Inositol lipids and DNA replication

Nerve Ending “Signal” Proteins GAP‐43, MARCKS, and BASP1

Mechanisms of growth cone pathfinding in the course of neuronal net formation as well as mechanisms of learning and memory have been under intense investigation for the past 20 years, but many aspects of these phenomena remain unresolved and even mysterious. "Signal" proteins accumulated mainly in the axon endings (growth cones and the presynaptic area of synapses) participate in the main brain processes. These proteins are similar in several essential structural and functional properties. The most prominent similarities are N-terminal fatty acylation and the presence of an "effector domain" (ED) that dynamically binds to the plasma membrane, to calmodulin, and to actin fibrils. Reversible phosphorylation of ED by protein kinase C modulates these interactions. However, together with similarities, there are significant differences among the proteins, such as different conditions (Ca2+ contents) for calmodulin binding and different modes of interaction with the actin cytoskeleton. In light of these facts, we consider GAP-43, MARCKS, and BASP1 both separately and in conjunction. Special attention is devoted to a discussion of apparent inconsistencies in results and opinions of different authors concerning specific questions about the structure of proteins and their interactions.

Expression of purinergic receptors in non-melanoma skin cancers and their functional roles in A431 cells

We investigated the use of purinergic receptors as a new treatment modality for nonmelanoma skin cancers. Purinergic receptors, which bind adenosine 5'-tri-phosphate, are expressed on human cutaneous keratinocytes. Previous work in rat and human epidermis suggested functional roles for purinergic receptors in the regulation of proliferation, differentiation, and apoptosis. Immunohistochemical analysis of frozen sections in human basal cell carcinomas and squamous cell carcinomas for P2X5, P2X7, P2Y1, P2Y2, and P2Y4 receptors was performed, accompanied by detailed analysis of archive material of tumor subtypes in paraffin sections. Functional studies were performed using a human cutaneous squamous cell carcinoma cell line (A431), where purinergic receptor subtype agonists were applied to cells and changes in cell number were quantified via a colorimetric assay. Immunostaining in paraffin sections was essentially the same as that in frozen sections, although more detail of the subcellular composition was visible. P2X5 and P2Y2 receptors were heavily expressed in basal cell carcinomas and squamous cell carcinomas. P2X7 receptors were expressed in the necrotic center of nodular basal cell carcinomas and in apoptotic cells in superficial multifocal and infiltrative basal cell carcinomas, and squamous cell carcinomas. P2Y1 receptors were only expressed in the stroma surrounding tumors. P2Y4 receptors were found in basal cell carcinomas but not in squamous cell carcinomas. P2X5 receptors appear to be associated with differentiation. The P2X7 receptor agonist benzoylbenzoyl-adenosine 5'-triphosphate and high concentrations of adenosine 5'-triphosphate (1000-5000 microM) caused a significant reduction in A431 cell number (p<0.001), whereas the P2Y2 receptor agonist uridine 5'-triphosphate caused a significant amount of proliferation (p<0.001). We have demonstrated that non-melanoma skin cancers express functional purinergic receptors and that P2X7 receptor agonists significantly reduce cell numbers in vitro.

Alteration of phosphatidylinositol transfer protein during global brain ischemia-reperfusion in gerbils

Phosphatidylinositol transfer proteins (PI-TPs) are responsible for the transport of phosphatidylinositol and other phospholipids. Moreover, these proteins are involved in vesicle transport and in the function of cytoskeleton. Our previous data indicated that brain ischemia affected phosphoinositides metabolism and the level of lipid derived second messengers. In this study, the effect of ischemia-reperfusion injury on the level of PI-TPs and of the role of NMDA receptor stimulation on the alteration of these proteins was investigated during reperfusion after 5 min of forebrain ischemia in gerbils. Some groups of animals were injected intraperitoneally with MK-801, an antagonist of NMDA receptor 30 min before ischemia. The levels of both PI-TP isoforms alpha+beta and separately the alpha-isoform were determined in cytosol and membrane fraction from brain cortex and hippocampus using Western blot analysis. In the cytosolic fractions, the concentration of both isoforms of PI-TP was 2 times higher when compared to the membrane fraction. In brain cortex, PI-TP alpha isoform consist about 32-44% but in hippocampus 72-82% of both isoforms (PI-TP alpha+beta) in cytosolic and membrane fraction respectively. Ischemia-reperfusion had no effect on PI-TPs in brain cortex. However, in hippocampus after 5 min ischemia and during whole reperfusion time up till 7 days the level of PI-TP alpha+beta and PI-TP alpha was significantly higher by about 20-55%, respectively when compared to control. MK-801 eliminated ischemia-reperfusion evoked alteration of PI-TPs. To confirm the role of NMDA receptor in PI-TP alteration additional experiments were carried out on PC-12 cells in culture. The results indicated that activation of NMDA receptor enhances significantly the level of PI-TP alpha. The competitive antagonist of NMDA receptor inhibited this effect. These results indicated that activation of NMDA receptor is connected with PI-TPs alteration and plays an important role in modulation of PI-TPs during ischemia-reperfusion injury that may have important physiopathological consequence.

Comparison of the fatty acid compositions in intraepithelial and infiltrating lesions of the cervix: part II, free fatty acid profiles

In the second part of this study, the emphasis is on the free fatty acids during cervical carginogenesis, since they may reflect active cell metabolism during this disease process. Lipids were extracted from biopsies of normal epithelial tissue (N) (n=36), cervical intraepithelial lesions (CIL) (n=47), and infiltrating lesions (Ca) (n=47) of the cervix. Samples, from which the free fatty acid compositions were determined, were saponified, methylated and analysed by GLC. In accordance with results obtained on total fatty acid compositions, essential fatty acid deficiency (EFAD) in the intraepithelial lesions, compared with normal tissue (linoleic acid, P< 0.01), and infiltrating lesions compared with intraepithelial lesions (linoleic acid and arachidonic acid, P< 0.01) were observed. High levels of oleic acid were also observed when infiltrating lesions were compared with normal tissue (P < 0.01). As previously mentioned by us in part I of this study, with regard to possible disturbances in metabolic pathways based on the total fatty acid profiles during stages of cervical cancer, EFAD is prevalent during cervical carcinogenesis. This EFAD in cancer cells may result in many defective cell mechanisms, since fatty acids are associated with biochemical events such as lipid peroxidation, signal transduction and immune responses. The high level of oleic acid in cancer cells is known to activate PKC and thus contribute to the continous growth stimulus thought to exist in malignant cells. From a therapeutic viewpoint, substantial changes in the fatty acid composition of the membranes can be produced in cancer cells by selective fatty acid supplementation strategies. At present, modifications of the fatty acid compositions of cell membranes represent an experimental model that has promoted increased understanding of lipid transportation, membrane remodelling, and the relationship between membrane lipids and membrane function. By addressing factors responsible for insufficient essential fatty acid levels, carginogenesis may be prevented or treated. The clinical feasibility of using modification of fatty acids in tumours or cancer by diet or perfusion as an adjunct to standard therapies should be tested.

Intracellular free calcium and growth changes in single human keratinocytes in response to vitamin D and five 20-epi-analogues

Vitamin D, 1,25(OH)2D3, decreases proliferation and promotes differentiation of keratinocytes, and other keratinocyte differentiation stimuli have been associated with an early rise in intracellular free calcium, [Ca2+]i. We therefore investigated the effect of 1,25(OH)2D3, its precursor D3 and five 20-epi-analogues (EB1089, KH1060, KH1139, MC1288, MC1301) on growth and [Ca2+]i levels of normal human keratinocytes. Cells were cultured in medium MCDB153 with an extracellular calcium concentration of 70 microM or 1 mM. All the analogues were more potent than 1,25(OH)2D3 at inducing the morphological changes of differentiation, but D3 was inactive. At concentrations down to 10(-8) M 1,25(OH)2D3, caused significant inhibition of growth, as assessed by counting cells and measurement of thymidine labelling. At 5 days 50% inhibition of growth occurred with 64 nM 1,25(OH)2D3 and 3330 nM D3. All the analogues were more potent than 1,25(OH)2D3, and KH1060 inhibited growth at 10(-10) M. In single keratinocytes [Ca2+]i was measured by microspectrofluorimetric techniques using the dye fura-2. No immediate rise in [Ca2+]i was observed following addition of 1,25(OH)2D3 or the analogues up to 10(-6) M. However 10(-7) M 1,25(OH)2D3 or the analogues induced a gradual increase in [Ca2+]i, significant at 4 h (P < 0.001), which increased further over 2-3 days. D3 had no effect on [Ca2+]i. Increases in [Ca2+]i following the differentiation stimuli of either 2 mM extracellular calcium or 1,25(OH)2D3 were similar at 48 h, increasing from 100 +/- 3 nM (mean +/- SEM) in control cells to 150 +/- 3 nM with 2 mM calcium and 144 +/- 6 nM with 10(-7) M 1,25(OH)2D3. The effect of extracellular calcium in raising [Ca2+]i within minutes was more rapid than 1,25(OH)2D3, but in combination the two were not additive.

Modulation of thymidine incorporation by kappa-opioid ligands in rat spinal cord-dorsal root ganglion co-cultures

beta-Endorphin, met-enkephalin and several mu-selective opioid agonists were shown to decrease thymidine incorporation into DNA in various neural cell cultures. We now report that the kappa-selective opioid agonists U50488, U69593 and MR2034 modulate [3H]thymidine incorporation into DNA in rat spinal cord-dorsal root ganglion co-cultures. U50488 at 10 microM increased by 60% thymidine incorporation in 6-day-old cultures. The thymidine incorporation induced by U50488 was blocked by the kappa-selective antagonist nor-binaltorphimine, as well as by pertussis toxin and LiCl. U50488 treatment stimulated phosphatidylinositol turnover by three-fold compared with untreated controls. These findings suggest that kappa-opioid agonists modulate DNA synthesis in spinal cord-dorsal root ganglion co-cultures through a mechanism which involves pertussis toxin-sensitive GTP-binding proteins, as well as activation of phosphatidylinositol turnover.

kappa-Opioid agonist modulation of [3H]thymidine incorporation into DNA: evidence for the involvement of pertussis toxin-sensitive G protein-coupled phosphoinositide turnover

A body of evidence has indicated that mu-opioid agonists can inhibit DNA synthesis in developing brain. We now report that kappa-selective opioid agonists (U69593 and U50488) modulate [3H]thymidine incorporation into DNA in fetal rat brain cell aggregates in a dose- and developmental stage-dependent manner, kappa agonists decreased thymidine incorporation by 35% in cultures grown for 7 days, and this process was reversed by the kappa-selective antagonist, norbinaltorphimine, whereas in 21-day brain cell aggregates a 3.5-fold increase was evident. Cell labeling by [3H]thymidine was also inhibited by the kappa-opioid agonist as shown by autoradiography. In addition, U69593 reduced basal rates of phosphoinositide formation in 7-day cultures and elevated it in 21-day cultures. Control levels were restored by norbinaltorphimine. Pertussis toxin blocked U69593-mediated inhibition of DNA synthesis. The action of kappa agonists on thymidine incorporation in the presence of chelerythrine, a protein kinase C (PKC) inhibitor, or in combination with LiCl, a noncompetitive inhibitor of inositol phosphatase, was attenuated in both 7- and 21-day cultures. These results suggest that kappa agonists may inhibit DNA synthesis via the phosphoinositide system with a pertussis toxin-sensitive G protein as transducer. In mixed glial cell aggregates, U50488 increased thymidine incorporation into DNA 3.1-fold, and this stimulation was reversed by the opioid antagonist naltrexone.

Growth and differentiation stimuli induce different and distinct increases in intracellular free calcium in human keratinocytes

The effect of growth and differentiation stimuli on intracellular free calcium ([Ca2+]i) in cultured human keratinocytes was investigated using micro-spectrofluorimetric techniques and the calcium-sensitive dye FURA-2. The mean [Ca2+]i of keratinocytes in 70 microM calcium medium was 104 +/- 3 nM (mean +/- SEM), significantly lower than the transformed keratinocyte line SVK14 (128 +/- 2 nM). When cultured in 2.0 mM calcium medium the [Ca2+]i increased in both normal and transformed keratinocytes to 135 +/- 4 nM and 180 +/- 4 nM, respectively. Keratinocytes grew more slowly in the absence of EGF, but [Ca2+]i was unaltered. Stimulation with EGF (10 ng/ml) induced, over 4 min, a large transient rise in [Ca2+]i up to 230 nm, due to an influx of extracellular calcium. Heterogeneity of keratinocytes was observed with 46% (n = 13) responding, but confluent or differentiated keratinocytes did not respond. TGF--beta (1 ng/ml) reduced cell growth without inducing differentiation and was not associated with any change in [Ca2+]i. The phorbol ester TPA (50 nM) induced irreversible growth arrest and terminal differentiation and increased the [Ca2+]i from 102 +/- 2 nM to 126 +/- 3 nM at 2 h, an effect similar to that of 2 mM extracellular calcium. Addition of 500 nM TPA was associated with a rise in [Ca2+]i, over several minutes to a plateau of 200-300 nM, due to release from internal stores and an influx of extracellular calcium. In normal human keratinocytes an increase in [Ca2+]i appears to be an early event in differentiation, whether induced by calcium or TPA, but not during growth inhibition without differentiation.

Evidence for the implication of phosphoinositol signal transduction in mu-opioid inhibition of DNA synthesis

An opioid receptor agonist, [D-Ala2,Me-Phe4,Glyol5]enkephalin (DAMGE), decreased [3H]thymidine incorporation into DNA of fetal rat brain cell aggregates. This action proved to depend on the dose of this enkephalin analog and the interval the aggregates were maintained in culture. The opioid antagonist naltrexone and the mu-specific antagonist cyclic D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr amide (CTOP) reversed the DAMGE effect, arguing for a receptor-mediated mechanism. The mu-opioid nature of this receptor was further established by inhibiting DNA synthesis with the highly mu-selective agonist morphiceptin and blocking its action with CTOP. Several other opioids, pertussis toxin, and LiCl also diminished DNA synthesis, whereas cholera toxin elicited a modest increase. Naltrexone completely reversed the inhibition elicited by the combination of DAMGE and low doses of LiCl but not by that of high levels of LiCl alone. The enkephalin analog also reduced basal [3H]inositol trisphosphate and glutamate-stimulated [3H]inositol monophosphate and [3H]inositol bisphosphate accumulation in the aggregates. These DAMGE effects were reversed by naltrexone and were temporally correlated with the inhibition of DNA synthesis. A selective protein kinase C inhibitor, chelerythrine, also inhibited thymidine incorporation dose-dependently. The effect of DAMGE was not additive in the presence of chelerythrine but appeared to be consistent with their actions being mediated via a common signaling pathway. These results suggest the involvement of the phosphoinositol signal transduction system in the modulation of thymidine incorporation into DNA by DAMGE.

Release of choline by phospholipase D and a related phosphoric diester hydrolase in human erythrocytes. 1H spin-echo n.m.r. studies

A previously detected phosphatidylcholine-specific phospholipase D from lysates of human red blood cells has been further characterized by 1H spin-echo n.m.r. spectroscopy. A second choline-releasing enzymic activity was observed after addition of glycerophosphocholine. Both of these phosphoric diester hydrolase activities were activated to different extents by different concentrations of calcium ions. Differences between the two activities were also observed on inhibition by barium and phosphate ions. These distinct, choline-yielding, reactions which occur in the cytoplasm of red blood cells may be involved in the regulation of the levels of membrane phosphatidylcholine.

Regulation of intracellular free calcium in normal murine keratinocytes

Cultured normal murine keratinocytes maintain a basal cell phenotype in medium with a Ca2+ concentration of 0.05 mM and differentiate when exposed for 28-48 h to medium supplemented with extracellular Ca2+ greater than 0.10 mM. Previous studies have documented Ca2+ activation of signaling pathways in the plasma membrane and tightly regulated cellular responses to small incremental changes in extracellular Ca2+. To determine if changes in free cytosolic calcium (Cai) are associated with these early signaling events, digital image analysis of fura-2-loaded keratinocytes was used to measure Cai in individual cells. Basal keratinocytes in 0.05 mM Ca2+ display a biphasic Cai increase when exposed to greater than 0.1 mM Ca2+ in serum-containing medium. These separate phases were controlled by different media components. Initial peak Cai occurred rapidly (within 60 s), was transient (lasting less than 5 min), and resulted from release of 10-20% of total intracellular Ca2+ stores. Peak Cai depended on serum concentration and was independent of extracellular Ca2+. This transient Cai response was lost as keratinocytes differentiated. Plateau Cai level was sustained (greater than 24 h) and depended on extracellular Ca2+, but not serum. The magnitude of plateau Cai increased incrementally following increases in extracellular Ca2+ as small as 0.02 mM. A similar biphasic Cai increase was noted in cultures of murine dermal fibroblasts stimulated by 1.2 mM Ca2+ and serum. However, fibroblasts did not lose the serum response in high-Ca2+ medium, and plateau Cai was not sensitive to small changes in extracellular Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cholecystokinin on cytosolic calcium in human pancreatic cancer cells

Cholecystokinin (CCK) has been shown to increase cytosolic calcium and stimulate enzyme release from pancreatic acinar cells and a rat acinar cell line, AR42J. CCK is also trophic to normal pancreas and pancreatic cancer; however, the cellular mechanisms which regulate CCK-stimulated growth are unknown. The effect of CCK on intracellular calcium was evaluated in four human pancreatic cancer cell lines known to grow in response to CCK but not secrete enzymes (SW-1990, MIA PaCa-2, BXPC-3 and PANC-1) and a rat acinar cell line (AR42J) shown to secrete enzymes but not grow with CCK. By using single cell fluorescence microscopy in fura-2 loaded cells, intracellular calcium [Ca2+]i was measured. After obtaining baseline fluorescent cell images, synthetic CCK-octapeptide (CCK8) was added to the cells and images of cell fluorescence captured. [Ca2+]i of the rat acinar cells increased (603%) over the baseline within the first minute after the addition of CCK (4.10(-13) M to 4.10(-10) M) in 77% of cells tested. In contrast [Ca2+]i failed to significantly change in the human cancer cells treated with CCK. To further localize the defect in hormone signal transduction in cancer cells, cells were suspended in low calcium media and the plasma membranes were selectively permeabilized with digitonin. Media free calcium concentration was continuously monitored by fura-2 fluorescence. Addition of inositol 1,4,5-trisphosphate (IP3) resulted in a marked increase in medium calcium concentration indicating IP3 was capable of releasing calcium from intracellular stores in both the AR42J rat acinar cell line and in the human pancreas cancer cell lines. In conclusion, CCK does not increase cytosolic calcium in human pancreatic cancer cells in contrast to rat acinar cells although all contain IP3-sensitive intracellular Ca2+ pools. Our results suggest that growth promoting and secretory effects of CCK on pancreatic cells may occur via two independent signalling pathways.

The synthesis and resolution of (+/-)-1,5,6-tri-O-benzyl-myo-inositol

Racemic 1,5,6-tri-O-benzyl-myo-inositol was prepared by five routes and converted into 1,5,6-tri-O-benzyl-2,3-O-isopropylidene-myo-inositol, the camphanates of which were readily separated by chromatography. The absolute configurations of the chiral derivatives were established by their conversion into the known chiral 1,4,5,6-tetra-O-benzyl-myo-inositols. 1D-1,5,6-Tri-O-benzyl-2,3-O-isopropylidene-myo-inositol was converted into 1D-1,3,5,6-tetra-O-benzyl-myo-inositol and thence into 1D-2,4-di-O-methyl-myo-inositol. 1D-1,5,6-Tri-O-benzyl-myo-inositol was converted into 1D-1,2,5,6-tetra-O-benzyl-myo-inositol, the diacetate of which is a chiral analogue of "thermosalient crystals". The potential of the above compounds for the synthesis of natural products is surveyed.

Expression of murine epidermal differentiation markers is tightly regulated by restricted extracellular calcium concentrations in vitro

Epidermal differentiation is characterized by a series of coordinated morphological and biochemical changes which result in a highly specialized, highly organized, stratified squamous epithelium. Among the specific markers expressed in differentiating epidermis are (a) two early spinous cell proteins, keratins 1 and 10 (K1 and K10); and (b) two later granular cell proteins, filaggrin and a cornified envelope precursor (CE). In vitro, epidermal basal cells are selectively cultured in 0.05 mM Ca2+ medium, and terminal differentiation is induced when the Ca2+ concentration is increased to 1 mM. However, only a small fraction of the cells express the markers K1, K10, CE, or filaggrin in the higher Ca2+ medium. To explore the factors required for marker expression, cultured epidermal cells were exposed to intermediate Ca2+ concentrations and extracts were analyzed using specific antibody and nucleic acid probes for the four markers of interest. These studies revealed that marker expression was enhanced at a restricted concentration of Ca2+ in the medium of 0.10-0.16 mM. At this Ca2+ concentration, both protein and mRNA levels for each marker were substantially increased, whereas at higher or lower Ca2+ concentrations they were diminished or undetected. The percentage of cells expressing each marker was increased two- to threefold in the permissive Ca2+ medium as determined by immunofluorescence analysis. This optimal level of Ca2+ was required both to initiate and sustain marker expression. At the permissive Ca2+ concentration, expression of the markers was sequential and similar to the order of appearance in vivo. K1 was expressed within 8-12 h and K10 was expressed in the ensuing 12-24-h period. CE and filaggrin were expressed in the subsequent 24 h. Inhibition of K1 expression by cycloheximide suggested that an inducible protein was involved. Other investigators have determined that a shallow Ca2+ gradient exists in epidermis, where the basal cells and spinous cells are in a Ca2+ environment substantially below serum Ca2+ levels. These in vitro results suggest that the Ca2+ environment is a fundamental regulator of expression of epidermal differentiation markers and provide an explanation for the existence of the Ca2+ gradient in vivo.