Genetic alterations disrupting the nuclear localization of the retinoblastoma-related gene RB2/p130 in human tumor cell lines and primary tumors

The prototypic tumor suppressor gene, the retinoblastoma gene (RB/ p105), is mutated in a variety of human tumors. However, to date, mutational data on retinoblastoma family members p107 and RB2/p130 in tumors is lacking. We studied the expression of pRb2/p130 by immunocytochemistry and Western blot analysis in a panel of human osteosarcoma and lymphoid cell lines. Only the lymphoid cell lines showed an abnormal cytoplasmic localization of pRb2/p130, suggesting possible alterations within the region of nuclear localization signaling. We screened these cell lines for genetic alterations of the RB2/p130 gene in the region of the putative bipartite nuclear localization signal (NLS). This region is highly homologous with that of the RB/p105 gene. In addition, we screened four primary Burkitt's lymphomas for genetic alterations in the RB2/p130 gene. Naturally occurring mutations, which disrupt the putative bipartite NLS, were found in lymphoma cell lines and primary tumors, but not in the osteosarcoma cell lines, where normal nuclear localization of the protein was detectable. Site-directed mutagenesis and transfection assay using NLS mutants displayed markedly reduced biological activity as measured by flow cytometric analysis. This study clearly describes RB2/ p130 as an important target for mutations and subsequent inactivation in lymphoma pathogenesis, thus validating that RB2/p130 is a classical tumor suppressor gene.

Mutations in the retinoblastoma-related gene RB2/p130 in lung tumors and suppression of tumor growth in vivo by retrovirus-mediated gene transfer

The retinoblastoma (Rb) family consists of the tumor suppressor pRb/p105 and related proteins p107 and pRb2/p130. Recent immunohistochemical studies of the retinoblastoma family of proteins in 235 specimens of lung cancer show the tightest inverse association between the histological grading in the most aggressive tumor types and pRb2/p130. This led us to study a panel of human lung cancers for mutations in the RB2/p130 gene. Mutations in the Rb-related gene RB2/p130 were detected in 11 of 14 (78.5%) primary lung tumors by single-strand conformation polymorphism and sequence analysis. A Moloney leukemia virus-based retroviral system was set up, and a comparable viral concentration of 1 x 10(7) infectious units/ml was obtained. Retrovirus-mediated delivery of wild-type RB2/p130 to the lung tumor cell line H23 potently inhibited tumorigenesis in vitro and in vivo, as shown by the dramatic growth arrest observed in a colony assay and the suppression of anchorage-independent growth potential and tumor formation in nude mice. The tumors transduced with the RB2/p130 retrovirus diminished in size after a single injection, and a 12-fold reduction in tumor growth after RB2/p130 transduction compared with the Pac-transduced tumors (92% reduction, P = 0.003) and lacZ-transduced tumors (93% reduction, P < 0.001) was found to be statistically significant. These findings provide the missing confirmation that RB2/p130 is a "bona fide" tumor suppressor gene and strengthen the hypothesis that it may be a candidate for cancer gene therapy for lung cancer.

Inhibition of phosphoinositide 3-kinase impairs pre-commitment cell cycle traverse and prevents differentiation in erythroleukaemia cells

During the early hours after exposure to differentiation inducing agents, Friend erythroleukaemia cells undergo alterations which commit them to cessation of growth and development of the characteristics of differentiation. Our current experiments have compared the expression and activity of phosphoinositide 3-kinase (PI 3-kinase) in control cells with cells undergoing differentiation which has been induced by dimethyl sulfoxide (DMSO). When the cultures were initiated with stationary phase cells and DMSO was added at the time of seeding, PI 3-kinase activity was stimulated in both treated and control cells during the first 3 h from seeding. This event appears to be a rate limiting step in commitment since pretreatment of cells with 10 microM LY294002 or down-regulation of p85 expression prior to adding DMSO completely prevents commitment to erythropoiesis. Accordingly, PI 3-kinase inhibition during the commitment period prevents DNA-binding of the transcription factor GATA-1, essential for erythroid differentiation. However, once cells are committed to differentiate, PI 3-kinase activity and expression dramatically decreases along with the differentiation programme, to become barely detectable after 96 h. Remarkably, LY294002 treatment leads to accumulation of cell in G1 phase and prevents DMSO-dependent cyclin D3 induction. Based on these data, we suggest that PI 3-kinase is rate limiting for the completion of the first round cycle of cell division required for initiation of erythrocytic differentiation. On the other hand, the late decrease of PI 3-kinase associated with the differentiation process seems to be part of the programmed shut off of genes not needed in mature erythrocytes.

Topology of inositol lipid signal transduction in the nucleus

An increasing body of evidence shows that many of the key inositol lipids and enzymes responsible for their metabolism reside in nuclei. Moreover, the association of the nuclear phosphoinositide cycle with progression through the cell cycle and commitment toward differentiation has built a wider picture of the implications of phosphoinositides in the control of nuclear functions. This article reviews a central aspect of inositide nuclear signaling, i.e., the spatial organization of the signaling system within the nucleus in relationship to the nuclear organization in functional domains. Most of the evidence obtained with a variety of confocal and electron microscopy immunocytochemical techniques indicates that the phosphoinositides, the enzymes required for their synthesis and hydrolysis, and the targets of the lipid second messengers are localized at ribonucleoprotein structures involved in the transcript processing in the interchromatin domains. These findings demonstrate that nuclear inositol lipids exist in a nonmembranous form, linked to structural nuclear proteins of the inner nuclear matrix. They also suggest that the inositol signaling in the nucleus is completely independent of that at the cell surface and that it probably preceded in evolution the systems that are present at the cytoskeletal and cell membrane level.

Phosphatidylinositol 3-kinase translocation to the nucleus is an early event in the interleukin-1 signalling mechanism in human osteosarcoma Saos-2 cells

Interleukin 1 (IL-1) is a proinflammatory cytokine which can elicit proliferative, differentiative, or metabolic responses. The molecular mechanisms by which IL-1 signals are transduced from the plasma membrane to the nucleus, although extensively studied, have not been completely elucidated. We previously demonstrated that human osteosarcoma Saos-2 cells incubated with IL-1 presented a rapid and transient increase of phospholipase C activity exclusively at the nuclear level. Moreover, we presented evidence that not only the canonical inositol lipid signalling pathway was involved, but also the D3-phosphorylated lipids generated by phosphatidylinositol 3-kinase (PI 3-kinase) were affected. The results of this study indicate that in Saos-2 cells PI 3-kinase is recruited and activated by IL-1 receptor I (IL-1RI) through binding of the SH2 domains to the consensus sequence on the C-terminal tail of the receptor, and that Tyr-479 is essential for PI 3-kinase activation. Moreover, IL-1 treatment triggers PI 3-kinase translocation to the nucleus; this event is rapid and transient in cells expressing high levels of IL-1RI (Saos-2/IL-1R) as well as in untransfected cells, although to a lesser extent. The data, based on immunochemical and immunocytochemical quantitative methods, indicate that PI 3-kinase translocation to the nucleus depends on PI 3-kinase activation. In fact, inactivation by two independent mechanisms, addition of specific PI 3-kinase inhibitors, or overexpression of a mutant form of IL-1RI, resulted in a substantial inhibition of PI 3-kinase translocation to the nucleus. These data suggest that PI 3-kinase recruitment by the activated receptor is a limiting step in PI 3-kinase activation and nuclear translocation. This early event in the IL-1 signalling mechanisms confirms that D3 inositides, as well as canonical inositides produced by nuclear phospholipase C isoforms, are involved in this pathway of activation of transcription factors.

Decreased expression of laminin beta 1 in chromosome 21-linked Bethlem myopathy

Muscle biopsies of four patients affected by chromosome 21-linked Bethlem myopathy were investigated by means of immunohistochemistry, with monoclonal antibodies for laminin chains, dystrophin and dystrophin associated glycoproteins. The objective of this study was to determine whether an altered molecular structure of collagen type VI, characteristic of Bethlem myopathy, could influence the expression of the protein complex linking the extracellular matrix with the subsarcolemmal cytoskeleton. Normal expression of all proteins was found except for laminin beta 1, along with an age related progressive deficiency of this protein in the muscle fibre basal lamina. This study shows that Bethlem myopathy linked to chromosome 21 is associated with a secondary decrease in laminin beta 1 expression.

Nuclear changes in a case of X-linked Emery-Dreifuss muscular dystrophy

Ultrastructural alterations in the nuclear architecture were found in skeletal muscle and skin cultured cells from a patient affected by X-linked Emery-Dreifuss muscular dystrophy (EMD) carrying a null mutation. The molecular defect of X-linked EMD is the absence of emerin, a nuclear envelope-associated protein which is considered a component of the nuclear lamina. The nuclear changes were present in skeletal muscle and skin cultured cells with a frequency of about 10% and 18%, respectively. The main structures of the nuclear periphery were involved: lamina and nuclear envelope-associated heterochromatin were affected, whereas the cisterna and the pore complexes appeared preserved, and the cytoplasm of the same cells appeared normal. Analogous localized defects were detectable by immunolabeling with antilamin A/C and B2 antibodies, as well as by selective propidium iodide chromatin staining. The lesions we describe could be the result of anomalous nuclear lamina organization in the absence of emerin.

The novel structural protein of human cytomegalovirus, pUL25, is localized in the viral tegument

Human cytomegalovirus UL25 codes for a structural phosphoprotein of 85 kDa (C. J. Baldick and T. Shenk, J. Virol. 70:6097-6105, 1996; M. C. Battista et al., J. Virol. 73:3800-3809, 1999). In this study we analyzed the intracellular and intraviral localization of pUL25 by confocal and immunoelectron microscopy and found that pUL25 is a component of the viral tegument and the dense body matrix, acquired during the late cytoplasmic phase of virus maturation.

Cytochemistry of the functional domains of the nucleus in normal and in pathologic conditions

By means of ultrastructural cytochemistry significant advances have been made in understanding the functional roles of many nuclear domains. This review gives schematic information about the main nuclear domains involved in replication, transcription, processing and transport of the transcripts in normal and in pathologic conditions. Particular attention is paid to a functional domain that appears to be involved in signal transduction. Data are reported on the intranuclear specific localization of key elements of the polyphosphoinositide signal transduction system in different cell types including human osteosarcoma cell lines. Compared with the compartmentalization of the cytoplasm, the nucleus has long been considered as relatively unstructured. On the other hand, fundamental nuclear functions, such as DNA replication and RNA transcription, can be molecularly characterized also in cell-free systems, suggesting that supramolecular organization is not so strictly required as for other cell functions occurring within intact cytoplasmic organelles. Nevertheless, a stringent organization is required for packing about 200 cm of DNA in the about 30 micron 3 of the nucleus. In the absence of membrane-delimited organelles, the nuclear organization is based on functional compartments, or domains, whose spatial localization involves the nuclear matrix, which shares many properties with the cytoskeleton. The nuclear domains are defined as structural compartments, not necessarily stable but dynamically variable, which perform specific metabolic functions through the partitioning of molecular complexes. Their identification has been made possible in the last few years by the development of specific nuclear probes for confocal and electron microscope immunocytochemistry. Therefore, the complex network of structures and enzymatic functions that make up the nucleus is in several cases yielding to molecular analysis, but a large part remains unknown (Strouboulis and Wolffe, 1996; Laemmli and Tjian, 1996). Rapid advances in understanding the functional role of the nuclear domains have been made recently: in particular, of the nuclear envelope, of the nucleolus, and of RNA splicing. In other cases, e.g. the precise localization of the nuclear domains involved in signal transduction, much remains to be clarified (Forbes and Johnson, 1997). It is conceivable that in the near future unexpected new nuclear domains will come to light and new nuclear functions may emerge, especially in field of post-transcriptional processing and transport of RNAs, and in the relationships between the nucleo-skeleton and enzymic fixed sites involved in replication, transcription and signal transduction. The aim of this review is to provide information about the morphological characteristics, the associated functions and the molecular composition of the main nuclear domains found to date. To simplify the exposition, the main data on each nuclear domain are reported in Tables, together with the principal references on the subject. Figures refer to original findings on some aspects of nuclear domain organization.

Phosphatidylinositol 3-kinase translocation to the nucleus is induced by interleukin 1 and prevented by mutation of interleukin 1 receptor in human osteosarcoma Saos-2 cells

Although interleukin 1 (IL-1) functions have been extensively characterized, the mechanisms by which IL-1 signals are transduced from the plasma membrane to the nucleus are less known. Recent evidence indicates that phosphatidylinositol 3-kinase (PI3-kinase) could be activated by a direct association with the activated IL-1 receptor. In this study we analyzed the effects of IL-1 on the intracellular distribution of PI3-kinase in wild-type Saos-2 human osteosarcoma cells, and in cell clones overexpressing type I IL-1 receptor (IL-1RI). PI3-kinase intracellular distribution displays two distinct patterns. In quiescent cells, PI3-kinase is distributed through the cytoplasm, although a portion is present in the nucleus; following stimulation with IL-1, PI3-kinase is redistributed, increasing in the nuclear compartment. Both immunoblotting and immunofluorescence data indicate that IL-1 causes a rapid and transient translocation of PI3-kinase from the cytoplasm to the nucleus. This phenomenon is prevented by PI3-kinase inhibitors, suggesting that the maintenance of PI3-kinase activity is essential for IL-1-induced translocation. Indeed, in cell clones stably transfected with Y479F receptor mutant, in which the binding of the enzyme to the activated receptor is blocked, IL-1-induced PI3-kinase translocation to the nucleus is completely prevented. These data suggest that PI3-kinase translocation to the nucleus upon IL-1R activation is an early event in IL-1 signaling mechanism, and may be involved in transcriptional activation.

P-glycoprotein subcellular localization and cell morphotype in MDR1 gene-transfected human osteosarcoma cells

Efflux of chemotherapy agents by P-glycoprotein at the plasma membrane is thought to be a major cause of cancer multidrug-resistance (MDR). However, the mechanism underlying the cellular accumulation and distribution of cytotoxic drugs is still poorly defined. We have recently found that P-glycoprotein is expressed also in the nucleus of MDR cell lines selected in doxorubicin (DXR), suggesting the possible involvement of this protein in the direct extrusion of the drug from the nucleus of resistant cells. In this study, we analyzed the subcellular localization of P-glycoprotein, in a series of U-2 OS osteosarcoma cell clones transfected with MDR1 gene in order to verify whether the nucleus is a constant site for the localization and functional activity of P-glycoprotein, and in which way some aspects of cell morphology related to MDR depend on the subcellular P-glycoprotein localization rather than on the exposure to the selective drug. Our results indicate that to achieve a subcellular drug distribution prevailing in the cytoplasm but not in the nucleus, a significant increase in the expression of P-glycoprotein at the different cellular compartments, including the plasma membrane, the cytoplasm, and the nucleus, is needed, although the in vitro drug resistance appears to be mainly dependent on the expression of P-glycoprotein at the cell surface. With regard to the morphological characteristics of MDR cells involving the cell surface and the chromatin arrangement, the influence of DXR appears to be prevalent, although P-glycoprotein overexpression cannot be excluded.

Immunofluorescence study of a muscle biopsy from a 1-year-old patient with Walker-Warburg syndrome

A previous study of two patients with Walker-Warburg syndrome (WWS) showed a severe deficiency of the extracellular matrix protein laminin beta2 chain and alpha-sarcoglycan (adhalin) in skeletal muscle fibers. More recently, however, other researchers have shown that in their WWS patients the expression of the laminin beta2 chain and alpha-sarcoglycan was normal. Here we describe a 1-year-old boy affected with WWS. We performed immunohistochemical studies on a muscle biopsy from this patient using monoclonal antibodies against dystrophin, dystrophin-associated glycoproteins and several proteins of the extracellular matrix. We confirm previously reports as far as the diminished expression of laminin beta2 chain and alpha-sarcoglycan is concerned. The expression of some other laminins was unusual, whereas the expression of collagen IV and VI was normal. These results suggest that complex syndromes like WWS are quite heterogeneous, although they might represent variant expressions of a single pathological entity.

Phosphatidylinositol 3-kinase is recruited to a specific site in the activated IL-1 receptor I

Interleukin 1 (IL-1) delivers a stimulatory signal which increases the expression of a set of genes by modulating the transcription factor NF-kappaB. The IL-1 receptors are transmembrane glycoproteins which lack a catalytic domain. The C-terminal portion of the type I IL-1 receptor (IL-IRI) is essential for IL-1 signalling and for IL-1 dependent activation of NF-kappaB. This portion contains a putative phosphatidylinositol 3-kinase (PI 3-kinase) binding domain (Tyr-E-X-Met), which is highly conserved between the human, mouse and chicken sequences, as well as the related cytoplasmic domain of the Drosophila receptor Toll. This observation prompted us to investigate the role of PI 3-kinase in IL-1 signalling. Here we report evidence that PI 3-kinase is recruited by the activated IL-IRI, causing rapid and transient activation of PI 3-kinase. We also show that the receptor is tyrosine phosphorylated in response to IL-1. Expression of a receptor mutant lacking the putative binding site for p85 demonstrates that Tyr479 in the receptor cytoplasmic domain is essential for PI 3-kinase activation by IL-1. Our results indicate that PI 3-kinase is likely to be an important mediator of some IL-1 effects, providing docking sites for additional signalling molecules.

Inositides in the nucleus: taking stock of PLC beta 1

The nucleus was shown to be a site for inositol lipid cycle which can be affected by treatment of quiescent cells with growth factors such as IGF-I. In fact, the exposure of Swiss 3T3 cells to IGF-I results in a rapid and transient increase in nuclear PLC beta 1 activity. In addition, several other reports have shown the involvement of PLC beta 1 in nuclear signalling in different cell types. Indeed, PLC beta 1 differs from the PLC gamma and della isozymes in that it has a long COOH-terminal sequence which contains a cluster of lysine residues that are critical for association with the nucleus. Although the demonstration of PtInsP and PtdInsP2 hydrolysis by nuclear PLC beta 1 established the existence of nuclear PLC signalling, the significance of this autonomous pathway in the nucleus has yet to be thoroughly clarified. By inducing both the inhibition of PLC beta 1 expression by antisense RNA and its overexpression we show that this nuclear PLC is essential for the onset of DNA synthesis following IGF-I stimulation of quiescent Swiss 3T3 cells. Moreover, using a different cell system, i.e. Friend erythroleukemia cells induced to differentiate towards erythrocytes, it has been evidenced that there is a relationship between the expression and activity of nuclear PLC beta 1 and the association of PI-PT alpha with the nucleus in that, when PLC activity ceases, in differentiated and resting cells at the same time there is a dramatic decrease of the association of PI-PT alpha with the nucleus.

Ataxin-3 is transported into the nucleus and associates with the nuclear matrix

It has been reported that the ataxin-3 protein containing a polyglutamine sequence in the pathological range (61-84Q) is localized within the nucleus of neuronal cells, whereas ataxin-3 with a normal repeat length (12-37Q) is predominantly a cytoplasmic protein. In this study, the subcellular localization of the full-length ataxin-3 protein with a glutamine sequence in the normal range (Q3KQ22) was analysed in two mammalian cell lines. Using two affinity-purified polyclonal antibodies raised against the N- or C-terminal portion of ataxin-3, the protein was detected predominantly, but not exclusively, in the nucleus of COS-7 as well as neuroblastoma cells by immunofluorescence and confocal laser scanning microscopy (CLSM). The distribution of the protein in these cellular compartments was confirmed by biochemical subcellular fractionations. Furthermore, CLSM revealed that the ataxin-3 protein present in the nucleus of neuroblastoma cells is associated with the inner nuclear matrix. Our results taken together with the finding of a nuclear localization signal in ataxin-3 indicate that the ataxin-3 protein per se translocates to the nucleus and that an expanded glutamine repeat is not essential for this transport.

Immunocytochemical detection of emerin within the nuclear matrix

Emerin, the protein whose production is altered in the X-linked form of Emery-Dreifuss muscular distrophy, has been hypothesized to be associated with the nuclear matrix on the basis of biochemical studies. In addition, immunocytochemical data reported its localization at the nuclear periphery, on the nuclear lamina, in sections of several normal tissues. We investigated the association of emerin with the nuclear matrix, by using cultured cells (SaOS-2, MG63 and HeLa-S3) and their in situ extracted matrix as a model, and immunocytochemical methods, both at the light and electron microscope level. Our results show a normal presence of emerin in the cultured cells and the specific persistence of emerin on the lamina of the in situ extracted nuclear matrix. This suggests a tight binding between emerin and the nuclear lamina independently from the interactions between the C-terminal hydrophobic domain of the protein and the inner nuclear membrane.

Hereditary motor and sensory neuropathy Lom type in an Italian Gypsy family

We describe a form of hereditary motor and sensory neuropathy (HMSN) affecting four siblings in an Italian family of Gypsy ethnic origin with both clinical and pathological findings very reminiscent of the HMSN Lom type (HMSNL), recently described in a group of Bulgarian Gypsies. Genetic analysis demonstrated linkage to chromosome 8q24 and conserved haplotypes in the HMSNL region, thus confirming that this is the first Gypsy family outside the Balkans suffering from the same disorder.

Increase of neuronal nitric oxide synthase in rat skeletal muscle during ageing

Nitric oxide synthases (NOS) are different widely expressed enzymes which produce the molecular messenger nitric oxide. The neuronal isoform of NOS (nNOS) is involved in several processes of the cell metabolism, most of which are, at present, not fully understood (neurotransmission, smooth muscle motility, myoblast and myocyte biology and others). In skeletal muscle nNOS is present mainly at the plasmalemma, where it is attached to the dystrophin-related proteins; in fact, in pathologies involving dystrophin, nNOS is altered as well. We report that in aged rats the nNOS amount in skeletal muscle increases both in the soluble and microsomal fractions and that an additional intracytoplasmic localisation appears.

Oral exfoliative cytology for the non-invasive diagnosis in X-linked Emery-Dreifuss muscular dystrophy patients and carriers

Emery-Dreifuss muscular dystrophy (EMD) is an inherited myopathy characterised by muscle contractures, progressive muscle wasting and weakness, with humeroperoneal distribution. Cardiac arrhythmia and heart conduction block are also important characteristics of this disease. The X-linked form of EMD is caused by the absence of emerin, encoded by the STA gene (Xq28). Emerin is normally localized in muscle and other tissues at the nuclear rim. Currently, muscle and skin biopsies are used for the immunohistochemical diagnosis. We demonstrate that emerin is present in the cheek oral mucosa, in the exfoliating epithelial cells, and we propose the collection of these cells as a new method for the diagnosis of X-linked EMD patients and the detection of carriers by immunofluorescence techniques: smears from healthy subjects contained about 98% emerin-positive cells, those from X-linked EMD patients contained none and those from carriers contained about 45%. The technique is completely non-invasive, simple, repeatable and inexpensive.

Localization of laminin alpha 2 chain in normal human central nervous system: an immunofluorescence and ultrastructural study

Recently, a rare form of congenital muscular dystrophy has been shown to be associated with a deficiency of laminin alpha 2 chain, a tissue-specific component of the basal lamina. Besides muscular dystrophy, children affected with this disorder also show electrophysiological and magnetic resonance imaging evidence of white matter involvement in the central nervous system (CNS). We have studied the precise localization of laminin alpha 2 chain in normal human brain, using specific electron microscopic techniques including thin-section fracture labeling and cryoultramicrotomy, in parallel with immunohistochemical techniques. We found that this laminin chain was localized to the basal lamina of all cerebral blood vessels, whereas blood vessels of the choroid plexus did not show any reaction. No positive reaction was found in meningeal blood vessels either. We hypothesize that in normal brain, laminin alpha 2 may be important for the selective filtration capability of the blood-brain barrier. The lack of laminin alpha 2 in cerebral vessels of children with laminin alpha 2-deficient congenital muscular dystrophy may cause impaired selective filtration, leading to leakage of plasma components and damage to the CNS. Further studies should be performed on patients affected by congenital muscular dystrophy associated with laminin alpha 2 deficiency to test this hypothesis.

Nuclear lipid-dependent signal transduction in human osteosarcoma cells

The enzymes and substrates involved in phosphoinositide signal transduction which have been detected in the nucleus of several cell types have been demonstrated to be responsive to agonists. The complexity of this aspect of inositide function has been previously analyzed in some cell models characterized by a mitogenic or differentiating response to specific factors. An interesting experimental model is represented by human derived osteosarcoma Saos-2 cells, characterized by the expression of high affinity receptors for interleukin 1 alpha (IL-1 alpha), which is one of the most potent stimulators of bone resorption. In particular, we investigated the earliest intracellular events following the binding of IL-1 alpha to its receptor, involving the inositide signal transduction pathway. Saos-2 cells present a partitioning of the phosphoinositidase (PLC) isoforms; in fact, the nucleus contains both PLC beta 1 and gamma 1, while the cytoplasm contains almost exclusively the gamma 1 isoform. IL-1 alpha evokes a rapid and transient increase of the PLC beta 1 activity in the nucleus, which causes the hydrolysis of phosphatidylinositol mono- and bis-phosphate. In response to IL-1 alpha, not only the canonical inositol lipid pathway appears to be involved; also the 3'-phosphorylated lipids generated by phosphatidylinositol 3-kinase (PI 3-K), which may act as second messengers, appear to be affected. In fact, Saos-2 cells present a nuclear PI 3-K activity which can be enhanced by the IL-1 alpha treatment. Among the possible targets of the second messengers released by the nuclear PLC beta 1 activation, we found that some protein kinase C isoforms, namely the epsilon and zeta, which are present within the nucleus, are activated after IL-1 alpha exposure. These activated PKC isoforms, in turn, could modulate the activity of the transcription factor NFkB, which, 5 min after IL-1 alpha treatment, has already translocated to the nucleus and bound to DNA to promote gene activation. The actual role of the inositide pathway in the Saos-2 cell function has also been investigated by utilizing cell clones transfected with the mouse sequence of the PLC beta 1.

Immunolocalization of several laminin chains in the normal human central and peripheral nervous system

Using specific monoclonal antibodies against different subunits of laminin, we studied the differential distribution pattern of several laminin chains in the central (CNS) and peripheral (PNS) nervous system. Laminin chains alpha 1, beta 1 and gamma 1, were found in the basement membrane (BM) of blood vessels in both CNS and PNS. In contrast, laminin alpha 2 though present in the BM of capillaries in the CNS, was completely absent from PNS capillaries. Laminins alpha 2, beta 1, gamma 1 could be detected in peripheral nerve, in the BM of Schwann cells, which did not contain Laminin alpha 1. The possible importance of laminin alpha 2 for myelination in the PNS as well as in the function of the blood-brain barrier in the CNS, and its potential relevance to the pathology of congenital muscular dystrophy associated with deficiency of this laminin chain, is discussed.

Intracellular detection of laminin alpha 2 chain in skin by electron microscopy immunocytochemistry: comparison between normal and laminin alpha 2 chain deficient subjects

The aim of this study is to localize the alpha 2 laminin chain in normal human skin. The methods used were immuno-gold cytochemistry on cryo-ultramicrotomy sections and thin-section-fracture-label, together with electron microscopy observation. Results were compared with light microscopy peroxidase immuno-staining. Both normal skin samples and skin biopsies from laminin alpha 2 chain deficient congenital muscular dystrophy affected patients were studied. The results show that, in normal skin, the laminin alpha 2 chain is spread throughout the cytoplasm of basal keratinocytes, while it appears associated with desmosomal tonofilaments in the spinous and granular epidermal layers; in skin samples from dystrophic patients the laminin alpha 2 chain was not detectable. These data suggest that the function of the laminin alpha 2 chain is different in the epidermis as compared to that in muscle and peripheral nerve, where it is localized in the basement membrane.

Redistribution of DNA topoisomerase II beta after in vitro stabilization of human erythroleukemic nuclei by heat or Cu++ revealed by confocal microscopy

Using confocal laser scanning microscope and a monoclonal antibody we have examined by means of indirect immunofluorescence techniques the distribution of DNA topoisomerase II beta (the 180-kDa nucleolar isoform of topoisomerase II) following stabilization of isolated nuclei by exposure to moderate heat (37 degrees or 42 degrees C) or Cu++. In intact cells the antibody specifically decorated the nucleoli. The same pattern was maintained if nuclei were incubated at 0 degree C in a buffer containing spermine/spermidine/KCl or stabilized by means of 0.5 mM Cu++ for 10 minutes at 0 degree C in the same buffer. On the contrary, if stabilization was performed by incubating the nuclei either at 37 degrees or 42 degrees C, the immunoreactivity dispersed all over the nucleus, forming numerous speckles. This phenomenon was not detected if, in addition to spermine/spermidine/KCl, the incubation buffer also contained 5 mM Mg++ and the temperature was 37 degrees C. If the stabilization was performed at 42 degrees C, Mg++ failed to maintain the original distribution of DNA topoisomerase II beta, as seen in intact cells. The analysis on 2-D optical section showed the alteration of the nucleolar profile, particularly at 37 degrees C, even when the samples were treated with Mg++. The 3-D reconstruction figured out the irregularity of the surface at 37 degrees C and the variations of the volume occupied by the fluorescent figures. These were in close proximity to each other both in intact cells and in 0 degree C incubated nuclei; they showed a certain degree of shrinkage in 0 degree C plus Cu++ exposed samples (-20% of the volume), and, on the contrary, the labeled structures were scattered in a volume increased two- or threefold when exposed to 37 degrees or 42 degrees C, respectively. The addition of Mg++ restored the original spatial relationship and volume at 37 degrees C, but not at 42 degrees C, where the volumetric analysis showed an increase of about 50%. Our results demonstrate that heat stabilization of isolated nuclei in a buffer without Mg++ (i.e., a technique often employed to prepare the nuclear matrix or scaffold) cannot be considered an optimal procedure to maintain the original distribution of protein within the nucleus.