Suppression of ICE and apoptosis in mammary epithelial cells by extracellular matrix

A novel matrix metalloproteinase gene (XMMP) encoding vitronectin-like motifs is transiently expressed in Xenopus laevis early embryo development

To study the role of matrix metalloproteinases (MMPs) in early vertebrate development, we cloned cDNAs for six different MMPs from the frog Xenopus laevis embryos at different stages of development and describe here a novel MMP called XMMP. Xenopus XMMP has 604 amino acids including a putative signal peptide of 22 residues. At the carboxyl-terminal end of the propeptide, XMMP has a 37-amino acid-long insertion domain containing a segment that is 38% identical with a rat vitronectin sequence between residues 108-135. Following this domain is an RRKR motif, a putative cleavage site for intracellular activation by furin proteinases. XMMP lacks a proline-rich linker peptide, or hinge region, typically found in other MMPs between the catalytic domain and carboxyl-terminal "hemopexin/vitronectin-like" domain. In XMMP, the carboxyl-terminal domain is composed of four tandem repeats that are 21-33% identical to a sequence (residues 213-264) encoded by vitronectin exon-5. Interestingly, XMMP gene is transiently expressed during Xenopus embryo development. XMMP mRNA of 3.0 kilobase pairs was undetected in the blastula stage embryo, induced in gastrula embryo, expressed in neurula embryo, and then down-regulated in pretailbud embryo. In comparison, other Xenopus MMP genes that we have cloned show a different developmental regulation. In blastula embryo, the only MMP gene expressed was found to be 92-kDa type IV collagenase, which was also expressed in the gastrula, neurula, and pretailbud embryos. Expression of stromelysin-1, stromelysin-3, and two different membrane type-MMPs was first detected in the neurula and pretailbud embryos. These results suggest that MMPs and the novel XMMP reported here play a role in Xenopus early development.

Overexpression of the integrin-linked kinase promotes anchorage-independent cell cycle progression

Cell adhesion to substratum has been shown to regulate cyclin A expression as well as cyclin D- and E-dependent kinases, the latter via the up-regulation of cyclin D1 and the down-regulation of cyclin-Cdk inhibitors p21 and p27, respectively. This adhesion-dependent regulation of cell cycle is thought to be mediated by integrins. Here we demonstrate that stable transfection and overexpression of the integrin-linked kinase (ILK), which interacts with the beta1 and beta3 integrin cytoplasmic domains, induces anchorage-independent cell cycle progression but not serum-independent growth of rat intestinal epithelial cells (IEC18). ILK overexpression results in increased expression of cyclin D1, activation of Cdk4 and cyclin E-associated kinases, and hyperphosphorylation of the retinoblastoma protein. In addition, ILK overexpression results in the expression of p21 and p27 Cdk inhibitors with altered electrophoretic mobilities, with the p27 from ILK-overexpressing cells having reduced inhibitory activity. The transfer of serum-exposed IEC18 cells from adherent cultures to suspension cultures results in a rapid down-regulation of expression of cyclin D1 and cyclin A proteins as well as in retinoblastoma protein dephosphorylation. In marked contrast, transfer of ILK-overexpressing cells from adherent to suspension cultures results in continued high levels of expression of cyclin D1 and cyclin A proteins, and a substantial proportion of the retinoblastoma protein remains in a hyperphosphorylated state. These results indicate that, when overexpressed, ILK induces signaling pathways resulting in the stimulation of G1/S cyclin-Cdk activities, which are normally regulated by cell adhesion and integrin engagement.

Immunolocalization of the ICE/Ced-3–Family Protease, CPP32 (Caspase-3), in Non-Hodgkin's Lymphomas, Chronic Lymphocytic Leukemias, and Reactive Lymph Nodes

Immunohistochemical analysis of the apoptosis-effector protease CPP32 (Caspase-3) in normal lymph nodes, tonsils, and nodes affected with reactive hyperplasia (n = 22) showed strong immunoreactivity in the apoptosis-prone germinal center B-lymphocytes of secondary follicles, but little or no reactivity in the surrounding long-lived mantle zone lymphocytes. Immunoblot analysis of fluorescence-activated cell sorted germinal center and mantle zone B cells supported the immunohistochemical results. In 22 of 27 (81%) follicular small cleaved cell non-Hodgkin's B-cell lymphomas, the CPP32-immunopositive germinal center lymphocytes were replaced by CPP32-negative tumor cells. In contrast, the large cell component of follicular mixed cells (FMs) and follicular large cell lymphomas (FLCLs) was strongly CPP32 immunopositive in 12 of 17 (71%) and in 8 of 14 (57%) cases, respectively, whereas the residual small-cleaved cells were poorly stained for CPP32 in all FLCLs and in 12 of 17 (71%) FMs, suggesting that an upregulation of CPP32 immunoreactivity occurred during progression. Similarly, cytosolic immunostaining for CPP32 was present in 10 of 12 (83%) diffuse large cell lymphomas (DLCLs) and 2 of 3 diffuse mixed B-cell lymphomas (DMs). Immunopositivity for CPP32 was also found in the majority of other types of non-Hodgkin's lymphomas studied. Plasmacytomas were CPP32 immunonegative in 4 of 12 (33%) cases, in contrast to normal plasma cells, which uniformly contained intense CPP32 immunoreactivity, implying downregulation of CPP32 in a subset of these malignancies. All 12 peripheral blood B-cell chronic lymphocyte leukemia specimens examined were CPP32 immunopositive, whereas 3 of 3 small lymphocytic lymphomas were CPP32 negative, suggesting that CPP32 expression may vary depending on the tissue compartment in which these neoplastic B cells reside. The results show dynamic regulation of CPP32 expression in normal and malignant lymphocytes.

Immunolocalization of the ICE/Ced-3–Family Protease, CPP32 (Caspase-3), in Non-Hodgkin's Lymphomas, Chronic Lymphocytic Leukemias, and Reactive Lymph Nodes

Immunohistochemical analysis of the apoptosis-effector protease CPP32 (Caspase-3) in normal lymph nodes, tonsils, and nodes affected with reactive hyperplasia (n = 22) showed strong immunoreactivity in the apoptosis-prone germinal center B-lymphocytes of secondary follicles, but little or no reactivity in the surrounding long-lived mantle zone lymphocytes. Immunoblot analysis of fluorescence-activated cell sorted germinal center and mantle zone B cells supported the immunohistochemical results. In 22 of 27 (81%) follicular small cleaved cell non-Hodgkin's B-cell lymphomas, the CPP32-immunopositive germinal center lymphocytes were replaced by CPP32-negative tumor cells. In contrast, the large cell component of follicular mixed cells (FMs) and follicular large cell lymphomas (FLCLs) was strongly CPP32 immunopositive in 12 of 17 (71%) and in 8 of 14 (57%) cases, respectively, whereas the residual small-cleaved cells were poorly stained for CPP32 in all FLCLs and in 12 of 17 (71%) FMs, suggesting that an upregulation of CPP32 immunoreactivity occurred during progression. Similarly, cytosolic immunostaining for CPP32 was present in 10 of 12 (83%) diffuse large cell lymphomas (DLCLs) and 2 of 3 diffuse mixed B-cell lymphomas (DMs). Immunopositivity for CPP32 was also found in the majority of other types of non-Hodgkin's lymphomas studied. Plasmacytomas were CPP32 immunonegative in 4 of 12 (33%) cases, in contrast to normal plasma cells, which uniformly contained intense CPP32 immunoreactivity, implying downregulation of CPP32 in a subset of these malignancies. All 12 peripheral blood B-cell chronic lymphocyte leukemia specimens examined were CPP32 immunopositive, whereas 3 of 3 small lymphocytic lymphomas were CPP32 negative, suggesting that CPP32 expression may vary depending on the tissue compartment in which these neoplastic B cells reside. The results show dynamic regulation of CPP32 expression in normal and malignant lymphocytes.

Regulation of Bcl-xL expression in human keratinocytes by cell-substratum adhesion and the epidermal growth factor receptor

Cell-substratum adhesion is an essential requirement for survival of human neonatal keratinocytes in vitro. Similarly, activation of the epidermal growth factor receptor (EGF-R) has recently been implicated not only in cell cycle progression but also in survival of normal keratinocytes. The mechanisms by which either cell-substratum adhesion or EGF-R activation protect keratinocytes from programmed cell death are poorly understood. Here we describe that blockade of the EGF-R and inhibition of substratum adhesion share a common downstream event, the down-regulation of the cell death protector Bcl-xL. Expression of Bcl-xL protein was down-regulated during forced suspension culture of keratinocytes, concurrent with large-scale apoptosis. Similarly, EGF-R blockade was accompanied by down-regulation of Bcl-xL steady-state mRNA and protein levels to an extent comparable to that observed in forced suspension culture. However, down-regulation of Bcl-xL expression by EGF-R blockade was not accompanied by apoptosis; in this case, a second signal, generated by passaging, was required to induce rapid and large-scale apoptosis. These findings are consistent with the conclusions that (i) Bcl-xL represents a shared molecular target for signaling through cell-substrate adhesion receptors and the EGF-R, and (ii) reduced levels of Bcl-xL expression through EGF-R blockade lower the tolerance of keratinocytes for cell death signals generated by cellular stress.

Adhesion molecules in the glomerular mesangium

Experimental evidence indicates that extensive "cross-talk" exists between glomerular cells, extracellular matrix molecules and soluble mediator substances affecting the proliferative and secretory phenotype of glomerular mesangial cells. Both matrix and cytokines regulate mesangial cell behavior in vitro and in vivo after binding to specific cell surface receptors. It appears as if the concerted action of insoluble and soluble ligands on mesangial cells involves a reciprocal regulation of matrix molecules and cytokines as well as expression and affinity of their respective receptors. Elucidation of the potential biologic and clinical relevance of cell-matrix interactions in the glomerular mesangium represents a challenging goal in current kidney research. This brief review summarizes recent investigations concerning regulation of expression and function of adhesion molecules and matrix receptors in the mesangium. In addition to results from cell culture studies, descriptive findings on expression and regulation of adhesion molecules and their potential role for altered mesangial cell behavior in glomerular disease is considered.

Integrins as signaling molecules and targets for tumor therapy

Adhesion molecules include ligands and receptors. Together they provide cells with anchorage and traction for migration, and the receptors also mediate signals that control cell polarity, survival, growth, differentiation and gene expression. Integrins are a major group of versatile adhesion receptors that serve both adhesive and signaling functions. They possess shared and unique specifics both outside and inside the cell. Many of the integrins share an affinity toward the RGD recognition sequence in their extracellular matrix ligands, but are still capable of distinguishing different RGD-containing proteins. The shared signaling pathways are likely to include changes in intracellular Ca2+ and PIP2 concentrations, and the activation of protein kinase C and focal adhesion kinase. Examples of integrin-specific signaling include that the alpha v beta 3 integrin (vitronectin receptor) can potentiate the effects of insulin and certain other growth factors and that the alpha 5 beta 1 integrin (fibronectin receptor) supports cell survival in serum-free cultures by up-regulating the anti-apoptosis protein Bcl-2. Another integrin function is that some integrins, in particular alpha 5 beta 1, are necessary for fibronectin matrix formation. Overexpression of alpha 5 beta 1, which results in the assembly of additional fibronectin matrix, reduces tumorigenicity of cultured tumor cells. Systemic treatment of tumor-bearing mice with an artificially generated fibronectin matrix suppresses metastasis. These and other findings indicate that the ligand binding and signaling functions of integrins offer targets for new therapeutic approaches.

Modulation of cell proliferation by the integrin cytoplasmic domain

Integrin adhesion receptors modulate cell functions, including cell proliferation and survival. The beta 1C integrin, an alternatively spliced form of beta 1A, containing a unique cytoplasmic domain sequence, inhibits cell growth in vitro. In vivo, the expression of beta 1C correlates with a benign, nonproliferative phenotype in epithelial cells. The studies discussed in this article indicate that modulation of cell proliferation, in normal or pathological conditions, might be achieved by the regulated expression of variant integrin subunits.

Interaction between Alzheimer's disease beta A4 precursor protein (APP) and the extracellular matrix: evidence for the participation of heparan sulfate proteoglycans

The interaction between the Alzheimer amyloid precursor protein (APP) and an intact extracellular matrix (ECM), matrigel, obtained from Engelbreth-Holm-Swarm tumors was evaluated. Based on quantitative analyses of the binding data obtained from solid phase binding assays, two binding sites on the ECM were identified for [125I]-APP (with apparent Kd1 of 1.0 x 10(-11) M and Kd2 of 1.6 x 10(-9) M respectively). Over 70% of [125I]-APP was displaced by heparin and N-desulfated heparin but not by chondroitin sulfate. Pretreatment of matrigel with heparitinase decreased the binding of [125I]-APP by 80%. beta-amyloid peptides (residues 1-40, 1-28, and 1-16) containing a heparin binding domain also displaced 80% of bound [125I]-APP, which was totally displaced by intact APP. The binding of [125I]-APP to matrigel increased by 210% with a decrease in the pH. These observations suggest that [125I]-APP interacts mainly with heparan sulfate proteoglycan present in the ECM. The binding of [125I]-APP to individual ECM components was also analyzed. [125I]-APP was found to bind laminin and collagen type IV but not fibronectin. However, when these ECM constituents were combined, the extent of APP-binding decreased significantly, to levels comparable to those obtained with intact matrigel, suggesting that multiple interactions may occur between ECM constituents and [125I]-APP. The results are discussed in terms of APP function and amyloidogenesis.

Strategies for optimal synthesis and secretion of heterologous proteins in the methylotrophic yeast Pichia pastoris

Numerous heterologous proteins have been produced at greater than gram per liter levels in the methylotrophic yeast, Pichia pastoris, using the methanol oxidase promoter. The factors that drastically influence protein production in this system include: copy number of the expression cassette, site and mode of chromosomal integration of the expression cassette, mRNA 5'- and 3'-untranslated regions (UTR), translational start codon (AUG) context, A+T composition of cDNA, transcriptional and translational blocks, nature of secretion signal, endogenous protease activity, host strain physiology, media and growth conditions, and fermentation parameters. All these factors should be considered in designing an optimal production system. The inherent ability of P. pastoris to convert the zymogen (pro-enzyme) form of matrix metalloproteinases (MMP) into active mature forms (which tend to self-degrade, and in some instances also cause damage to cells), largely limits the use of this system for the production of MMP. However, this problem can be partly alleviated by co-expression of tissue inhibitor of MMP (TIMP-1).

Reversion of the malignant phenotype of human breast cells in three-dimensional culture and in vivo by integrin blocking antibodies

In a recently developed human breast cancer model, treatment of tumor cells in a 3-dimensional culture with inhibitory beta1-integrin antibody or its Fab fragments led to a striking morphological and functional reversion to a normal phenotype. A stimulatory beta1-integrin antibody proved to be ineffective. The newly formed reverted acini re-assembled a basement membrane and re-established E-cadherin-catenin complexes, and re-organized their cytoskeletons. At the same time they downregulated cyclin D1, upregulated p21(cip,wat-1), and stopped growing. Tumor cells treated with the same antibody and injected into nude mice had significantly reduced number and size of tumors in nude mice. The tissue distribution of other integrins was also normalized, suggesting the existence of intimate interactions between the different integrin pathways as well as adherens junctions. On the other hand, nonmalignant cells when treated with either alpha6 or beta4 function altering antibodies continued to grow, and had disorganized colony morphologies resembling the untreated tumor colonies. This shows a significant role of the alpha6/beta4 heterodimer in directing polarity and tissue structure. The observed phenotypes were reversible when the cells were disassociated and the antibodies removed. Our results illustrate that the extracellular matrix and its receptors dictate the phenotype of mammary epithelial cells, and thus in this model system the tissue phenotype is dominant over the cellular genotype.

Human vascular smooth muscle cells express interleukin-1beta-converting enzyme (ICE), but inhibit processing of the interleukin-1beta precursor by ICE

Local immunoregulatory processes during normal vascular biology or pathogenesis are mediated in part by the production of and response to cytokines by vessel wall cells. Among these cytokines interleukin (IL)-1 is considered to be of major importance. Although vascular smooth muscle (SMC) and endothelial cells (EC) expressed both IL-1alpha and IL-1beta as cell-associated, 33-kilodalton (kD) precursors, SMC neither contained detectable mature IL-1beta, nor processed recombinant IL-1beta precursor into its mature 17-kD form. Thus, we investigated the expression and function of IL-1beta-converting enzyme (ICE) in vascular cells. We demonstrate in processing experiments with recombinant IL-1 precursor molecules that EC processed IL-1beta, in contrast to SMC. Despite the failure of SMC to process IL-1beta, these cells expressed ICE mRNA, immunoreactive ICE protein, and the expected IL-1beta nucleotide sequence. The lack of processing was explained by our finding that extracts of SMC specifically and concentration dependently blocked processing of IL-1beta precursor by recombinant or native ICE. The initial biochemical characterization of the inhibitory activity showed that it is heat-labile, has a molecular size of 50-100 kD, and is associated to the cell membrane compartment. Inhibition of processing, i.e., activation of IL-1beta precursor by SMC may constitute a novel regulatory mechanism during normal vascular biology or pathogenesis of vascular diseases.

Ameliorative effect of MK-801 on retinal ischemia

The efficacy of MK-801, an N-methyl-D-aspartate receptor antagonist, was evaluated in a rat model of retinal ischemia induced by elevated intraocular pressure. Intraperitoneal injection of MK-801 at 0, 1, 3 and 10 mg/kg was given immediately after reperfusion. At 7 days after reperfusion, the inner retinal thickness, as measured from histologic sections of the retinas, of the 10 mg/kg treated group showed significant beneficial effect, while the other doses had no significant effect. Retinal ganglion cell counts on flat preparations of the retinas showed a beneficial dose dependent effect of MK-801 with the lowest dose showing no effect, 3 mg/kg showing marginal effects and 10 mg/kg showing significant effects. Intravitreal infusion of MK-801 during the ischemic period suppressed ischemia/reperfusion-induced internucleosomal DNA fragmentation measured at 18 hours after the insult as well as retinal tissue responses measured at 7 days. These findings suggested that the NMDA receptors may have an important role in ischemia-reperfusion insult as well as in mediating ischemia-induced apoptosis of retinal neurons. In addition, we demonstrated that pharmacological modulation of apoptotic cell death may affect the final tissue responses in vivo.

Mammary-derived signals activate programmed cell death during the first stage of mammary gland involution

Programmed cell death (PCD) of mammary alveolar cells during involution commences within hours of the end of suckling. Locally, milk accumulates within alveolar lumens; systemically, levels of lactogenic hormones fall. Four experimental models were used to define the role of local factors as compared with systemic hormones during the first and second stages of involution. In three models, milk release was disrupted in the presence of systemic lactogenic hormones: (i) sealing of the teats, (ii) mammary gland transplants that cannot release milk due to the absence of a teat connection, and (iii) inactivation of the oxytocin gene. The ability of systemic hormones to preserve lobular-alveolar structure without blocking PCD was illustrated using a fourth transgenic model of lactation failure. During the first stage of involution, local signals were sufficient to induce alveolar PCD even in the presence of systemic lactogenic hormones. PCD coincided with bax induction, decreased expression of milk proteins, block of prolactin signal transduction through Stat5a and 5b, and activation of Stat3. The two stages of mammary gland involution are regulated by progressive gain of death signals and loss of survival factors. This study demonstrates that genetic events that occur during the first reversible stage are controlled by local factors. These mammary-derived death signals are dominant over protective effects related to systemic hormone stimulation.

Identification of a novel antiapoptotic protein, GAM-1, encoded by the CELO adenovirus

We have developed a simple screening method to identify genes that mimic bcl-2 or adenovirus E1B 19K in enhancing cell survival after transfection and have used this method to identify such a gene in the avian adenovirus CELO. The gene encodes a novel 30-kDa nuclear protein, which we have named GAM-1, that functions comparably to Bcl-2 and adenovirus E1B 19K in blocking apoptosis. However, GAM-1 has no sequence homology to Bcl-2, E1B 19K, or any other known antiapoptotic proteins and thus defines a novel antiapoptotic function.

Cell anchorage regulates apoptosis through the retinoblastoma tumor suppressor/E2F pathway

Epithelial cells are dependent upon adhesion to extracellular matrix for survival. We show that loss of beta1 integrin receptor contact with extracellular matrix signals the inhibition of G1 cyclin-dependent kinase activity. This loss of cyclin-dependent kinase activity leads to accumulation of the hypophosphorylated (active) form of the retinoblastoma tumor suppressor protein (Rb). We present evidence that in epithelial cells deprived of matrix contact, the growth suppression signal elicited by hypophosphorylated Rb opposes stimulatory signals from serum growth factors, leading to a cell cycle conflict that triggers apoptosis. This apoptotic pathway is modulated by Bcl-2 through a novel mechanism that regulates Rb phosphorylation. We present evidence that the Rb-dependent apoptotic pathway functions in vivo in the apoptosis of the prostate glandular epithelium following castration.

Target protease specificity of the viral serpin CrmA. Analysis of five caspases

When ectopically expressed in animal cells, cytokine response modifier A (CrmA), a product of the cowpox virus, prevents programmed cell death initiated by a variety of stimuli. Since CrmA is a proteinase inhibitor, its target is probably a protease that promotes cell death. The identification of this target is crucial in delineating essential regulation points that modulate the apoptotic program. We have compared the kinetics of interaction of CrmA with five proteases that may play a role in apoptosis. Four of the proteases, all members of the caspase family, are inhibited with widely different rates and affinities ranging over 5 orders of magnitude. One is not inhibited at all under the experimental conditions. CrmA is quite selective in its ability to inhibit caspases, showing the highest affinity for interleukin-1beta-converting enzyme and the second highest for the caspase FLICE (Ki = 0.95 nM), identified as a component of the intracellular signaling complex recruited by ligation of the death receptor Fas. On the basis of comparative inhibitor kinetics, we propose that CrmA is unlikely to inhibit the caspases Yama, Mch2, or LAP3 in vivo but that its inhibition of FLICE is of a magnitude for this protease to be a key target of CrmA during Fas-mediated apoptosis. Therefore, our results support the hypothesis that FLICE catalyzes a crucial step in the promotion of cell death.

Induction of apoptosis in human neuroblastoma cells by abrogation of integrin-mediated cell adhesion

The survival, proliferation and differentiation of neuroblastoma (NB) cells are largely dependent on adhesion to extracellular matrix (ECM) proteins. Integrin occupancy seems to play a primary role. To elucidate the role of integrin heterodimers during neuronal cell death, we have analysed the changes in integrin expression in 2 human NB cell lines which represent different stages of neuronal maturation. Retinoic acid (RA) had different effects on the 2 NB cell lines: on LAN-5 cells it acted as a differentiation-promoting agent, while it had an anti-proliferative effect on GI-LI-N cells, driving them to apoptosis. Indeed, this occurrence was evidenced by the visualization of a "DNA ladder" on gel electrophoresis, by propidium iodide staining, and by DNA flow cytofluorimetric analysis. RA treatment rapidly and drastically decreased integrin expression and cell adhesion on GI-LI-N cells. These findings were also obtained by treating both NB cell lines with the apoptotic agent fenretinide. Furthermore, treatment of NB cells with anti-sense oligonucleotides to beta 1 integrin chain specifically induced chromatin condensation and nucleosomal DNA laddering. Moreover, blocking cell-matrix interactions by means of perturbing antibody against beta 1 subunit resulted in the induction of typical features of apoptotic cells. In conclusion, these findings indicate that abrogation of cell adhesion through down-modulation of integrin receptors plays a crucial role in the induction of neuroblastoma programmed cell death.

The PI 3-kinase/Akt signaling pathway delivers an anti-apoptotic signal

Serum and certain growth factors have the ability to inhibit programmed cell death (apoptosis) and promote survival. The mechanism by which growth factors deliver an anti-apoptotic signal and the mechanism by which this survival signal is uncoupled from mitogenesis are not clear. We studied five downstream effectors of growth factor receptors--Ras, Raf, Src, phosphoinositide 3-kinase (PI 3-kinase), and Akt (PKB)--for their abilities to block apoptosis. Activated forms of Ras, Raf, and Src, although transforming, were not sufficient to deliver a survival signal upon serum withdrawal. In contrast, inhibition of PI 3-kinase accelerated apoptosis, and an activated form of the serine/threonine kinase Akt, a downstream effector of PI 3-kinase, blocked apoptosis. The ability of Akt to promote survival was dependent on and proportional to its kinase activity. In Rat1a fibroblasts, activated Akt did not alter Bcl-2 or Bcl-X(L) expression but inhibited Ced3/ICE-like activity. Thus, the PI 3-kinase/Akt (PKB) signaling pathway transduces a survival signal that ultimately blocks Ced3/ICE-like activity. These results suggest that uncoupling of survival and mitogenesis can be explained by differing abilities of distinct mitogens to efficiently induce the PI 3-kinase/Akt signaling pathway.

Activation of multiple interleukin-1beta converting enzyme homologues in cytosol and nuclei of HL-60 cells during etoposide-induced apoptosis

Recent genetic and biochemical studies have implicated cysteine-dependent aspartate-directed proteases (caspases) in the active phase of apoptosis. In the present study, three complementary techniques were utilized to follow caspase activation during the course of etoposide-induced apoptosis in HL-60 human leukemia cells. Immunoblotting revealed that levels of procaspase-2 did not change during etoposide-induced apoptosis, whereas levels of procaspase-3 diminished markedly 2-3 h after etoposide addition. At the same time, cytosolic peptidase activities that cleaved DEVD-aminotrifluoromethylcoumarin and VEID-aminomethylcoumarin increased 100- and 20-fold, respectively; but there was only a 1. 5-fold increase in YVAD-aminotrifluoromethylcoumarin cleavage activity. Affinity labeling with N-(Nalpha-benzyloxycarbonylglutamyl-Nepsilon-biotin yllysyl)aspartic acid [(2,6-dimethylbenzoyl)oxy]methyl ketone indicated that multiple active caspase species sequentially appeared in the cytosol during the first 6 h after the addition of etoposide. Analysis on one- and two-dimensional gels revealed that two species comigrated with caspase-6 and three comigrated with active caspase-3 species, suggesting that several splice or modification variants of these enzymes are active during apoptosis. Polypeptides that comigrate with the cytosolic caspases were also labeled in nuclei of apoptotic HL-60 cells. These results not only indicate that etoposide-induced apoptosis in HL-60 cells is accompanied by the selective activation of multiple caspases in cytosol and nuclei, but also suggest that other caspase precursors such as procaspase-2 are present but not activated during apoptosis.

Expression of a dominant negative mutant of interleukin-1 beta converting enzyme in transgenic mice prevents neuronal cell death induced by trophic factor withdrawal and ischemic brain injury

To explore the role of the interleukin (IL)-1 beta converting enzyme (ICE) in neuronal apoptosis, we designed a mutant ICE gene (C285G) that acts as a dominant negative ICE inhibitor. Microinjection of the mutant ICE gene into embryonal chicken dorsal root ganglial neurons inhibits trophic factor withdrawal-induced apoptosis. Transgenic mice expressing the fused mutant ICE-lacZ gene under the control of the neuron specific enolase promoter appeared neurologically normal. These mice are deficient in processing pro-IL-1 beta, indicating that mutant ICEC285G blocks ICE function. Dorsal root ganglial neurons isolated from transgenic mice were resistant to trophic factor withdrawal-induced apoptosis. In addition, the neurons isolated from newborn ICE knockout mice are similarly resistant to trophic factor withdrawal-induced apoptosis. After permanent focal ischemia by middle cerebral artery occlusion, the mutant ICEC285G transgenic mice show significantly reduced brain injury as well as less behavioral deficits when compared to the wild-type controls. Since ICE is the only enzyme with IL-1 beta convertase activity in mice, our data indicates that the mutant ICEC285G inhibits ICE, and hence mature IL-1 beta production, and through this mechanism, at least in part, inhibits apoptosis. Our data suggest that genetic manipulation using ICE family dominant negative inhibitors can ameliorate the extent of ischemia-induced brain injury and preserve neurological function.

Fibronectin-stimulated signaling from a focal adhesion kinase-c-Src complex: involvement of the Grb2, p130cas, and Nck adaptor proteins

The focal adhesion kinase (FAK), a protein-tyrosine kinase (PTK), associates with integrin receptors and is activated by cell binding to extracellular matrix proteins, such as fibronectin (FN). FAK autophosphorylation at Tyr-397 promotes Src homology 2 (SH2) domain binding of Src family PTKs, and c-Src phosphorylation of FAK at Tyr-925 creates an SH2 binding site for the Grb2 SH2-SH3 adaptor protein. FN-stimulated Grb2 binding to FAK may facilitate intracellular signaling to targets such as ERK2-mitogen-activated protein kinase. We examined FN-stimulated signaling to ERK2 and found that ERK2 activation was reduced 10-fold in Src- fibroblasts, compared to that of Src- fibroblasts stably reexpressing wild-type c-Src. FN-stimulated FAK phosphotyrosine (P.Tyr) and Grb2 binding to FAK were reduced, whereas the tyrosine phosphorylation of another signaling protein, p130cas, was not detected in the Src- cells. Stable expression of residues 1 to 298 of Src (Src 1-298, which encompass the SH3 and SH2 domains of c-Src) in the Src- cells blocked Grb2 binding to FAK; but surprisingly, Src 1-298 expression also resulted in elevated p130cas P.Tyr levels and a two- to threefold increase in FN-stimulated ERK2 activity compared to levels in Src- cells. Src 1-298 bound to both FAK and p130cas and promoted FAK association with p130cas in vivo. FAK was observed to phosphorylate p130cas in vitro and could thus phosphorylate p130cas upon FN stimulation of the Src 1-298-expressing cells. FAK-induced phosphorylation of p130cas in the Src 1-298 cells promoted the SH2 domain-dependent binding of the Nck adaptor protein to p130cas, which may facilitate signaling to ERK2. These results show that there are additional FN-stimulated pathways to ERK2 that do not involve Grb2 binding to FAK.

Fibronectin and fibronectin receptors in lung development

Fibronectin (FN) is a cell adhesive extracellular matrix protein highly expressed in developing lungs. Although the role of FN in lung development remains to be elucidated, several observations suggest that it plays important roles in many developmental processes. In vitro, FN can affect the migration, proliferation, differentiation, and even apoptosis of various cell types, all considered necessary for organogenesis. The cellular effects of FN are primarily mediated by cell surface heterodimeric receptors of the integrin family. Ligand binding to these receptors triggers the activation of intracellular signaling events responsible for alterations in gene transcription and, ultimately, cell function. Immunohistochemical analysis of embryos revealed increased deposition of FN during the pseudoglandular stage of lung development, coinciding with the period of branching morphogenesis. This observation, together with the strategic location of FN around developing airways predominantly at cleft sites, suggests a role in airways formation. This hypothesis is supported by studies showing that reagents capable of preventing FN-FN receptor binding inhibit branching morphogenesis in murine lung explants. Less is known about the potential role of FN in other aspects of lung development. However, in vitro studies suggest that FN may affect vessel formation, alveolar epithelial cell differentiation and lung growth and maturation.

Amniotic membrane transplantation for persistent epithelial defects with ulceration

PURPOSE

To determine whether preserved human amniotic membrane can be used as an alternative substrate for treating persistent corneal epithelial defects with sterile ulceration.

METHODS

Amniotic membrane transplantation was performed in 11 eyes of 11 consecutive patients with corneal ulcers of different causes that had persisted for a mean +/- SD of 17.5 +/- 13.9 weeks.

RESULTS

Ten patients healed in 3.9 +/- 2.3 weeks (P < .01) without recurrence for 9.0 +/- 5.9 months. One patient failed to heal because of preexisting corneal perforation pursuant to severe rheumatoid arthritis.

CONCLUSION

Amniotic membrane transplantation may be considered an alternative method for treating persistent epithelial defects and sterile ulceration that are refractory to conventional treatment and before considering treatment by conjunctival flaps or tarsorrhaphy.

Coordinated expression of matrilysin during TPA-induced apoptosis of LNCaP cells: two parallel processes affected by TPA

Matrix metalloproteinases (MMPs) are upregulated by growth factors and 12-O-tetradecanoyl-phorbol-13-acetate (TPA). TPA (10 nM) induced apoptosis in LNCaP cells grown in serum-free medium at high seeding density, and increased mRNA and secreted protein levels for the MMP matrilysin. While the TPA-augmented increase in matrilysin mRNA was seen at 4 h, secreted matrilysin protein levels at 8 h, TPA-induced DNA ladder formation was seen only at 10 h and the TPA-induced apoptosis was detected at 12 h. The sequence of events suggested a functional role for matrilysin in apoptosis. However, when the MMP inhibitor BB-2516 was used (25 microM, with IC50 of 20 nM for matrilysin), there was no effect of BB-2516 on TPA-induced apoptosis in LNCaP cells (P = 0.2072). This observation indicates that MMPs including matrilysin do not play a primary role in TPA-induced apoptosis in LNCaP cells. We conclude that the TPA-induced apoptosis and the regulation of matrilysin (a TPA-response element (TRE)-containing gene), are independent and parallel processes.

Misregulation of stromelysin-1 expression in mouse mammary tumor cells accompanies acquisition of stromelysin-1-dependent invasive properties

Stromelysin-1 is a member of the metalloproteinase family of extracellular matrix-degrading enzymes that regulates tissue remodeling. We previously established a transgenic mouse model in which rat stromelysin-1 targeted to the mammary gland augmented expression of endogenous stromelysin-1, disrupted functional differentiation, and induced mammary tumors. A cell line generated from an adenocarcinoma in one of these animals and a previously described mammary tumor cell line generated in culture readily invaded both a reconstituted basement membrane and type I collagen gels, whereas a nonmalignant, functionally normal epithelial cell line did not. Invasion of Matrigel by tumor cells was largely abolished by metalloproteinase inhibitors, but not by inhibitors of other proteinase families. Inhibition experiments with antisense oligodeoxynucleotides revealed that Matrigel invasion of both cell lines was critically dependent on stromelysin-1 expression. Invasion of collagen, on the other hand, was reduced by only 40-50%. Stromelysin-1 was expressed in both malignant and nonmalignant cells grown on plastic substrata. Its expression was completely inhibited in nonmalignant cells, but up-regulated in tumor cells, in response to Matrigel. Thus misregulation of stromelysin-1 expression appears to be an important aspect of mammary tumor cell progression to an invasive phenotype.

Induction of apoptosis and CPP32 expression by thyroid hormone in a myoblastic cell line derived from tadpole tail

During amphibian metamorphosis, the tail and gills that are useful in aquatic life but inappropriate for terrestrial activity are induced to degenerate completely in several days by endogenous thyroid hormone (TH). The dramatic resorption of the tadpole tail has attracted a good deal of attention as an experimental system of cell death, but the mechanism has not been well characterized. To facilitate in vitro analysis, we have established a myoblast cell line (XLT-15) derived from the Xenopus laevis tadpole tail. This cultured cell line died in response to TH and exhibited positive TUNEL reaction and internucleosomal DNA cleavage. Simultaneously, expression of the Xenopus CPP32/apopain/Yama gene was up-regulated by TH in the cell line as it is in regressing tadpole tail, whereas interleukin-1beta-converting enzyme (ICE) mRNA is around 1 copy/cell in tail and undetectable in XLT-15 cells. A CPP32/apopain/Yama inhibitor (acetyl-Asp-Glu-Val-Asp-aldehyde) prevented TH-induced apoptosis of XLT-15 cells, but an ICE inhibitor (acetyl-Tyr-Val-Ala-Asp-aldehyde) did not. These results suggested that an increase of CPP32/apopain/Yama gene expression is involved in TH-dependent apoptosis of XLT-15 and tadpole tail resorption during metamorphosis.

Intestinal tumorigenesis is suppressed in mice lacking the metalloproteinase matrilysin

Matrix metalloproteinases (MMPs) classically have been implicated in basement membrane destruction associated with late-stage tumor cell invasion and metastasis. However, recent studies have demonstrated that one MMP family member, matrilysin, is expressed in a high percentage of early-stage human colorectal tumors. We analyzed matrilysin expression in benign intestinal tumors from mice heterozygous for the ApcMin allele (Min/+) and found that the mRNA was induced in the majority (88%) of these adenomas. Protein was detected in the tumor cells, where, surprisingly, it was predominantly immunolocalized to the lumenal surface of dysplastic glands rather than the basement membrane or extracellular matrix. To address the role of matrilysin in Min intestinal tumorigenesis, we generated Min/+ mice deficient in this MMP by gene targeting and homologous recombination. The absence of matrilysin resulted in a reduction in mean tumor multiplicity in Min/+ animals of approximately 60% and a significant decrease in the average tumor diameter. Based on these findings, we conclude that matrilysin is a suppressor of the Min phenotype, possibly by functioning in a capacity independent of matrix degradation. These results argue for the use of MMP inhibitors in the treatment and prevention of early-stage colon cancer.

Fibronectin suppresses apoptosis in normal human melanocytes through an integrin-dependent mechanism

Recent reports show that components of the extracellular matrix function as cell survival factors through the suppression of apoptosis (programmed cell death). In this report we show that attachment to fibronectin suppresses apoptosis of normal human fetal and neonatal melanocytes in vitro and that prevention of attachment to underlying matrix or attachment to poly-L-lysine is a potent inducer of apoptosis in melanocytes. A role for the beta1-integrin family in mediating cell survival signals was shown by the ability of beta1-blocking antibodies to enhance apoptosis in melanocytes attached to fibronectin, and by the ability of anti-beta1 antibodies immobilized on solid supports to suppress apoptosis in melanocytes. Cytochalasin D reversed the effect of fibronectin on the suppression of apoptosis in melanocytes, suggesting that an intact cytoskeleton is required for transduction of survival signals. A human metastatic melanoma cell line, SKMEL28, was resistant to apoptosis when grown in suspension or on poly-L-lysine, even after 4 d in culture in the absence of exogenous growth factors. These results suggest that fibronectin suppresses apoptosis in normal human melanocytes through an integrin-dependent pathway and that significant differences in the control of anchorage-dependent regulation of apoptosis exist in melanocytes and melanoma cells.

Role of interleukin-1 beta converting enzyme (ICE) in acute myelogenous leukemia cell proliferation and programmed cell death

The proinflammatory cytokine interleukin (IL)-1 has been shown to play a pivotal role in stimulating acute myelogenous leukemia (AML) cell proliferation. The gene for its prominent IL-1 beta form produces a 31-kDa precursor protein (pro-IL-1 beta) that is biologically inactive unless cleaved to its mature form by a cytoplasmic cysteine protease termed Il- 1 beta converting enzyme (ICE). Although ICE was first thought to be a unique enzyme with a single biologic activity, several investigators have demonstrated that ICE shares sequence homology with the protein product of ced-3, the gene for cell death of the nematode Caenorhabditis elegans, and induces apoptosis in different experimental models. It was therefore hypothesized that ICE may either augment the production of mature IL-1 beta and stimulate the proliferation of cells, in which IL-1 beta acts as an autocrine growth factor, or induce apoptosis. Recent data indicate that ICE is a member of an increasingly recognized family of cysteine proteases. Unlike ICE, the other members of this family do not cleave pro-IL-1 beta but are effective inducers of apoptotic cell death, whereas ICE acts primarily as an IL-1 beta converting enzyme. Because IL-1 beta serves as either an autocrine or paracrine growth factor in AML, we recently investigated the effect of ICE inhibition on AML colony growth and found that ICE inhibition reduced the production of mature IL-1 beta and suppressed AML progenitor proliferation. Our data suggest that ICE does not function as an apoptosis gene in AML but rather increases mature Il-1 beta production and AML cell proliferation. It is possible, therefore, that ICE inhibitors may be beneficial in AML therapy.

Activation of a CrmA-insensitive, p35-sensitive pathway in ionizing radiation-induced apoptosis

The response of eukaryotic cells to ionizing radiation (IR) includes induction of apoptosis. However, the signals that regulate this response are unknown. The present studies demonstrate that IR treatment of U-937 cells is associated with: (i) internucleosomal DNA fragmentation; (ii) cleavage of poly(ADP-ribose) polymerase; (iii) cleavage of protein kinase C delta; and (iv) induction of an Ac-DEVD-p-nitroanilide cleaving activity. Overexpression of the cowpox protein CrmA blocked tumor necrosis factor (TNF)-induced apoptosis but had no effect on IR-induced DNA fragmentation or cleavage of poly(ADP-ribose) polymerase and protein kinase C delta. By contrast, overexpression of the baculovirus p35 protein blocked both IR- and TNF-induced apoptosis. The results further demonstrate that the IR-induced proteolytic activity is directly inhibited by the addition of purified recombinant p35, but not by CrmA. We show that the CPP32 protease is sensitive to p35 and not CrmA. We also show that IR induces activation of CPP32 and that this event, like induction of apoptosis, is sensitive to overexpression of p35 and not CrmA. These findings indicate that IR-induced apoptosis involves activation of CPP32 and that this CrmA-insensitive apoptotic pathway is distinct from those induced by TNF and certain other stimuli.

EGF-R dependent regulation of keratinocyte survival

Tissue organization and maintenance within multicellular organisms is in part dependent on the ability of cells to undergo programmed cell death or apoptosis. Conversely, disruption of cell death pathways often is associated with tumor development. At present, the molecular control of apoptosis in epithelial cells is poorly understood. Here we describe evidence linking epidermal growth factor-receptor (EGF-R) activation to survival of normal human keratinocytes in culture. Inhibition of EGF-R activation by an anti-EGF-R antagonistic monoclonal antibody (mAb 425), followed by detachment of keratinocytes from the substratum, induced extensive death with several features of apoptosis in keratinocyte cultures. Other, non-epithelial normal human cells including melanocytes and fibroblasts, did not show this effect. Similar to EGF-R blockade by mAb 425, inhibition of the EGF-R tyrosine kinase activity using tyrphostin AG1478 resulted in lack of attachment and extensive cell death upon passaging. Attachment to keratinocyte-derived ECM partially resuced mAb 425-treated keratinocytes from cell death, indicating that adhesion-dependent and EGF-R-dependent signal transduction pathways serve partially overlapping but not redundant roles in supporting keratinocyte survival.

Inhibition of Ced-3/ICE-related proteases does not prevent cell death induced by oncogenes, DNA damage, or the Bcl-2 homologue Bak

There is increasing evidence for a central role in mammalian apoptosis of the interleukin-1 beta-converting enzyme (ICE) family of cysteine proteases, homologues of the product of the nematode "death" gene, ced-3. Ced-3 is thought to act as an executor rather than a regulator of programmed cell death in the nematode. However, it is not known whether mammalian ICE-related proteases (IRPs) are involved in the execution or the regulation of mammalian apoptosis. Moreover, an absolute requirement for one or more IRPs for mammalian apoptosis has yet to be established. We have used two cell-permeable inhibitors of IRPs, Z-Val-Ala-Asp.fluoromethylketone (ZVAD.fmk) and t-butoxy carbonyl-Asp.fluoromethylketone (BD.fmk), to demonstrate a critical role for IRPs in mammalian apoptosis induced by several disparate mechanisms (deregulated oncogene expression, ectopic expression of the Bcl-2 relative Bak, and DNA damage-induced cell death). In all instances, ZVAD.fmk and BD.fmk treatment inhibits characteristic biochemical and morphological events associated with apoptosis, including cleavage of nuclear lamins and poly-(ADP-ribose) polymerase, chromatin condensation and nucleosome laddering, and external display of phosphatidylserine. However, neither ZVAD.fmk nor BD.fmk inhibits the onset of apoptosis, as characterized by the onset of surface blebbing; rather, both act to delay completion of the program once initiated. In complete contrast, IGF-I and Bcl-2 delay the onset of apoptosis but have no effect on the kinetics of the program once initiated. Our data indicate that IRPs constitute part of the execution machinery of mammalian apoptosis induced by deregulated oncogenes, DNA damage, or Bak but that they act after the point at which cells become committed to apoptosis or can be rescued by survival factors. Moreover, all such blocked cells have lost proliferative potential and all eventually die by a process involving cytoplasmic blebbing.

Degeneration of Cajal-Retzius cells in the developing cerebral cortex of the mouse after ablation of meningeal cells by 6-hydroxydopamine

In the central nervous system, the neurotoxic drug 6-hydroxydopamine (6-OHDA) selectively deletes central catecholaminergic neurons and meningeal cells. Meningeal cells are known to contribute to brain development and their specific degeneration leads to disorganized neuronal positioning. We have analyzed whether a particular population of cortical pioneer neurons, the Cajal-Retzius (CR) cells, which lie just below meningeal cells, is also affected by 6-OHDA treatment. We show that application of 6-OHDA to the cortical surface leads to a rapid degeneration of CR cells, without affecting other cortical neurons. The ablation of CR cells was prevented by normetanephrine, which blocks the 6-OHDA uptake into meningeal cells. These results indicate that the disappearance of CR cells after 6-OHDA treatment may be a result of the ablation of the meningeal cells and suggest a trophic dependence of CR cells upon meningeal cells.

Both wild-type and strongly attenuated bovine leukemia viruses protect peripheral blood mononuclear cells from apoptosis

Bovine leukemia virus (BLV) and the human T-cell leukemia viruses belong to the same subfamily of oncoviruses. Although much attention has focused on the mechanisms of cell proliferation and transformation by these viruses, experiments on the apoptotic process have yielded conflicting data in in vitro cell culture. Experimental infection of sheep with BLV proviruses offers the opportunity to analyze apoptosis in vivo. Here, we show that BLV-infected peripheral mononuclear cells, cultivated ex vivo, are protected from spontaneous programmed cell death. Moreover, the virus is able to specifically interfere with the apoptotic program of infected B lymphocytes. Strongly attenuated mutant proviruses that harbor deletions in the G4 and/or R3 genes also decrease the global susceptibility to apoptosis at levels similar to those obtained with the wild-type virus. In addition, cell culture supernatants from wild-type and mutant viruses can prevent uninfected cells from undergoing programmed cell death. These observations demonstrate that the R3 and G4 genes are not required to maintain both direct and indirect protection against apoptosis. They also imply that the level of programmed cell death observed ex vivo is independent of the amounts of proviruses in the animals. The failure of these cells to undergo apoptosis might be related to the pathogenesis induced by BLV.

Apoptosis is increased in a model of diabetes-impaired wound healing in genetically diabetic mice

Impaired wound healing is a common complication of diabetes mellitus. The underlying pathophysiology of diabetes-impaired healing is poorly understood. In the present study we have compared cell proliferation rates, apoptosis (programmed cell death), the myofibroblast marker alpha-smooth muscle actin and procollagen I mRNA expression, between diabetic and control mice. Full-thickness skin wounds were made in non-obese diabetic (NOD) mice and C57B6 controls. NOD mice showed a marked retardation of wound healing at both 7 and 14 days after wounding. Comparison of cell proliferation rates 7 days after wounding, using 5-bromo-2'-deoxy-Uridine incorporation, showed higher rates of cell proliferation in controls (88.1 +/- 12.8) than in NOD wounds (52.1 +/- 9.9, p < 0.02, n = 4). Immunohistochemical detection of alpha-smooth muscle actin, showed a later onset in diabetic wounds, suggesting that wound contraction may be delayed in the diabetic animals. In situ hybridisation for alpha 1 (I) procollagen mRNA expression, showed reduced procollagen I expression in the diabetic wounds when compared with controls. Lastly, there appeared to be higher levels of apoptosis in diabetic wounds, shown by the terminal transferase mediated UTP nick end-labelling technique. Apoptotic cells were rare in control wounds confirming previous studies, which showed that apoptosis occurs late in normal wound healing as the wound matures into scar tissue. In conclusion, we hypothesize that reduced cell proliferation, retarded onset of the myofibroblast phenotype, reduced procollagen I mRNA expression and aberrant control of apoptotic cell death may contribute to impaired wound healing seen in this diabetic model.

Presence of functional NMDA receptors in a human neuroblastoma cell line

Data are presented that provide convincing evidence for the expression of structurally normal and functional NMDA receptors by acetylcholine-producing human LA-N-2 neuroblastoma cells in culture. Reverse transcription and polymerase chain reaction (RT-PCR), followed by cloning and DNA sequencing, revealed the presence in these cells of mRNA representing the key subunit, NMDAR1, of the receptor. This mRNA was further demonstrated by Northern analysis to be the same size as that described for human neurons. The neutral red cytotoxicity assay was utilized to examine the influence on these neuroblastoma cells of a 48-h incubation with either L-glutamic acid or the specific NMDA agonist N-phthalamoyl-L-glutamic acid (NPG). Cell cytotoxicity was shown by this assay to be increased through incubation with glutamate at 1 and 10 mM by 27 and 37%, and through incubation with NPG at 0.1 and 1 mM by 28 and 46%. A possible mechanism of these toxic effects was further evaluated using the whole-cell configuration of the patch-clamp technique and the specific NMDA agonists (+/-)1-aminocyclobutane-cis-1,3-dicarboxylic acid (ACDA) and NPG. Using this procedure, a voltage-dependent tetrodotoxin-sensitive inward sodium current was found to be increased (x 1.5) by L-glutamic acid and by both NMDA agonists in the presence of glycine. Another voltage-gated inward current, probably carried by calcium ions, was increased three- to fourfold. Hence, these glutamate activities observed in human LA-N-2 neuroblastoma cells appear to occur through the activation of functional NMDA receptors in much the same way as reported for neurons, and both glutamate and NMDA agonists can be toxic to these neuroblastoma cells. Our findings, therefore, suggest this cell line will provide a model suitable for investigating the mechanisms of NMDA-related long-term potentiation (LTP) in neurons and of the NMDA-related neurotoxic effects of glutamate in disease states that involve a reduction in cholinergic function.

Differential effect of components of the extracellular matrix on differentiation and apoptosis

BACKGROUND

Epithelial cells are closely associated with a basement membrane, but the intimate relationships that affect growth, differentiation and survival remain enigmatic. We have previously reported that granulosa cells adjacent to the basement membrane of the ovarian follicle have a higher degree of differentiation compared with cells located distal to the basement membrane. By contrast, granulosa cells distal to the basement membrane are the first to undergo apoptosis during follicular atresia. Moreover, growth of granulosa cells in vitro on a naturally produced basement-membrane-like extracellular matrix (ECM) enhances progesterone production and the cellular response to gonadotropic hormones by an undefined mechanism.

RESULTS

To investigate the effect of the ECM on granulosa cell differentiation and death, primary granulosa cells were cultured on ECMs that lacked or contained bFGF (basic fibroblast growth factor). These otherwise identical ECMs were deposited by HR9 mouse endodermal cells, which do not synthesize bFGF, or by HR9 cells transfected with the bFGF gene. Both ECMs provided protection against apoptosis in serum-free medium, but only the bFGF-containing ECM maintained expression of the steroidogenic P450scc enzyme system and the production of progesterone. Moreover, culturing the cells on this ECM enhanced the expression of the 30 kDa steroid acute regulatory protein which plays a key role in steroid hormone biosynthesis. Laminin, but not fibronectin, was able to replace the ECM in protecting the cells from apoptosis; but not in maintaining steroidogenesis, whereas bFGF was able to enhance steroidogenesis without protecting the cells against apoptosis. Cells cultured on both ECMs or laminin had a well-developed actin cytoskeleton compared with cells cultured on non-coated dishes, which underwent apoptosis.

CONCLUSIONS

Cellular responses to ECM are mediated by the combined action of macromolecular constituents and regulatory molecules, such as bFGF, that are sequestered and stored in the ECM. ECM or laminin protects against cell death by interacting with specific integrin receptors and maintaining a well-developed actin cytoskeleton. ECM-bound bFGF provides differentiation signals for granulosa cells, which are in intimate contact with the ECM. Thus, a clear distinction can be made between the survival activity and the differentiation stimulus exerted by the ECM on epithelial cells.

Proteoglycans and related components in plant cells

After the context is set by a brief description of the plant cell surface, emphasis is placed on one class of cell surface components, the arabinogalactan proteins. An expansion of knowledge regarding the structure, expression, and function of these proteoglycans has been initiated and is being sustained through new experimental approaches, including the development of monoclonal antibody probes and the cloning of cDNAs corresponding to core polypeptides. An examination of the structure of both the polypeptide and carbohydrate components of arabinogalactan proteins is presented with emphasis placed on recently deduced core polypeptide sequences. Information about the biosynthesis and turnover of arabinogalactan proteins is incomplete, especially with regard to the carbohydrate component. Although functions of arabinogalactan proteins have not been clearly identified, regulated expression and several other lines of evidence point to involvement in plant reproductive development, pattern formation, and somatic embryogenesis, as well as in the underlying processes of cell division, cell expansion, and cell death. Arabinogalactan proteins are compared with animal proteoglycans and mucins, and the results of searches for plant analogues of other animal extracellular matrix components are examined.

Reattachment to a substrate prevents apoptosis of human retinal pigment epithelium

BACKGROUND

Epithelial cells generally fail to survive in suspension. Harvesting human retinal pigment epithelium (RPE) for transplantation may separate the cells from their extracellular matrix and induce apoptosis. We investigated whether reattachment of RPE to a substrate will prevent apoptosis.

METHODS

Second-passage human RPE cells were plated onto tissue culture plastic precoated with extracellular matrix, fibronectin or laminin, uncoated tissue culture plastic, untreated plastic and untreated plastic coated with 4% agarose. Reattachment rates were determined for each substrate 24 h after plating. The TUNEL technique was used to determine apoptosis rates in attached cells, unattached cells and the entire cell population.

RESULTS

Attachment rates were as follows: ECM-coated tissue culture plastic-->fibronectin-coated tissue culture plastic-->laminin-coated tissue culture plastic-->uncoated tissue culture plastic-->untreated plastic-->agarose-coated untreated plastic. Apoptosis rates for the entire cell population increased as the RPE cell attachment rate decreased. The proportion of apoptotic cells in the entire population was inversely related to the percent attached cells (r = -0.95).

CONCLUSION

Reattachment of harvested RPE to a substrate decreased the rate of RPE apoptosis in vitro. RPE cells which are removed from their substrate prior to transplantation must reattach rapidly to a substrate to prevent apoptosis.

Regulation and significance of apoptosis in the stem cells of the gastrointestinal epithelium

In rapidly proliferating tissues the stringent control of cell proliferation and cell death by apoptosis is central to the maintenance of tissue homeostasis. In the gastrointestinal tract most work studying the control of tissue cell number has traditionally focused on the growth factor control of proliferation, and the changes that occur during carcinogenesis. However, in recent years it has become increasingly apparent that the control of apoptosis is also crucial. Apoptosis is an important mechanism for eliminating both excess normal cells and those cells which have sustained damage; therefore maintaining a tissue, i.e., stem cells with preserved DNA integrity. In this review the incidence of apoptosis in the stem cells of both the small and large intestine will be discussed in relation to the expression of a number of apoptosis regulating genes (e.g. p53, Bcl-2, bax) within these cells. The importance of apoptosis as a means of controlling stem cell number (and therefore cellular output) will be addressed, as will the mechanisms by which any alterations to this process may contribute to malignancy.

Expression of interleukin-1 beta converting enzyme gene family and bcl-2 gene family in the rat brain following permanent occlusion of the middle cerebral artery

Recent investigations have been suggesting that some neuronal subpopulations may die via programmed cell death after focal ischemic injury. To clarify the possible roles of the genes involved in the cell-death program, this study examined the expression of three members of the interleukin-1 beta converting enzyme (Ice) gene family (Ice, Nedd2, and Yama/CPP32) and two members of the bcl-2 gene family (bcl-2 and bcl-x) in the rat brain after permanent occlusion of the middle cerebral artery. Northern blot analysis revealed a transient induction of Nedd2 mRNA 8 h after the ischemic insult (3.8-fold) and an increase in Yama/CPP32 mRNA 16 to 24 h after the insult (5.8-fold at 24 h), whereas the expression of Ice remained constant. The expression of bcl-2 and bcl-x remained constant after the ischemic insult. Taking into account the key role of the Ice gene family in the execution of programmed cell death, the induction of Ice gene family might play a causative role in apoptotic cell death.