[Isolation and structure elucidation of cirensenosides Q and R]

Two new saponins (cirensenoside Q and R) were isolated from the leaves of Oplopanax elatus. Their structures were elucidated as follows: Q, gypsogenin 3-O-beta-glucopyranosyl-28-O-alpha-L-rhamnopyranosyl(1-->4)-beta-D- glucopyranosyl(1-->6)-beta-D-glucopyranoside; R, 3 beta-hydroxylup-20(29)-ene-23-al-28-oic acid 3-O-beta-D-glucopyranosyl-28-O-alpha-L-rhamnopyranosyl(1-->4)-beta-D- glucopyranosyl(1-->6)-beta-D-glucopyranoside, respectively.

Inhibition of protein kinase C-dependent noradrenaline release by wortmannin in PC12 cells

Wortmannin is a specific phosphatidylinositol 3-kinase inhibitor, and it inhibits secretion in many cell types. Previously we reported that high K+ and external ATP stimulated a Ca2+ influx and [3H]-noradrenaline ([3H]NA) release from rat pheochromocytoma cell line 12 (PC12) cells in the presence of extracellular CaCl2. Addition of phorbol 12-myristate 13-acetate (PMA) stimulated [3H]NA release by itself and enhanced the maximal responses of high K+ and ATP. In this study, we investigated the effects of wortmannin on NA release from PC12 cells. Wortmannin inhibited the [3H]NA release induced by high K+ and ATP, and the stimulatory effects of PMA, in a dose-dependent manner. Wortmannin caused 50% inhibition of high K+-induced [3H]NA release at a concentration of 2.78+/-0.68 microM (n = 5). The increased cytosolic free Ca2+ concentrations ([Ca2+]i), induced by ATP, were not inhibited by wortmannin. Wortmannin inhibited PMA-induced phosphorylation of a 80-kDa protein in the cytosol fraction of PC12 cells. Calphostin C, a specific protein kinase C inhibitor, also inhibited high K+-, ATP-, and PMA-induced NA release, and the phosphorylation of the 80-kDa protein induced by PMA. Mastoparan, an amphiphilic tetradecapeptide from wasp venom, stimulated NA release in the presence or absence of extracellular CaCl2. Neither wortmannin nor calphostin C inhibited the NA release induced by mastoparan. These findings suggest that wortmannin inhibits the PKC-dependent pathway, not [Ca2+]i mobilization, resulting in the inhibition of NA release from PC12 cells.

[2 cases of lung disease caused by Mycobacterium avium complex occurred in middle-aged women without underlying disorders, which we observed for more than 30 years]

We reported 2 cases of Mycobacterium avium complex lung disease occurred in middle-aged women without underlying disorders, which we could observe for more than 30 years. One case was a 42-year-old woman started with bloody sputum, and the other was a 43-year-old woman with cough and sputum. In both cases, chest X ray films were normal on their first visit. More than 15 years after their first visit, Mycobacterium avium complex was isolated from their sputum or bronchial washing. During the observation, a cluster of small nodules in the periphery of the lung and bronchiectasis appeared and deteriorated, and excretion of the bacilli increased gradually. Their past history and family history were normal. Since lung disease caused by Mycobacterium avium complex progresses very slowly, long-time observation would be necessary to consider its pathogenesis.

Theiler's murine encephalomyelitis virus subgroup strain-specific infection in a murine macrophage-like cell line

We compared infection of a murine macrophage-like cell line, J774-1, with two Theiler's murine encephalomyelitis virus subgroup strains. The GDVII strain, which is highly virulent and produces acute polioencephalomyelitis in mice, did not actively replicate in J774-1 cells, although there was a significant inhibition in cellular protein synthesis. In contrast, the DA strain, which is less virulent and causes demyelination with a persistent virus infection, productively infected J774-1 cells; however, there was less virus produced than in BHK-21 cells, and there was little if any cellular protein shutoff. These in vitro data may provide some explanation for the biological activities that are observed between both subgroup strains.

Transesophageal Doppler echocardiographic assessment of systolic and diastolic coronary blood flow velocities at baseline and during adenosine triphosphate-induced coronary vasodilation in chronic aortic regurgitation

Few reports exist on the changes in systolic and diastolic coronary flow velocities (CFVs) at baseline and during coronary vasodilation in patients with chronic aortic regurgitation (AR). We examined the left anterior descending CFVs in 21 patients with AR (11 patients with mild AR and 10 patients with moderate to severe AR), 9 patients without AR (no AR group), and 6 patients who had undergone surgery for moderate to severe AR (postoperation group) with transesophageal Doppler echocardiography. Adenosine triphosphate (ATP) was infused into a peripheral right arm vein at four different doses (35, 70, 100, and 140 micrograms/kg/min). Coronary flow velocity response in systole and diastole was calculated as the ratio of systolic peak and mean and diastolic peak and mean CFVs during maximal ATP infusion to those at baseline. The systolic peak and mean CFVs and the diastolic peak and mean CFVs at baseline were significantly increased in the moderate to severe group compared with those in the other groups (p < 0.05, respectively). Systolic and diastolic CFVs were significantly increased during ATP infusions in the four groups. No significant differences of systolic and diastolic CFVs were observed among the four groups during maximal ATP infusion. The coronary flow velocity response calculated from the peak and mean diastolic CFVs were significantly decreased in the moderate to severe group (1.6 +/- 0.3 and 1.7 +/- 0.4) compared with those in the other three groups (3.6 +/- 0.7 and 3.2 +/- 1.1 in the no AR group, 2.6 +/- 0.6 and 2.5 +/- 0.4 in the mild group, and 2.5 +/- 0.7 and 2.4 +/- 0.6 in the postoperation group) (p < 0.05, respectively). In conclusion, the systolic and diastolic left CFVs at baseline appeared to be significantly increased in patients with moderate to severe chronic AR. However, the velocities during coronary vasodilation by ATP were equal to those in other groups, resulting in a decrease of coronary flow velocity response in systole and diastole.

Aldosterone-producing adrenocortical carcinoma metastases found seven years after adrenalectomy

We report a case of metastatic adrenocortical carcinoma detected 7 years after adrenalectomy. A 52-year-old woman, who had undergone adrenalectomy for an aldosterone-producing adrenocortical carcinoma at age 45, was found on examination by computerized tomography to have enlarged paraaortic lymph nodes. These nodes were surgically resected, and the histological diagnosis from the resected tissue was metastatic adrenocortical carcinoma. The patient has now survived for more than 9 years following the original adrenalectomy. Evidence suggests that this was a slow-growing tumor, because the primary tumor was sharply demarcated and the metastases were found 7 years after the original operation. We believe that aggressive surgical resection of metastatic lesions could lead to prolonged survival in patients with adrenocortical carcinomas of this type.

Giant cerebral arterial aneurysm in an infant: report of a case and review of 42 previous cases in infants with cerebral arterial aneurysm

A giant cerebral aneurysm with subarachnoidal hemorrhage in a 4-month-old female infant is reported. The clinical course was complicated by an electrolyte imbalance and unexpected intoxication by phenobarbital. She died as a result of the third episode of rerupture of the aneurysm on the 16th day after onset. Histological findings showed that the aneurysm was of the saccular type, 35 x 20 x 22 mm in size, arising from the basilar artery. The aneurysmal wall consisted microscopically of fibrous tissue with partial absence or fragmentation of the internal elastic lamina and muscular lamina. Forty-three cases of cerebral aneurysms during the first year of life including the present case were summarized and it was found that they could be characterized as follows: (i) a high incidence of onset in early infancy; (ii) larger than 10 mm; (iii) a large number arose from the posterior circulation of the circle of Willis; and (iv) a poor prognosis of non-operated groups, especially in the posterior circulation.

Pertussis toxin-insensitive effects of mastoparan, a wasp venom peptide, in PC12 cells

Recent studies have shown that mastoparan, an amphiphilic peptide derived from wasp venom, modifies the secretion of neurotransmitters and hormones from a variety of cell types. Mastoparan interacts with heterotrimeric guanine nucleotide-binding proteins (G proteins) such as Gi and G(o), which are ADP-ribosylated by pertussis toxin (PTX) and thereby uncoupled from receptors. Previously, some of the effects of mastoparan including secretion were reported to be modified selectively by PTX but not by cholera toxin (CTX). In the present study, we examined the influence of bacterial toxins on the effects of mastoparan in PC12 cells. Mastoparan stimulated [3H]noradrenaline (NA) release from prelabeled PC12 cells in the absence of CaCl2, although high K+ or ATP-stimulated the release in a Ca(2+)-dependent manner. Pretreatment with CTX, not PTX, for 24 h inhibited mastoparan-stimulated [3H]NA release. Mastoparan inhibited forskolin-stimulated cyclic AMP accumulation in a dose-dependent manner, although mastoparan had no effect by itself. Pretreatment with PTX completely abolished the inhibitory effect of carbachol via Gi on cyclic AMP accumulation and partially reduced the effect of mastoparan. However, the inhibitory effect of 20 microM mastoparan was not modified by pretreatment with PTX. Thus, we investigated the effect of mastoparan on CTX-catalyzed [32P]ADP-ribosylation of proteins in PC12 cells. A subunit of CTX (CTX-A) catalyzed [32P]ADP-ribosylation of many proteins in the cytosolic fraction of PC12 cells. One of these was a 20 kDa protein, named ADP-ribosylating factor (ARF). The addition of mastoparan to assay mixtures inhibited ADP-ribosylation of many proteins including ARF and CTX-A in the presence of the cytosolic fraction. In the absence of the cytosolic fraction, however, mastoparan slightly enhanced ADP-ribosylation of bovine serum albumin and auto-ADP-ribosylation by CTX-A. Mastoparan did not inhibit ADP-ribosylation of the alpha subunit of Gs in the membrane fraction. These findings suggest that 1) mastoparan interacts with PTX-insensitive and CTX-sensitive factor(s) to stimulate NA release, and 2) mastoparan interacts with ARF inhibiting its activity to enhance the ADP-ribosylation reaction by CTX. ARF may be an exocytosis-linked G protein.

P2 purinoceptor-mediated stimulation of adenylyl cyclase in PC12 cells

PC12 pheochromocytoma cells have P2 purinoceptors which are activated by ATP and coupled to Ca2+ influx and catecholamine release. Also PC12 cells have adenosine receptors coupled positively to adenylyl cyclase, and cyclic AMP regulates cell functions such as catecholamine release. The effects of ATP and ATP analogs on cyclic AMP accumulation in PC12 cells were investigated in this study. ATP and adenosine 5'-0-(3-thiotriphosphate) stimulated cyclic AMP accumulation at low concentrations up to 300 microM but showed inhibitory effects above this concentration. 2',3'-O-(4-Benzoyl)benzoyl ATP and 2-methylthio ATP showed similar effects, although the responses were very limited. Addition of adenosine 5'-O-(2-thiodiphosphate) (ADP beta S) or beta, gamma-methylene ATP, but not alpha, beta-methylene ATP, stimulated cyclic AMP accumulation markedly without causing an inhibitory phase. The effects of ATP, ADP beta S and beta, gamma-methylene ATP were not inhibited by adenosine deaminase or specific antagonists to A1 and A2 adenosine receptors. Neither ADp beta S nor beta, gamma-methylene ATP showed any effect on Ca2+ influx or noradrenaline release. Suramin, a P2 receptors antagonists, had no inhibitory effect against ATP analog-stimulated cyclic AMP accumulation, although reactive blue 2 inhibited the beta, gamma-methylene ATP-stimulated reaction but not that up-regulated by ADP beta S. These findings suggest that the pharmacological characteristics of these ATP receptors coupled to adenylyl cyclase are clearly different from those of ligand-gated ion channels defined by P2X purinoceptors, which have been cloned and shown to be coupled to Ca2+ influx and catecholamine release in PC12 cells. The existence of a new type of P2 purinoceptor-mediating stimulation of adenylyl cyclase is proposed in PC12 cells.

NO donors stimulate noradrenaline release from rat hippocampus in a calmodulin-dependent manner in the presence of L-cysteine

Nitrogen oxides (NO) such as nitric oxide have been suggested to potentiate neurotransmitter release in a variety of neuronal cells. In this study, we showed that NO donors stimulate the release of noradrenaline (NA) from rat hippocampus both in vivo and in vitro. Co-addition of NO donors (sodium nitroprusside [SNP] or S-nitroso-N-acetylpenicillamine [SNAP]) and thiol compounds (dithiothreitol [DTT] or L-cysteine) stimulated [3H]NA release from prelabeled hippocampal slices. Microdialysis in freely moving rats was used to ascertain the role of NO in control of NA release from the hippocampus in vivo. Co-addition of SNAP and L-cysteine stimulated endogenous NA release within 30 min. The concentration of NA peaked between 30-60 min to almost 3 times basal level. Another thiol compound, glutathione, had no effect on [3H]NA release in the presence of SNP or SNAP. In the presence of SNAP, the effect of L-cysteine was much higher than that of the D-isomer, although SNAP did not show stereospecificity. The effect of SNAP/L-cysteine was rapid and the maximal increase in [3H]NA release was attained 0-1 min after application, which was similar in time course to the effect of KCI. Unlike the release by KCI, SNAP/L-cysteine-stimulated NA release was independent of extracellular CaCl2. However, pretreatment with the calmodulin antagonists W-7 or trifluoperazine significantly reduced the SNAP/L-cysteine-stimulated [3H]NA release. Formation of nitric oxide and activation of guanylate cyclase by nitric oxide were not responsible for SNAP/L-cysteine-stimulated NA release. These findings suggest that NO donors stimulate NA release from the hippocampus in the presence of thiol compounds such as L-cysteine in vivo and in vitro in a calmodulin-dependent, Ca(2+)-and cyclic GMP-independent manner. The physiological roles of thiol compounds such as L-cysteine or glutathione as intermediates of NO are discussed.

Autocrine loop through cholecystokinin-B/gastrin receptors involved in growth of human leukemia cells

The cholecystokinin (CCK)-B/gastrin receptor binds two brain-gut hormones, CCK and gastrin, with high affinities. These peptides have a trophic effect on gastrointestinal cells expressing the receptor in vivo as well as in vitro. Recently, this receptor mRNA was reported to be expressed in immunocytes localized in the lamina propria of normal rat stomach mucosa. Here, we studied the receptor expression in human hematopoietic cells in order to determine whether they play a role in cell growth. The CCK-B/gastrin receptor mRNA was detectable in the polymorphonuclear (PMN) cells but not in the mononuclear cells of normal peripheral white blood cells by reverse transcription-polymerase chain reaction. The receptor transcript was, however, expressed in human leukemia cell lines (14 of 18 cell lines tested) derived from not only myeloid, but also T- and B- lymphoid lineages. The CCK-B/gastrin receptors on several leukemia cell lines were shown to be biologically active by demonstrating ligand-dependent cell proliferation in serum-deprived medium. Interestingly, a human CCK-B/gastrin receptor specific antagonist, YM022, but not its stereotype isoform, selectively inhibited the DNA synthesis of THP-1, MOLT-16, MOLT-14, and CCRF-CEM in the absence of exogenous peptide ligands. Further investigation revealed that these leukemia cell lines and normal PMN cells also expressed gastrin mRNA. These results suggest that growth of human leukemia cells is promoted by an autocrine mechanism through the CCK-B/gastrin receptors.

Sodium nitroprusside stimulates noradrenaline release from rat hippocampal slices in the presence of dithiothreitol

It is becoming apparent that nitrogen monoxide (NO) such as nitric oxide has regulatory roles for neuronal cell functions. We examined the role of NO using NO donors on [3H]noradrenaline (NA) release from prelabeled rat hippocampal slices. Sodium nitroprusside (SNP), which had no effect by itself, stimulated [3H]NA release in a dose-dependent manner (ED50 = 0.5 mM) in the presence of dithiothreitol (DTT). The stimulatory effect of SNP with DTT, but not high K+, was observed in an extracellular Ca(2+)-free buffer. The maximal effect of SNP was obtained after incubation for 1-2 h with DTT in buffer at physiological pH (7.4). The simultaneous addition of SNP and DTT to the slices induced a small effect, and the effect of SNP declined after 3.5 h. SNP stimulated cyclic GMP accumulation in the slices without DTT. NaNO2 and 1-hydroxy-2-oxo-3,3-bis(2-aminoethyl)-1-triazene (a generator of nitric oxide), which stimulated cyclic GMP accumulation by themselves, did not stimulate [3H]NA release in the presence and absence of DTT. 3-Morpholinosydnonimine HC1 (a generator of peroxynitrite) had no effect on the release. The stimulatory effect of SNP and DTT on NA release was inhibited 40% by nitric oxide scavengers such as oxyhemoglobin and 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxy-3-oxide, although cyclic GMP accumulation induced by NO donors was completely inhibited. These findings suggest that SNP reacts with DTT to produce unknown active species, and that cyclic GMP is not a mediator for SNP-stimulated NA release.

Renal leiomyoma: a case report

We report a case of renal leiomyoma. A 46-year-old woman was found incidentally to have a solid and cystic renal mass on computerized tomography. The angiogram revealed no neovascularity. Nephrectomy was performed. Histologically, it was diagnosed as renal leiomyoma of vascular type. Although preoperative diagnosis of renal leiomyoma is difficult due to the various radiological findings, we should always consider this tumor in the differential diagnosis of renal tumors.

Refractory thrombocytopenia with chromosome 11q23 abnormality

Although cytopenia is a common manifestation of myelodysplastic syndrome (MDS), isolated thrombocytopenia is rare. The term "refractory thrombocytopenia" (RTC) has been proposed as a counterpart of refractory anemia. We describe here a case of RTC associated with chromosome abnormality on 11q23. A 59-year-old man was admitted because of severe thrombocytopenia. A bone marrow examination revealed an increased number of micromegakaryocytes and the absence of normal-sized megakaryocytes without obvious dysplasia in either the myeloid or the erythroid lineage. A remarkable increase of GPIIb/IIIa (CD41a)-positive precursor cells in the bone marrow was observed. Cytogenetic examination detected the chromosome abnormality, an addition on chromosome 11q23. Translocation of the HRX gene was not detectable by Southern blot analysis. The diagnostic problems of isolated thrombocytopenia and possible participation of gene(s) on chromosome 11q23 in megakaryocytopoiesis as well as early hematopoiesis are discussed.

G(o) protein does not regulate ATP-stimulated [Ca2+]i elevation or noradrenaline release in PC12 cells

The roles of G(o), a heterotrimeric GTP binding (G) protein with a 40-kDa alpha subunit and which is localized predominantly in neuronal cells, in exocytosis have been discussed recently. PC12 pheochromocytoma cell line is a convenient model in which to study the Ca(2+)-dependent mechanisms of the neurosecretory process. The stimulation of ATP receptors or addition of KCl stimulated an elevation of cytosolic free Ca2+ concentration ([Ca2+]i) and [3H]noradrenaline (NA) release in PC12 cells. In this study, we investigated the roles of G(o) in ATP- and KCl-stimulated reactions. Nerve growth factor treatment for 2 days and transfection of PC12 cells with cDNA of subunit of (G(o alpha) had no effect on ATP-stimulated [3H]NA release, although both treatments increased levels of the G(o alpha) and its trimeric form by about twofold over those in unstimulated cells. The [Ca2+]i rise induced by ATP in NGF-treated cells was similar to that in control cells, although the maximal response was slightly smaller. Cholera toxin treatment for 2 days inhibited ATP- and KCl-stimulated NA release, although this treatment caused an approximately twofold increase in the level of G(o). Pertussis toxin treatment, which ADP ribosylated over 90% of endogenous G proteins such as G(o), had no effect on ATP-stimulated reactions. These findings show that G(o) does not directly regulate ATP-stimulated Ca2+ channels or the NA release process in PC12 cells. Cholera toxin-sensitive protein(s) may regulate exocytosis.

Antiproliferative effect of a novel cholecystokinin-B/gastrin receptor antagonist, YM022

Cholecystokinin (CCK)-B and gastrin receptors are expressed on a variety of human tumor cells. Recently, we have demonstrated that the human brain CCK-B receptors are identical to the gastrin receptors derived from the stomach mucosa, and that the brain-gut peptides, CCK-8 and gastrin I are mitogenic for mouse NIH 3T3 fibroblasts expressing human CCK-B/gastrin receptors (N-hCCKBR). In this report, we evaluated the antiproliferative potency of CCK-B/gastrin receptor antagonists by using N-hCCKBR cells. Among several antagonists, a benzodiazepine derivative, YM022 had the most potent activities in competing with [125I]CCK-8 or [125I]gastrin I binding, inhibition of CCK-8- or gastrin I-induced phosphoinositide hydrolysis and increasing cytoplasmic free calcium. Interestingly, a potent antagonist for rat CCK-B/gastrin receptors did not have such activities in N-hCCKBR cells. YM022 inhibited the CCK-8- or gastrin I-induced [methyl-3H]thymidine incorporation of N-hCCKBR cells in a dose-dependent manner. In the absence of exogenous peptide ligands, YM022 also inhibited the proliferation of several human cancer cell lines expressing the genes for both gastrin and its receptor. These results suggest that YM022 could intervene in the autocrine stimulation of human tumor cell lines through CCK-B/gastrin receptors. N-hCCKBR cells are an excellent tool to screen for novel human CCK-B/gastrin receptor antagonists possessing antiproliferative activity for human cancer cells.

A 11.5-kb 5'-terminal cDNA sequence of chicken breast muscle connectin/titin reveals its Z line binding region

A partial 5'-region cDNA (11.5 kb) of chicken breast muscle connectin/titin encoding 3752 amino acids was sequenced. The predicted amino acid sequence contains 31 immunoglobulin C2 motifs and 10 interdomains. The sequence suggests a skeletal muscle type of connectin isoforms. Immunoelectron microscopic studies using antisera raised against several products of the cDNA fragments expressed in E. coli revealed that a region of some 800 amino acids from the N terminus of connectin is involved in its binding to the Z line in a sarcomere.

Murine model of invasive pulmonary aspergillosis following an earlier stage, noninvasive Aspergillus infection

Aspergillus spp. occasionally cause invasive pulmonary aspergillosis following noninvasive infection in patients with underlying bronchopulmonary disorders regardless of their systemic immunological conditions. We developed a murine model of invasive pulmonary aspergillosis following an earlier stage, noninvasive Aspergillus infection. BALB/c mice were inoculated intratracheally with agarose beads containing Aspergillus fumigatus conidia. Two weeks after inoculation, half of the mice were immunosuppressed with cortisone acetate. During a 4-week observation period, the survival rate of infected immunosuppressed mice was significantly lower (P < 0.01) than that of infected nonimmunosuppressed mice. The number of CFU in the lungs gradually decreased in the nonimmunosuppressed mice, whereas a time-related significant increase (P < 0.05) of CFU was demonstrated in the immunosuppressed mice. In the lungs of the nonimmunosuppressed mice, there was marked accumulation of neutrophils, lymphocytes, and macrophages (in this order) around the agarose beads in the bronchi. Aspergillus hyphae were surrounded by the inflammatory cells and did not invade the lung parenchyma. In contrast, in the immunosuppressed mice, Aspergillus hyphae proliferated markedly and invaded the lung parenchyma after immunosuppression. In this model, the two-dimensional extents of the lesions were also evaluated with an image-processing system. Time-related increase of the area of peribronchial necrotic lesions was significant (P < 0.05) after immunosuppression. This model should therefore be useful for investigating the pathophysiology of noninvasive Aspergillus infection and invasive pulmonary aspergillosis and also for clarifying the mechanism of conversion to the invasive disease from the noninvasive stage.

Elevated serum levels of manganese superoxide dismutase in polymyositis and dermatomyositis

We studied serum concentrations of manganese superoxide dismutase (Mn SOD) and copper-zinc superoxide dismutase (Cu/Zn SOD) in 22 patients with polymyositis and dermatomyositis (PM/DM), 87 patients with four types of muscular dystrophy, 20 patients with amyotrophic lateral sclerosis, and 15 patients with collagen vascular diseases (CVD). Serum levels of Mn SOD were increased only in the patients with PM/DM and CVD, and the elevation was more prominent in those with PM/DM. Levels of Cu/Zn SOD were slightly elevated in some patients with PM/DM and Duchenne muscular dystrophy. In patients with PM/DM, the change in Mn SOD levels corresponded to disease activity as closely as or more closely than those of creatine kinase. The results indicate that serum Mn SOD may be a useful clinical marker for PM/DM.

[Receptor-mediated signal transduction]

The elucidation for the mechanism of receptor-mediated signal transduction has been the aim of our extensive studies. Cyclic AMP, which was controlled by membrane adenylyl cyclase, was an intracellular signal (the first second messenger in cells proposed by Sutherland) given by hormones and neurotransmitters. The GTP-binding (G) proteins play an important role in communication between membrane receptors and the adenylyl cyclase catalytic unit. One (Gs) of the G proteins is involved in the activation, while the other (Gi) is involved in the inhibition of adenylyl cyclase. Islet-activating protein (IAP, pertussis toxin, PTX) catalyses the transfer of the ADP-ribose moiety of NAD to the alpha subunit of Gi, resulting in a complete loss of the Gi functions. In some cases, arachidonic acid (AA) regulates cell functions as a second messenger. AA serves as a precursor to a number of biologically active lipids including prostaglandins and leukotrienes. Activation of cell surface receptors of many cell types results in the release of AA from membrane phospholipids by phospholipase A2 (PLA2). A new family of PLA2 has been discovered in the cytosol of various cells. The activation of receptor-mediated AA release by cytosolic PLA2 was also regulated by PTX-sensitive G proteins. PTX treatment inhibited cell growth of fibroblasts by serum and growth factors. G proteins have been involved in receptor-receptor interactions in neuronal cells. These findings suggest the regulatory roles of cell surface receptors-coupled G proteins in signal transductions and cell functions.

Cholecystokinin-B/gastrin receptors mediate rapid formation of actin stress fibers

Specific receptors for brain-gut peptide hormones, cholecystokinin (CCK) and gastrin, are expressed in a variety of human tumor cells. CCK and gastrin promote the growth of NIH3T3 cells into which the CCK-B/gastrin receptor had been introduced via a eukaryotic expression vector. In this study, we have examined the effect of CCK-8 on the actin cytoskeleton by using two mouse fibroblast cell lines expressing human CCK-B/gastrin receptors. Treatment with very low concentration of CCK-8 (10(-10) M) induced the formation of actin stress fibers within one minute. Stress fiber formation increased for 30 min. In contrast, a potent mitogen for fibroblasts, platelet-derived growth factor (PDGF), initially induced membrane ruffling and, later, a weak formation of stress fibers. Microinjection of rho GDP dissociation inhibitor or Clostridium botulinum ADP-ribosyltransferase C3 which is known to impair the function of a small GTP-binding protein, rho p21, inhibited the stress fiber formation by CCK-8 as well as by PDGF. These results indicate that CCK-B/gastrin receptor could regulate stress fiber formation in a rho p21-dependent manner. The signals from CCK-B/gastrin receptor might affect cell growth as well as cell motility or adhesion by regulating the actin cytoskeleton.