Immunocytochemical expression of protein kinase C isoenzymes alpha, delta, epsilon and zeta in differentiating chick chondrocytes in vitro

In our previous work we have investigated the expression of the serine-threonine kinase protein kinase C (PKC) in the vertebral column of mouse foetuses. In the present work we would verify the expression of four PKC-isoenzymes (alpha, delta, epsilon, zeta) in two distinct phases of the chondrogenesis and the endochondral osteogenesis in vitro. We performed primary cultures of chondrocytes collected from tibiae of 6-day old chick embryos. This cells were cultured for 20 days and than collected on coverslips (stage 1 culture). Other cells of the stage 1 were undergone further differentiation towards the phenotype of osteoblast-like cells (stage 2 culture), in accord to the protocol of Descalzi Cancedda et al. (1992). In stage 1 culture, PKC-epsilon was the most expressed isoform, whereas PKC-alpha exhibited the least intense positivity. In stage 2 culture, PKC-alpha was the most expressed isoform, whereas a marked decrease of PKC-epsilon expression was detected compared to stage 1. No relevant differences were evidenced as regards,the expression of PKC-zeta between the two considered cell culture stages. On these bases, it could be reasonable that these PKC-isoenzymes may be involved at different levels in chondrocytes differentiation as well as in the endochondral ossification process.

Cell proliferation rates and fibronectin arrangement as parameters for biocompatibility evaluation of dental metal alloys in vitro

A short-term (72-96 hours) biocompatibility evaluation in vitro of four single phase dental metal alloys was conducted by determining cell proliferation rates correlated to the organization of the extracellular matrix protein fibronectin in human fibroblast cultures. Immunocytochemical methods were performed to detect both cell proliferation rates by 5-bromodeoxyuridine (BrdU) incorporation, and fibronectin arrangement, i.e., diffuse in the extracellular matrix, organized in fibrils or in focal adhesions. We showed that cell proliferation rates were related to fibronectin expression. In particular, a higher percentage of cells in the S-phase were related to a predominance of fibronectin organized both in fibrils and in focal adhesions. The alloy with the highest Au content seemed the most biocompatible among those tested, since it behaved in a very similar manner to the controls. On the contrary, fibroblasts exposed to the alloy with the highest percentage of Ag had the most different behavior as compared to the controls. We can assume that a correlation exists between fibronectin organization and the percentage of BrdU-positive cells and that these parameters are varying with the different metal composition of the alloys. The observation of fibronectin arrangement together with cell proliferation rates could be considered a useful tool to determine the biocompatibility of these biomaterials.

Enhanced nuclear diacylglycerol kinase activity in response to a mitogenic stimulation of quiescent Swiss 3T3 cells with insulin-like growth factor I

Results from several laboratories have established the existence in the nucleus of an autonomous polyphosphoinositide cycle, which is involved in both cell proliferation and differentiation. A key step of intranuclear polyphosphoinositide metabolism is the phospholipase C-mediated generation of diacylglycerol (DAG). In insulin-like growth factor (IGF)-I-stimulated Swiss 3T3 cells, a transient elevation of intranuclear DAG levels is essential for attracting the alpha isoform of protein kinase C (PKC) to the nucleus. Previous evidence has shown that the nucleus also contains DAG kinase, i.e., the enzyme that yields phosphatidic acid from DAG, thus terminating PKC-mediated signaling events. Here we show that IGF-I treatment of quiescent Swiss 3T3 cells results in the stimulation of nuclear DAG kinase activity. Time course analysis showed an inverse relationship between nuclear DAG mass and DAG kinase activity levels. After IGF-I treatment, maximal enhancement of DAG kinase activity was measured in the internal matrix domain of the nucleus. PKC-alpha remained within the nuclear compartment, even when nuclear DAG mass returned to basal levels. This was conceivably due to interactions with specific nuclear PKC-binding proteins, some of which were identified as lamins A, B, and C and protein C23/nucleolin. Treatment of cells with two DAG kinase inhibitors, R59022 and R59949, blocked the IGF-I-dependent rise in nuclear DAG kinase activity and maintained elevated intranuclear levels of DAG. The two inhibitors also markedly potentiated the mitogenic effect of IGF-I. These results suggest that nuclear DAG kinase plays a key role in regulating the levels of DAG present in the nucleus and that DAG is a key molecule for the mitogenic effect that IGF-I exerts on Swiss 3T3 cells.

Nuclear matrix protein is released from apoptotic white cells during cold (1-6 degrees C) storage of concentrated red cell units and might induce antibody response in multiply transfused patients

BACKGROUND

A previous study showed that white cells in blood units undergo apoptosis during storage.

STUDY DESIGN AND METHODS

The present study attempts to show the release of nuclear matrix protein (NMP) in the supernatants of red cell units and to determine whether antibodies against nuclear components may be present in multiply transfused patients; the methods employed were enzyme-linked immunosorbent assay, flow cytometry, microscopy, immunoblotting, immunofluorescence, and confocal laser-scanning microscopy.

RESULTS

NMP is released from white cells in the supernatant of packed red cell units upon cold storage (1-6 degrees C). The concentration of NMP correlates well with the degree of apoptosis, as analyzed by flow cytometry, nuclear dye staining, and DNA gel electrophoresis. Immunofluorescence also shows that white cells undergoing apoptosis (pre-G(1) peak, as seen by propidium iodide staining and flow cytometry) have an NMP content lower than control cells, which confirms an actual release of NMP. Moreover, immunoblotting analysis and immunofluorescent staining showed that, in 4 of 38 multiply transfused patients, autoantibodies against NMPs were present without any clinical or laboratory sign of autoimmune disease. One of the sera, recognizing a 64-kDa NMP, immunostained nuclear dots that were identified as coiled bodies because of their colocalization with p 80 coilin.

CONCLUSION

NMP is released in the supernatant of red cell units. The results obtained from patients suggest that nuclear proteins released during apoptosis, once transfused, may induce an immune response in multiply transfused patients.

Increase in nuclear phosphatidylinositol 3-kinase activity and phosphatidylinositol (3,4,5) trisphosphate synthesis precede PKC-zeta translocation to the nucleus of NGF-treated PC12 cells

We and others have previously demonstrated the existence of an autonomous nuclear polyphosphoinositide cycle that generates second messengers such as diacylglycerol (DAG), capable of attracting to the nucleus specific protein kinase C (PKC) isoforms (Neri et al. (1998) J. Biol. Chem. 273, 29738-29744). Recently, however, nuclei have also been shown to contain the enzymes responsible for the synthesis of the non-canonical 3-phosphorylated inositides. To clarify a possible role of this peculiar class of inositol lipids we have examined the question of whether nerve growth factor (NGF) induces PKC-zeta nuclear translocation in PC12 cells and whether this translocation is dependent on nuclear phosphatidylinositol 3-kinase (PI 3-K) activity and its product, phosphatidylinositol 3,4, 5-trisphosphate [PtdIns(3,4,5)P(3)]. NGF increased both the amount and the enzyme activity of immunoprecipitable PI 3-K in PC12 cell nuclei. Activation of the enzyme, but not its translocation, was blocked by PI 3-K inhibitors wortmannin and LY294002. Treatment of PC12 cells for 9 min with NGF led to an increase in the nuclear levels of PtdIns(3,4,5)P(3). Maximal translocation of PKC-zeta from the cytoplasm to the nucleus (as evaluated by immunoblotting, enzyme activity, and confocal microscopy) occurred after 12 min of exposure to NGF and was completely abrogated by either wortmannin or LY294002. In contrast, these two inhibitors did not block nuclear translocation of the conventional, DAG-sensitive, PKC-alpha. On the other hand, the specific phosphatidylinositol phospholipase C inhibitor, 1-O-octadeyl-2-O-methyl-sn-glycero-3-phosphocholine, was unable to abrogate nuclear translocation of the DAG-insensitive PKC-zeta. These data suggest that a nuclear increase in PI 3-K activity and PtdIns(3,4,5)P(3) production are necessary for the subsequent nuclear translocation of PKC-zeta. Furthermore, they point to the likelihood that PKC-zeta is a putative nuclear downstream target of PI 3-K during NGF-promoted neural differentiation.-Neri, L. M., Martelli, A. M., Borgatti, P., Colamussi, M. L., Marchisio, M., Capitani, S. Increase in nuclear phosphatidylinositol 3-kinase activity and phosphatidylinositol (3,4, 5) trisphosphate synthesis precede PKC-zeta translocation to the nucleus of NGF-treated PC12 cells.

Scanning electron microscopic detection of nuclear structures involved in DNA replication

In order to evaluate at the ultrastructural level the three dimensional chromatin arrangement during interphase and particularly during the S phase, the immunogold detection of Bromodeoxyuridine (BrdU), as a marker of DNA synthesis, was performed in human HeLa, HL60, and in murine Friend leukemia cells (FLC). Field emission in lens scanning electron microscopy analysis of ultrathin cryosections revealed the presence of a regular three-dimensional network of fibers in dispersed chromatin. This spatial architecture was apparently constituted mainly of 10 nm filaments organized in loops of about 80-100 nm. Nodal points and the overlapping of such coils appeared as thicker structures of about 30 nm in diameter. Thin filaments of about 5 nm did not show a regular distribution. This three-dimensional fiber organization seemed quite constant in the dispersed chromatin of all the cell lines analyzed. The DNase treatment of the samples selectively removed the 10 nm class fibers, whereas the BrdU labeling confirmed the presence of newly synthesized DNA organized into chromatin units with a regular arrangement. These data suggest that the 10 nm chromatin fiber likely represents the DNA condensation order at which DNA duplication starts and the main weft of a three dimensional network within the interphase nucleus.

Spatial distribution of lamin A and B1 in the K562 cell nuclear matrix stabilized with metal ions

When the nucleus is stripped of most DNA, RNA, and soluble proteins, a structure remains that has been referred to as the nuclear matrix, which acts as a framework to determine the higher order of chromatin organization. However, there is always uncertainty as to whether or not the nuclear matrix, isolated in vitro, could really represent a skeleton of the nucleus in vivo. In fact, the only nuclear framework of which the existence is universally accepted is the nuclear lamina, a continuous thin layer that underlies the inner nuclear membrane and is mainly composed of three related proteins: lamins A, B, and C. Nevertheless, a number of recent investigations performed on different cell types have suggested that nuclear lamins are also present within the nucleoplasm and could be important constituents of the nuclear matrix. In most cell types investigated, the nuclear matrix does not spontaneously resist the extraction steps, but must rather be stabilized before the application of extracting agents. In this investigation, by immunochemical and morphological analysis, we studied the effect of stabilization with different divalent cations (Zn(2+), Cu(2+), Cd(2+)) on the distribution of lamin A and B1 in the nuclear matrix obtained from K562 human erythroleukemia cells. In intact cells, antibodies to both lamin A and B1 mainly stained the nuclear periphery, although some immunoreactivity was detected in the nuclear interior. The fluorescent lamin A pattern detected in Cu(2+)- and Cd(2+)-stabilized nuclei was markedly modified, whereas Zn(2+)-incubated nuclei showed an unaltered pattern of lamin A distribution. By contrast, the distribution of lamin B1 in isolated nuclei was not modified by the stabilizing cations. When chromatin was removed by nuclease digestion and extraction with solutions of high ionic strength, a previously masked immunoreactivity for lamin A, but not for lamin B1, became evident in the internal part of the residual structures representing the nuclear matrix. Our results indicate that when metal ions are used as stabilizing agents for the recovery of the nuclear matrix, the distribution of both lamin A and lamin B1 in the final structures, corresponds to the pattern we have very recently reported using different extraction procedures. This observation strengthen the concept that intranuclear lamins may act as structural components of the nuclear matrix.

Multiple biological responses activated by nuclear protein kinase C

Protein kinase C is a family of serine-threonine kinases that are physiologically activated by a number of lipid cofactors and are important transducers in many agonist-induced signaling cascades. To date, 12 different isozymes of this kinase have been identified and are believed to play distinct regulatory roles. Protein kinase C was thought to reside in the cytosol in an inactive conformation and translocate to the plasma membrane upon cell activation by different stimuli. Nevertheless, a growing body of evidence has illustrated that this family of isozymes is capable of translocating to other cellular sites, including the nucleus. Moreover, it seems that some protein kinase C isoforms are resident within the nucleus. A wealth of data is being accumulated, demonstrating that nuclear protein kinase C isoforms are involved in the regulation of several critical biological functions such as cell proliferation and differentiation, neoplastic transformation, and apoptosis. In this review, we will discuss the most significant findings concerning nuclear protein kinase C which have been published during the past 5 years.

Nuclear phospholipase C: a novel aspect of phosphoinositide signalling

The role of polyphosphoinositides in cellular signalling is well known and recently it has also been shown that the nucleus is a site for both synthesis and hydrolysis of the phosphorylated forms of phosphatidylinositol. It has been demonstrated that phospholipase C specific for inositol lipids (PLC) is one of the main steps of the inositol lipid cycle. The PLC beta family, and especially type beta 1, has given rise to considerable interest since, due to their common COOH-terminus they show nuclear localisation in addition to that at the plasma membrane. It is well established that an autonomous intranuclear inositide cycle exists, and that this cycle is endowed with conventional lipid kinases, phosphatases and PLCs. Among this latter the beta 1 type undergoes stimulation or inhibition under different stimuli and this implicates the beta 1 isoform as a key enzyme for mitogen-activated cell growth as well as for differentiation. Indeed, both the overexpression and the down-regulation of PLC beta 1, by means of antisense mRNA, have demonstrated that PLC plays a role in the nuclear compartment.

The pro-apoptotic drug camptothecin stimulates phospholipase D activity and diacylglycerol production in the nucleus of HL-60 human promyelocytic leukemia cells

It has recently been reported (T. Shimizu et al., J. Biol. Chem., 273: 8669-8674, 1998) that the pro-apoptotic drug, camptothecin, an inhibitor of topoisomerase I, induces a protein kinase C-alpha-mediated phosphorylation of lamin B in HL-60 cells, which precedes both degradation of lamin B and fragmentation of DNA. In this paper, we report that, in HL-60 cells exposed to camptothecin, there is a rapid and sustained increase of nuclear protein kinase C-alpha activity that is due to an increase in the amount of protein kinase C-alpha present in the nucleus. The enhancement of nuclear kinase C activity is preceded by an increase in the mass of nuclear diacylglycerol. As demonstrated by its sensitivity to propranolol, the nuclear diacylglycerol mass increase is due to the activation of a phospholipase D. Indeed, inhibitors of neither phosphatidylcholine-specific phospholipase C nor phosphoinositide-specific phospholipase C blocked the rise in nuclear diacylglycerol. In vitro assays also demonstrated the activation of a nuclear phospholipase D, but not of a phosphoinositide-specific phospholipase C, after treatment with camptothecin. Propranolol was also able to block the rise in nuclear protein kinase C-alpha activity, thus suggesting that the increase in diacylglycerol mass is important for the activation of the kinase at the nuclear level. Moreover, propranolol was capable of drastically reducing the number of HL-60 cells that underwent apoptosis after treatment with camptothecin. Our results show the activation during apoptosis of a phospholipase D-mediated signaling pathway operating at the nuclear level. This pathway may represent an attractive therapeutic target for the modulation of apoptotic events in human disease.

Biochemical and morphological changes in the nuclear matrix prepared from apoptotic HL-60 cells: effect of different stabilizing procedures

Apoptotic cell death is characterized by deep morphological changes that take place in the nucleus. It is unclear whether modifications also occur in the nuclear matrix, a mainly proteinaceous structure that conceivably acts as a nuclear framework. We have investigated whether biochemical and morphological alterations of the nuclear matrix prepared from apoptotic HL-60 cells were dependent on the manipulations to which isolated nuclei were subjected before DNase I digestion and 2 M NaCl extraction. Our results showed that the stabilizing procedures employed to preserve the inner fibrogranular network and nucleolar remnants of the matrix (i.e., a 37 degrees C incubation; exposure to sodium tetrathionate at 4 degrees C; exposure to sodium tetrathionate at 37 degrees C) had no effect on the protein recovery of apoptotic nuclear matrices, which was always approximately two- to fivefold less than in control matrices. Moreover, one- and two-dimensional gel analysis of nuclear matrix proteins showed that, in apoptotic samples, striking quantitative changes were present, as compared with controls. Once again, these changes were seen irrespective of the stabilizing procedures employed. Also, transmission electron microscope analysis showed similar morphological alterations in all types of apoptotic nuclear matrices. By contrast, the immunofluorescent distribution of the 240-kDa NuMA protein seen in apoptotic samples was more sensitive to the stabilizing treatments. Our results indicate that the biochemical and morphological changes of the apoptotic nuclear matrix are largely independent of the isolation protocols and strengthen the contention that destruction of the nuclear matrix network is one of the key events leading to apoptotic nuclear destruction.

Influence of different metal ions on the ultrastructure, biochemical properties, and protein localization of the K562 cell nuclear matrix

The higher order of chromatin organization is thought to be determined by the nuclear matrix, a mainly proteinaceous structure that would act as a nucleoskeleton. The matrix is obtained from isolated nuclei by a series of extraction steps involving the use of high salt and nonspecific nucleases, which remove chromatin and other loosely bound components. It is currently under debate whether these structures, isolated in vitro by unphysiological extraction buffers, correspond to a nucleoskeleton existing in vivo. In most cell types investigated, the nuclear matrix does not spontaneously resist these extractions steps; rather, it must be stabilized before the application of extracting agents. In this study nuclei, isolated from K562 human erythroleukemia cells, were stabilized by incubation with different metal ions (Ca2+, Cu2+, Zn2+, Cd2+), and the matrix was obtained by extraction with 2 M NaCl. By means of ultrastructural analysis of the resulting structures, we determined that, except for Ca2+, all the other metals induced a stabilization of the matrix, which retained the inner fibrogranular network and residual nucleoli. The biochemical composition, analyzed by two-dimensional gel electrophoresis separation, exhibited a distinct matrix polypeptide pattern, characteristic of each type of stabilizing ion employed. We also investigated to what extent metal ions could maintain in the final structures the original distribution of three inner matrix components, i.e. NuMA, topoisomerase IIalpha, and RNP. Confocal microscopy analysis showed that only NuMa, and, to a lesser extent, topoisomerase IIalpha, were unaffected by stabilization with divalent ions. On the contrary, the fluorescent RNP patterns detected in the resulting matrices were always disarranged, irrespective of the stabilization procedure. These results indicate that several metal ions are powerful stabilizing agents of the nuclear matrix prepared from K562 erythroleukemia cells and also strengthen the concept that NuMA and topoisomerase IIalpha may act as structural components of the nuclear matrix.

Insulin-like growth factor-I-dependent stimulation of nuclear phospholipase C-beta1 activity in Swiss 3T3 cells requires an intact cytoskeleton and is paralleled by increased phosphorylation of the phospholipase

Swiss 3T3 mouse fibroblasts were exposed to 10 microM colchicine to disrupt microtubules, then stimulated with insulin-like growth factor-I. Immunoprecipitation experiments showed that insulin-like growth factor-I receptor and insulin receptor substrate-1 were tyrosine phosphorylated to the same extent in both cells treated with colchicine and in those not exposed to the drug. Moreover, the activity of phosphatidylinositol 3-kinase was not affected by incubation with colchicine. While in nuclei prepared from cells not exposed to colchicine it was possible to detect an insulin-like growth factor-I-dependent increase in the mass of diacylglycerol, as well as stimulation of phospholipase C activity, no similar changes were observed in nuclei obtained from cells treated with colchicine. Activation of the nuclear phospholipase activity was paralleled by an increase of its phosphorylation. Immunofluorescent studies revealed that mitogen-activated protein kinase did not translocate towards the nucleus when the cytoskeleton was depolymerized. These results show that in Swiss 3T3 cells some as yet unknown events necessary for the insulin-like growth factor-I-dependent activation of nuclear polyphosphoinositide metabolism require the presence of an intact cytoskeleton and are situated down-stream the activation of insulin receptor substrate-1 and phosphatidylinositol 3-kinase. Activation of nuclear phospholipase C-beta1 might be linked to its phosphorylation and translocation of mitogen-activated protein kinase to the nucleus.

Lamin A is part of the internal nucleoskeleton of human erythroleukemia cells

Nuclear lamins are the most abundant components of the nuclear lamina, a 10-50-nm-thick fibrous layer underlying the inner nuclear envelope membrane. Nevertheless, a number of recent investigations performed on epithelial and fibroblast cells have suggested that nuclear lamins are also present within the nucleoplasm and could be important constituents of the nucleoskeleton. We have studied the subnuclear distribution of lamins A and B1 in human erythroleukemia cells by using immunoblotting analysis and immunofluorescent staining of fractionated nuclei. In intact cells and isolated nuclei, antibodies to lamins A and B1 mainly stained the nuclear periphery, although some immunoreactivity was detected in the nuclear interior. However, when chromatin was removed by nuclease digestion and extraction with nonionic detergent or solutions of high ionic strength, a previously masked immunoreactivity for lamin A, but not for lamin B1, became evident in the internal part of the residual structures representing the nuclear matrix or scaffold. Preferential localization of lamin A to the inner part of the nucleus was also demonstrated by the presence of the majority of lamin A in the solubilized inner nuclear network subfraction. In contrast, lamin B1 was mainly recovered in the fraction corresponding to the nuclear periphery. Double labeling experiments showed that lamin A, but not lamin B1, colocalized with coiled and GATA-1 bodies. Thus, our results support the hypothesis that lamin A, but not lamin B1, may be a component of an internal nucleoskeleton in human erythroleukemia cells.

Biochemical and morphological characterization of the nuclear matrix from apoptotic HL-60 cells

We have characterized the nuclear matrix-intermediate filament fraction from control and apoptotic HL-60 cells. Apoptosis was induced by exposure to the topoisomerase I inhibitor, camptothecin. By means of two-dimensional polyacrylamide gel electrophoresis, striking qualitative and quantitative differences were seen in the protein composition of the nuclear matrix-intermediate filament fraction obtained from apoptotic cells in comparison with controls. Western blotting analysis of apoptotic nuclear matrix proteins revealed degradation of some (topoisomerase IIalpha, SAF-A) but not other (SATB1 and nucleolin) components. Moreover, immunofluorescent staining for typical matrix antigens (NuMA protein, lamin B, SC-35) showed that in 35-40% of the structures prepared from apoptotic samples, marked changes in the subnuclear distribution of these proteins were present. Striking morphological differences between control and apoptotic samples were also detected at the ultrastructural level. These results demonstrate that both biochemical and morphological changes can be detected in the nuclear matrix prepared from apoptotic HL-60 cells.

Lipid signaling and cell responses at the nuclear level

The nucleus is known to be a site for an active lipid metabolism. Although phospholipids are present in the nuclear envelope, evidence suggests that they are also located further inside the nucleus. The function of these intranuclear lipids has escaped clarification for many years. Early experiments showed that they can interact with DNA double helix affecting its thermal stability and can influence RNA synthesis in isolated nuclei. However, in the last 10 years several investigations have suggested that they may be involved in signal transduction pathways at the nuclear level and a growing body of evidence supports this hypothesis.

Nuclear diacylglycerol produced by phosphoinositide-specific phospholipase C is responsible for nuclear translocation of protein kinase C-alpha

It is well established that an independent inositide cycle is present within the nucleus, where it is involved in the control of cell proliferation and differentiation. Previous results have shown that when Swiss 3T3 cells are treated with insulin-like growth factor-I (IGF-I) a rapid and sustained increase in mass of diacylglycerol (DAG) occurs within the nuclei, accompanied by a decrease in the levels of both phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate. However, it is unclear whether or not other lipids could contribute to this prolonged rise in DAG levels. We now report that the IGF-I-dependent increase in nuclear DAG production can be inhibited by the specific phosphatidylinositol phospholipase C inhibitor 1-O-octadeyl-2-O-methyl-sn-glycero-3-phosphocholine or by neomycin sulfate but not by the purported phosphatidylcholine-phospholipase C specific inhibitor D609 or by inhibitors of phospholipase D-mediated DAG generation. Treatment of cells with 1-O-octadeyl-2-O-methyl-sn-glycero-3-phosphocholine or neomycin sulfate inhibited translocation of protein kinase C-alpha to the nucleus. Moreover, exposure of cells to 1-O-octadeyl-2-O-methyl-sn-glycero-3-phosphocholine, but not to D609, dramatically reduced the number of cells entering S-phase upon stimulation with IGF-I. These results suggest that the only phospholipase responsible for generation of nuclear DAG after IGF-I stimulation of 3T3 cells is PI-PLC. When this activity is inhibited, neither DAG rise is seen nor PKC-alpha translocation to the nucleus occurs. Furthermore, this PI-PLC activity appears to be essential for the G0/G1 to S-phase transition.

Atypical isoenzymes of PKC-iota, -lambda, -mu: relative distribution in mouse foetal and neonatal organs

PKC-iota, -lambda and -mu are recently cloned and characterized as members of the alternative group of this family of protein kinases. We performed an immunohistochemical study about the expression of PKC-iota, -lambda and -mu in tissues and organs of mouse foetuses and newborn mice, in order to evaluate their peculiar functions during the developmental stages. The specificity of the antibodies was tested by Western-blotting experiments with whole extracts from 15-day mouse foetuses or neonatal mice. Cryostat sections of mouse foetal and neonatal organs were reacted with monoclonal (anti -iota and -lambda) or polyclonal (anti -mu) antibodies. The staining intensity was expressed in standardized arbitrary units from 0 to 250. An almost general increasing expression from foetal to neonatal samples, with the highest immunostaining for PKC-mu, was observed in all investigated organs, thus suggesting that PKC atypical isoforms are quantitatively expressed with a significant relationship with the proceeding of developmental phases. Marked differences were revealed also as far as the distribution of these isoforms was concerned in well defined cell populations, particularly in lung, stomach and kidney. These results suggest that various cell populations, in important phases of proliferating and differentiating events, produce atypical PKC isoforms that are conceivably involved in regulating signal transducing events. Therefore, PKC-iota, -lambda, -mu isoforms may have well defined functions in regulating the growth or the program of cell proliferation and differentiation.

Prereplicative increase of nuclear matrix-bound DNA polymerase-alpha and primase activities in HeLa S3 cells following dilution of long-term cultures

We investigated the association of DNA polymerase and DNA primase activity with the nuclear matrix in HeLa S3 cells diluted with fresh medium after having been cultured without any medium change for 7 days. Flow cytometric analysis demonstrated that just before dilution about 85% of the cells were in the G1 phase of the cycle, whereas 8% were in the S phase. After dilution with fresh medium, 18-22 h were required for the cell population to attain a stable distribution with respect to the cell cycle. At that time, about 38% of the cells were in the S phase. DNA polymerase and DNA primase activity associated with the nuclear matrix prepared from cells just before dilution represented about 10% of nuclear activity. As judged by [3H]-thymidine incorporation and flow cytometric analysis, an increase in the number of S-phase cells was evident at least 6 h after dilution. However, as early as 2 h after dilution into fresh medium, a striking prereplicative increase of the two activities was seen in the nuclear matrix fraction but not in cytosol or isolated nuclei. Both DNA polymerase and primase activities bound to the matrix were about 60% of nuclear activity. Overall, the nuclear matrix was the cell fraction where the highest induction (about 10-fold) of both enzymatic activities was seen at 30 h after dilution, whereas in cytosol and isolated nuclei the increase was about two- and fourfold, respectively. Typical immunofluorescent patterns given by an antibody to 5-bromodeoxyuridine were seen after dilution. These findings, which are at variance with our own previous results obtained with cell cultures synchronized by either a double thymidine block or aphidicolin exposure, strengthen the contention that DNA replication is associated with an underlying nuclear structure and demonstrate the artifacts that may be generated by procedures commonly used to synchronize cell cultures.

Intranuclear distribution of HMGI/Y proteins. An immunocytochemical study

The intranuclear distribution of HMGI/Y proteins was analyzed by immunofluorescent staining in several cell lines using a polyclonal antibody that stained a fibrogranular network. In actively growing 3T3 fibroblasts, HMGI/Y proteins were mainly localized to heterochromatin masses, whereas in quiescent cells they were more diffusely distributed. Double labeling experiments showed a co-localization of HMGI/Y with DNA topoisomerase IIalpha. These results are in agreement with previously published biochemical data and indicate a possible involvement of HMGI/Y proteins in several nuclear functions, including chromatin organization and gene expression.

Expression of Rab3D N135I inhibits regulated secretion of ACTH in AtT-20 cells

Rab proteins are small molecular weight GTPases that control vesicular traffic in eucaryotic cells. A subset of Rab proteins, the Rab3 proteins are thought to play an important role in regulated exocytosis of vesicles. In transfected AtT-20 cells expressing wild-type Rab3D, we find that a fraction of the protein is associated with dense core granules. In the same cells, expression of a mutated isoform of Rab3D, Rab3D N135I, inhibits positioning of dense core granules near the plasma membrane, blocks regulated secretion of mature ACTH, and impairs association of Rab3A to membranes. Expression of Rab3D N135I does not change the levels of ACTH precursor or the efficiency with which the precursor is processed into ACTH hormone and packaged into dense core granules. We also find that cells expressing mutated Rab3D differentiate to the same extent as untransfected AtT-20 cells. We conclude that expression of Rab3D N135I specifically impairs late membrane trafficking events necessary for ACTH hormone secretion.

Changes in the subnuclear distribution of two RNA metabolism-related proteins can be detected in nuclear scaffold or matrix prepared by different techniques

The nuclear scaffold or matrix is a mainly proteinaceous structure thought to act as a nucleoskeleton determining the higher order organization of eukaryotic chromatin. These structures are prepared from isolated nuclei by a series of extraction steps involving the use of ionic detergents or high salt, and restriction enzymes or non-specific nucleases to remove chromatin and other loosely bound components. Since these treatments are harsh and unphysiological, the question remains open as to whether or not these structures, isolated in vitro, correspond to a nucleoskeleton existing in vivo. Recently, it has been demonstrated that the majority of nuclear matrix proteins are involved in RNA metabolism. In this study we have employed a morphological approach involving the use of confocal laser scanning microscopy and indirect immunofluorescence techniques to analyze whether two widely employed methods to prepare the nuclear scaffold or matrix can maintain the spatial distribution of two polypeptides involved in RNA metabolism, i.e., a 105-kDa component of spliceosomes and a ribonucleoprotein antigen. We demonstrate that the localization of these polypeptides changes, in some cases dramatically, in the final nucleoskeletal structures when compared with intact cells. Only when isolated nuclei were stabilized in vitro with the cross-linking agent sodium tetrathionate (NaTT) prior to extraction with 2 M NaCl and DNase I digestion, were the immunofluorescent patterns displayed by the nuclear matrix indistinguishable from those detected in intact cells. These results emphasize the usefulness of NaTT in studying putative nucleoskeletal structures, but also show that the methods currently employed to prepare the nuclear scaffold or matrix may create in vitro artifacts.

Different concentrations of Mg++ ions affect nuclear matrix protein distribution during thermal stabilization of isolated nuclei

The nuclear matrix, a proteinaceous network believed to be a scaffolding structure determining higher-order organization of chromatin, is usually prepared from intact nuclei by a series of extraction steps. In most cell types investigated the nuclear matrix does not spontaneously resist these treatments but must be stabilized before the application of extracting agents. Incubation of isolated nuclei at 37C or 42C in buffers containing Mg++ has been widely employed as stabilizing agent. We have previously demonstrated that heat treatment induces changes in the distribution of three nuclear scaffold proteins in nuclei prepared in the absence of Mg++ ions. We studied whether different concentrations of Mg++ (2.0-5 mM) affect the spatial distribution of nuclear matrix proteins in nuclei isolated from K562 erythroleukemia cells and stabilized by heat at either 37C or 42C. Five proteins were studied, two of which were RNA metabolism-related proteins (a 105-kD component of splicing complexes and an RNP component), one a 126-kD constituent of a class of nuclear bodies, and two were components of the inner matrix network. The localization of proteins was determined by immunofluorescent staining and confocal scanning laser microscope. Mg++ induced significant changes of antigen distribution even at the lowest concentration employed, and these modifications were enhanced in parallel with increase in the concentration of the divalent cation. The different sensitivity to heat stabilization and Mg++ of these nuclear proteins might reflect a different degree of association with the nuclear scaffold and can be closely related to their functional or structural role.

The influence of dental metal alloys on cell proliferation and fibronectin arrangement in human fibroblast cultures

The biocompatibility of six single-phase dental metal alloys was studied by determining cell proliferation rates correlated to the arrangement of fibronectin (FN) in fibroblast cultures. Immunocytochemical methods were used to detect cell proliferation by 5-bromodeoxyuridine (BrdU) incorporation, and FN organization [i.e. diffuse in the extracellular matrix and organized in fibrils or in focal adhesions (FA)] in human fibroblast cultures. Cell proliferation rates were related to FN arrangement and in particular a higher percentage of cells in the S-phase was related to a predominance of FA. The greatest difference in behaviour compared to that of the controls was detected after 120 and 168 hr: at these times, as well as at previous ones, the alloy with the highest Au content seemed the most biocompatible among those tested, as it behaved in a very similar way to the controls. In contrast, fibroblasts exposed to the other five alloys showed different behaviours from the controls. It is assumed that a correlation exists between FN organization and the percentage of BrdU-positive cells, and that these features vary in the presence of different alloys. The observation of FN arrangement together with cell proliferation rates could be another useful tool in determining the biocompatibility of dental metal alloys.