Domain-specific phosphorylation of vimentin and glial fibrillary acidic protein by PKN

PKN is a serine/threonine protein kinase with a catalytic domain homologous to the protein kinase C family and unique N-terminal leucine zipper-like sequences. Using analyses with the yeast two-hybrid system and in vitro binding assay, we found that the regulatory domain of PKN interacted with vimentin. We then examined whether PKN would phosphorylate vimentin in vitro. Vimentin proved to be an excellent substrate for PKN, and the phosphorylation of vimentin by PKN occurred in the head domain with the result of a nearly complete inhibition of its filament formation in vitro. Similar results were also obtained with another type III intermediate filament protein, glial fibrillary acidic protein (GFAP). These results raise the possibility that PKN may regulate filament structures of vimentin and GFAP by domain-specific phosphorylation.

Involvement of MAP kinase and c-fos signaling in the inhibition of cell growth by somatostatin

Somatostatin significantly suppressed cell growth of the mouse insulinoma-derived cell line MIN6. MIN6 cells exhibited high-affinity binding of somatostatin with 50% inhibitory concentration value of 0.9 nM. RNA blot analysis revealed that MIN6 cells expressed only SSTR3 among the five somatostatin receptors so far identified. Treatment of MIN6 cells with somatostatin significantly reduced the serum-induced c-fos expression levels. On the other hand, somatostatin (100 nM) treatment of MIN6 cells cultured in medium containing 10% serum transiently increased c-fos expression levels to 282 +/- 4.7% and then significantly decreased them to 27 +/- 7.6% of the levels before treatment. Mitogen-activated protein (MAP) kinase activity transiently increased to 656 +/- 91.2% and decreased thereafter to 39 +/- 13.3% of the activity before the addition of somatostatin (100 nM) into the medium. In addition, the stimulatory effect of somatostatin on c-fos expression and MAP kinase activity (early effect) was not altered by pertussis toxin (PTX), whereas the suppressive effect of somatostatin on c-fos expression and MAP kinase activity (late effect) was mitigated by PTX. These findings suggest that an inhibition of c-fos expression mediated by cross talk between PTX-sensitive G protein signaling and receptor tyrosine kinase signaling is one of the mechanisms by which somatostatin inhibits cell growth in MIN6 cells.

Sequence variants in the pancreatic islet beta-cell inwardly rectifying K+ channel Kir6.2 (Bir) gene: identification and lack of role in Caucasian patients with NIDDM

Signals derived from the metabolism of glucose in pancreatic beta-cells lead to insulin secretion via the closure of ATP-sensitive K+ channels (KATP). The cloning of the gene encoding the beta-cell inward rectifier Kir6.2 (Bir), a subunit of the beta-cell KATP channel, provided the opportunity to look for mutations in this gene that might contribute to the impaired insulin secretion of NIDDM. By single-strand conformational polymorphism (SSCP) analysis on 35 Northern-European Caucasian patients with NIDDM, six sequence variants were detected: Glu10gag-->Lys10aag (E1OK), Glu23gag-->Lys23aag (E23K), Leu270ctg-->Val270gtg (L270V), Ile337atc-->Val337gtc (I337V), and two silent mutations. Allelic frequencies for the missense variants were compared between the NIDDM group (n = 306) and nondiabetic control subjects (n = 175) and did not differ between the two groups. Pairwise allelic associations indicated significant linkage disequilibrium between the variants in Kir6.2 and between them and a nearby pancreatic beta-cell sulfonylurea receptor (SUR1) missense variant (S1370A), but these linkage disequilibria did not differ between the NIDDM and control groups. The results of these studies thus revealed that mutations in the coding region of Kir6.2 1) were not responsible for the previously noted association of the SUR1 variants with NIDDM (Inoue H et al., Diabetes 45:825-831, 1996) and 2) did not contribute to the impaired insulin secretion characteristic of NIDDM in Caucasian patients.

Inhibition of tumor necrosis factor-alpha and interleukin-1-beta production by beta-adrenoceptor agonists from lipopolysaccharide-stimulated human peripheral blood mononuclear cells

The effects of beta-adrenoceptor agonists (beta-agonists) on the production of tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta) and interleukin-8 (IL-8) by lipopolysaccharide (LPS)-stimulated human peripheral blood mononuclear cells (PBMCs) were investigated. The beta-agonists, procaterol, clenbuterol, fenoterol and terbutaline, inhibited TNF-alpha and IL-1 beta production in a concentration-dependent manner, whereas they had no effect on IL-8 production. TNF-alpha production was inhibited more potently than IL-1 beta. Dibutyryl cyclic AMP (dbcAMP) also inhibited the production of TNF-alpha and IL-1 beta, but not IL-8. TNF-alpha production was almost completely inhibited by dbcAMP, whereas IL-1 beta production appeared to be partially refractory even at the highest concentration examined. Both procaterol and theophylline elevated cAMP levels in LPS-stimulated PBMCs, but the effect of procaterol was limited. The inhibition of TNF-alpha and IL-1 beta production by procaterol was additively potentiated with theophylline. dl-Propranolol, a beta-adrenoceptor antagonist, abrogated the inhibition of TNF-alpha and IL-1 beta production by procaterol. These results indicate that beta-agonists inhibit the production of proinflammatory cytokines, such as TNF-alpha and IL-1 beta, by elevating intracellular cAMP levels. These properties of beta-agonists might be beneficial in the treatment of allergic inflammation.

Phosphorylation-dependent control of structures of intermediate filaments: a novel approach using site- and phosphorylation state-specific antibodies

Site-specific phosphorylation of intermediate filament (IF) proteins on serine and threonine residues leads to dynamic alterations in filament structure. Site- and phosphorylation state-specific antibodies for IF proteins can visualize spatial and temporal distribution of site-specific IF protein phosphorylations in the cell. These antibodies are also useful to identity IF kinases involved in cellular events, including cell signaling and cell cycle.

Myosin binding subunit of smooth muscle myosin phosphatase at the cell-cell adhesion sites in MDCK cells

We examined the intracellular localization of the myosin binding subunit (MBS) of smooth muscle myosin phosphatase. In MDCK cells in a confluent monolayer of polarized epithelial sheet, MBS was concentrated to the cell-cell adhesion sites. Double-immunofluorescence analysis with anti-MBS and anti-beta-catenin antibodies showed that MBS was mainly localized at the adherens junction. Furthermore, MBS was translocated reversibly between the cytosol and the cell-cell adhesion sites during the formation and disappearance of cell-cell contacts. These data suggest that MBS may play an important role in the regulation of the cell-cell adhesion.

Biochemical and cellular effects of roscovitine, a potent and selective inhibitor of the cyclin-dependent kinases cdc2, cdk2 and cdk5

Cyclin-dependent kinases (cdk) play an essential role in the intracellular control of the cell division cycle (cdc). These kinases and their regulators are frequently deregulated in human tumours. Enzymatic screening has recently led to the discovery of specific inhibitors of cyclin-dependent kinases, such as butyrolactone I, flavopiridol and the purine olomoucine. Among a series of C2, N6, N9-substituted adenines tested on purified cdc2/cyclin B, 2-(1-ethyl-2-hydroxyethylamino)-6-benzylamino-9-isopropylpurine (roscovitine) displays high efficiency and high selectivity towards some cyclin-dependent kinases. The kinase specificity of roscovitine was investigated with 25 highly purified kinases (including protein kinase A, G and C isoforms, myosin light-chain kinase, casein kinase 2, insulin receptor tyrosine kinase, c-src, v-abl). Most kinases are not significantly inhibited by roscovitine. cdc2/cyclin B, cdk2/cyclin A, cdk2/cyclin E and cdk5/p35 only are substantially inhibited (IC50 values of 0.65, 0.7, 0.7 and 0.2 microM, respectively). cdk4/cyclin D1 and cdk6/cyclin D2 are very poorly inhibited by roscovitine (IC50 > 100 microM). Extracellular regulated kinases erk1 and erk2 are inhibited with an IC50 of 34 microM and 14 microM, respectively. Roscovitine reversibly arrests starfish oocytes and sea urchin embryos in late prophase. Roscovitine inhibits in vitro M-phase-promoting factor activity and in vitro DNA synthesis in Xenopus egg extracts. It blocks progesterone-induced oocyte maturation of Xenopus oocytes and in vivo phosphorylation of the elongation factor eEF-1. Roscovitine inhibits the proliferation of mammalian cell lines with an average IC50 of 16 microM. In the presence of roscovitine L1210 cells arrest in G1 and accumulate in G2. In vivo phosphorylation of vimentin on Ser55 by cdc2/cyclin B is inhibited by roscovitine. Through its unique selectivity for some cyclin-dependent kinases, roscovitine provides a useful antimitotic reagent for cell cycle studies and may prove interesting to control cells with deregulated cdc2, cdk2 or cdk5 kinase activities.

Effect of prednisolone on IgE-dependent biphasic cutaneous reaction in BALB/c mice

1. The effect of prednisolone on IgE-dependent, antigen-induced biphasic cutaneous reaction in BALB/c mice was investigated. 2. The biphasic cutaneous reaction with peak responses at 1 h and 24 h after antigen stimulation was suppressed by prednisolone administered 2 h before the challenge. 3. Although antigen challenge increased the expression of IL-1 beta and TNF-alpha mRNA in the mouse ear, prednisolone did not affect the increase. 4. Anti-IL-1 beta antibodies inhibited the later phase of biphasic cutaneous reaction, whereas anti-TNF-alpha antibodies inhibited both phases of the reaction. 5. Prednisolone inhibited edematous reactions caused by both IL-1 beta and TNF-alpha. 6. Proinflammatory cytokines, such as IL-1 beta and TNF-alpha, participate in the development of the biphasic cutaneous reaction, especially in its later phase, in mice, and prednisolone inhibits the reaction by suppressing the action of cytokines, at least in part.

PACAP/VIP receptors in pancreatic beta-cells: their roles in insulin secretion

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide belonging to the vasoactive intestinal polypeptide (VIP)/glucagon/secretin family. We have isolated a third PACAP receptor subtype, designated PACAPR-3, by molecular cloning. The cDNA encoding PACAPR-3 has been isolated from a mouse insulin-secreting beta-cell line MIN6 cDNA library. Mouse PACAPR-3 is a protein of 437 amino acids that has 50% and 51% identity with rat PACAP type I and type II receptors, respectively. We have expressed PACAPR-3 in mammalian cells and Xenopus oocytes. PACAPR-3 binds to VIP as well as PACAP-38 and -27, with a slightly higher affinity for PACAP-38, and is positively coupled to adenylate cyclase. PACAP-38, -27, and VIP evoked Ca2+ activated-Cl- currents in Xenopus oocytes. RNA blotting studies reveal that PACAPR-3 mRNA is expressed widely in tissues and cell lines, including pancreatic islets, insulin-secreting cell lines (MIN6, HIT-T15, and RINm5F), lung, brain, stomach, colon, and heart. Furthermore, insulin secretion from the MIN6 cells is stimulated significantly by PACAP-38 and VIP. The possible mechanisms of insulin secretion by PACAP and VIP are also discussed.

[Development of beta 2-selective, long-acting agonists]

beta 2-Agonists have been the main bronchodilator drugs used in the symptomatic treatment of asthma. Regular use of beta 2-agonists, however, is well known to produce tolerance to their bronchoprotective effect. It has been pointed out that the over-treatment with beta 2-agonists may be associated with worsening asthma and increased risk of life-threatening attacks. To reduce the cardiovascular side effects, compounds with advanced beta 2-selectivity have been examined and established. Newly developed beta 2-selective agonists are structurally stable and long-acting. Some of them are reported to be effective for treatment of late asthmatic response, although conventional beta-agonists are thought to be relatively ineffective.

Egg activation induced by osmotic pressure change and the effects of amiloride on the cryopreservation of mouse oocytes

Activation of oocytes is caused by osmotic pressure change in some species. However, cryopreservation of oocytes occurs in the presence of osmotic pressure change induced by cryoprotectants. We investigated the effect of 5-(N,N,-dimethyl)-amiloride (NNDMA), a selective inhibitor of Na+/H+ exchange, on the cryopreservation and osmotic activation of mouse oocytes. The percentage (23.2%) of degenerate oocytes after cryopreservation in the presence of NNDMA was found to be lower than that (39.5%) of untreated oocytes. After thawing, the percentage (23.6%) of oocytes which could be fertilized following cryopreservation in the presence of NNDMA was significantly higher than that of untreated (18.0%) oocytes. These results suggest that amiloride increased the survival rate after thawing following cryopreservation. To investigate the effect of NNDMA on oocyte activation caused by the cryoprotectant, dimethyl sulphoxide (DMSO) was used to induce osmotic pressure change. NNDMA was found to inhibit cortical granule exocytosis, the second polar body emission and pronuclear formation which occurs upon activation due to osmotic pressure change. It also inhibited the increase in phosphorylation of many proteins including 33 and 45 kDa proteins, which occurs, during fertilization and chemical oocyte activation. In contrast, protein phosphorylation was not inhibited by W7, a calmodulin inhibitor. The actions of these inhibitors suggest that oocyte activation induced by osmotic pressure change involves a pathway mediated by Na+/H+ exchange which may be distinct from the Ca-calmodulin pathway. Amiloride may be a useful drug for increasing the rate of survival of cryopreserved oocytes.

Identification of histone H2A.X as a growth factor secreted by an androgen-independent subline of mouse mammary carcinoma cells

Shionogi carcinoma 115 (SC 115) cells and Chiba subline 2 (CS 2) cells are clones of an androgen-responsive mouse tumor cell line and its autonomous subline, respectively. We have shown previously that CS 2 cells produce a heparin-binding growth factor that stimulates the growth of SC 115 cells as well as the growth of themselves. In this study, a growth factor was purified from serum-free conditioned media of CS 2 cells cultured without testosterone. A heparin-binding fraction showed growth- promoting activity on SC 115 cells and BALB/3T3 cells. The amino acid sequence analysis revealed that the components were identical to histones H2A.1 and H2A.X. Since histone H2A purified from bovine thymus had almost no growth-promoting activity on SC115 cells, histone H2A.X was assumed to be a growth factor. cDNA of histone H2A.X was cloned from a library of CS 2 cells, and its sequence was confirmed. The expressed product of histone H2A.X cDNA in Escherichia coli showed remarkable stimulatory effects on growth of SC 115 cells cultured in the absence of testosterone. These results indicate that histone H2A.X is secreted from CS 2 cells cultured without testosterone and plays a role as a growth factor.

Expression of dopamine transporter at the tips of growing neurites of PC12 cells

The four kinds of oligopeptides specific in amino acid sequence to a rat dopamine transporter (DAT), peptide-1-peptide-4, were chemically synthethized. An attempt to produce antipeptide antibodies against these oligopeptides was made with an in vitro immunization method. Two monoclonal antibodies, MAbs H-1a and H-1b, were produced against one of the oligopeptides, peptide-1. Western blot analysis confirmed that the two antibodies recognized an approximately 85,000 Da protein in a synaptosomal fraction prepared from the rat striatum but none in the fraction from the cerebellum. The specificity of the antibody to DAT was also confirmed by an antibody absorption test using two synthetic oligopeptides, one of which is specific only to DAT. These results have confirmed the specificity of the present antibody to DAT. The expression and subcellular localization of DAT were immunohistochemically examined with MAbs H-1a and H-1b in PC12 cells treated with nerve growth factor (NGF). The antibody labeled the surface of PC12 cells. When the cells were treated with NGF, the expression of DAT was significantly emphasized, first in the area mainly including the Golgi apparatus and rough endoplasmic reticulum and then on the surface of growth cones from the beginning of neurite outgrowth. DAT was detected by Western blot analysis in a microsomal fraction prepared from PC12 cells. The activity of DAT in the PC12 cells was pharmacologically confirmed by the uptake of [3H]-dopamine and blockade by uptake inhibitors. The NGF treatment doubled the dopamine uptake activity. GBR12909, a specific inhibitor of DAT, blocked the [3H]-dopamine at a concentration of 10(-7) M. The expression of DAT and norepinephrine transporter (NET) mRNA in the PC12 cells was examined by reverse transcriptase-polymerase chain reaction (RT-PCR). DAT mRNA significantly increased in the NGF-treated cells after 7 days of incubation, whereas NET mRNA markedly decreased.

Visualization of protein kinase activities in single cells by antibodies against phosphorylated vimentin and GFAP

Vimentin and glial fibrillary acidic protein (GFAP) are intermediate filament proteins expressed in the cytoplasm of various types of cells. The head domains of these proteins are phosphorylated by various protein kinases. Site- and phosphorylation-specific antibodies which recognize a phosphorylated serine/threonine residue in the head domains and its flanking sequence provide a useful tool to monitor and visualize protein kinase activities in single cells.

Kir2.2v: a possible negative regulator of the inwardly rectifying K+ channel Kir2.2

We have cloned the human genes encoding the inwardly rectifying K+ (Kir) channel subunits, Kir2.2 (hKir2.2) and its variant, termed hKir2.2v. When expressed in Xenopus oocytes, hKir2.2 produced strong inwardly rectifying K+ currents, whereas the expression of hKir2.2v did not elicit significant currents. Coexpression of hKir2.2v with hKir2.2 showed an hKir2.2v inhibition of hKir2.2 K+ currents, indicating that it acts as a negative regulator of hKir2.2 channel activity. Mutational analysis of hKir2.2v and studies of chimeras between hKir2.2 and hKir2.2v suggest that the intracellular C-terminal region of hKir2.2v participates in the negative regulation of the hKir2.2v channel activity.

A family of sulfonylurea receptors determines the pharmacological properties of ATP-sensitive K+ channels

We have cloned an isoform of the sulfonylurea receptor (SUR), designated SUR2. Coexpression of SUR2 and the inward rectifier K+ channel subunit Kir6.2 in COS1 cells reconstitutes the properties of K(ATP) channels described in cardiac and skeletal muscle. The SUR2/Kir6.2 channel is less sensitive than the SUR/Kir6.2 channel (the pancreatic beta cell KATP channel) to both ATP and the sulfonylurea glibenclamide and is activated by the cardiac K(ATP) channel openers, cromakalim and pinacidil, but not by diazoxide. In addition, SUR2 binds glibenclamide with lower affinity. The present study shows that the ATP sensitivity and pharmacological properties of K(ATP) channels are determined by a family of structurally related but functionally distinct sulfonylurea receptors.

Cloning and pharmacological characterization of a fourth P2X receptor subtype widely expressed in brain and peripheral tissues including various endocrine tissues

We have isolated cDNA encoding a fourth member (P2X-4) of the ATP receptor P2X receptor family from a rat pancreatic islet cDNA library. Rat P2X-4 is a protein of 388 amino acids which shares 50%, 49%, and 47% identity with P2X-1, P2X-2, and P2X-3, respectively, and has two putative transmembrane segments. Rat P2X-4 mRNA is widely expressed in brain and peripheral tissues, including various endocrine tissues, and it is also expressed in various hormone-secreting cell lines. We have heterologously expressed the cloned P2X-4 in Xenopus laevis oocytes and have characterized its pharmacological properties. ATP, its analogs and ADP activate cation-selective ion channels. The order of agonist potency is ATP ADP 2-methyl- thioATP(2MeSATP) >> alpha beta-methelene-ATP (alpha betameATP). ATP-evoked currents are only partially blocked by suramin, reactive blue-2, or H2DIDS. The present study suggests that P2X-4, with pharmacological properties distinct from those of P2X-1+, P2X-2, and P2X-3, mediates extracellular ATP-induced biological effects in non-neuronal cells, including endocrine cells, as well as in neuronal cells.

TNF-alpha participates in an IgE-mediated cutaneous reaction in mast cell deficient, WBB6F1-W/Wv mice

The participation of tumor necrosis factor-alpha (TNF-alpha) in a IgE-mediated cutaneous reaction in WBB6F1-W/Wv (W/Wv), mast cell deficient, mice and the effect of prednisolone on this cutaneous reaction were investigated. Mice were passively sensitized by an intravenous injection of monoclonal anti-dinitrophenol (DNP) IgE, and their ears challenged epicutaneously with dinitrofluorobenzene 24 h later. The cutaneous reaction estimated by ear thickness reached a peak 48-72 h after the antigen challenge. A monoclonal anti-tumor necrosis factor (TNF)-alpha antibody inhibited the IgE-mediated cutaneous reaction. An increase of TNF-alpha mRNA was demonstrated 4 h after the application of antigen by the reverse transcriptase-polymerase chain reaction. The injection of recombinant murine TNF-alpha induced a cutaneous reaction which peaked at 24 h in nonsensitized mice. Prednisolone at doses of 3 to 10 mg/kg clearly inhibited the IgE-mediated cutaneous reaction, however, it did not affect the expression of TNF-alpha-mRNA. Prednisolone at doses of 1 to 10 mg/kg clearly inhibited the TNF-alpha-induced cutaneous reaction. These results suggest that TNF-alpha plays a role in the IgE-mediated cutaneous reaction in W/Wv mice and that prednisolone inhibits the cutaneous reaction at least in part by inhibiting the action of TNF-alpha.

Primary structure of light and heavy chain variable regions of antibodies recognizing phosphorylated vimentins

We determined the primary structure of three types of monoclonal antibodies against phosphorylated vimentin, 4A4, YT33, and MO82, which recognize phosphorylated Ser55, Ser33, and Ser82 on vimentin, respectively. The amino acid sequences between these antibodies and the anti-phosphotyrosine antibodies previously reported, (Asn/Gln)-X-(Gln/Tyr)-Ser-Tyr in the complimentarity determining region (CDR) 3 of the light chain of 4A4 and YT33, Asn-Pro-Asn-(Asn/Ser)-Gly-X-(Ser/Thr)-(Ser/Thr)-Tyr-Asn-Gln-(Arg/Lys)-Ph e-Lys in the heavy chain CDR2 of MO82, and Lys-X-Ser-(Ser/Asn) in the heavy chain CDR3 of YT33 and MO82, were highly conserved. These motifs may play a role in recognizing phosphate groups of phosphoserine and phosphotyrosine.