Amplitude-dependent modulation of brush border enzymes and proliferation by cyclic strain in human intestinal Caco-2 monolayers

Little is known about the effects of repetitive deformation during peristaltic distension and contraction or repetitive villus shortening on the proliferation and differentiation of the intestinal epithelium. We sought to characterize the effects of repetitive deformation of a physiologically relevant magnitude and frequency on the proliferation and differentiation of human intestinal epithelial Caco-2 cells, a common cell culture model for intestinal epithelial biology. Human intestinal epithelial Caco-2 cells were cultured on collagen-coated membranes deformed by -20 kPa vacuum at 10 cycles/minute, producing an average 10% strain on the adherent cells. Proliferation was assessed by cell counting and 3H-thymidine incorporation. Alkaline phosphatase and dipeptidyl dipeptidase specific activity were measured in cell lysates. Since cells at the membrane periphery experience higher strain than cells in the center, the topography of brush border enzyme histochemical and immunohistochemical staining was analyzed for strain-dependence. Cyclic strain stimulated proliferation compared to static cells. Proliferation was highest in the membrane periphery where strain was maximal. Strain also modulated differentiation independently of its mitogenic effects, selectively stimulating dipeptidyl dipeptidase while inhibiting alkaline phosphatase. Strain-associated enzyme changes were also maximal in areas of greatest strain. The PKC inhibitors staurosporine and calphostin C ablated strain mitogenic effects while intracellular PKC activity was increased by strain. The strain-associated brush border enzyme changes were attenuated but not blocked by PKC inhibition. Thus, strain of a physiologically relevant frequency and magnitude promotes proliferation and modulates the differentiation of a well-differentiated human intestinal epithelial cell line in an amplitude-dependent fashion. PKC may be involved in coupling strain to increased proliferation.     

Differential effects of mucosal pH on human (Caco-2) intestinal epithelial cell motility, proliferation, and differentiation

Mucosal pH abnormalities are associated with anastomotic dehiscence, ischemia, and malignancy. We postulated that intraluminal pH influences intestinal epithelial motility, proliferation, and differentiation and studied extracellular pHo (7.0-8.5) effects on human (Caco-2) intestinal epithelial motility, proliferation, and differentiation. Mucosal healing was modeled by sheet migration and differentiation by alkaline phosphatase and dipeptidyl dipeptidase specific activity. In parallel differentiation and motility studies, we inhibited proliferation with mitomycin to dissociate indirect mitogenic effects. Intracellular pHi was quantitated using BCECF/AM at varying extracellular pHo and in migrating cells. Motility was maximal at pHo 7.6 and proliferation at 7.2. Each decreased with acidity and alkalinity. By contrast, brush border enzyme activity was lowest at pHo 7.0 and highest at pHo 8.5. pHi was highest at pHo 8.5. Migrating cell pHi was higher than static cell pHi. Thus, extracellular pHo deviations perturb Caco-2 pHi homeostasis and motility. Alkalinity promotes differentiation while acidity induces proliferation and limits differentiation.     

From famine to feast: the role of methylglyoxal production in Escherichia coli

Intestinal epithelial cell differentiation is closely regulated during normal cell renewal, maturation, and malignant transformation. Since tyrosine phosphorylation influences differentiation in other cell types and has been reported to vary between crypt cells to differentiated villus tip cells, we investigated the influence of tyrosine phosphorylation in colonocyte differentiation, by using human colonic Caco-2 cells as a model and expression of the brush border enzymes alkaline phosphatase (AKP) and dipeptidyl peptidase (DPDD) as differentiation markers. We studied three tyrosine kinase inhibitors with different modes of action and specificities, viz., genistein, erbstatin analog (EA), and tyrphostin, and the tyrosine phosphatase inhibitor sodium orthovanadate. AKP- and DPDD-specific activities were assayed in protein-matched cell lysates by synthetic substrate digestion. We also correlated the effects of these agents on brush border enzyme activity with tyrosine phosphorylation of phosphoproteins by Western blotting. Genistein (5-75 mg/ml) dose-dependently stimulated AKP and DPDD with a maximal stimulation at 75 mg/ml by 158.6+/- 17.5% and 228.6+/-37.1% of control values, respectively (n=12, P<0.001). The inactive analog genistin had no effect. Tyrphostin (25 mM) similarly stimulated AKP and DPDD by 138. 6+/-6.6% and 131.8+/-1.5% of control values (n=12, P<0.001). Unexpectedly, EA (0.1-10 mM) had the opposite effect, inhibiting AKP- and DPDD-specific activity significantly at 10 mM with a maximal 14.8+/-6.4% and 26.5+/-2.5% of control values (n=12, each P<0.001). Sodium orthovanadate had a discordant effect on these two differentiation markers. Orthovanadate dose-dependently increased AKP to a maximal 188.5+/-16.1% of basal activity at 1.5 mM but decreased DPDD activity at 1.5 mM to 47.2+/-3.8% (n=9, P<0.001 each). The effects of each agent were preserved when proliferation was blocked with mitomycin C, suggesting that the modulation of phenotype by these agents was independent of any effects of proliferation. The tyrosine phosphorylation of several phosphoprotein bands was affected differently by these agents. In particular, the tyrosine phosphorylation of one 70-kDa to 71-kDa band was increased by genistein and tyrophostin but deceased by EA. The different effects of these modulators of tyrosine kinase activity raise the possibility that at least two independent enzymes or pathways regulating tyrosine phosphorylation modulate intestinal epithelial differentiation. Furthermore, tyrosine phosphorylation of the 70-kDa to 71-kDa phosphoprotein may be important in the intracellular signaling by which intestinal epithelial cell differentiation is controlled.     

Migration of retinal pigment epithelium cells in vitro is regulated by protein kinase C

The migration of retinal pigment epithelial (RPE) cells is an important step in various pathologic conditions, including subretinal neovascularization (SRN) and proliferative vitreoretinopathy (PVR). Therefore, elucidation of the mechanism of RPE migration may be useful in devising effective treatment for these disorders. Since protein kinase C (PKC) has been shown to regulate the migration of other cell types, we studied the effects of PKC agonists and antagonists on RPE migration. We used an in vitro wound healing model in which a small area of a confluent monolayer of bovine RPE cells was denuded with a razor blade. The cultures were subsequently incubated with agents known to stimulate [phorbol 12-myristate 13-acetate (PMA)] or inhibit (calphostin C, staurosporine) PKC. After 20 hr, migration was measured as the number of cells that had entered the denuded area. We also measured the translocation of PKC from the cytosol to the membrane in order to determine the activation or inhibition of PKC by PMA and calphostin C in the cells. The phorbol ester PMA stimulated migration by 41%, and calphostin C and staurosporine inhibited migration by 38% and 31%, respectively, in a medium supplemented with 10% serum. To determine the requirement for serum in this modulation, we also measured the effects of PMA and calphostin C on RPE migration in serum-free medium. Under these conditions, basal migration was greatly decreased, but PMA stimulated migration by 177% and calphostin C inhibited migration by 93%. Since PKC modulation is known to induce the proliferation of cells, we also tested the effects of these agents on growth-inhibited migration by pretreating the cells with the antiproliferative drug mitomycin C. We found that modulation of PKC under these conditions equally affected growth-inhibited and growth-dependent migration. Therefore, based on the increase in RPE migration induced by a PKC agonist, and the decrease in migration caused by PKC antagonists, it is suggested that PKC-mediated signal transduction plays a crucial role in RPE cell migration. This knowledge may be useful in devising effective treatments for SRN and PVR.     

The role of vascular endothelial growth factor and interleukins in the pathogenesis of severe ovarian hyperstimulation syndrome

Recent studies have suggested that the proliferation of malignant gliomas may result from activation of protein kinase C (PKC)-mediated pathways; conversely, inhibition of PKC may provide a strategy for blocking tumor growth. In the current studies, we examined the effect of a novel PKC inhibitor, calphostin C, which is a selective, highly potent, photo-activatable inhibitor of the PKC regulatory domain, on the proliferation and viability of three established and three low-passage malignant glioma cell lines, four low-passage low-grade glioma cell lines, and in adult human and neonatal rat non-neoplastic astrocyte cell lines in vitro. Under light-treated conditions, calphostin C consistently inhibited cell proliferation in each of the tumor cell lines and in the neonatal rat astrocyte cell line with a 50% effective concentration of 30 to 50 ng/ml (40 to 60 nm), which was comparable to the previously reported median inhibitory concentration (IC50) for PKC inhibition by calphostin C. Complete elimination of proliferation was achieved at concentrations of 50 to 100 ng/ml (60 to 125 nM). Cell viability decreased sharply with calphostin C concentrations of 100 to 300 ng/ml (125 to 380 nM). In contrast, under light-shielded conditions, calphostin C had a comparatively modest effect on cell proliferation and viability, with a median effective concentration of approximately 300 ng/ml. No significant inhibition of proliferation was noted in the non-neoplastic adult astrocyte cell line under either light-treated or light-shielded conditions. These findings provide further evidence that PKC may play an essential role in mediating the proliferation of both benign and malignant glioma cells in vitro and may also contribute to the proliferation of non-neoplastic immature astrocytes. Light-sensitive inhibition of proliferation and viability by agents such as calphostin C may provide a novel strategy for applying photodynamic therapy to the treatment of neoplastic glial cells.     

End-plate voltage-gated sodium channels are lost in clinical and experimental myasthenia gravis

Although the signaling pathways leading to hydrogen peroxide (H2O2)-induced endothelial monolayer permeability remain ambiguous, cytoskeletal proteins are known to be essential for maintaining endothelial integrity and regulating solute flux through the monolayer. We have recently demonstrated that thrombin-induced actin reorganization in bovine pulmonary artery endothelial cells (BPAEC) requires activation of both myosin light chain kinase (MLCK) and protein kinase C (PKC). Therefore, the present study was designed to investigate the effects of H2O2 on actin reorganization in BPAEC. H2O2 initiated sustained recruitment of actin to the cytoskeleton and transient myosin recruitment in a time- and concentration-dependent manner. The H2O2-induced actin recruitment was significantly inhibited by the calmodulin antagonists, W7 and TFP, but not by the MLCK inhibitor, KT5926, nor the PKC inhibitors, H7 and calphostin C. H2O2 also caused actin filament rearrangement in BPAEC with disruption of the dense peripheral bands and formation of stress fibers. These alterations occurred prior to actin translocation to the cytoskeleton and are prevented by inhibition of either MLCK or PKC. High concentrations of H2O2 transiently attenuated PKC activity but slightly increased the phosphorylation of the prominent PKC substrate and actin-binding protein, myristoylated alanine-rich C kinase substrate (MARCKS), by 5 min. However, MARCKS phosphorylation was reduced to below basal levels by 30 min. On the other hand, H2O2 induced a time- and dose-dependent phosphorylation of myosin light chains which was eliminated by both MLCK and PKC inhibitors. These data suggest that MLCK contributes to H2O2-induced myosin light chain phosphorylation and actin rearrangement and that PKC may play a permissive role. Neither of these enzymes appears to be involved in the H2O2-induced recruitment of actin to the cytoskeleton.     

Antisense oligonucleotides targeting protein kinase C-alpha, -beta I, or -delta but not -eta inhibit lipopolysaccharide-induced nitric oxide synthase expression in RAW 264.7 macrophages: involvement of a nuclear factor kappa B-dependent mechanism

The signaling pathway for protein kinase C (PKC) activation and the role of PKC isoforms in LPS-induced nitric oxide (NO) release were studied in RAW 264.7 macrophages. The tyrosine kinase inhibitor genestein attenuated LPS-induced NO release and inducible nitric oxide synthase (iNOS) expression, as did the phosphoinositide-specific phospholipase C (PI-PLC) inhibitor U73122 and the phosphatidylcholine-specific phospholipase C (PC-PLC) inhibitor D609. LPS stimulated phosphatidylinositol (PI) hydrolysis and PKC activity in RAW cells; both were inhibited by genestein. The PKC inhibitors (staurosporine, calphostin C, Ro 31-8220, or Go 6976) or long-term 12-O-tetradecanoylphorbol 13-acetate (TPA) treatment also resulted in inhibition of LPS-induced NO release and iNOS expression. Western blot analysis showed expression of PKC-alpha, -betaI, -delta, -eta, and -zeta in RAW cells; down-regulation of PKC-alpha, -betaI, and -delta, but not -eta, was seen after long-term TPA treatment, indicating the possible involvement of one or all of PKC-alpha, -betaI, and -delta, but not -eta, in LPS-mediated effects. Treatment with antisense oligonucleotides for these isoforms further demonstrated the involvement of PKC-alpha, -betaI, and delta, but not -eta, in LPS responses. Stimulation of cells with LPS for 1 h caused activation of NF-kappaB in the nuclei by detection of NF-kappaB-specific DNA-protein binding; this was inhibited by genestein, U73122, D609, calphostin C, or antisense oligonucleotides for PKC-alpha, -betaI, and -delta, but not -eta. These data suggest that LPS activates PI-PLC and PC-PLC via an upstream tyrosine kinase to induce PKC activation, resulting in the stimulation of NF-kappaB DNA-protein binding, then initiated the expression of iNOS and NO release. PKC isoforms alpha, betaI, and delta were shown to be involved in the regulation of these LPS-induced events.     

pH dependence of the formation of an M-type intermediate in the photocycle of 13-cis-bacteriorhodopsin

Phosphatidic acid (PA) dose-dependently induced superoxide (O2-) production of electropermeabilized human neutrophils but not of intact neutrophils, indicating that PA induces the activation of NADPH oxidase by acting on an intracellular target. The O2- production by PA was not inhibited by protein kinase C (PKC) inhibitors, such as staurosporine and calphostin C, and an inhibitor of PA phosphohydrolase, propranolol. These observations suggest that the activation of the oxidase by PA is independent of the activity of PKC and may dominate the activation by diacylglycerol which is formed from PA via the action of PA phosphohydrolase. Furthermore, the production by PA, as well as that by phorbol myristate acetate, was inhibited by cyclic AMP and GDP beta S. Therefore, PA seems to act at a site downstream of PKC.     

Protective ability of acetylsalicylic acid (aspirin) to scavenge radiation induced free radicals in J774A.1 macrophage cells

Indirect studies suggested that protein kinase C (PKC) has a role in sperm motility and the acrosome reaction. Physiological inducers of the sperm acrosome reaction include progesterone, which can increase intracellular calcium ([Ca2+]i), tyrosine phosphorylation of proteins and chloride efflux in human spermatozoa. PKC may be involved in progesterone-stimulated acrosome reaction, although controversial results have been obtained concerning the effect of PKC inhibition on progesterone-stimulated [Ca2+]i increase. In the present study, we investigated the direct effect of progesterone on the activity of PKC, as well as the effect of a panel of PKC inhibitors on progesterone-stimulated [Ca2+]i increase and tyrosine phosphorylation of proteins. We found that progesterone stimulates sperm PKC activity and that PKC inhibition with staurosporine and bisindolylmaleimide partially reversed the effect of progesterone on acrosome reaction, indicating an involvement of the enzyme in the effect of the steroid. We next evaluated the effect of three different PKC inhibitors (sangivamycin, staurosporine and bisindolylmaleimide) on progesterone-stimulated [Ca2+]i increase. Neither short-term (15 min) nor long-term (90 min) preincubation with any of the three compounds had a substantial effect on the stimulatory effect of progesterone on sperm [Ca2+]i. Nor was responsiveness to progesterone affected by either short-term (determining activation of PKC) or long-term (determining down-regulation of PKC) incubation with the tumour promoter phorbol myristate acetate (PMA), a known non-physiological stimulator of PKC. These results indicate that progesterone-stimulated calcium influx is independent of PKC activation. In addition, we found that preincubation with PKC inhibitors had a stimulatory effect per se on tyrosine phosphorylation of sperm proteins. When compared with the appropriate control, the effect of progesterone on tyrosine phosphorylation was slightly (but not significantly) reduced by the inhibitors, sangivamycin, staurosporine and bisindolylmaleimide, but was significantly inhibited by calphostin C. These results do not permit a final conclusion on the involvement of PKC in progesterone-stimulated tyrosine phosphorylation of sperm proteins. However, the lack of effect of PMA on tyrosine phosphorylation indicates that PKC stimulation is not sufficient to induce this effect. In conclusion, our results indicate that PKC plays a role in progesterone-induced acrosome reaction and that progesterone-stimulated PKC activation is downstream to stimulation of calcium influx by the steroid.     

Protein kinase C eta mediates lipopolysaccharide-induced nitric-oxide synthase expression in primary astrocytes

The signaling pathway involved in protein kinase C (PKC) activation and role of PKC isoforms in lipopolysaccharide (LPS)-induced nitric oxide (NO) release were studied in primary cerebellar astrocytes. LPS caused a dose- and time-dependent increase in NO release and inducible NO synthase (iNOS) expression. The tyrosine kinase inhibitor, genestein, the phosphatidylcholine-phospholipase C inhibitor, D609, and the phosphatidate phosphodrolase inhibitor, propranolol, attenuated the LPS effects, whereas the PI-PLC inhibitor, U73122, had no effect. The PKC inhibitors (staurosporine, Ro 31-8220, Go 6976, and calphostin C) also inhibited LPS-induced NO release and iNOS expression. However, long term (24 h) pretreatment of cells with 12-O-tetradecanoyl phorbol-13-acetate (TPA) did not affect the LPS response. Previous results have shown that TPA-induced translocation, but not down-regulation, of PKCeta occurs in astrocytes (Chen, C. C., and Chen, W. C. (1996) Glia 17, 63-71), suggesting possible involvement of PKCeta in LPS-mediated effects. Treatment with antisense oligonucleotides for PKCeta or delta, another isoform abundantly expressed in astrocytes, demonstrated the involvement of PKCeta, but not delta, in LPS-mediated effects. Stimulation of cells for 1 h with LPS caused activation of nuclear factor (NF)-kB in the nuclei as detected by the formation of a NF-kB-specific DNA-protein complex; this effect was inhibited by genestein, D609, propranolol, or Ro 31-8220 or by PKCeta antisense oligonucleotides, but not by long term TPA treatment. These data suggest that in astrocytes, LPS might activate phosphatidylcholine-phospholipase C and phosphatidylcholine-phospholipase D through an upstream protein tyrosine kinase to induce PKC activation. Of the PKC isoforms present in these cells, only activation of PKCeta by LPS resulted in the stimulation of NF-kB-specific DNA-protein binding and then initiated the iNOS expression and NO release. This is further evidence demonstrating that different members of the PKC family within a single cell are involved in specific physiological responses.     

Involvement of protein kinase C in agonist-stimulated goldfish ovulation

The effects of two protein kinase C (PKC) inhibitors, calphostin C and staurosporine, on the in vitro ovulation of goldfish (Carassius auratus) oocytes were investigated. Ovulation was stimulated by prostaglandin (PG) F2 alpha (PGF2 alpha, 2.0 micrograms/ml), by sodium orthovanadate (0.1 mM), by a combination of the phorbol ester phorbol 12-myristate-13-acetate (PMA, 0.1 micrograms/ml) and calcium ionophore A23187 (0.05 micrograms/ml), by thapsigargin (0.2 micrograms/ml), and by elevated pH (8.1). In addition, the effects of these inhibitors on the PKC activity of the goldfish follicle wall was determined by use of a specific peptide substrate phosphorylation assay. At 0.1 microM, staurosporine significantly blocked ovulation induced by all agents. However, at lower (0.01 microM) levels it blocked only PMA/A23187-induced ovulation. In contrast, calphostin significantly blocked only PMA/A23187-induced ovulation, although there was a decrease in pH-induced ovulation at lower calphostin concentrations. Both calphostin and staurosporine blocked follicular PKC activity at levels that were inhibitory to ovulation. In addition, staurosporine significantly blocked PKC activity at levels even lower than those needed to block ovulation. The combined results suggest that orthovanadate, PGF2 alpha, and thapsigargin do not require PKC activation for the induction of ovulation, whereas PMA/A23187 does.     

Absorption-enhancing mechanism of EDTA, caprate, and decanoylcarnitine in Caco-2 cells

The mechanism of paracellular expansion by absorption enhancers, e.g., EDTA, sodium caprate (C10), and decanoylcarnitine (DC), was studied, the focus being on the process of actin microfilament contraction in the tight junction. The effects of various inhibitors such as KN-62 (a specific inhibitor of Ca2+/calmodulin dependent protein kinase), H7 (a protein kinase C (PKC) inhibitor), and W7 (a calmodulin antagonist) were examined on the paracellular expansion by the enhancers in Caco-2 cells. From the experimental results, the following mechanisms were suggested. EDTA activates PKC by depletion of extracellular calcium via chelation resulting in expansion of the paracellular route. C10 increases the intracellular calcium level by an interaction with the cell membrane independent of cell polarity resulting in contraction with actin microfilament. DC interacts specifically with the apical membrane to increase the intracellular calcium level, but the mechanistic details subsequent to the increase of calcium are not clear.     

Criteria to assess in vivo performance and bioequivalence of generic controlled-release formulations of carbamazepine

Ocular surface mucin is secreted from both goblet cells in the conjunctival epithelium and corneal epithelial cells. To clarify its mechanism of secretion in corneal epithelial cells, a rat cornea organ culture system was used to evaluate the second messenger roles of cyclic-AMP (cAMP), cyclic-GMP (cGMP) and protein kinase C (PKC) in modulating mucin-like glycoprotein secretion. Rat cornea sections (3 mm diameter) were cultured in TC-199 medium, and radiolabeled with sodium sulfate for 18 hr. After washing, the corneas were treated with various second messenger modulating agents for 30 min. The culture media were reacted with Dolichos biflorus (DBA)-lectin, and mucin-like glycoprotein was isolated. Then the radioactivity of DBA-binding mucin-like glycoprotein was isolated. Then the radioactivity of DBA-binding mucin-like glycoprotein was measured. There was a time-dependent increase in mucin-like glycoprotein was measured. There was a time-dependent increase in mucin-like glycoprotein secretion, whereas after corneal epithelial debridement the secretion was markedly inhibited by 81%. Mucin-like glycoprotein secretion was stimulated in a dose-dependent manner following elevation of cAMP levels by exposure to either forskolin, dibutyryl cAMP or 3-isobutyl-1-methylxanthine. Concomitant exposure to the cAMP dependent protein kinase inhibitor, KT5720 completely inhibited their stimulatory effects. Neither exposure to dibutyryl cGMP nor nitroprusside affected mucin-like glycoprotein secretion. Stimulation by PKC, phorbol 12, 13-dibutyrate (PDBu) also increased mucin-like glycoprotein secretion in a dose-dependent fashion. The PKC inhibitor, calphostin C completely inhibited the stimulation by PDBu of mucine-like glycoprotein secretion. These results demonstrate that corneal epithelial cells secrete mucin-like glycoprotein, which is mediated by cAMP and PKC signal transduction pathways.     

Stimulation of cell elongation in teleost rod photoreceptors by distinct protein kinase inhibitors

The rod photoreceptors of teleost retinas elongate in the light. To characterize the role of protein kinases in elongation, pharmacological studies were carried out with rod fragments consisting of the motile inner segment and photosensory outer segment (RIS-ROS). Isolated RIS-ROS were cultured in the presence of membrane-permeant inhibitors that exhibit selective activity toward specific serine/threonine protein kinases. We report that three distinct classes of protein kinase inhibitors stimulated elongation in darkness: (1) cyclic-AMP-dependent protein kinase (PKA)-selective inhibitors (H-89 and KT5720), (2) a protein kinase C (PKC)-selective inhibitor (GF 109203X) that affects most PKC isoforms, and (3) a kinase inhibitor (H-85) that does not affect PKC and PKA in vitro. Other kinase inhibitors tested neither stimulated elongation in darkness nor inhibited light-induced elongation; these include the myosin light chain kinase inhibitors ML-7 and ML-9, the calcium-calmodulin kinase II inhibitor KN-62, and inhibitors or activators of diacylglycerol-dependent PKCs (sphingosine, calphostin C, chelerythrine, and phorbol esters). The myosin light chain kinase inhibitors as well as the PKA and PKC inhibitors H-89 and GF 109203X all enhanced light-induced elongation. These observations suggest that light-induced RIS-ROS elongation is inhibited by both PKA and an unidentified kinase or kinases, possibly a diacylglycerol-independent form of PKC.     

Suppression of GnRH gene expression in GT1-1 hypothalamic neuronal cells: action of protein kinase C

We attempted to elucidate molecular mechanisms of gonadotropin-releasing hormone (GnRH) gene regulation by the protein kinase C (PKC) pathway in GT1-1 cells. Activation of PKC with 12-tetra-decanoylphorbol-13-acetate (TPA) or inhibition with staurosporine or calphostin C down-regulated GnRH mRNA levels. A serial deletion mutant analysis revealed that this suppression was mediated by the proximal region (-187/-69) of the mouse GnRH promoter. TPA transiently induced c-fos mRNA, whereas staurosporine or calphostin C failed to do so. However, PKC inhibitors blocked the TPA-evoked c-fos induction. Over-expression of PKC alpha down-regulated GnRH promoter activity, indicating that PKC activation was sufficient to inhibit GnRH gene expression. These results suggest that both activation and inhibition of PKC decrease the GnRH gene expression in the GT1-1 cells probably through different signal cascade mechanisms.     

International trends in the incidence of cervical cancer: I. Adenocarcinoma and adenosquamous cell carcinomas

The integrin alpha9beta1 is one of the recently identified integrins whose expression is restricted to specialized tissues. Its exact function is still unknown. In the present study, we have analyzed the expression of the alpha9 subunit in human fetal and adult small intestinal and colonic epithelia as well as in intestinal cell lines by indirect immunofluorescence, immunoprecipitation, Western blot, and Northern blot. In intact tissues, the antigen was restricted to the basolateral domain of epithelial cells in intestinal crypts at the fetal stage and was absent in the adult. The alpha9beta1 integrin was also detected in the intestinal cell lines HIEC-6 and Caco-2/15. The presence of alpha9beta1 in HIEC-6 was found to be consistent with their proliferative crypt-like status. In Caco-2/15 cells, the integrin was present at high levels in proliferating cells but was downregulated when cells cease to grow and undertake their differentiation. EGF treatment, which is known to maintain Caco-2/15 cells in a proliferative state, resulted in higher levels of alpha9 as compared to control cells. Taken together, these observations suggest a relation between integrin alpha9beta1 expression and proliferation in human intestinal cells.     

PKC and tyrosine kinase involvement in amyloid beta (25-35)-induced chemotaxis of microglia

Microglia are activated by amyloid beta (Abeta) in vivo and in vitro, and Abeta-activated microglia may be involved in the pathogenesis of Alzheimer's disease (AD). We investigated the mechanism of microglial chemotaxis induced by Abeta (25-35), an active fragment of Abeta. Abeta (25-35) 0.1 and 1 nM stimulated microglial chemotaxis. The protein kinase C (PKC) inhibitors chelerythrine (0.5 and 2 microM), calphostin C (1 microM) and staurospine (10 nM) significantly inhibited the microglial chemotaxis induced by Abeta (25-35) (1 nM). The chemotactic effect of Abeta (25-35) on microglia was desensitized by pretreatment of microglia with 1 ng/ml 12-O-tetradecanoylphorbol 13-acetate (TPA). Pretreatment of cells with Abeta (25-35) (1 nM) also desensitized the chemotactic effect by Abeta (25-35) (1 nM). The desensitization by TPA or Abeta (25-35) was inhibited when staurosporine was present in the pretreatment media. The tyrosine kinase inhibitor herbimycin A (0.1 and 1 microM) significantly inhibited the microglial chemotaxis induced by Abeta (25-35) (1 nM). Based on these observations, it seems likely that PKC and tyrosine kinase are involved in the Abeta-induced chemotaxis of microglia.     

A hepatocyte-targeted conjugate capable of delivering biologically active colchicine in vitro

The regulatory mechanism of Bcl-2 protein expression was investigated in SH-SY5Y cells, the human neuroblastoma cell line that expresses natively Bcl-2 proteins. WHen the cells were treated with 12-O-tetradecanoylphorbol 13-acetate (TPA) or retinoic acid, the level of Bcl-2 protein was increased compared with the control. These effects were inhibited by pretreatment with a protein kinase C (PKC) inhibitor, staurosporine or calphostin C. The level of Bcl-2 protein was also increased by treatment with carbachol, a muscarinic acetylcholine receptor (mAChR) agonist, and the effect were also inhibited by pretreatment with staurosporine or calphostin C. An addition, a carbachol-induced increase in Bcl-2 protein levels and a transient elevation of [Ca2+]i were inhibited by pretreatment with 4-DAMP (4-diphenylacetoxy-N-methylpiperidine), an m3 mAChR antagonist. In contrast, the level of Bcl-2 protein was decreased by treatment with dibutyryl cAMP (diBu-cAMP), forskolin, or cholera toxin, and the effects of diBu-cAMP were inhibited by pretreatment with a protein kinase A (PKA) inhibitor, H-89. From these results, we suggest that the expression of Bcl-2 proteins is regulated by PKC and PKA in positive and negative manners, respectively, in SH-SY5Y cells. Furthermore, the nucleosomal DNA fragmentation induced by serum depletion for 4 h was observed in SH-SY5Y cells when the level of Bcl-2 protein was down-regulated by treatment with 1 mM diBu-cAMP for 3 days, although the DNA fragmentation by serum depletion for 4 h was not observed in nontreatment cells, indicating that Bcl-2 proteins whose expression is regulated by PKC and PKA play important roles in serum depletion-induced apoptosis.     

Tonic regulation of excitation-contraction coupling by basal protein kinase C activity in isolated cardiac myocytes

A high-speed imaging technique was used to investigate the effects of inhibitors and activators of protein kinase C (PKC) on the [Ca2+]i transients and contraction of fura-2 loaded rat ventricular cardiac myocytes. The amplitude of the [Ca2+]i transient was reduced following treatment with 100 nM phorbol 12,13-dibutyrate (PDBu), whereas the PKC inhibitors staurosporine (0.5 microM) and calphostin C (10 microM) increased [Ca2+]i transient amplitude, elevated basal [Ca2+]i and slowed the decay of the [Ca2+]i transient. These changes were paralleled by similar alterations in the rate and extent of cell shortening. The activity of nitrendipine-sensitive Ca2+ channels was monitored indirectly as the rate of Mn2+ quench of cytosolic fura-2 in electrically-paced cells. PDBu reduced Mn2+ influx by six-fold, whereas staurosporine and calphostin C increased the influx rate by eight-fold and seven-fold over basal quench, respectively. The caffeine releasable Ca2+ pool was reduced in the presence of PDBu and increased transiently in presence of staurosporine. The effects of PKC activation and inhibition on sarcoplasmic reticulum Ca2+ content may be secondary to alterations of sarcolemmal Ca2+ influx. However, the PKC inhibitors also decreased the rate of sarcoplasmic reticulum Ca2+ uptake in permeabilized myocytes, suggesting that a direct effect of PKC on the sarcoplasmic reticulum may contribute to the prolongation of the [Ca2+]i transient under these conditions. The present work demonstrates that basal PKC activity has a potent depressant effect, mediated primarily through inhibition of sarcolemmal Ca2+ influx, which may play a key role in setting the basal tone of cardiac muscle.