Effects of Simulated Microgravity on the Morphology and Function of Neonatal Porcine Cell Clusters Cultured with and without Sertoli Cells

Human islet allografts are well known to induce full and sustained remission of hyperglycemia, with complete normalization of key metabolic parameters. Nevertheless, acquiring human islets, even from cadaveric human donor pancreases, remains a significant impediment to successful transplantation therapy for diabetes. To overcome this difficulty, neonatal porcine cell clusters (NPCCs) have been considered for human islet substitutes because they are easily obtained by collagenase digestion of the neonatal piglet pancreas. Currently, the major hurdle in using NPCCs for xenograft is the delay (time lag) in achieving the posttransplant normalization of blood glucose levels in animal diabetic recipients. The present work is the first attempt to evaluate whether incubation of NPCCs in simulated microgravity, in the presence or absence of Sertoli cells (SC), may reduce the maturation time lag of β-cells by differentiation acceleration in vitro, thereby expediting production, viability, and acquisition of functional competence of pretransplantation β-cell-enriched islets. Following a 3-day incubation period, NPCCs maintained in conventional culture, NPCCs incubated in simulated microgravity in the HARV biochamber, and NPCCs plus co-incubated SC in simulated microgravity were examined for viability, morphology, and insulin secretion. Results show that NPCCs grown alone in the HARV biochamber are superior in quality, both in terms of viability and functional competence, when compared to other culture pretreatment protocols. This finding strongly suggests that NPCC pretreatment in simulated microgravity may enhance the transplantation success of NPCCs in the diabetic recipient.

Targeting the PI3K/Akt/mTOR signaling pathway in B-precursor acute lymphoblastic leukemia and its therapeutic potential

B-precursor acute lymphoblastic leukemia (B-pre ALL) is a malignant disorder characterized by the abnormal proliferation of B-cell progenitors. The prognosis of B-pre ALL has improved in pediatric patients, but the outcome is much less successful in adults. Constitutive activation of the phosphatidylinositol 3-kinase (PI3K), Akt and the mammalian target of rapamycin (mTOR) (PI3K/Akt/mTOR) network is a feature of B-pre ALL, where it strongly influences cell growth and survival. RAD001, a selective mTORC1 inhibitor, has been shown to be cytotoxic against many types of cancer including hematological malignancies. To investigate whether mTORC1 could represent a target in the therapy of B-pre ALL, we treated cell lines and adult patient primary cells with RAD001. We documented that RAD001 decreased cell viability, induced cell cycle arrest in G0/G1 phase and caused apoptosis in B-pre ALL cell lines. Autophagy was also induced, which was important for the RAD001 cytotoxic effect, as downregulation of Beclin-1 reduced drug cytotoxicity. RAD001 strongly synergized with the novel allosteric Akt inhibitor MK-2206 in both cell lines and patient samples. Similar results were obtained with the combination CCI-779 plus GSK 690693. These findings point out that mTORC1 inhibitors, either as a single agent or in combination with Akt inhibitors, could represent a potential therapeutic innovative strategy in B-pre ALL.

Cytotoxic activity of the novel Akt inhibitor, MK-2206, in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive neoplastic disorder arising from T-cell progenitors. T-ALL accounts for 15% of newly diagnosed ALL cases in children and 25% in adults. Although the prognosis of T-ALL has improved, due to the use of polychemotherapy schemes, the outcome of relapsed/chemoresistant T-ALL cases is still poor. A signaling pathway that is frequently upregulated in T-ALL, is the phosphatidylinositol 3-kinase/Akt/mTOR network. To explore whether Akt could represent a target for therapeutic intervention in T-ALL, we evaluated the effects of the novel allosteric Akt inhibitor, MK-2206, on a panel of human T-ALL cell lines and primary cells from T-ALL patients. MK-2206 decreased T-ALL cell line viability by blocking leukemic cells in the G(0)/G(1) phase of the cell cycle and inducing apoptosis. MK-2206 also induced autophagy, as demonstrated by an increase in the 14-kDa form of LC3A/B. Western blotting analysis documented a concentration-dependent dephosphorylation of Akt and its downstream targets, GSK-3α/β and FOXO3A, in response to MK-2206. MK-2206 was cytotoxic to primary T-ALL cells and induced apoptosis in a T-ALL patient cell subset (CD34(+)/CD4(-)/CD7(-)), which is enriched in leukemia-initiating cells. Taken together, our findings indicate that Akt inhibition may represent a potential therapeutic strategy in T-ALL.

Nuclear lipids: new functions for old molecules?

It is becoming increasingly evident that stimulation of nuclear lipid metabolism plays a central role in many signal transduction pathways that ultimately result in various cell responses including proliferation and differentiation. Nuclear lipid metabolism seems to be at least as complex as that existing at the plasma membrane. However, a distinctive feature of nuclear lipid biochemical pathways is their operational independence from their cell periphery counterparts. Although initially it was thought that nuclear lipids would serve as a source for second messengers, recent evidence points to the likelihood that lipids present in the nucleus also fulfil other roles. The aim of this review is to highlight the most intriguing advances made in the field over the last year, such as the production of new probes for the in situ mapping of nuclear phosphoinositides, the identification of two sources for nuclear diacylglycerol production, the emerging details about the peculiar regulation of nuclear phosphoinositide synthesizing enzymes, and the distinct possibility that nuclear lipids are involved in processes such as chromatin organization and pre-mRNA splicing.

Sertoli cell-induced adult rat islet beta-cell mitogenesis: causative pathways

We have previously observed that in vitro co-incubation of rat pre-pubertal Sertoli cells (SC), or their dialyzed/concentrated secretory products with homologous islets, resulted in significant stimulation of the islet beta-cell mitotic index. Aim of the present work was to assess both the specificity and nature of the mechanisms underlying this phenomenon. For this purpose, first we tested astrocytes (AA), separated and purified from the rat brain cortex, where they are known to release a number of growth factors and neurotrophic cytokines, for co-incubation with the islets. However, under the same experimental conditions used for SC, AA did not induce any changes in the beta-cell life cycle, thereby confirming specificity of SC, with respect to induction of beta-cell mitogenicity. For the second purpose, we examined the products of PD-1, a gene located in the cytoplasm of SC, where it promotes spermatogenesis. By blocking the protein encoded by PD-1, under appropriate culture conditions, we observed that the SC-induced increase in beta-cell mitotic activity lost its statistical significance, which suggested a role of PD-1 with respect to SC-related mitogenic properties on beta-cells. These findings corroborate the idea that SC, by either direct contact, or by means of their secretory products, clearly affect the islet beta-cell mitotic rate. Preliminarily, PD-1 gene, located in the cytoplasm of SC, might be one of the factors involved with the induction of beta-cell mitotic activity. In conclusion, SC-induced beta-cell mitotic activity is specific, seemingly mediated by humoral factors whose acting mechanisms have started being unfolded.

Protein kinase C isoforms and lipid second messengers: a critical nuclear partnership?

A growing body of evidence, accumulated over the past 15 years, has highlighted that the protein kinase C family of isozymes is capable of translocating to the nucleus or is resident within the nucleus. The comprehension of protein kinase C isoform regulation within this organelle is under development. At present, it is emerging that lipid second messengers may play at least two roles in the control of nuclear protein kinase C: on one side they serve as chemical attractants, on the other they directly modulate the activity of specific isoforms. One of the best characterized lipid second messenger that could be involved in the regulation of nuclear PKC activity is DAG. The existence of two separate pools of nuclear DAG suggests that this lipid second messenger might be involved in distinct pathways that lead to different cell responses. Nuclear phosphatidylglycerol, D-3 phosphorylated inositol lipids and nuclear fatty acids are involved in a striking variety of critical biological functions which may act by specific PKC activation. The fine tuning of PKC regulation in cells subjected to proliferating or differentiating stimuli, might prove to be of great interest also for cancer therapy, given the fact that PKC-dependent signaling pathways are increasingly being seen as possible pharmacological target in some forms of neoplastic diseases. In this article, we review the current knowledge about lipid second messengers that are involved in regulating the translocation and/or the activity of different protein kinase C isoforms identified at the nuclear level.

Cellular support systems for alginate microcapsules containing islets, as composite bioartificial pancreas

To improve the functional performance of microencapsulated islets, we examined the effects of putative cellular support systems, consisting of rat purified Sertoli cells (SC) and astrocytes (AA), on coenveloped allogeneic islets. Coincubation of islets with SC but not AA, resulted in significant stimulation of beta cell mitogenesis, coupled with a significant increase in in vitro glucose-stimulated insulin release. Preliminarily, the xenotransplantation of coencapsulated rat islets and homologous SC significantly prolonged remission of hyperglycemia in diabetic mice.

Sertoli cell-induced reversal of adult rat pancreatic islet beta-cells into fetal-like status: potential implications for islet transplantation in type I diabetes mellitus

BACKGROUND

Clinical success of pancreatic islet allograft (TX) for the therapy of diabetes mellitus is hampered by several pitfalls, primarily including the restricted availability of donor tissue and the immune- and/or non-immune-related TX's early loss, with the latter not necessarily being prevented by the host's general immunosuppression. Finally, adult islet beta-cells normally exhibit minimal proliferation capacity, which would not permit restoration of an eventually declining TX mass.

METHODS

To address the limited beta-cell growth capacity, we have examined whether in vitro co-culturing adult rat islets (I) with prepubertal homologous Sertoli cells (SC) would stimulate I beta-cell expansion. SC-derived effects on the islets were studied in vitro, both morphologically (confocal laser microscopy) and functionally (glucose-stimulated insulin release). We have also preliminarily examined the in vivo impact of microencapsulated SC + I co-cultures on TX in diabetic mice.

RESULTS

In vitro, we observed that SCs promoted significant beta-cell replication, as I beta-cell mitotic activity increased from 1% to greater than 8%, which coincided with the adult elements reversing into fetal-like status. This finding was coupled with significantly greater insulin release either in basal or in response to glucose, as compared with controls.

CONCLUSIONS

Addition of SC to islets promotes reversal of the adult beta-cell elements into fetal-like conditions, thereby providing a new, potentially powerful tool that could significantly enhance the functional performance of islet TX in diabetic recipients.

Phosphatidylinositol 3-kinase translocates to the nucleus of osteoblast-like MC3T3-E1 cells in response to insulin-like growth factor I and platelet-derived growth factor but not to the proapoptotic cytokine tumor necrosis factor alpha

Changes in the metabolism of nuclear inositides phosphorylated in the D3 position of the inositol ring, which may act as second messengers, mainly have been linked to cell differentiation. To clarify a possible role of this peculiar class of inositides also during cell proliferation and/or apoptosis, we have examined the issue of whether or not in the osteoblast-like clonal cell line MC3T3-E1 it may be observed an insulin-like growth factor-I (IGF-I)- and platelet-derived growth factor (PDGF)-dependent nuclear translocation of an active phosphatidylinositol 3-kinase (PI 3-K). We found that both the growth factors increased rapidly and transiently both the amount and the activity of immunoprecipitable nuclear PI 3-K. Intranuclear PI 3-K exhibited a massive tyrosine phosphorylation on the p85 regulatory subunit. Moreover, by means of coimmunoprecipitation experiments, we showed the presence, in isolated nuclei, of the p110beta catalytic subunit of PI 3-K. Enzyme translocation was blocked by the specific PI 3-K inhibitor LY294002. In contrast, intranuclear translocation of PI 3-K did not occur in response to the proapoptotic cytokine tumor necrosis factor alpha (TNF-alpha). IGF-I was able to counteract the apoptotic stimulus of TNF-alpha and this was accompanied by the intranuclear translocation of PI 3-K. LY294002 inhibited both intranuclear translocation of PI 3-K and the rescuing effect of IGF-I. These findings strongly suggest that an important step in the signaling pathways that mediate both cell proliferation and survival is represented by the intranuclear translocation of PI 3-K.

Translocation of Akt/PKB to the nucleus of osteoblast-like MC3T3-E1 cells exposed to proliferative growth factors

An active phosphatidylinositol 3-kinase (PI3K) has been shown in nuclei of different cell types. The products of this enzyme, i.e. inositides phosphorylated in the D3 position of the inositol ring, may act as second messengers themselves. Nuclear PI3K translocation has been demonstrated to be related to an analogous translocation of a PtdIns(3,4,5)P(3) activated PKC, the zeta isozyme. We have examined the issue of whether or not in the osteoblast-like clonal cell line MC3T3-E1 there may be observed an insulin-like growth factor-I- (IGF-I) and platelet-derived growth factor- (PDGF) dependent nuclear translocation of an active Akt/PKB. Western blot analysis showed a maximal nuclear translocation after 20 min of IGF-I stimulation or after 30 min of PDGF treatment. Both growth factors increased rapidly and transiently the enzyme activity of immunoprecipitable nuclear Akt/PKB on a similar time scale and after 60 min the values were slightly higher than the basal levels. Enzyme translocation was blocked by the specific PI3K inhibitor, LY294002, as well as cell entry into S-phase. Confocal microscopy showed an evident increase in immunostaining intensity in the nuclear interior after growth factor treatment but no changes in the subcellular distribution of Akt/PKB when a LY294002 pre-treatment was administered to the cells. These findings strongly suggest that the intranuclear translocation of Akt/PKB is an important step in signalling pathways that mediate cell proliferation.

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.

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.

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.

Monocytic differentiation of HL-60 cells is characterized by the nuclear translocation of phosphatidylinositol 3-kinase and of definite phosphatidylinositol-specific phospholipase C isoforms

Immunochemical and immunocytochemical data indicate that nuclei of HL-60 cells contain different enzymes involved in the phosphoinositide cycle, such as PI 3-K and the phosphatidylinositol-specific PLC isoforms beta3, gamma1 and gamma2. These enzymes translocate differently to the nuclear fraction when HL-60 cells are treated with differentiating doses of vitamin D3: PI 3-K translocated progressively to the nucleus in parallel with full differentiation until 96 hours. PLC beta3 increased until 72 hours of treatment and then lowered its intranuclear amount and PLC gamma1 was unchanged at all the examined times. PLC gamma2 nuclear translocation increased progressively until 96 hours of vitamin D3 administration. A fourth PLC isozyme, beta2, present in the cytoplasm of untreated cells, translocates to the cytoplasm after vitamin D3 addition and reaches the highest concentration at the end of monocytic differentiation. Terminal monocytic differentiation was characterized at the nuclear level by high levels of PI 3-K and PLC gamma2 and by the novel expression of PLC beta2. We then observed that the xi isoform of PKC, constitutively present in nuclei of HL-60 cells, translocated to the nucleus when cells were induced to differentiate along the monocytic lineage, but the nuclear translocation of PKC xi was blocked as a consequence of PI 3-K inhibition by Wortmannin. These findings indicate that the main components of the noncanonical and canonical inositol lipid signal transduction pathways, including PI 3-K, PLC beta2 and beta3, PLC gamma2, undergo nuclear translocation and may therefore play a relevant role during monocytic differentiation at the nuclear level. Furthermore, PKC xi nuclear translocation appears to be related to PI 3-K activity.

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.

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.

Phosphoinositide 3-kinase activity is essential for all-trans-retinoic acid-induced granulocytic differentiation of HL-60 cells

Phosphoinositide 3-kinase (PI 3-K) activity increases in HL-60 cells that are induced to granulocytic differentiation by all-trans-retinoic acid. Immunochemical and immunocytochemical analyses by confocal microscopy also reveal an increase in the amount of the enzyme, which is particularly evident at the nuclear level. Inhibition of PI 3-K activity by nanomolar concentrations of wortmannin and of its expression by transfection with an antisense fragment of p85alpha prevented the differentiative process. The data obtained indicate that PI 3-K activity plays an essential role in promoting granulocytic differentiation.

Management of adrenal cysts

Adrenal cysts have been traditionally managed by excision to rule out malignancy. We reviewed the 613 cases of adrenal cysts (including 6 new cases of our own) to evaluate whether this is still appropriate. Descriptive statistics and distribution of each pathologic type have been updated, based on 515 cases, and have changed from statistics compiled on 155 cases by G. A. Absehouse et al. Only seven per cent of all adrenal cysts are malignant or potentially malignant. There is only one reported case of a malignancy found in a nonfunctioning adrenal cyst that was initially thought to be benign. In this case, no CT or aspiration was performed. There have been 19 cases of adrenal cysts managed with aspiration. All were nonfunctioning and benign. One had a bloody aspirate. Reaccumulation occurred in 32 per cent of the cases (six cases); six per cent were symptomatic, four per cent were excised. Follow up was available in 15 cases from 4 months to 3.5 years. Management of the patient with a suspected adrenal cyst should include a careful history and physical and biochemical screening to rule out a functioning lesion. A CT scan, and aspiration of the cyst with a cystogram should be performed to confirm a simple cyst of the adrenal. If the suspicion of malignancy is low, and the lesion is nonfunctional, the adrenal cyst may be managed by aspiration alone. If the cyst recurs and is asymptomatic, it may be observed. If a symptomatic cyst recurs, it may be reaspirated or excised.

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.

Phosphatidylinositol 3-kinase in HL-60 nuclei is bound to the nuclear matrix and increases during granulocytic differentiation

We have used HL-60 leukemia cells to investigate phosphatidylinositol 3-kinase (PI 3-K) during granulocytic differentiation at the nuclear level. Nuclei of HL-60 cells showed a constitutive presence of PI 3-K that increased when cells were treated with differentiating doses of ATRA. PI 3-K was also detected tightly bound to nuclear matrices of HL-60 cells, isolated by nuclease treatment and high salt extraction. Four days of ATRA treatment induced a striking increase of nuclear matrix bound PI 3-K. In situ morphological analysis by confocal microscopy showed the translocation of PI 3-K to the nucleus and to the subnuclear fractions. PI 3-K enzymatic activity was stimulated during the granulocytic differentiation process and parallelled the increase in content of nuclei and subnuclear fractions. PI 3-K activity was recovered in nuclei also without the addition of exogenous substrates, consistent with the presence of both substrates and enzyme in the nucleus. These results indicate that specific intracellular localization of PI 3-K determines the production of different phosphoinositides in the sites of the enzyme translocation, and suggest that 3-phosphoinositide metabolism may play a specific role in the nucleus, candidating PI 3-K as a key enzyme in promoting granulocytic differentiation of HL-60 cells.

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.

K562 erythroid and HL60 macrophage differentiation downregulates polycystin, a large membrane-associated protein

Polycystin, the PKD1 gene product mutated in autosomal dominant polycystic kidney disease, is a large membrane protein which is important in the differentiation of epithelial tubular structure. Furthermore, PKD1 mRNA is expressed in various tissues and in neoplastic cell lines particularly, suggesting that polycystin might be involved in differentiation and/or proliferation of other cell types. Therefore, in order to investigate such a possible role, polyclonal antibodies against a recombinant polycystin peptide were raised and used to study polycystin expression in human leukemia cell lines committed to differentiation. Using Western blot and laser scanning confocal microscopy analyses, we demonstrated expression of polycystin in erythroleukemia K562 cells as a membrane-associated polypeptide of approximately 450 kDa, mainly localized in cell-cell contacts. Protein size and subcellular distribution were similar to those found in the kidney epithelial KJ29 cell line. In addition, K562 cell erythroid differentiation induced by hemin was characterized by a reduction in polycystin expression, as measured by Western blot and Northern blot analyses. Cytofluorimetric analysis indicated that upon hemin treatment there was a progressive reduction in the number of polycystin-expressing cells as well as in proliferation rate. Furthermore, reduction in proliferating and polycystin-expressing cells was also observed in K562 cells after serum starvation. When serum was added to the serum-deprived cells an increase in cell number as well as in number of polycystin-positive cells was observed. In addition, polycystin, also expressed in promyelocytic leukemia HL60 cells, was downregulated when macrophage differentiation in HL60 was induced by TPA. Therefore, in these leukemic cells downregulation of polycystin appeared to be closely related to reduction in cell proliferation and to induction of differentiation. This suggests that polycystin may play a relevant role in these cell processes.

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.

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.

Changes of nuclear PI-PLC gamma1 during rat liver regeneration

We have previously demonstrated that rat liver nuclei contain PI-PLC beta1 and gamma1 in the inner nuclear matrix and lamina associated with specific phosphodiesterase activity (Bertagnolo et al., 1995, Cell Signall. 7, 669-678). Since compensatory hepatic growth is an informative and well characterized model for natural cell proliferation, the presence of specific PI-PLC isoforms and their activity as well as PIP2 recovery were studied at various regenerating times, ranging from 3 to 22 h after partial hepatectomy. Three PI-PLC isoforms (beta1, gamma1, delta1) were examined in control and regenerating liver cells by using specific antibodies. By means of in situ immunocytochemistry and confocal microscopy, PI-PLC beta1 was found mainly in the nucleoplasm and this pattern was not modified after hepatectomy. On the contrary, the nuclear gamma1 isoform showed a marked decrease at 3 and 16 h after hepatectomy, but a clear increase at 22 h covering with bright intensity the whole nucleus. The PI-PLC delta1 isoform, which is exclusively cytoplasmic, was not altered during rat liver regeneration. By western blotting analysis on whole cell homogenates, none of the PI-PLC isozymes under study showed proliferation-linked modification. However, analyses of isolated nuclei identified changes in the nucleus associated PI-PLC gamma1 that paralleled the in situ observation whereas the beta1 isoform was unmodified at all the times examined. Nuclear phosphodiesterase activity on PIP2 was lower at 3 and 16 h, in comparison with sham operated rats, increased at 6 h and reached the highest value after 22 h. Consistently, the recovery of PIP2, obtained in conditions that optimise PIP-kinase activity, showed a marked decrease at 3 h and an increase up to 16 h of liver regeneration, followed by a further decrease at 22 h. These data are consistent with a close relationship between cell proliferation and the nuclear inositide cycle, depending, in rat liver, predominantly on the modulation of the gamma1 isoform of PI-PLC.

Subnuclear localization of S/MAR-binding proteins is differently affected by in vitro stabilization with heat or Cu2+

The nuclear matrix, a proteinaceous entity thought to be a scaffolding structure that determines the higher order organization of eukaryotic 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 extractions, but must rather be stabilized before the application of extracting agents such as high salt solutions or lithium diiodosalicylate. We have examined the effect of two widely used stabilization procedures on the localization of nuclear matrix proteins. Four individual polypeptides were studied, all of which are scaffold or matrix-associated region (S/MAR)-binding proteins: SATB1, SAF-A/hnRNP-U, NuMA , and topoisomerase II alpha. Nuclei were isolated from K562 human erythroleukemia cells in a buffer containing spermine, spermidine, KCl and EDTA, and the nuclear matrix or scaffold was obtained by extraction with lithium diiodosalicylate after stabilization by heat treatment (37 degrees or 42 degrees C) or incubation with Cu2+ ions. When the localization of individual proteins was determined by immunofluorescent staining and confocal scanning laser microscopy, markedly different consequences of the two stabilization strategies became evident, ranging from a total maintenance of the localization (NuMA and topoisomerase II alpha) to a marked redistribution (SATB1 and SAF-A/hnRNP-U). Our results seem to indicate that a reevaluation of stabilization protocols employed for the preparation of the nuclear matrix is desirable, especially by performing morphological controls.

Intranuclear translocation of phospholipase C beta2 during HL-60 myeloid differentiation

Phospholipases C (PLC) beta3, gamma1, and gamma2 were detected in nuclei of HL-60 promyelocitic leukaemia cells. When HL-60 cells undergo terminal myeloid differentiation in the presence of ATRA, the beta2 isoform appeared inside nuclei and was up-regulated until 72 hours of ATRA treatment. The beta3 isozyme was also increased until 72 hours and both isoforms lowered their intranuclear amount at 96 hours and following days of treatment. By contrast PLC gamma1 and gamma2 progressively increased in the nucleus during granulocytic differentiation even after 72 hours of treatment. Terminal differentiation was characterised by the expression of high levels of PLC gamma1 and gamma2 and by low levels of PLC beta2 and beta3 in the nucleus. PIP2 and PIP hydrolysis paralleled the prevalence of the beta or gamma subfamily, respectively. Moreover, at all the examined times no changes of PLCs in the whole cell were detectable, indicating a de novo nuclear translocation of the beta2 and an increased accumulation of beta3, gamma1, and gamma2 isoforms. Thus, the intranuclear presence, expression, and activity of PLC isozymes, which are modulated during differentiation of HL-60 cells, implicate a role for nuclear phosphoinositide signalling in the process of cell maturation. In particular the nuclear translocation of PLC beta2 candidates this PLC as a key enzyme in the granulocytic differentiative commitment of HL-60 cells.

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.

Enhanced resolution of specific chromosome and nuclear regions by reflectance laser scanning confocal microscopy

DNA sequences digested by HaeIII and reconstructed by in situ nick translation employing digoxigenin-labelled nucleotides are usually revealed either by horseradish peroxidase or FITC fluorescence. To obtain a significant improvement in terms of resolution, sensitivity and specificity, colloidal gold has been used instead of FITC (as the reporter molecule) to reveal the labelled DNA. Colloidal gold and propidium iodide were visualised by employing the reflectance mode and the 488-nm laser line of a confocal laser scanning microscope. In chromosomes, the fluorescent reaction pattern showed diffuse areas of labelling in which it was impossible to identify any specific kind of banding along the arms. In some chromosomes and, in particular, 1 and 9, a C-negative banding due to the negativity of the centromeric areas was seen. A more accurate localisation on chromosomes, including telomeric regions, often organised in spot pairs that resembled an R-like banding, was detected using 1-nm colloidal gold. A fine labelling was also demonstrated in nuclei, especially at their peripheral heterochromatin. The non-fading properties of colloidal gold combined with visualisation by reflectance confocal laser scanning microscopy demonstrated the possibility of obtaining a higher spatial resolution than when using conventional fluorophores or higher laser wavelength. This improved way to study the localization of HaeIII digestion sites in single chromosomes and in interphase nuclei made the reaction a valuable tool for the detection of antigens or of specific DNA sequences in biological preparations.

Increase of nuclear phosphatidylinositol 4,5-bisphosphate and phospholipase C beta 1 is not associated to variations of protein kinase C in multidrug-resistant Saos-2 cells

The multidrug resistance (MDR) phenotype that is mediated by an overexpression of P-glycoprotein, has been suggested to be related also to an increased activity of protein kinase C (PKC) and to changes in phospholipid pattern. By electron microscope quantitative immunocytochemistry, we investigated whether PKC and other elements of the polyphosphoinositide signal transduction system are affected in an MDR variant of the human osteosarcoma cell line Saos-2. These cells, which are characterized by an increased expression of P-glycoprotein not only at the plasma membrane but also at the nuclear level, showed increased intranuclear amounts of phosphatidylinositol 4,5-bisphosphate and of phospholipase C beta 1, while both the amount and activity of both nuclear and cellular PKC were not modified with respect to sensitive cells. These results suggest that, in this model, the changes observed in the elements of nuclear signal transduction could be related to previously reported modifications of the MDR phenotype, but that P-glycoprotein phosphorylation is not dependent from increased PKC activity.

Nuclear scaffold proteins are differently sensitive to stabilizing treatment by heat or Cu++

The distribution of three nuclear scaffold proteins (of which one is a component of a particular class of nuclear bodies) has been studied in intact K562 human erythroleukemia cells, isolated nuclei, and nuclear scaffolds. Nuclear scaffolds were obtained by extraction with the ionic detergent lithium diidosalicylate (LIS), using nuclei prepared in the absence of divalent cations (metal-depleted nuclei) and stabilized either by a brief heat exposure (20 min at 37C or 42C) or by Cu++ ions at 0C. Proteins were visualized by in situ immunocytochemistry and confocal microscopy. Only a 160-kD nuclear scaffold protein was unaffected by all the stabilization procedures performed on isolated nuclei. However, LIS extraction and scaffold preparation procedures markedly modified the distribution of the polypeptide seen in intact cells, unless stabilization had been performed by Cu++. In isolated nuclei, only Cu++ treatment preserved the original distribution of the two other antigens (M(r), 125 and 126 kD), whereas in heat-stabilized nuclei we detected dramatic changes. In nuclear scaffolds reacted with antibodies to 125 and 126-kD proteins, the fluorescent pattern was always disarranged regardless of the stabilization procedure. These results, obtained with nuclei prepared in the absence of Mg+2 ions, indicate that heat treatment per se can induce changes in the distribution of nuclear proteins, at variance with previous suggestions. Nevertheless, each of the proteins we have studied behaves in a different way, possibly because of its specific association with the nuclear scaffold.

The nuclear matrix: a critical appraisal

It is becoming increasingly clear that the cell nucleus is a highly structurized organelle. Because of its tight compartmentalization, it is generally believed that a framework must exist, responsible for maintaining such a spatial organization. Over the last twenty years many investigations have been devoted to identifying the nuclear framework. Structures isolated by different techniques have been obtained in vitro and are variously referred to as nuclear matrix, nucleoskeleton or nuclear scaffold. Many different functions, such as DNA replication and repair, mRNA transcription, processing and transport have been described to occur in close association with these structures. However, there is still much debate as to whether or not any of these preparations corresponds to a nuclear framework that exists in vivo. In this article we summarize the most commonly-used methods for obtaining preparations of nuclear frameworks and we also stress the possible artifacts that can be created in vitro during the isolation procedures. Emphasis is placed also on the protein composition of the frameworks as well as on some possible signalling functions that have been recently described to occur in tight association with the nuclear matrix.

Multiple fluorescence and reflectance simultaneous detection by confocal microscopy of HaeIII digested DNA sequences

Human metaphase chromosomes were isolated and digested in situ with HaeIII restriction enzyme to detect cytosine and guanine-rich sequences (CpG islands), which are known to be associated with most of the mammalian genes. Digested DNA was reconstructed by in situ nick translation employing digoxigenin-labeled nucleotides. The DNA sequences were revealed by antibodies conjugated either with fluorescein isothiocyanate or 1-nm colloidal gold. DNA was counterstained with propidium iodide. A sensitive, high resolution method for visualizing three signals, simultaneously excited by a single argon laser line of 488 nm has been developed. The green fluorescence of fluorescein isothiocyanate was detected in combination with the red fluorescence of propidium iodide, and the third signal was imaged by employing the reflectance mode of the confocal microscope after silver enhancement of the gold beads. The high reflectance intensity, the accurate localization and the non-fading properties of colloidal gold made the reaction a valuable tool for the detection of antigens and, as a consequence, of specific DNA sequences in chromosome preparations. Overlaying of three signals allowed the simultaneous observation of distinct structures: total DNA, as well as fluorescein- and gold-labeled sequences after in situ nick translation, or total DNA and centromeric sequences of two different chromosome pairs (17 and X) after in situ hybridization. The use of HaeIII restriction enzyme that cut CpG islands combined with in situ nick translation identified the chromosome sites where active, inactive or housekeeping genes can be located. In chromosomes, the fluorescent reaction pattern showed large areas of labeling, while a more defined staining, often organized in spot pairs that resembled an R-like banding, was detected when the reflected mode was used. These results are confirmed by the observation that R-like bands actually are multiple symmetrical spots localized on sister chromatids. In addition, some chromosomes, and in particular 1 and 9, displayed a C-negative banding due to the negativity of the centromeric areas. Reflectance confocal scanning microscopy and in situ nick translation represent a powerful tool to study the in situ genome organization.

Changes of nuclear protein kinase C activity and isotype composition in PC12 cell proliferation and differentiation

To establish whether protein kinase C was involved in the nuclear events underlying cell differentiation and proliferation, rat pheochromocytoma PC12 cells, serum-starved for 24 h, were treated with either differentiating doses of nerve growth factor or high serum concentrations, which represented a powerful mitogenic stimulus. Western blot analysis with isoform-specific antibodies, performed on whole cell homogenates, cytoplasms, and purified nuclei, showed that PKC isotypes alpha, beta I, beta II, delta, epsilon, eta, and zeta were expressed in PC12 cells and that all of them, except for beta I, were found at the nuclear level, variably modulated depending on the cell treatment. Compared to serum-stimulated cells, in which an early (1 day) and marked rise of protein kinase C activity was followed by a plateau, nerve growth factor-treated cells showed a progressive increase of protein kinase C activity coincident with the onset and maintenance of the differentiated phenotype. Western blot analysis of nuclei isolated from fully differentiated cells demonstrated an increase of protein kinase C alpha, paralleled by enhanced phosphotransferase activity along with the nerve growth factor treatment, and complete loss of the delta isotype. In contrast, in nuclei of proliferating PC12 cells, after an early but modest increase at 1 day of mitogenic stimulation, protein kinase C activity reached a plateau. Isotype-specific analysis indicated a concomitant increase of protein kinase C beta II, delta, and zeta and the appearance of protein kinase C epsilon and eta at the nuclear level. Considering the relative intensity of the cytoplasmic and nuclear immunoreactive bands under the three conditions examined, clear-cut translocation to the nucleus occurred for PKC epsilon and eta in serum-stimulated cells. Additional nuclear accumulation of PKC by translocation from the cytoplasm was prominently induced for the zeta isoform after mitogenic stimulation and for PKC alpha during prolonged NGF treatment. Our data suggest that nuclear translocation and selective activation of distinct protein kinase C isoforms play a relevant role in the control of proliferation and differentiation of the same cell type and that nuclear protein kinase C is crucial to the induction and persistence of the differentiated neuronal phenotype of PC12 cells.

Analysis by confocal microscopy of the behavior of heat shock protein 70 within the nucleus and of a nuclear matrix polypeptide during prolonged heat shock response in HeLa cells

By means of confocal laser scanning microscopy and indirect fluorescence experiments we have examined the behavior of heat-shock protein 70 (HSP70) within the nucleus as well as of a nuclear matrix protein (M(r) = 125 kDa) during a prolonged heat-shock response (up to 24 h at 42 degrees C) in HeLa cells. In control cells HSP70 was mainly located in the cytoplasm. The protein translocated within the nucleus upon cell exposure to hyperthermia. The fluorescent pattern revealed by monoclonal antibody to HSP70 exhibited several changes during the 24-h-long incubation. The nuclear matrix protein showed changes in its location that were evident as early as 1 h after initiation of heat shock. After 7 h of treatment, the protein regained its original distribution. However, in the late stages of the hyperthermic treatment (17-24 h) the fluorescent pattern due to 125-kDa protein changed again and its original distribution was never observed again. These results show that HSP70 changes its localization within the nucleus conceivably because it is involved in solubilizing aggregated polypeptides present in different nuclear regions. Our data also strengthen the contention that proteins of the insoluble nucleoskeleton are involved in nuclear structure changes that occur during heat-shock response.

Identification of PI-PLC beta 1, gamma 1, and delta 1 in rat liver: subcellular distribution and relationship to inositol lipid nuclear signalling

The subcellular distribution of PI-PLC beta 1, gamma 1, and delta 1 has been investigated in rat liver by western blot and immunohistochemical analysis with a panel of isoform-specific antibodies. The data obtained in situ on cryo-sectioned tissue indicate that PI-PLC beta 1 is predominantly nuclear, while gamma 1 is largely cytoplasmic and delta 1 is sharply restricted to the cytoplasm. In fractionation experiments, the Western blot analysis indicated that the recovery of the nuclear isoforms beta 1 and gamma 1 was not affected by the removal of the nuclear membrane, and that the two enzymes persisted in nuclear matrix and lamina, obtained after nuclease digestion and extraction with high salt and detergent. The assay of the phosphodiesterase activity in different cell fractions correlates with the observed relative abundance of the enzymes, and specific inhibition with neutralizing anti-beta 1 and -gamma 1 isoforms confirms that these are the enzymes active at the nuclear level. These results demonstrate that in rat liver cells, as in other cell types, different members of the PI-PLC family show a discrete intracellular distribution, and suggest that PI-PLC beta 1 and gamma 1 play a central role in modulating the nuclear phosphoinositide cycle.

The effect of sodium tetrathionate stabilization on the distribution of three nuclear matrix proteins in human K562 erythroleukemia cells

Using both conventional fluorescence and confocal laser scanning microscopy we have investigated whether or not stabilization of isolated human erythroleukemic nuclei with sodium tetrathionate can maintain in the nuclear matrix the same spatial distribution of three polypeptides (M(r) 160 kDa and 125 kDa, previously shown to be components of the internal nuclear matrix plus the 180-kDa nucleolar isoform of DNA topoisomerase II) as seen in permeabilized cells. The incubation of isolated nuclei in the presence of 2 mM sodium tetrathionate was performed at 0 degrees C or 37 degrees C. The matrix fraction retained 20-40% of nuclear protein, depending on the temperature at which the chemical stabilization was executed. Western blot analysis revealed that the proteins studied were completely retained in the high-salt resistant matrix. Indirect immunofluorescence experiments showed that the distribution of the three antigens in the final matrix closely resembled that detected in permeabilized cells, particularly when the stabilization was performed at 37 degrees C. This conclusion was also strengthened by analysis of cells, isolated nuclei and the nuclear matrix by means of confocal laser scanning microscopy. We conclude that sodium tetrathionate stabilization of isolated nuclei does not alter the spatial distribution of some nuclear matrix proteins.

Immunocytochemical evaluation of protein kinase C translocation to the inner nuclear matrix in 3T3 mouse fibroblasts after IGF-I treatment

The complex pathway which links the agonist-cell membrane receptor binding to the response at the genome level involves, among other elements, protein kinase C (PKC). Agonists acting at the cell membrane can affect an autonomous nuclear polyphosphoinositide signaling system inducing an activation of nuclear phosphoinositidase activity and a subsequent translocation of PKC to the nuclear region. The fine localization of PKC has been investigated by means of electron microscopy quantitative immunogold labeling in 3T3 mouse fibroblasts, mitogenically stimulated by IGF-I. The enzyme, which in untreated cells is present in the cytoplasm, except for the organelles, and in the nucleoplasm, after IGF-I treatment is reduced in the cytoplasm and almost doubled in the nucleus. The PKC isoform translocated to the nucleus is the alpha isozyme, which is found not only associated with the nuclear envelope but mainly with the interchromatin domains. By using in situ matrix preparations, PKC appears to be retained at the nuclear matrix level, both at the nuclear lamina and at the inner nuclear matrix, suggesting a direct involvement in the phosphorylation of nuclear proteins which are responsible for the regulation of DNA replication.

Immunocytochemical detection of the specific association of different PIC isoforms with cytoskeletal and nuclear matrix compartments in PC12 cells

The increasing evidence of discrete roles of phosphoinositidase C (PIC) isoforms and the assessment of their localization in the cytoskeleton and in the nucleus support the involvement of particular isotypes of this enzyme in signal transduction at multiple levels. PC12 rat pheochromocytoma is one of the few cell lines expressing three immunologically distinct isoforms of PIC. We have analyzed the subcellular distribution of the PIC beta 1, gamma 1 and delta 1 isoforms using confocal and electron microscope immunocytochemistry. PIC beta 1 is mainly found in the nucleus and is associated with interchromatin domains. On the other hand, the PIC gamma 1 isoform is found in the nucleus and in the cytosol, while PIC delta 1 is exclusively cytoplasmic. Immunoblot and immunocytochemical experiments indicate that the various PIC isoforms are differently bound to structural cell compartments, such as cytoskeletal and nuclear matrix elements. In fact, PIC beta 1 and PIC gamma 1 isoforms are tightly associated with the nuclear matrix, while only about 50% of PIC gamma 1 is associated with the cytoskeleton after DNase I and high salt extractions. PIC gamma 1 is almost completely soluble under these conditions. These results further confirm the complexity of the inositide signal transduction mechanism, which involves several PIC isoforms, specifically localized in different cell compartments and support the existence of a membrane-unrelated inositol lipid-dependent signalling in the nuclear interior.

In vitro heat exposure induces a redistribution of nuclear matrix proteins in human K562 erythroleukemia cells

By using both conventional and confocal laser scanning microscopy with three monoclonal antibodies recognizing nuclear matrix proteins we have investigated by means of indirect fluorescence whether an incubation of isolated nuclei at the physiological temperature of 37 degrees C induces a redistribution of nuclear components in human K562 erythroleukemia cells. Upon incubation of isolated nuclei for 45 min at 37 degrees C, we have found that two of the antibodies, directed against proteins of the inner matrix network (M(r) 125 and 160 kDa), gave a fluorescent pattern different from that observed in permeabilized cells. By contrast, the fluorescent pattern did not change if nuclei were kept at 0 degrees C. The difference was more marked in case of the 160-kDa polypeptide. The fluorescent pattern detected by the third antibody, which recognizes the 180-kDa nucleolar isoform of DNA topoisomerase II, was unaffected by heat exposure of isolated nuclei. When isolated nuclear matrices prepared from heat-stabilized nuclei were stained by means of the same three antibodies, it was possible to see that the distribution of the 160-kDa matrix protein no longer corresponded to that observable in permeabilized cells, whereas the fluorescent pattern given by the antibody to the 125-kDa polypeptide resembled that detectable in permeabilized cells. The 180-kDa isoform of topoisomerase II was still present in the matrix nucleolar remnants. We conclude that a 37 degrees C incubation of isolated nuclei induces a redistribution of some nuclear matrix antigens and cannot prevent the rearrangement in the spatial organization of one of these antigens that takes place during matrix isolation in human erythroleukemia cells. The practical relevance of these findings is discussed.

Nuclear translocation of phosphatidylinositol 3-kinase in rat pheochromocytoma PC 12 cells after treatment with nerve growth factor

Immunocytochemical analysis of PI 3-kinase localization in PC 12 cells demonstrates that the enzyme translocates to the nucleus after cell treatment with differentiating doses of NGF. The association of PI 3-kinase to the nucleus occurs rapidly (within minutes) and increases with the time of exposure of NGF. We suggest that PI-3 kinase specific localization may determine the production of novel phosphoinositides in cell compartments targeted to effect diverse cell responses. The nuclear translocation is consistent with accumulating data on the existence of a nuclear inositol lipid cycle which could also include 3-phosphorylated inositides, participating to the modulation of the cell response to extracellular stimuli.

An immunohistochemical study of protein kinase C distribution in fetal mouse vertebral column

Using polyclonal antibodies we have studied the distribution of protein kinase C in fetal mouse low thoracic vertebrae. By means of a pan protein kinase C antiserum recognizing the catalytic domain of the enzyme, we show that protein kinase C is markedly expressed in chondrocytes before birth. The enzyme seems to be very abundant in the more mature cells that are close to ossification centres as well as the periphery of the intervertebral disc, although it can also be detected in chondrocytes. In order to establish which protein kinase C isoenzyme(s) the chondrocytes produce, we employed polyclonal isoenzyme-specific antisera developed against three calcium-dependent isoforms (alpha, beta, gamma) and three calcium-independent isoforms (delta, epsilon, zeta). Secondary antibody conjugated to alkaline phosphatase revealed that chondrocytes markedly express the beta-isoform. Cells were also weakly stained by the anti-epsilon serum. The immunostaining was completely abolished by pre-incubating primary antibodies with the peptide antigens to which they were raised. These results suggest that protein kinase C (and particularly the beta isoform) could play an important role in mouse fetal chondrogenesis of the vertebral column.

Selective nuclear translocation of protein kinase C alpha in Swiss 3T3 cells treated with IGF-I, PDGF and EGF

To determine the subcellular distribution of PKC after GFs treatment we have employed a combined immunochemical and in situ confocal microscopy analysis. In quiescent Swiss 3T3 cells only a faint PKC positivity was observable in the nucleus while a strong reaction was seen in the cytoplasm. IGF-I and to a lesser extent PDGF and EGF induced, after 45 min of treatment, a nuclear translocation of PKC detected by a pan-anti-PKC antibody and nuclear fluorescence was distributed in the nuclear interior except for the nucleolar regions. Bombesin and FGF did not affect the sub-cellular distribution of the enzyme. To further the understanding of which PKC isoform was involved in the translocation process, we have tested nine isozyme-specific anti-PKC antibodies. Immunoblotting analysis revealed the presence in Swiss 3T3 fibroblasts of alpha, beta I, epsilon and zeta isoforms. In isolated nuclei from GF-exposed cells only the alpha isozyme was detected: immunostaining was very intense after IGF-I treatment and clearly observable after PDGF and EGF stimulation. This result was strongly supported by the in situ confocal microscopy which parallels the Western blot analysis. These data demonstrate that several, but not all, GFs acting through tyrosine kinase receptor induce the intranuclear translocation of PKC alpha and, because of the dramatic effect of IGF-I, strengthen the case for a link between the activation of nuclear inositol lipid cycle and PKC translocation induced by this GF.

Phosphoinositide signaling in nuclei of Friend cells: phospholipase C beta down-regulation is related to cell differentiation

Previous investigations have demonstrated the existence of an autonomous intranuclear inositide cycle endowed with conventional lipid kinases and phospholipase C (PLC) which is the isoform beta in Swiss 3T3 cells, PC12 pheochromocytoma cells, human osteosarcoma SaOS-2 cells, and rat liver. The presence of PLC has been investigated in nuclei of Friend erythroleukemia cells. Both beta and gamma isoforms are present in these nuclei. When Friend cells undergo terminal erythroid differentiation in the presence of dimethyl sulfoxide the PLC beta isoform is down-regulated as shown by immunochemical and immunocytochemical analysis, by determination of enzymatic activity directly and in the presence of neutralizing monoclonal antibodies and also by Northern blot for PLC beta message. By contrast, the amount of PLC gamma and its activity are unaffected by erythroid differentiation. Thus, the presence of a nuclear PLC beta, the activity and expression of which are modulated during differentiation of erythroleukemia cells, implicates a role for nuclear phosphoinositide signaling in the processes of cell determination and indicates the nuclear PLC beta as a key enzyme of the cycle in relation to the erythroid differentiative commitment of murine erythroleukemia cells.