Transglutaminase crosslinking and structural studies of the human small proline rich 3 protein

The cell envelope (CE) is a vital structure for barrier function in terminally differentiated dead stratified squamous epithelia. It is assembled by transglutaminase (TGase) cross-linking of several proteins, including SPR3 in certain specialized epithelia normally subjected to mechanical trauma. We have expressed recombinant human SPR3 in order to study its cross-linking properties. It serves as a complete substrate for, and is cross-linked at similar efficiencies by, the three enzymes (TGases 1, 2 and 3) that are widely expressed in many epithelia. Multiple adjacent glutamines (4, 5, 16, 17, 18, 19 and 167) and lysines (6, 21, 164, 166 and 168) of only head and tail domain sequences are used for cross-linking. However, each enzyme preferentially uses certain residues on the head domain. Moreover, our in vitro data suggest a defined temporal order of cross-linking of SPR3 in vivo: It is first cross-linked by TGase 3 into short intra- and inter-chain oligomers which are later further cross-linked to the CE by TGase 1. To investigate the absence of cross-linking in the central domain (e.g. lysine in position 2 of each of the 16 repeats) we performed structural studies on recombinant SPR3 and on a synthetic peptide containing three repeats of the central domain. 2D H-1 NMR spectroscopy, TOCSY and ROESY, shows strong and medium intensity NOEs connectivities along the amino acid sequence with one weak long range NOE contact between Thr and Cys of subsequent repeats. Distance geometry computation on the basis of intensities of NOEs found generated 50 compatible structures grouped in three main families differing by the number of H-bonds. These measurements were repeated at different concentrations of trifluoroethanol (TFE)-water mixture, an alpha-helical promoting solvent, in order to check the stability of the conformations determined; no changes were observed up to 50% TFE in solution. Also temperature changes did not produce any variation in the ROESY spectrum in the same condition as above. The NMR and circular dichroism data strongly indicate the presence of an ordered (not alpha-helix nor beta-sheet) highly flexible structure in the eight amino acids repetitive units of SPR3, confirming the prediction of one possible beta-turn per each repeating unit. Thus, biochemical and biophysical data, strongly support SPR3 to function as a flexible cross-bridging protein to provide tensile strength or rigidity to the CE of the stratified squamous epithelia in which it is expressed.

Acquisition of ordered conformation by the N-terminal domain of the human small proline rich 2 protein

The cornified cell envelope (CE) is a crucial structure for barrier function in terminally differentiated dead stratified squamous epithelia. It is assembled by transglutaminase enzymes (TGases) that cross-link several proteins such as loricrin and the small proline rich (SPR) proteins. Human SPR2 protein is cross-linked with widely differing efficiencies by TGases 1, 2, and 3 using exclusively residues in the N- and C-terminal domains. In order to understand if the absence of the cross-linking catalyzed by TGases in the central domain is due to the conformation adopted, we have investigated the structural properties in solution of three peptides that correspond to the N-terminal domain, to three repeats of the central domain, and to the C-terminal domain. Together, the NMR and CD data strongly indicate the presence of a highly flexible non alpha-helix, non beta-sheet structure in SPR2. Thus, SPR2 appears to function as a flexible cross-bridging protein to provide tensile strength or rigidity to the CE of the stratified squamous epithelia in which it is expressed.

A possible growth factor role of IL-6 in neuroectodermal tumours

Preliminary data have shown that IL-6 may act as an autocrine growth factor to control proliferation. We further characterised the role of IL-6 in tumour growth as an autocrine/paracrine growth factor in neuroectodermal tumours. We evaluated the production and secretion of IL-6 by seven human melanoma, five neuroblastoma and one glioblastoma cell lines. Moreover, we determined their IL-6-dependent growth in serum free-medium or under minimal growth-supplement conditions: IL-6 dependent growth was observed in two non-IL-6 producing melanoma and in one neuroblastoma cell lines. In addition, expression of IL-6 mRNA and peptide was increased by retinoic acid. The data support the hypothesis that IL-6 contributes to neuroectodermal tumour growth, even though it shows a less potent effect than other reported growth factor such as IGF-II.

Nitric oxide-donor compounds inhibit lipoxygenase activity

The nitric oxide (N0-releasing agents sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) inhibit dioxygenase activity of lipoxygenase in human platelets and human CHP100 neuroblastoma cells, leading the latter to necrosis. The effect of both NO-donors on the dioxygenase reaction was investigated by using soybean lipoxygenase type II (LOX-2) as a model for the mammalian enzyme. SNP and SNAP were competitive inhibitors of LOX-2, with inhibition constants of 525 microM and 710 microM, respectively. Both compounds inactivated LOX-2 by reducing the catalytic iron to the inactive Fe(II) form and counteracted the H2O2-mediated activation of the LOX-2 catalyzed dioxygenase reaction. Similarly, the co-oxidative and per-oxidative activities of LOX-2 were also inhibited by the NO-releasing agents. These findings suggest that the biological role played by NO can be mediated, at least in part, by the inactivation of lipoxygenase, a key-enzyme for the arachidonic acid metabolism in human cells.

Tamoxifen and somatostatin affect tumours by inducing apoptosis

Tamoxifen is a commonly used chemotherapeutic agent in human breast cancer, although some tumours develop resistance. Somatostatin is also being introduced as an anti-tumour agent. Here we show that the action of these drugs is, at least partly, due to their induction of apoptosis. Both 50 nM somatostatin, and 60 nM tamoxifen significantly enhanced the percentage of cells undergoing apoptosis, when compared to untreated or oestrogen treated control cells. This effect was observed in SK-N-BE(2) human neuroblastoma cells and in MCF-7G human breast cancer cells but not in their drug-resistant counterpart MCF-7A which showed a very low rate of spontaneous programmed cell death. Finally, we propose a simple test of the sensitivity and resistance of individual tumours to these agents by assessing their ability to induce apoptosis in vitro as measured by flow cytometry.

PKA and PKC activation induces opposite glial fibrillary acidic protein (GFAP) expression and morphology changes in a glioblastoma multiform cell line of clonal origin

Possible differentiation mechanisms were investigated in a glioblastoma multiform cell line (GL15) presenting an undifferentiated phenotype with weak glial fibrillary acidic protein (GFAP) and strong vimentin (VIM) expression. Serum-free conditions induced time-dependent increases of GFAP-mRNA and GFAP protein levels, associated with a process-bearing astrocytic morphology. Activation of protein kinase C (PKC) by tumor promoter phorbol 12-myrystate 13-acetate (PMA) induced a rapid morphological differentiation and a decrease in GFAP mRNA, whereas the GFAP level remained unchanged. Such parameters were shown to characterize a physiological differentiation stage in astroglial cultures. Treatment of process-bearing GL15 cells with dibutyryl cyclic AMP (dbcAMP), a protein kinase A (PKA) activator, induced a time-dependent decrease in the GFAP mRNA and GFAP protein levels and reverted morphological changes induced by serum-free conditions. Neither PMA nor dbcAMP influenced the VIM mRNA expression. In GL15 cells, PKC and PKA activation have opposite effects. Understanding the role of these kinases in malignant transformation and in the in vitro differentiation process is of both basic and clinical interest.

Functional beta-glucan receptor expression by a microglial cell line

In the central nervous system, the functions of microglia appear crucial after brain damage, when phagocytes eliminate cell debris, acting as the scavengers of the brain. Diseases where an active role for microglia has been proposed recently include Alzheimer's disease, the acquired immune deficiency syndrome (AIDS) and multiple sclerosis. Only recently has it been possible to obtain a microglial cell line retaining morphological and functional aspects of these cells and their secretory products. Sugar receptors are expressed by a variety of phagocytes in primary cultures, but in contrast, are absent on the majority of the described macrophage-like cell lines. We here establish, by 4 degrees C binding experiments, that this murine cell line, called BV-2, expresses a high level (9.86 +/- 0.91 x 10(5); n = 3) of beta-glucan receptors. At 37 degrees C, BV-2 cells show high phagocytic power that can only be inhibited by the free polysugar beta-laminarin (a poly-glucose) and not by mannan (a poly-mannose) as described for macrophages. The beta-glucan receptor expressed by the microglial cell line BV-2 is fully functional in phagocytosis of unopsonized heat-killed yeast particles.

Bone formation markers and pain palliation in bone metastases treated with strontium-89

In several bone disorders, including those with metastatic involvement, changes in procollagen type I C-terminal and type III N-terminal peptides are detected, as indications of altered bone metabolism. Assessment of bone turnover could play a role in the evaluation of response to Strontium-89 used as palliative treatment in symptomatic bone metastases from various primary tumors. A correlation between bone formation rate markers procollagen I and III and efficacy of ionic Strontium-89 was shown in a group of 13 patients who underwent treatment with 4 mCi of Strontium-89 for painful bone metastases: 5 from breast, 7 from prostate, and 1 from lung carcinoid cancer. Assessed as a modification of analgesic intake, pain, and ambulation, there were 6 complete remissions, 3 partial remissions, and 4 nonresponders. The duration of the response was from 2 to 11 months. Procollagen I and III levels were found to be highly abnormal in those with no benefit from Strontium-89 administration but were in the normal range or only slightly elevated in those achieving complete or partial pain control, thus correlating with the clinical response.

Putative role of antioxidant enzymes and glyoxalases in carcinogenesis

The effects various drugs exert on antioxidant enzyme and glyoxalase activity in rat livers were studied. All drugs tested provoked a marked reduction in glutathione peroxidase and a small drop in both glyoxalase I and II activity. It is hypothesized that the substances tested support tumour development by neutralizing organic peroxides, thereby favouring the oxidation of carcinogens and, as a consequence, the formation of metabolites that trigger neoplastic transformation. The reduction in glyoxalase activity is probably attributable to the enhanced cell proliferation induced by the treatment.

Characterisation of a human glioblastoma cell line (LI) expressing hypothalamic and pituitary hormones

The human glioblastoma cell line LI showed morphological features typical of its neuroectodermal origin. Cells were positive by immunofluorescence to GFAP, MHC class II, and L1 determinants. Cytogenetic analysis showed the presence of a modal chromosome number of 63, ranging from 58 to 69 chromosomes (DNA index was 1.6). Northern blot analysis demonstrated the presence of mRNA transcripts specific for transglutaminase C (type II or "tissue"), growth-hormone releasing-hormone (GHRH), insulin-like growth factor II (IGF-II), and proopiomelanocortin (POMC). The GHRH mRNA was present in two different sizes, one similar to the normal hypothalamic species of 0.75 kb, whilst the second species was a large transcript of approximately 10 kb size. Treatment with 5 microM retinoic acid or 5 mM alpha-difluoromethylornithine for 5 days sharply reduced the growth rate and also induced modulation of the ultrastructure and antigenic profile. This cell line may be useful to study glial differentiation and the relationship of GHRH, IGF-II and POMC expression with differentiation in neuroectodermal tumours.

The 'natural' hybrid haemoglobin from mule. Interrelationships with its parent haemoglobins from horse and donkey

The equilibrium O2-binding properties of the hybrid haemoglobin (Hb) present in vivo in erythrocytes from mule and of its parent Hbs from horse and donkey were compared with special reference to the effect of heterotropic ligands such as Cl-, D-glycerate 2,3-bisphosphate (DPG) and inositol hexakisphosphate. All these Hbs display a decreased effect by polyphosphates, confirming that what has been observed for horse Hb [Giardina, Brix, Clementi, Scatena, Nicoletti, Cicchetti, Argentin & Condò (1990) Biochem. J. 266, 897-900] is common to other equine species, at least from a qualitative standpoint. However, different quantitative aspects can be detected, which can be accounted for by a different role for the two types of chain in characterizing the binding free energy for the various heterotropic effectors. In particular, it is shown that the binding mode of DPG and inositol hexakisphosphate displays different features since long-range effects can be observed clearly for inositol hexakisphosphate but not for DPG. In general terms, in spite of a different intrinsic O2 affinity, the modulation of functional properties by third ligands leads these Hbs to behave, under physiological conditions, similarly to human HbA. It might represent an interesting example of how different species with similar functional needs find different ways to produce a similar functional behaviour.

Redox buffering ability of lymphoid cells evaluated by the oxidation of 2',7'-dichlorofluorescin

The redox buffering activity of several lymphoid cells against endogenous and exogenous H2O2 has been evaluated using 2',7'-dichlorofluorescin diacetate (DCFH2-DA). The mechanism of 2',7'-dichlorofluorescin (DCFH2) oxidation has also been investigated. It was found that while the oxidation by external H2O2 is completely inhibited by azide or cyanide, the oxidation by endogenous species is still present, even under anaerobic conditions. The data herein reported indicate that autoxidation and peroxidation of DCFH2 are distinct reactions. Hence only by addition of increasing concentrations of exogenous hydrogen peroxide, the fluorescence of DCF can be used to evaluate the cellular ability of scavenging H2O2. By this method we have found that the erythroleukaemia cell line K562 and promyelocytic line HL-60 show a faster rate of DCFH2 oxidation than peripheral blood leukocytes (PBL), mature T-cells (MOLT-3 and MOLT-4) and B-cells (DAUDI). Using this method the balance between antioxidant enzymes activity and the redox state of the cell can be easily assessed by fluorescence both in single cells and in cell populations.

Effects of dimethylsulfoxide on Friend erythroleukemic cell proliferation and on the activity of enzymes involved in this process

Variations in catalase, glutathione peroxidase (GP) and adenylate cyclase (AC) activity in murine erythroleukemic (MEL) cells were studied during multiplication and dimethylsulfoxide (DMSO)-induced differentiation. The results demonstrated that, although DMSO favors the incorporation of 3H-thymidine into DNA of treated cells, it slows down cell multiplication. Increased incorporation was also observed in superoxide dismutase (SOD)-treated cells. DMSO also determined an early and significant drop in AC activity and a late fall in catalase activity, whereas there was no significant variation in GP activity in parallel with the decreased cell multiplication that accompanied cell differentiation. We hypothesize that DMSO and SOD favor 3H-thymidine incorporation by neutralizing the reactive forms of oxygen and that the reduction in catalase and AC activity is closely related to the mitotic activity of MEL cells.

Possible role of certain antioxidant enzymes in dimethylnitrosamine-induced liver carcinogenesis

An investigation was carried out to establish whether the reduction in catalase, glutathione peroxidase and superoxide dismutase activity, normally observed in liver tumours, is an early event and therefore of pathogenetic importance, or whether it is a late occurrence. Experiments performed on dimethylnitrosamine-treated hepatectomized and non-hepatectomized rats show that the decrease in activity of these enzymes is entirely due to hepatectomy, since the tumour-inducing doses of dimethylnitrosamine failed to provoke variations in the activity of these enzymes, in either normal or regenerating liver.

Replicative behaviour of ascites tumour cells transplanted in BALB C mice of different sex

The present research demonstrates that cells from an ascites tumour (ATP C+) multiply more actively in the peritoneum of male mice, provided they are maintained alive in this environment for long periods of time by weekly transplants in animals of the same sex. Solid tumours obtained by inoculating ATP C+ cells, removed from the peritoneum of male mice, into the subcutaneous dorsal region of castrated male mice, grew more rapidly than those obtained by inoculating the same cells removed from the peritoneum of female mice, always provided that the cells had been passaged at length in animals of the same sex. Cytogenetical studies of these two cell subpopulations revealed that cells reproduced for 2 years in males had a less stabile karyotype and a greater incidence of acrocentric associations.

Different behaviour of normal and neoplastic cells cultured in vitro in the presence of catalase and superoxide dismutase

Chicken embryo fibroblasts and hepatocytes were studied in the presence of catalase and superoxide dismutase in order to establish whether these enzymes had the capacity to favour cell multiplication as previously shown for in vitro tumour ascites cells (ATP C+). The results indicate that, unlike ATP C+ cells, both fibroblasts and hepatocytes are inhibited in their multiplication by superoxide dismutase. Similar effects are exerted on hepatocytes by catalase, whereas the multiplication of fibroblasts is favoured by high doses of this enzyme. Enzyme determinations revealed high levels of catalase and superoxide dismutase in hepatocytes, whereas both enzymes were poor in fibroblasts and ATP C+.

Antagonism between catalase and ascorbic acid in control of normal and neoplastic cell multiplication

The authors studied the effects of a treatment with ascorbic acid on in vitro multiplication of ascites tumour cells (ATP C+), of fibroblast-like cells and of hepatocytes from chick embryos, by measuring [3H]thymidine incorporation into DNA. The results obtained show that the ATP C+ cells are the most sensitive to the toxic effects of the experimental treatment, while the hepatocytes are the most resistant cell population. A treatment with catalase was able to greatly reduce the damage caused by ascorbic acid on the ATP C+ cells. It is hypothesized that ascorbic acid inhibits cell multiplication by the H2O2 formed by its oxidation and that the cells having the highest level of catalase are more resistant to its toxic effects.

Cell multiplication of an ascites tumour in the presence of superoxide dismutase and catalase

Superoxide dismutase and catalase were demonstrated to favour the multiplication of ascites tumour cells in vitro. It is proposed that these enzymes neutralize the O2-. and H2O2 that may accumulate in the neoplastic cell and that cell damage occurs because the cellular levels of both enzymes are low.

Inhibition of the binding of 7,12-dimethylbenz[a]anthracene to DNA by ascorbic acid, reduced glutathione and cysteine in chick embryo cells cultured in vitro

A study on the capacity of ascorbic acid, reduced glutathione and cysteine to interfere with 3H-7,12-dimethylbenz[a]anthracene (3H-DMBA) binding to DNA in cultured fibroblast-like cells from 11-day-old chick embryos showed that, although the total amount of 3H-DMBA in the treated cells was greater than in the untreated cells, the DNA-bound 3H-DMBA was less. Comparisons between the various experimental groups demonstrated that the greater 3H-DMBA in the ascorbic acid-, reduced glutathione-, and cysteine-treated groups could not be attributed to an initially higher number of cells, nor to a treatment-induced increase in DNA synthesis. It is proposed that the three substances examined inhibit the oxidative degradation of 3H-DMBA, thereby favoring its accumulation within the cell and reducing the formation of DNA-binding metabolites.

Influence of sexual hormones on solid tumor growth and ATP C+ cell replication

Solid tumors obtained by implanting ATP C+ cells subcutaneously into the back of BALB/cf/Had/Se substrain mice developed more rapidly in males than females. Experiments conducted on gonadectomized animals demonstrated that female gonads inhibit the development of this tumor. Studies on ATP C+ cells cultured in vitro with various doses of male and female hormones showed that mainly progesterone, but to a lesser extent also estradiol, significantly inhibit cell proliferation with respect to testosterone. The treatment of normal and gonadectomized animals with testosterone and progesterone confirms the results obtained in vitro. Analyses carried out on ATP C+ cells do not reveal presence of estradiol and progesterone receptors.