 30 min, 2 h, and 4 h treatment. However, 24 h treatment caused a partial down-regulation of these PKC isozymes PKC-zeta was not significantly translocated and down-regulated at any of the times tested. 5. In conclusion, these results suggest that activation of PKC may inhibit the receptor-mediated phosphoinositide hydrolysis and consequently attenuate the [Ca2+]i increase or inhibit both responses independently. The translocation of PKC-alpha, beta I, beta II, delta, epsilon, and theta induced by PMA caused an attenuation of 5-HT-stimulated IP3 accumulation and Ca2+ mobilization in TSMCs.

Inhibitory effect of phorbol ester on bradykinin-induced phosphoinositide hydrolysis and calcium mobilization in cultured canine tracheal smooth muscle cells

Regulation of the increase in inositol 1,4,5-trisphosphate (IP3) production and intracellular Ca2+ concentration ([Ca2+]i) by protein kinase C (PKC) was investigated in cultured canine tracheal smooth muscle cells (TSMCs). Stimulation of TSMCs by bradykinin (BK) led to IP3 formation and caused an initial transient peak followed by a sustained elevation of [Ca2+]i in a concentration-dependent manner. Pretreatment of TSMCs with phorbol 12-myristate 13-acetate (PMA, 1 microM) for 30 min blocked the BK-induced IP3 formation and Ca2+ mobilization. However, this inhibition was reduced after incubating the cells for 4 h with PMA. Inactive phorbol ester, 4 alpha-phorbol 12,13-didecanoate at 1 microM, did not inhibit these responses to BK. Prior treatment with staurosporine (1 microM), a PKC inhibitor, inhibited the effect of PMA on the BK-induced response, suggesting that the effect of PMA is mediated by the activation of PKC. In parallel experiments, a change of PKC activity was observed. PMA rapidly decreased PKC activity in the cytosol of TSMCs, while increasing it transiently in the cell membranes within 30 min. Thereafter the membrane-associated PKC activity decreased and persisted for at least 24 h of PMA treatment. Moreover, treatment with 1 microM PMA for 2 and 24 h did not significantly change the KD and Bmax of the BK receptor for [H]BK binding (control: KD = 2.3 +/- 0.3 nM, Bmax = 25.2 +/- 1.4 fmol/mg protein). These results suggest that activation of PKC inhibit IP3 accumulation and consequently attenuate [Ca2+]i increase or inhibit independently both responses. The PMA-induced inhibition of responses to BK was associated with an increase in membranous PKC activity.

Inhibitory Effect of Phorbol Ester on Carbachol-Induced Signal Transduction in Cultured Canine Tracheal Smooth Muscle Cells

Regulation of the increases in inositol 1,4,5-trisphosphate (IP(3)) production and intracellular Ca(2+) concentration ([Ca(2+)](i)) by activation of protein kinase C (PKC) was investigated in cultured canine tracheal smooth muscle cells (TSMCs). Stimulation of TSMCs by carbachol led to IP(3) formation and caused an initial transient peak of [Ca(2+)](i) followed by a sustained elevation in a concentration-dependent manner. Pretreatment of TSMCs with phorbol 12-myristate 13-acetate (PMA, 1 &mgr;M) for 30 min blocked the carbachol-induced IP(3) formation and Ca(2+) mobilization. Following preincubation, carbachol-induced Ca(2+) mobilization recovered within 24 h. The concentrations of PMA that gave half-maximal inhibition of carbachol-induced IP(3) formation and increase in [Ca(2+)](i) were 7 and 4 nM, respectively. Prior treatment of TSMCs with staurosporine (1 &mgr;M), a PKC inhibitor, inhibited the ability of PMA to attenuate carbachol-induced responses. Inactive phorbol ester, 4alpha-phorbol 12,13-didecanoate at 1 &mgr;M, did not inhibit these responses to carbachol. The K(d) and B(max) of the muscarinic receptor for [(3)H]N-methylscopolamine binding were not significantly changed by PMA treatment. PMA also decreased PKC activity in the cytosol of TSMCs, while increasing it transiently in the membranes within 30 min. Thereafter, the membrane-associated PKC activity decreased and persisted for at least 24 h of PMA treatment. Taken together, these results suggest that activation of PKC may inhibit phosphoinositide hydrolysis and consequently attenuate the [Ca(2+)](i) increase or inhibit both responses independently. The inhibition by PMA of carbachol-induced responses was inversely correlated with membranous PKC activity. Copyright 1995 S. Karger AG, Basel

Effect of phorbol ester on phosphoinositide hydrolysis and calcium mobilization induced by endothelin-1 in cultured canine tracheal smooth muscle cells

Regulation of the increase in inositol 1,4,5-trisphosphate (IP3) production and intracellular Ca2+ concentration ([Ca2+]i) by protein kinase C (PKC) was investigated in cultured canine tracheal smooth muscle cells (TSMCs). Stimulation of TSMCs by endothelin-1 (ET-1) led to IP3 formation and caused an initial transient peak followed by a sustained elevation of [Ca2+]i in a concentration-dependent manner. Pretreatment of TSMCs with phorbol 12-myristate 13-acetate (PMA, 1 microM) for 30 min blocked the ET-1-induced IP3 formation and Ca2+ mobilization. However, this inhibition was reduced after incubating the cells for 8 h with PMA. Following preincubation, ET-1-induced Ca2+ mobilization recovered with time and reached the same extent of control cells within 48 h. The concentrations of PMA that gave half-maximal inhibition (-logEC50) of ET-1-induced IP3 formation and increase in [Ca2+]i were 8.6 and 8.4 M, respectively. Prior treatment of TSMCs with staurosporine (1 microM), a PKC inhibitor, inhibited the ability of PMA to attenuate ET-1-induced responses, suggesting that the inhibitory effect of PMA is mediated through the activation of PKC. In parallel with the effect of PMA on the ET-1-induced IP3 formation and Ca2+ mobilization, a change of PKC activity was observed in TSMCs. PMA rapidly decreased PKC activity in the cytosol of TSMCs, while increasing it transiently in the membranes within 30 min. Thereafter the membrane-associated PKC activity decreased and persisted for at least 24 h of PMA treatment. Taken together, these results suggest that activation of PKC may inhibit the phosphoinositide hydrolysis and consequently attenuate the [Ca2+]i increase or inhibit independently both responses. The PMA-induced inhibition of responses to ET-1 was associated with an increase in membranous PKC activity.

Effect of phorbol ester on phosphoinositide hydrolysis and calcium mobilization in cultured canine tracheal smooth muscle cells

In cultured canine tracheal smooth muscle cells (TSMCs), muscarinic receptor stimulation led to phosphoinositide (PI) hydrolysis, formation of inositol phosphates (IPs), and mobilization of intracellular Ca2+. Desensitization of IPs accumulation and Ca2+ mobilization evoked by carbachol was investigated using [3H]inositol labelling and Ca(2+)-sensitive dye fura-2. Treatment of TSMCs with phorbol 12-myristate 13-acetate (PMA) for 30 min blocked the carbachol-stimulated formation of IPs and mobilization of Ca2+. The concentrations of PMA that gave half-maximal and maximal inhibition of carbachol-induced IPs accumulation were 70 nM and 1 microM, respectively. The inhibitory effect of PMA on carbachol-induced responses was reversed by staurosporine, a protein kinase C (PKC) inhibitor, suggesting that the inhibitory effect of PMA was mediated through the activation of PKC. Treatment of TSMCs with PMA for 24 h, the cells remained the ability to response to carbachol-induced IPs accumulation and Ca2+ mobilization with the same extent as that observed in the control group. Inactive phorbol ester, 4 alpha-phorbol 12, 13-didecanoate at 1 microM, did not inhibit the responses. The KD and Bmax of the muscarinic receptor for [3H]N-methyl scopolamine binding were not significantly changed by PMA treatment for either 30 min or 24 h. The locus of this inhibition was further investigated by examining the effect of PMA on AlF4(-)-stimulated IPs accumulation in canine TSMCs. AlF4(-)-induced response was inhibited by PMA treatment, supporting that G protein(s) can be directly activated by AlF4- which was uncoupled to phospholipase C (PLC) by PMA treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptor-operated Ca2+ signaling and crosstalk in stimulus secretion coupling

In the cells of higher eukaryotic organisms, there are several messenger pathways of intracellular signal transduction, such as the inositol 1,4,5-trisphosphate/Ca2+ signal, voltage-dependent and -independent Ca2+ channels, adenylate cyclase/cyclic adenosine 3',5'-monophosphate, guanylate cyclase/cyclic guanosine 3',5'-monophosphate, diacylglycerol/protein kinase C, and growth factors/tyrosine kinase/tyrosine phosphatase. These pathways are present in different cell types and impinge on each other for the modulation of the cell function. Ca2+ is one of the most ubiquitous intracellular messengers mediating transcellular communication in a wide variety of cell types. Over the last decades it has become clear that the activation of many types of cells is accompanied by an increase in cytosolic free Ca2+ concentration ([Ca2+]i) that is thought to play an important part in the sequence of events occurring during cell activation. The Ca2+ signal can be divided into two categories: receptor- and voltage-operated Ca2+ signal. This review describes and integrates some recent views of receptor-operated Ca2+ signaling and crosstalk in the context of stimulus-secretion coupling.

Host mediators in gingival crevicular fluid: implications for the pathogenesis of periodontal disease

During the past few years, a considerable number of studies have examined different aspects of the host response in gingival crevicular fluid (GCF), including the relationship of specific markers to the active phases of periodontal disease. Various indicators of the acute inflammatory response (the lysosomal enzymes beta-glucuronidase and collagenase, the cytoplasmic enzyme aspartate aminotransferase, and the arachidonic acid metabolite PGE2) have been shown to be associated with clinical attachment loss in chronic adult periodontitis in man and experimental periodontitis in animal models. In contrast, the relationship of indicators of the humoral immune response in GCF to active periodontal disease is equivocal. Furthermore, a number of indicators of the cellular immune response have been identified recently in GCF (i.e., Interleukin-1 alpha, IL-1 beta, tumor necrosis factor-alpha), but their relationship to active phases of periodontal disease have not been studied. The polymorphonuclear leukocyte (PMN) is the cellular hallmark of acute inflammation. Evidence from the GCF studies suggests that hyperreactivity of these cells plays a critical role in the active phases of some forms of periodontal disease. Metabolic activation of PMN can be associated with a number of potentially destructive reactions. The major effector mechanism for tissue destruction that can be specifically identified with the PMN is the synergistic effect of the release of PMN proteases and the generation of reactive oxygen metabolites by these cells. Priming of the PMN, where the PMN response is enhanced by agents that do not initiate the response, may be an important mechanism for PMN activation in the crevicular environment; for example, cytokines such as IL-1 beta and TNF-alpha, and lipopolysaccharides released from subgingival Gram-negative bacteria, can serve this function. The hypothesis proposed here argues that in addition to the severe forms of periodontal disease that have been associated with qualitative or quantitative PMN defects, tissue destruction in the periodontum can be observed with hyperreactivity of these cells. These differing conclusions do not create a dilemma, but may represent opposite ends of a balance that is no longer in equilibrium.

Tyrosine phosphorylation and oxygen consumption induced by G proteins in neutrophils

In neutrophils, receptor-mediated activation of the respiratory burst requires ATP, possibly for phosphotransferase reactions. The oxidative response is only partially inhibited by blockers of protein kinase C, suggesting the involvement of other kinases. Recent evidence has demonstrated activation of tyrosine phosphorylation in chemoattractant-stimulated cells. This effect is likely mediated by G proteins because it is obliterated by pretreatment with pertussis toxin. In this report we have attempted to correlate the respiratory burst and phosphotyrosine accumulation induced by activation of G proteins, accomplished by treatment of electroporated cells with nonhydrolyzable analogues of GTP. In cells stimulated with guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) both responses displayed similar time course and concentration dependence. The guanine nucleotide selectivity sequence and the divalent cation requirements were also similar for both responses. These similarities suggest a relationship between tyrosine phosphorylation and the activation of the NADPH oxidase. GTP gamma S-induced phosphotyrosine accumulation was found to be inhibited by pretreatment of the cells with phorbol esters, underlining the existence of regulatory interactions between different signal transduction pathways in neutrophils.

Pretreatment of mouse striatal neurons in primary culture with 17 beta-estradiol enhances the pertussis toxin-catalyzed ADP-ribosylation of G alpha o,i protein subunits

Pretreatment of striatal neurons from mouse embryos in primary culture with 17 beta-estradiol (10(-9) M, 24 h) enhanced the ADP-ribosylation of G alpha o,i proteins catalyzed by pertussis toxin (PTX). As estimated by quantitative ADP-ribosylation of G alpha s with cholera toxin and immunoblot experiments using anti-G alpha o and anti-G beta sera, 17 beta-estradiol pretreatment did not modify the levels of the major GTP-binding protein (G protein) constituent subunits G alpha s, G alpha o, and G beta. Thus, 17 beta-estradiol should induce a qualitative modification of these G proteins, perhaps by stabilizing the association of the heterotrimers G alpha o,i beta gamma, which are the targets of PTX. Such a hypothesis is in agreement with observations indicating that 17 beta-estradiol both suppressed the D2 dopamine- and opiate receptor-induced inhibitions of adenylate cyclase activity and enhanced the positive coupling between biogenic amine receptors (D1 dopamine, beta-adrenergic, and A2 adenosine) and adenylate cyclase. In addition, PTX pretreatment, which is known to uncouple receptors associated with Go,i proteins and thus to impair the dissociation of the heterotrimers G alpha o,i beta gamma, mimicks the effects of the steroid on the responses of adenylate cyclase to inhibitory and stimulatory agonists. Finally, the chemical specificity of the steroids was the same in the ADP-ribosylation as in the adenylate cyclase experiments: Testosterone (10(-9) M) mimicked the effects of 17 beta-estradiol, whereas 17 alpha-estradiol, progesterone, and dexamethasone did not.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular heterogeneity of the subclasses of islet-activating protein (pertussis toxin)-sensitive GTP-binding proteins in porcine thyroid tissue

From porcine thyroid cell membranes, we purified five GTP-binding proteins (G-proteins); Nos. 1 to 3 have 41-kDa alpha-subunits, and Nos. 4 and 5 have 40-kDa alpha-subunits. They were chromatographically (Mono Q) separable and served as specific substrates for islet-activating protein (pertussis toxin). G-proteins 1 and 2 were indistinguishable from porcine brain Gi1 with respect to three criteria, i.e., mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), pI of the ADP-ribosylated alpha-subunit, and immunoreactivity. G-protein 3 was identified as Gi3 by immunoreactivity. The SDS-PAGE and isoelectric focusing (IEF) analyses identified G-proteins 4 and 5 as being chromatographically heterogeneous subtypes of Gi2 in comparison with a pure porcine brain preparation. The IEF analysis also disclosed that each of the Gi1, Gi2, and Gi3 subspecies isolated in the present study has a minor component characterized by a slightly lower pI of its alpha-subunit. We conclude that porcine thyroid tissue contains at least Gi1, Gi2, and Gi3, and that each is made up of heterogeneous populations.

Receptor-effector coupling by G proteins

The primary structure of G proteins as deduced from purified proteins and cloned subunits is presented. When known, their functions are discussed, as are recent data on direct regulation of ionic channels by G proteins. Experiments on expression of alpha subunits, either in bacteria or by in vitro translation of mRNA synthesized from cDNA are presented as tools for definitive assignment of function to a given G protein. The dynamics of G protein-mediated signal transduction are discussed. Key points include the existence of two superimposed regulatory cycles in which upon activation by GTP, G proteins dissociate into alpha and beta gamma and their dissociated alpha subunits hydrolyze GTP. The action of receptors to catalyze rather than regulate by allostery the activation of G proteins by GTP is emphasized, as is the role of subunit dissociation, without which receptors could not act as catalysts. To facilitate the reading of this review, we have presented the various subtopics of this rapidly expanding field in sections 1-1X, each of which is organized as a self-contained sub-chapter that can be read independently of the others.

Leukocyte adhesion molecules deficiency: its structural basis, pathophysiology and implications for modulating the inflammatory response

Understanding the molecular basis of a rare inherited disease, Leu-CAM deficiency in humans, has underscored the importance of the cellular component of inflammation and unravelled the complex series of homotypic and heterotypic cell interactions necessary for mobilization of leukocytes to infected sites. Furthermore, this disease has shown that several apparently distinct cellular inflammatory responses (e.g. aggregation, adhesion to endothelium, directed migration and phagocytosis) are mechanistically related and mediated by a set of molecules which belong to a larger group of adhesion molecules (Integrins) mediating similar phenomena critical for immune surveillance, lymphocyte homing, morphogenesis and thrombogenesis. This disease also showed the relative biologic importance of CD11/CD18 in leukocytes. CD11/CD18 are more critical for the functions of phagocytic cells as compared to lymphocytes although similar inhibitory effects of anti-CD11/CD18 mAbs can be demonstrated in vitro. Expression and function of CD11/CD18 is regulated at several levels which include formation of stable heterodimers, qualitative changes in the receptor and quantitative changes in the levels of expression of the receptors and their ligands. We have identified inherited single amino acid substitutions on CD18 which impair heterodimer formation and cell surface expression, thus accounting for the pathogenesis of Leu-CAM deficiency. We also found a stimulus-induced phosphorylation of CD18, which is transient in nature when elicited through other surface receptors. This may be important in regulation of CD11/CD18 receptor avidity, recycling, endocytosis and cross-talk with other receptors. Finally, realization of the profound impairment in the acute cellular inflammatory response present in Leu-CAM deficiency has permitted novel ways of controlling the inflammatory response in several situations were inflammation serves an injurious rather than a beneficial role to the host.

Free radicals and antioxidants in the pathogenesis of eye diseases

There is fairly convincing evidence that free radical mechanisms are involved in the pathogenesis of cataracts and uveitis and that antioxidants may be protective. Studies on retinal degeneration are almost entirely limited to dietary manipulation of vitamins C and D. Unfortunately, antioxidant properties are not easily isolated from other metabolic effects of vitamins. Cataracts, uveitis, and retinal degeneration cause nearly one-third of all blindness. The evidence that free radical mechanisms are important in the pathogenesis of these diseases is compelling incentive to encourage more extensive and detailed investigation.

Purification and characterization of predominant G-protein from bovine lung membranes. Biochemical and immunochemical comparison with Gi1 and Go purified from brain

The predominant guanine nucleotide-binding protein (G-protein) of bovine lung membranes, termed GL, has been purified and compared biochemically, immunochemically and functionally with Gi and Go purified from rabbit brain. The purified GL appeared to have a similar subunit structure to Gi and Go, being composed of alpha, beta and possibly gamma subunits. On Coomassie Blue-stained SDS/polyacrylamide gels and immunoblots, the alpha subunit of GL (GL alpha) displayed an intermediate mobility (40 kDa) between those of Gi and Go (Gi alpha and Go alpha). GL alpha was [32P]ADP-ribosylated in the presence of pertussis toxin and [32P]NAD+. Analysis of [32P]ADP-ribosylated alpha subunits by SDS/polyacrylamide-gel electrophoresis and isoelectric focusing showed that GL alpha was distinct from Gi alpha and Go alpha, but very similar to the predominant G-protein in neutrophil membranes. Immunochemical characterization also revealed that GL was distinct from Gi and Go, but was indistinguishable from the G-protein of neutrophils, which has been tentatively identified as Gi2 [Goldsmith, Gierschik, Milligan, Unson, Vinitsky, Maleck & Spiegel (1987) J. Biol. Chem. 262, 14683-14688]. In functional studies, higher Mg2+ concentrations were required for guanosine 5'-[gamma-[35S]thio]triphosphate (GTP[35S]) binding to GL than were required for nucleotide binding to Go, whereas Gi showed a Mg2+-dependence similar to that of GL. The kinetics of GTP[35S] binding to GL was quite different from those of Gi and Go; t1/2 values of maximal binding were 30, 15 and 5 min respectively. In contrast, the rate of hydrolysis of [gamma-32P]GTP by GL (t1/2 approximately 1 min) was approx. 4 times faster than that by Gi or Go. These results indicated that the predominant G-protein purified from lung is structurally and functionally distinct from Gi and Go of brain, but structurally indistinguishable from Gi2 of neutrophils.

Characterization of the membrane-associated GTPase activity: effects of chemotactic factors and toxins

Membranes prepared from rabbit neutrophils exhibit GTPase activity which can be stimulated by the chemotactic factor fMet-Leu-Phe. The maximum contribution of the ATPase activities to the basal and the fMet-Leu-Phe-stimulated GTPase activities are less than 20% and 9%, respectively. The basal GTPase activity has a Vmax = 34.2 +/- 1.3 (pmol/mg protein, min) and a Km = 0.39 +/- 0.03 microM; and the fMet-Leu-Phe-stimulated has a Vmax = 52.3 +/- 2.5 (pmol/mg protein, min), and a Km = 0.29 +/- 0.02 microM. The GTPase activity can be stimulated by fMet-Leu-Phe and leukotriene B4. Unlike these two chemotactic factors, concanavalin A does not stimulate this GTPase activity. In addition, the rise in intracellular concentration of free calcium produced by concanavalin A is not inhibited by pertussis toxin treatment. Both the basal and stimulated GTPase activities are affected by pertussis toxin, cholera toxin and N-ethylmaleimide.

Different effects of phorbol ester on angiotensin II- and stable GTP analogue-induced activation of polyphosphoinositide phosphodiesterase in membranes isolated from rat renal mesangial cells

Pretreatment with pertussis toxin inhibits angiotensin II-induced activation of polyphosphoinositide phosphodiesterase in rat renal mesangial cells [Pfeilschifter & Bauer (1986) Biochem. J. 236, 289-294]. Furthermore, activation of protein kinase C by the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) and by 1-oleoyl-2-acetylglycerol (OAG) abolishes angiotensin II-induced formation of inositol trisphosphate (IP3) in mesangial cells [Pfeilschifter (1986) FEBS Lett. 203, 262-266]. Using membrane preparations of [3H]inositol-labelled mesangial cells we tried to obtain further insight as to the step at which protein kinase C might interfere with the signal transduction mechanism in mesangial cells. Angiotensin II (100 nM) stimulates IP3 formation from membrane preparations of [3H]inositol-labelled mesangial cells with a half-maximal potency of 1.1 nM. The angiotensin II-induced formation of IP3 is enhanced by GTP. This effect of angiotensin II is completely blocked by the competitive antagonist [Sar1,Ala8]angiotensin II. Guanosine 5'-[gamma-thio]triphosphate (GTP gamma S) and guanosine 5'-[beta gamma-imido]triphosphate (Gpp[NH]p), non-hydrolysable analogues of GTP, stimulate IP3 production in the absence of angiotensin II with Kd values of 0.19 microM and 2.4 microM, respectively. Angiotensin II augments the increase in IP3 formation induced by GTP gamma S. However, when mesangial cells were pretreated with TPA there was a dose-dependent inhibition of the synergistic action of angiotensin II on GTP gamma S-induced IP3 production. Comparable results are obtained with OAG, while the non-tumour-promoting phorbol ester 4 alpha-phorbol 12,13-didecanoate is without effect. These results suggest that activation of protein kinase C in mesangial cells does not impair phosphoinositide hydrolysis by stable GTP analogues but somehow seems to interfere with the stimulatory interaction of the occupied angiotensin II receptor with the transducing G-protein.

The mechanism of angiotensin-induced desensitization of adrenal glomerulosa cells

Superfusion of isolated rat adrenal glomerulosa cells for 6 h with a medium containing 2.5 nM angiotensin II (AII) reduces the aldosterone response to AII, corticotropin and potassium. Here we report that under such conditions there is a decrease in the capacity of the cells to form inositol phosphates in response to a subsequent stimulation with AII. The capacity to convert corticosterone to aldosterone is also reduced by a prior exposure to AII. Superfusion with a high-potassium medium has no such an effect. Reduced phosphoinositide response may be responsible for the decreased aldosterone stimulation by AII, the inhibition of the late stage of aldosterone biosynthesis may account for the heterologous character of desensitization.

Molecular basis of activation and regulation of the phagocyte respiratory burst

The molecular basis of activation and regulation of the phagocyte respiratory burst is discussed with particular reference to the role of inositol phospholipid hydrolysis, guanine nucleotide coupling proteins, and activation of protein kinase C.

G-protein dissociation, GTP-GDP exchange and GTPase activity in control and PMA treated neutrophils stimulated by fMet-Leu-Phe

The addition of the chemotactic factor fMet-Leu-Phe to cell homogenates causes a decrease in the pertussis toxin catalyzed ADP-ribosylation of a 41 kDa protein. The fMet-Leu-Phe induced decrease is not abolished in homogenates prepared from phorbol 12-myristate 13-acetate treated neutrophils. This decreased ribosylation probably reflects a dissociation of the GTP-binding protein oligomer that is not followed by association, possibly because of the release of the alpha-subunit into the suspending medium. Furthermore, fMet-Leu-Phe stimulates the binding of radiolabelled guanylylimidodiphosphate to membrane preparations. Again, the stimulated binding of guanylylimidodiphosphate is not affected by treating the intact neutrophils with phorbol 12-myristate 13-acetate. In addition leukotriene B4, platelet activating factor and fMet-Leu-Phe activate a high-affinity GTPase in membrane preparations. The basal level of this GTPase activity is dramatically inhibited in membrane preparations isolated from cells treated with phorbol 12-myristate 13-acetate. On the other hand, the fMet-Leu-Phe stimulated component is only marginally reduced. The present findings suggest that PMA does not prevent receptor G-protein interaction.

Inhibition of stimulated cell responses by phorbol esters and other activators of protein kinase C: sites of action

The addition of the protein kinase C activator phorbol esters to cell suspension a few minutes prior to stimulation inhibits the agonists-induced biochemical changes and cell responses. This inhibition is prevented by protein kinase C inhibitors. Activation of protein kinase C down regulates the stimulated responses by affecting one or more of the steps in the exitation-response coupling. This includes the receptors, the quanine-nucleotide-binding protein, the activity or distribution of phospholipase C, and other steps.

Intracellular acidification, guanine-nucleotide binding proteins, and cytoskeletal actin

The addition of propionic acid to rabbit neutrophils causes cell acidification and increases the amount of actin associated with the cytoskeleton. Both responses are rapid, and while the cell acidification is somewhat long-lasting, the increase in cytoskeletal actin is transient. It reaches a maximum value within 15 seconds and then returns to the basal level. Unlike fMet-Leu-Phe, however, propionic acid does not cause a rise in the intracellular concentration of free calcium. Pretreatment of the cells with pertussis toxin inhibits the propionic acid-produced increase in cytoskeletal actin but not the decrease in intracellular pH. However, the rate of return to the base line of the cell acidification produced by propionic acid is diminished in cells pretreated with pertussis toxin. On the other hand, both the decrease in intracellular pH and the increase in cytoskeletal actin produced by fMet-Leu-Phe are inhibited by pertussis toxin treatment. The results presented here suggest two important points. First, while cell acidification may trigger directly or indirectly the association of actin with the cytoskeleton, it is certainly not sufficient. Second, a functional guanine-nucleotide regulatory protein is required for stimulated cytoskeletal actin. One or more components of the G-protein and/or their effects on phosphoinositide hydrolysis may increase the number of actin monomers and the availability of preexisting actin filaments to these monomers.

Effects of thrombin, phorbol myristate acetate and prostaglandin D2 on 40-41 kDa protein that is ADP ribosylated by pertussis toxin in platelets

Intact platelets were stimulated with thrombin and the amount of GTP-binding protein (G-protein) oligomers was assessed by measuring ADP ribosylation of 40-41 kDa protein by pertussis toxin in isolated membranes. The toxin substrate fell by 57-62% in 10-60 s, but then returned towards normal over 5 min. Recovery was greatly enhanced by removal of thrombin from receptors with hirudin. Phorbol myristate acetate increased ADP-ribosylatable protein, but only back to initial levels prior to PMA. In contrast prostaglandin D2 plus theophylline (which increase cyclic AMP) did not increase ADP ribosylation, but could completely block the fall of the toxin substrate caused by thrombin. These results indicate that activation of thrombin receptors promotes the dissociation of G-protein oligomers to release free alpha-subunits, and this effect can be modulated by protein kinase C and cyclic AMP-dependent protein kinase. The possible relationships of these findings to the regulation of stimulus-response coupling in platelets is discussed.