Calcium mobilisation modulates growth of lens cells

Screening pathogenic genes in oral squamous cell carcinoma based on the mRNA expression microarray data

Oral squamous cell carcinoma (OSCC) is one of the most common malignancies and its survival rate has barely improved over the past few decades. The purpose of this study was to screen pathogenic genes of OSCC via microarray analysis. The mRNA expression microarray datasets (GSE2280 and GSE3524) were downloaded from the Gene Expression Omnibus (GEO) database. In GSE2280, there were 22 OSCC samples without metastasis and 5 OSCC samples with lymph node metastasis. In GSE3524, there were 16 OSCC samples and 4 normal tissue samples. The differentially expressed genes (DEGs) in OSCC samples with lymph node metastasis compared with those without metastasis (named as DEGs-1), and the DEGs in OSCC samples compared with normal tissue samples (named as DEGs-2), were obtained via limma package. The Database for Annotation, Visualization and Integrated Discovery (DAVID) was used to perform the functional enrichment analyses of DEGs-1 and DEGs-2. The miRNA-gene pairs of overlaps among DEGs were screened out with the TargetScan database, and the miRNA-gene regulated network was constructed by Cytoscape software. A total of 233 and 410 DEGs were identified in the sets of DEGs-1 and DEGs-2, respectively. DEGs-1 were enriched in 188 Gene Ontology (GO) terms and 8 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, and DEGs-2 were enriched in 228 GO terms and 6 KEGG pathways. In total, 126 nodes and 135 regulated pairs were involved in the miRNA-gene regulated network. Our study indicated that transglutaminase 2 (TGM2) and Islet 1 (ISL1) may be biomarkers of OSCC and their metastases. Moreover, it provided some potential pathogenic genes (e.g. P2RY2 and RAPGEFL1) in OSCC.

P2X and P2Y receptors—role in the pathophysiology of the nervous system

Purinergic signalling plays a crucial role in proper functioning of the nervous system. Mechanisms depending on extracellular nucleotides and their P2 receptors also underlie a number of nervous system dysfunctions. This review aims to present the role of purinergic signalling, with particular focus devoted to role of P2 family receptors, in epilepsy, depression, neuropathic pain, nervous system neoplasms, such as glioma and neuroblastoma, neurodegenerative diseases like Parkinson’s disease, Alzheimer’s disease and multiple sclerosis. The above-mentioned conditions are associated with changes in expression of extracellular ectonucleotidases, P2X and P2Y receptors in neurons and glial cells, as well as releasing considerable amounts of nucleotides from activated or damaged nervous tissue cells into the extracellular space, which contributes to disturbance in purinergic signalling. The numerous studies indicate a potential possibility of using synthetic agonists/antagonists of P2 receptors in treatment of selected nervous system diseases. This is of particular significance, since numerous available agents reveal a low effectiveness and often produce side effects.

Muscarinic receptor agonists and antagonists: effects on ocular function

Muscarinic agonists act mainly via muscarinic M₃ cholinoceptors to cause contraction of the iris sphincter, ciliary muscle and trabecular meshwork as well as increase outflow facility of aqueous humour. In the iris dilator, the effect of muscarinic agonists is species dependent but is predominantly relaxation via muscarinic M₃ receptors. In the conjunctiva, muscarinic agonists stimulate goblet cell secretion which contributes to the protective tear film. Muscarinic M₂ and M₃ receptors appear mainly involved. In the lens muscarinic agonists act via muscarinic M₁ receptors to produce depolarization and increase [Ca(2+)](i). All five subtypes of muscarinic receptor are present in the retina. In the developing retina, acetylcholine appears to limit purinergic stimulation of retinal development and decrease cell proliferation. In the adult retina acetylcholine and other muscarinic agonists may have complex effects, for example, enhancing light-evoked neuronal firing in transient ON retinal ganglion cells and inhibiting firing in OFF retinal ganglion cells. In the lacrimal gland, muscarinic agonists activate M₃ receptors on secretory globular acinar cells to stimulate tear secretion and also cause contraction of myoepithelial cells. In Sjögren's syndrome, antibodies to the muscarinic M₃ receptor disrupt normal gland function leading to xerophthalmia although the mechanism of action of the antibody is still not clear. Atropine and pirenzepine are useful in limiting the development of myopia in children probably by an action on muscarinic receptors in the sclera, although many other muscarinic receptor antagonists are not effective.

Regulation of cytosolic phospholipase A2 (cPLA2alpha) and its association with cell proliferation in human lens epithelial cells

PURPOSE

To investigate the molecular mechanism for cytosolic phospholipase A2 (cPLA(2)α) regulation and its association to platelet-derived growth factor (PDGF)-induced cell proliferation.

METHODS

cPLA(2)α was examined using human lens epithelial (HLE) B3 cells. Reactive oxygen species (ROS) generation induced by PDGF was analyzed by luminescence assay. Cell proliferation was measured by cell counting and by BrdU assay. Human cPLA(2)α gene was cloned via RT-PCR followed by site-directed mutagenesis to construct HLE B3 cells expressing either inactive cPLA(2)α enzyme with S228A mutation (S228A), or cPLA(2)α truncated at the calcium-binding C2 domain (C2D). Activity of cPLA(2)α was measured by arachidonic acid (AA) release from cell membranes using [(3)H]-arachidonic acid prelabeled cells. The effect of intracellular calcium level on cPLA(2)α function was examined by treating cells with ionomycin (calcium influx), thapsgargin (endoplasmic reticulum [ER] calcium store release) or 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis (BAPTA; calcium chelator). Activation of extracellular signal-regulated kinases (ERK), JNK, p38, or Akt was detected by Western blot analysis using specific antibodies.

RESULTS

S228A mutant showed suppressed PDGF-induced reactive oxygen species generation, ERK and JNK activation (no effect on p38 or Akt), and cell proliferation in comparison with the vector alone (Vec) control. Calcium-binding C2 domain cells lost the ability of membrane translocation and activation of cPLA(2)α. PDGF cell signaling was calcium-dependent, and the calcium was supplied either from the external flux or endoplasmic reticulum store. However, enrichment of cellular calcium not only augmented PDGF function, but also demonstrated a cPLA(2)α-dependent calcium-signaling cascade that led to cell proliferation.

CONCLUSIONS

cPLA(2)α is regulated by calcium mobilization and mitogen-activated protein kinases (MAPK) activation. Both PDGF mitogenic action and calcium signaling are cPLA(2)α-dependent.

The mechanisms of calcium homeostasis and signalling in the lens

Excessive Ca(2+) can be detrimental to cells and raised levels of Ca(2+) in human lenses with cortical cataract have been found to play a major role in the opacification process. Ca(2+) homeostasis is therefore, recognised as having fundamental importance in lens pathophysiology. Furthermore, Ca(2+) plays a central role as a second messenger in cell signalling and mechanisms have evolved which give cells exquisite control over intracellular Ca(2+) ([Ca(2+)](i)) via an array of specialised regulatory and signalling proteins. In this review we discuss these mechanisms as they apply to the lens. Ca(2+) levels in human aqueous humour are approximately 1 mM and there is a large, 10,000 fold, inwardly directed gradient across the plasma membrane. In the face of such a large gradient highly efficient mechanisms are needed to maintain low [Ca(2+)](i). The Na(+)/Ca(2+) exchanger (NCX) and plasma membrane Ca(2+)-ATPase (PMCA) actively remove Ca(2+) from the cells, whereas the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) sequesters Ca(2+) in the endoplasmic reticulum (ER) Ca(2+) store. In lens epithelial cells the dominant role is played by the ATPases, whilst in the fibre cells NCX activity appears to be more important. Usually, [Ca(2+)](i) can be increased in a number of ways. Ca(2+) influx through the plasma membrane, for example, is mediated by an array of channels with evidence in the lens for the presence of voltage-operated Ca(2+) channels (VOCCs), receptor-operated Ca(2+) channels (ROCCs) and channels mediating store-operated Ca(2+) entry (SOCE). Ca(2+) signalling is initiated via activation of G-protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTK) of which the lens expresses a surprisingly diverse array responding to various neurotransmitters, hormones, growth factors, autocoids and proteases. Downstream of plasma membrane receptors are IP(3)-gated channels (IP(3)Rs) and ryanodine receptors (RYRs) located in the ER, which when activated cause a rapid increase in [Ca(2+)](i) and these have also been identified in the lens. Through an appreciation of the diversity and complexity of the mechanisms involved in Ca(2+) homeostasis in normal lens cells we move closer to an understanding of the mechanisms which mediate pathological Ca(2+) overload as occurs in the process of cataract formation.

Nucleotides in ocular secretions: their role in ocular physiology

The eye is the sense organ that permits the detection of light owing to the existence of a sophisticated neuronal array, called the retina, which is responsive to photons. The correct functioning of this complex system requires the coordination of several intraocular structures that ultimately permit the perfect focusing of images on the neural retina. Light has to pass through different media: the tear, the cornea, aqueous humour, lens, and vitreous humour before it reaches the retina. Moreover, the composition and structure of some of these media can change due to several physiological mechanisms. Nucleotides are active components of the humours bathing relevant ocular structures. The tear contains nucleotides and dinucleotides that control the process of tearing, wound healing and protects of superficial infections. In the inner eye, the aqueous humour also presents a collection of mono and dinucleotides that affect pupil contraction, aqueous humour production and accommodation. Behind the lens and between this structure and the retina the vitreous humour can modify the physiology of the retinal cells, mostly the ganglion cells. By investigating the actions of nucleotides and dinucleotide present in the ocular humours we will be able not only to understand the functioning of the ocular structures but also to develop new pharmacological therapies for pathologies such as dry eye, glaucoma or retinal detachment.

AQP0-LTR of the CatFr mouse alters water permeability and calcium regulation of wild type AQP0

Aquaporin 0 (AQP0) is the major intrinsic protein of the lens and its water permeability can be modulated by changes in pH and Ca2+. The Cataract Fraser (Cat Fr) mouse accumulates an aberrant AQP0 (AQP0-LTR) in sub-cellular compartments resulting in a congenital cataract. We investigated the interference of AQP0-LTR with normal function of AQP0 in three systems. First, we created a transgenic mouse expressing AQP0 and AQP0-LTR in the lens. Expression of AQP0 did not prevent the congenital cataract but improved the size and transparency of the lens. Second, we measured water permeability of AQP0 co-expressed with AQP0-LTR in Xenopus oocytes. A low expression level of AQP0-LTR decreased the water permeability of AQP0, and a high expression level eliminated its calcium regulation. Third, we studied trafficking of AQP0 and AQP0-LTR in transfected lens epithelial cells. At low expression level, AQP0-LTR migrated with AQP0 toward the cell membrane, but at high expression level, it accumulated in sub-cellular compartments. The deleterious effect of AQP0-LTR on lens development may be explained by lowering water permeability and abolishing calcium regulation of AQP0. This study provides the first evidence that calcium regulation of AQP0 water permeability may be crucial for maintaining normal lens homeostasis and development.

Growth factor receptor signalling in human lens cells: role of the calcium store

In the human lens, stimulation of tyrosine-kinase coupled growth factor receptors such as epidermal growth factor receptor (EGFR) can induce calcium release from endoplasmic reticulum (ER) stores. The present study investigated the impact of calcium store inactivation on EGFR signalling, cell growth and death in a well-characterised human lens cell line (FHL124). FHL124 cells were routinely cultured in Eagle's minimum essential medium (EMEM) supplemented with 10% foetal calf serum (FCS) and seeded on 24-well plates (DNA and protein synthesis), tissue culture dishes (growth assay, western immunoblot), and glass coverslips (immunocytochemistry). DNA and protein synthesis rates were quantified by measuring the incorporation of (3)H-thymidine and (35)S-methionine into FHL124 cells in serum-free EMEM or EMEM supplemented with thapsigargin (Tg) (100 nM and 1 microM). Longer-term growth was assessed by quantifying the increase in area over time of a circular patch of seeded cells. EGFR was identified using anti-EGFR mouse monoclonal antibody and visualised by fluorescence microscopy with ALEXA 488 conjugated secondary antibody. Programmed cell death was determined by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) assay method. Activation of the mitogen-activated protein kinase (MAPK) signalling protein extracellular signal-regulated kinase (ERK) and the cell cycle proteins CDK2 and P27(kip1) were detected by western immunoblot techniques. Inactivation by > or =100 nM Tg inhibited both protein and DNA synthesis although the effect on the latter was greatest. The cell cycle activator CDK2 was reduced by Tg, while the inhibitor P27(kip1) was increased along with the percentage of apoptotic cells. A single, maximal epidermal growth factor (EGF) (10 ng ml(-1)) exposure induced receptor internalization and increased ERK phosphorylation. Both internalisation and ERK activation were unaffected by the presence of Tg. However, reduced internalisation and ERK activation followed repeated EGF applications in the presence of Tg. Additionally, ERK activation by submaximal EGF concentrations was reduced by store depletion. An intact endoplasmic reticulum calcium store therefore plays a significant role in human lens cell survival and growth.

The metabotropic P2Y4 receptor participates in the commitment to differentiation and cell death of human neuroblastoma SH-SY5Y cells

Extracellular nucleotides exert a variety of biological actions through different subtypes of P2 receptors. Here we characterized in the human neuroblastoma SH-SY5Y cells the simultaneous presence of various P2 receptors, belonging to the P2X ionotropic and P2Y metabotropic families. Western blot analysis detected the P2X1,2,4,5,6,7 and P2Y1,2,4,6, but not the P2X3 and P2Y12 receptors. We then investigated which biological effects were mediated by the P2Y4 subtype and its physiological pyrimidine agonist UTP. We found that neuronal differentiation of the SH-SY5Y cells with dibutiryl-cAMP increased the expression of the P2Y4 protein and that UTP itself was able to positively interfere with neuritogenesis. Moreover, transient transfection and activation of P2Y4 also facilitated neuritogenesis in SH-SY5Y cells, as detected by morphological phase contrast analysis and confocal examination of neurofilament proteins NFL. This was concurrent with increased transcription of immediate-early genes linked to differentiation such as cdk-5 and NeuroD6, and activity of AP-1 transcription family members such as c-fos, fos-B, and jun-D. Nevertheless, a prolonged activation of the P2Y4 receptor by UTP also induced cell death, both in naive, differentiated, and P2Y4-transfected SH-SY5Y cells, as measured by direct count of intact nuclei and cytofluorimetric analysis of damaged DNA. Taken together, our data indicate that the high expression and activation of the P2Y4 receptor participates in the neuronal differentiation and commitment to death of SH-SY5Y cells.

Sodium-calcium exchange influences the response to endothelin-1 in lens epithelium

Studies were conducted to examine the possible involvement of Na+-Ca2+ exchanger in determining the magnitude of the endothelin-1 (ET-1)-receptor-mediated calcium signal in porcine lens epithelial cells. Cytoplasmic calcium concentration was measured in primary cultured cells loaded with Fura-2. ET-1 (100 nM) caused cytoplasmic calcium to increase transiently to approximately 250 nM from a baseline of approximately 65 nM. The calcium increase decayed to a sustained plateau 35-45 nM above the baseline. Both the peak and plateau component of the ET-1 calcium response were abolished by PD145065, an ET receptor antagonist, and by cyclopiazonic acid (CPA) (10 microM). In calcium-free bathing solution, only the plateau was abolished. In the presence of ouabain, low-sodium bathing solution or bepridil, a sodium-calcium exchange inhibitor, peak height more than doubled. Bepridil also increased the peak height of the calcium response to ATP. The half-time for decay of the ET-1 and ATP calcium peak was increased several folds by bepridil, ouabain and low-sodium conditions. Measurements of ionomycin-releasable calcium suggested calcium store size was not increased in bepridil-treated cells. Taken together findings suggest inhibition of sodium-calcium exchange increases the magnitude of the receptor-initiated store-release phase of the ET-1 calcium signaling response as the result of impaired calcium clearance from the cytoplasm.

Regulation of sarco/endoplasmic Ca2+ -ATPase expression by calcium in human lens cells

Maintenance of cellular calcium levels is critical to cell function. Loss of calcium homeostasis might be a contributing factor to the development of cataract in the lens. In lens epithelium, calcium is involved in cell signaling and its precise regulation is vital. In this study, we investigated the regulation of sarco/endoplasmic reticulum Ca(2+)-ATPase2b (SERCA2b) and SERCA3 isoform expression in cultured epithelial B-3 cells from human lenses. Both mRNA and membrane proteins samples were collected for semi quantitative RT-PCR using GAPDH as a control. Western blot analyses were performed on membrane samples.Thapsigargin, a SERCA isoform inhibitor which causes increased cytosolic levels elicited dose-and time-dependent up-regulation of SERCA3 at both mRNA and protein levels; SERCA2b expression was unaffected. Both EGTA and actinomycin partially inhibited the thapsigargin-induced SERCA3 up-regulation. These results indicate that the up-regulation of SERCA3 by thapsigargin is dependent on a calcium-mediated pathway that is likely to occur at the transcription level.

Extracellular nucleotides inhibit growth of human oesophageal cancer cells via P2Y(2)-receptors

Extracellular ATP is known to inhibit growth of various tumours by activating specific purinergic receptors (P2-receptors). Since the therapy of advanced oesophageal cancer is unsatisfying, new therapeutic approaches are mandatory. Here, we investigated the functional expression and potential antiproliferative effects of P2-purinergic receptors in human oesophageal cancer cells. Prolonged incubation of primary cell cultures of human oesophageal cancers as well as of the squamous oesophageal cancer cell line Kyse-140 with ATP or its stable analogue ATP gamma S dose-dependently inhibited cell proliferation. This was due to both an induction of apoptosis and cell cycle arrest. The expression of P2-receptors was examined by RT-PCR, immunocytochemistry, and [Ca(2+)](i)-imaging. Application of various extracellular nucleotides dose-dependently increased [Ca(2+)](i). The rank order of potency was ATP=UTP>ATP gamma S>ADP=UDP. 2-methylthio-ATP and alpha,beta-methylene-ATP had no effects on [Ca(2+)](i). Complete cross-desensitization between ATP and UTP was observed. Moreover, the phospholipase C inhibitor U73122 dose-dependently reduced the ATP triggered [Ca(2+)](i) signal. The pharmacological features strongly suggest the functional expression of G-protein coupled P2Y(2)-receptors in oesophageal squamous cancer cells. P2Y(2)-receptors are involved in the antiproliferative actions of extracellular nucleotides. Thus, P2Y(2)-receptors are promising target proteins for innovative approaches in oesophageal cancer therapy.

Effects of long-term acidification of extracellular pH on ATP-induced calcium mobilization in rabbit lens epithelial cells

ATP-induced calcium (Ca2+) mobilization was investigated in rabbit lens epithelial cells that had been cultured in a medium with pH of 7.4 (group 1), 7.2 (group 2), or 7.0 (group 3) for 10 to 21 d. Intracellular free Ca2+ ([Ca2+]i and pH (pHi) were measured by using fluorescent dyes, fura-2 and BCECF, respectively. The long-term acidification decreased the pHi to 7.15 +/- 0.01, from 7.22 +/- 0.01, in group 2 and to 7.09 +/- 0.01 in group 3. The administration of 10 micromol/l ATP produced an initial peak followed by a sustained increase in [Ca2+]i in the lens cells of group 1. Both the initial peak and the sustained increase in [Ca2+]i were enhanced in groups 2 and 3. The initial peak was abolished by pretreatment with 1 micromol/l thapsigargin, an ER Ca2+ pump inhibitor, but was not affected by the removal of extracellular Ca2+. On the other hand, the sustained increase was suppressed either by the thapsigargin treatment or by the Ca2+ removal. Treatment with only thapsigargin caused a sustained increase in [Ca2+]i that was greater in group 3 than in group 1. These results suggest that (1) the ATP-induced initial peak in [Ca2+]i is due to Ca2+ release from the intracellular stores, (2) the sustained increase in [Ca2+]i is mediated through either Ca2+ influx from the extracellular space or Ca2+ release from the store triggered by the Ca2+ influx, and (3) long-term, moderate acidification enhances both the initial peak and the sustained increase in [Ca2+)]i in rabbit lens epithelial cells. One possible mechanism of the ATP-induced Ca2+ influx seems to be a capacitative Ca2+ entry pathway.

Induction of matrix metalloproteinases 2 and 9 following stress to the lens

Matrix metalloproteinase 2 and 9 (MMP-2 and 9, also known as gelatinase A and B) have been implicated in a number of eye diseases, but their possible involvement in lens pathology is yet to be determined. In the present study, we therefore investigated a possible role of matrix metalloproteinases in cataract and posterior capsule opacification. Whole porcine lenses were removed from the eye and cultured in either Eagles Minimum Essential Medium (EMEM) or EMEM supplemented with 1 m M hydrogen peroxide. The medium was sampled and changed every 2 days. On some occasions a sham cataract operation was performed on cultured lenses. The resulting capsular bag was secured to a Petri dish and cultured in EMEM. Culture media from all preparations were analysed for MMP-2 and 9 activity by gelatin zymography. Media samples from lenses which maintained clarity over the 6 day culture period did not display any detectable gelatinolytic activity. However, media from cataractous lenses demonstrated a gelatinolytic band, which had similar molecular weights to the pro-form of MMP-2. In addition to this band, bands with a similar molecular weight to pro-MMP-9 and its dimeric form were also detected in samples obtained from capsular bag preparations within 24 hr. The data presented indicate that normal lenses have undetectable gelatinase activity. However, there is an associated expression of gelatinases with pathological states of the lens, and therefore gelatinase expression could play an important role in cataractogenesis and posterior capsule opacification.

Calcium cell signalling and cataract: role of the endoplasmic reticulum

The lens possesses an impressive array of G-protein receptors that are coupled to the release of intracellular calcium. They include members of the muscarinic, adrenergic and purinergic families and activation of the former has been implicated in cataract for some time. There are several possible mechanisms whereby activation of such receptors could give rise to cataract. A prolonged increase in intracellular calcium would be expected to activate proteases such as calpain and so could induce unscheduled and irreversible breakdown of important structural proteins. It has recently been shown that activation of G-protein receptors also modulates lens cell growth, and any interference with the highly controlled pattern of cell growth and development within the lens is also likely to have catastrophic consequences. If the calcium store is totally inactivated in lens cells, for example by exposure to thapsigargin, then growth ceases. This finding provides a means of inhibiting the lens cell growth which leads to posterior capsular opacification (PCO). For example, it has been shown that thapsigargin-coated intraocular lenses totally inhibit lens cell growth within cultured capsular bags, and if this technology could be transferred to the clinic then it could provide a simple and relatively inexpensive means of preventing PCO.

Effects of ATP and its analogues on [Ca2+]i dynamics in the rabbit corneal epithelium

Adenosine-5'-triphosphate (ATP) plays a pivotal role in various tissues as an extracellular transmitter. ATP released from nerve endings and/or damaged cells may elicit reactions in adjacent cells. To identify such reactions, we investigated the dynamics of the intracellular calcium ion concentrations ([Ca2+]i) in the rabbit corneal epithelium during ATP-stimulation. Intact epithelial sheets isolated from corneal tissue were loaded with Fura-2, and [Ca2+]i dynamics in each cell layer were analyzed using a digital imaging system (Argus 50/CA). Normal architecture was preserved, suggesting that functional integrity remained intact. Perfusion with HEPES-buffered Ringer's solution containing ATP (10 microM) and uridine-5'-triphosphate (UTP; 10 microM) caused a biphasic [Ca2+]i increase in the superficial layer that manifested itself as a rapid initial spike followed by a long-lasting plateau phase. Adenosine-5'-diphate (10 microM) elevated the [Ca2+]i level, but induced only the initial spike, which was smaller than those induced by ATP and UTP. Adenosine (10 microM) did not elicit any [Ca2+]i changes in the epithelial cells. Suramin (10 microM; a P2 receptor antagonist) blocked the ATP-induced [Ca2+]i increase, whereas the P2X receptor agonists, alpha, beta-methylene ATP (10 microM), 2-methyl-thio ATP (10 microM) and Benzoylbenzoyl ATP (10 microM), did not elicit any increases in [Ca2+]i. In the basal cell layer, ATP-induced [Ca2+]i dynamics were biphasic, while oscillatory fluctuations of [Ca2+]i were induced in the wing cells of the mid layer of the corneal epithelium by ATP stimulation. Ca2+ oscillations were sometimes synchronized among adjacent wing cells, but these waves did not propagate to other cell layers. These results suggest that extracellular ATP elicits a [Ca2+]i increase mainly via P2Y receptors. In addition, synchronized Ca2+ oscillation in the wing cell layer indicates that intracellular events may spread to neighboring cells within the layer.

Thapsigargin inhibits a potassium conductance and stimulates calcium influx in the intact rat lens

1. An increase in lens cell calcium has long been associated with cortical cataract. Recently, it has been shown that thapsigargin induces a rise in lens cell calcium by release from endoplasmic reticulum stores. The effects of this rise on the optical and membrane characteristics of the lens were studied in the isolated rat lens. 2. The electrical characteristics of the isolated, perifused rat lens were measured using a two-internal microelectrode technique that permits measurement of plasma membrane conductance (Gm), membrane potential (Vm) and junctional conductance in the intact lens. 3. Thapsigargin (1 microM) induced a rapid overall depolarization of Vm that was accompanied by first a decrease and then an increase in Gm. 4. Replacing external Na+ with tetraethylammonium (TEA) abolished the decrease in Gm. However, a transient increase phase was still observed. 5. The changes in conductance were further characterized by measuring 22Na+ and 45Ca2+ influxes into the isolated lens. Thapsigargin (1 microM) induced a transient increase in 45Ca2+, but did not affect Na+ influx. 6. The Ca2+ channel blocker La3+ (10 microM) totally inhibited the thapsigargin-induced Ca2+ influx. It also blocked the increase in Gm observed in control and in Na+-free-TEA medium. In the absence of external calcium, thapsigargin induced a small depolarization in Vm. 7. These data indicate that thapsigargin induces both a decrease in K+ conductance and an increase in Ca2+ conductance. These probably result from release of stored Ca2+ and subsequent activation of store-operated Ca2+ channels (capacitative Ca2+ entry). 8. Thapsigargin application over the time course of these experiments (24 h) had no effect on junctional conductance or on the transparency of the lens.

Expression of functional P2-purinergic receptors in primary cultures of human colorectal carcinoma cells

Primary cell cultures of human colorectal carcinomas were established and characterized immunocytochemically. In the isolated cancer cells intracellular Ca2+ concentrations ([Ca2+]i) were measured by the fura-2 method. Stimulation with either extracellular ATP or UTP caused a biphasic rise of [Ca2+]i in a dose-dependent manner and cross-desensitization between both nucleotides was observed. The rank order of potency was ATP >== UTP > ATP-gamma-S > ADP > adenosine which is characteristic for a P2U-receptor subtype. Selective agonists of P1-, or P2X- purinoceptors had no effect on [Ca2+]i. The initial rise in [Ca2+]i was independent of extracellular calcium [Ca2+]e, whereas the second phase was not observed under [Ca2+]e-free conditions suggesting a capacitative Ca2+-entry-mechanism. Intracellular Ca2+ mobilization was proven by use of the Ca2+-ATPase inhibitor thapsigargin. P2U-specific mRNA could be detected by RT-PCR in both colorectal tumor tissues and in the human colorectal cancer cell line HT 29. In HT 29 cells, the hydrolysis-resistant ATP analog ATP-gamma-S inhibited cell proliferation and, also, induced apoptosis in a dose-dependent manner. Thus, human colorectal cancer cells express functional P2U-receptors which may play a role in the regulation of cell proliferation and apoptosis.

Expression of HGF/SF in mesothelioma cell lines and its effects on cell motility, proliferation and morphology

The expression of hepatocyte growth factor/scatter factor (HGF/SF) was studied in 12 mesothelioma cell lines characterized by either an epithelioid or a fibroblast-like phenotype. Conditioned media from these lines were analysed by bioassay and ELISA, and HGF/SF was detected in three cell lines, all with a fibroblast-like or mixed morphology. None of eight epithelioid cell lines expressed the factor. Thus, for these cell lines, the ability to secrete HGF/SF correlated with the cell phenotype. Following on from these observations, two cell lines, BR and BT, with a fibroblast-like and an epithelioid phenotype, respectively, were further investigated. Both cell lines expressed the Met receptor but only BR secreted HGF/SF. Both cell lines responded to exogenous HGF/SF treatment by a change of morphology but in different ways: BR became more elongated and bipolar, while BT formed more spread-out cell colonies. HGF/SF acted as a paracrine effector on the epithelioid BT cells and stimulated both cell-spreading and proliferation. Interestingly, BT cells spread but did not scatter in response to exogenous HGF/SF. In contrast BR cells showed only some stimulation of cell motility with HGF/SF and no increase in cell proliferation was observed. Because HGF/SF was previously found in the pleural effusion fluids of patients with malignant mesothelioma and in paraffin-embedded tumour tissues, it is concluded that HGF/SF may well stimulate the growth and spread of malignant mesothelioma in vivo by paracrine and/or autocrine mechanisms.

Thapsigargin-coated intraocular lenses inhibit human lens cell growth

Cataract is responsible for rendering several million people blind throughout the world and is also by far the most common cause of low visual acuity. Although cataract surgery is common, routine and effective, posterior capsule opacification (PCO) occurs in 30-50% of patients following modern cataract surgery. This condition arises from stimulated cell growth within the capsular bag after surgery. The resulting decline in visual acuity requires expensive laser treatment, and PCO therefore prevents modern cataract surgery from being carried out routinely in underdeveloped countries. The present study, using a human lens capsular bag culture system, has confirmed that cells from a wide age range of donors proliferate in the absence of added serum protein and explains why PCO is such a common problem even in aged patients. This study also provides one possible solution for PCO by using polymethylmethacrylate (PMMA) implanted intraocular lenses as a drug delivery system. PMMA lenses coated with thapsigargin, a hydrophobic inhibitor of endoplasmic reticulum (ER) (Ca2+)-ATPase, greatly reduced cell growth in the capsular bag at relatively low coating concentrations (200 nM) but, more significantly, induced total cell death of the residual anterior epithelial cells at higher concentrations (>2 microM).