Investigating the mechanical properties of zona pellucida of whole human oocytes by atomic force spectroscopy

The role of mechanics in numerous biological processes is nowadays recognized, while in others, such as the fertilization process, it is still neglected. In the case of oocytes the description of their mechanical properties could improve the comprehension of the oocyte-spermatozoon interaction and be helpful for application in in vitro fertilization (IVF) clinics. Herein the mechanical properties of whole human oocytes (HOs) immediately after retrieval are investigated by indentation measurements with atomic force spectroscopy under physiological conditions. Measurements are performed on immature (metaphase I - MI) and mature (metaphase II - MII) HOs. According to their morphological characteristics MII-HOs are classified as "suitable" and "rejected"; these latter would be usually rejected for intracytoplasmic sperm injection (ICSI). For all maturation stages we observe that the elastic response of the zona pellucida (ZP) outer layer was different and distinguishable from the rest of the ZP-HO. The elasticity of this ZP outer layer varies with maturation and quality: stiffness decreases from immature MI to good quality MII, up to poor-quality rejected MII. An indirect analysis with IVF outcome indicates that the ZP outer layer of analysed HOs donated by women who achieved pregnancy is stiffer than that of HOs from women with negative outcome. Our findings suggest that mechanical properties can represent important oocyte quality indicators that may be exploited for the design of innovative ICSI dedicated cell sorters.

Looking for Calcium Phosphate Composite Suitable to Study Osteoclast Endocytosis: Preliminary Observations

One of the issues regarding in vitro study of bone resorption is the synthesis of a bone-like biomaterial forming a thin layer onto either glass or plastic. The synthesis of a bone-like material suitable for in vitro studies can be valuable both to investigate osteoclast differentiation, that in vivo proceeds within the local microenvironment of bone and to understand how its presence triggers activation of macrophages present in situ when bone is damaged (a scenario that can occur for example in case of bone fracture). Despite the intensive studies committed to recreate synthetic bone analogues, the most used substrates for in vitro studies on bone resorption are slices of bone or dentine. Therefore morphological investigations (i.e. fluorescence analysis and phase contrast) are strongly compromised due to the thickness of the bone analogue. In the present study, with the aim to guarantee a versatile (and easy to be made) substrate, that could be suitable to study cell adhesion and morphology by epifluorescence, phase contrast and TEM, we developed a biomaterial containing a calcium phosphate salt and type I collagen. This material (made specifically for in vitro studies) forms a very thin layer that allowed to merge the morphological information derived from phase-contrast and epifluorescence observation, making possible the observation of the interface between cell and matrix. Moreover the electron microscopy evaluation of the endocytosis performed on cell differentiated could be more suitable because sample does not need the process of demineralization.

Production of in vivo-biotinylated rotavirus particles

Although inserting exogenous viral genome segments into rotavirus particles remains a hard challenge, this study describes the in vivo incorporation of a recombinant viral capsid protein (VP6) into newly assembled rotavirus particles. In vivo biotinylation technology was exploited to biotinylate a recombinant VP6 protein fused to a 15 aa biotin-acceptor peptide (BAP) by the bacterial biotin ligase BirA contextually co-expressed in mammalian cells. To avoid toxicity of VP6 overexpression, a stable HEK293 cell line was constructed with tetracycline-inducible expression of VP6–BAP and constitutive expression of BirA. Following tetracycline induction and rotavirus infection, VP6–BAP was biotinylated, recruited into viroplasms and incorporated into newly assembled virions. The biotin molecules in the capsid allowed the use of streptavidin-coated magnetic beads as a purification technique instead of CsCl gradient ultracentrifugation. Following transfection, double-layered particles attached to beads were able to induce viroplasm formation and to generate infective viral progeny.

AMP-dependent kinase/mammalian target of rapamycin complex 1 signaling in T-cell acute lymphoblastic leukemia: therapeutic implications

The mammalian target of rapamycin (mTOR) serine/threonine kinase is the catalytic subunit of two multi-protein complexes, referred to as mTORC1 and mTORC2. Signaling downstream of mTORC1 has a critical role in leukemic cell biology by controlling mRNA translation of genes involved in both cell survival and proliferation. mTORC1 activity can be downmodulated by upregulating the liver kinase B1/AMP-activated protein kinase (LKB1/AMPK) pathway. Here, we have explored the therapeutic potential of the anti-diabetic drug, metformin (an LKB1/AMPK activator), against both T-cell acute lymphoblastic leukemia (T-ALL) cell lines and primary samples from T-ALL patients displaying mTORC1 activation. Metformin affected T-ALL cell viability by inducing autophagy and apoptosis. However, it was much less toxic against proliferating CD4(+) T-lymphocytes from healthy donors. Western blot analysis demonstrated dephosphorylation of mTORC1 downstream targets. Unlike rapamycin, we found a marked inhibition of mRNA translation in T-ALL cells treated with metformin. Remarkably, metformin targeted the side population of T-ALL cell lines as well as a putative leukemia-initiating cell subpopulation (CD34(+)/CD7(-)/CD4(-)) in patient samples. In conclusion, metformin displayed a remarkable anti-leukemic activity, which emphasizes future development of LKB1/AMPK activators as clinical candidates for therapy in T-ALL.

Clathrin-dependent endocytosis of membrane-bound RANKL in differentiated osteoclasts

Bone is continuously repaired and remodelled through well-coordinated activity of osteoblasts that form new bone and osteoclasts, which resorb it. Osteoblasts synthesize and secrete two key molecules that are important for osteoclast differentiation, namely the ligand for the receptor of activator of nuclear factor κB (RANKL) and its decoy receptor osteoprotegerin (OPG). Active membrane transport is a typical feature of the resorbing osteoclast during bone resorption. Normally, one resorption cycle takes several hours as observed by monitoring actin ring formation and consequent disappearance in vitro. During these cyclic changes, the cytoskeleton undergoes remarkable dynamic rearrangement. Active cells show a continuous process of exocytosis that plays an essential role in transport of membrane components, soluble molecules and receptor-mediated ligands thus allowing them to communicate with the environment. The processes that govern intracellular transport and trafficking in mature osteoclasts are poorly known. The principal methodological problem that have made these studies difficult is a physiological culture of osteoclasts that permit observing the vesicle apparatus in conditions similar to the in vivo conditions. In the present study we have used a number of morphological approaches to characterize the composition, formation and the endocytic and biosynthetic pathways that play roles in dynamics of differentiation of mature bone resorbing cells using a tri-dimensional system of physiologic coculture.

Synergistic proapoptotic activity of recombinant TRAIL plus the Akt inhibitor Perifosine in acute myelogenous leukemia cells

To potentiate the response of acute myelogenous leukemia (AML) cells to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) cytotoxicity, we have examined the efficacy of a combination with perifosine, a novel phosphatidylinositol-3-kinase (PI3K)/Akt signaling inhibitor. The rationale for using such a combination is that perifosine was recently described to increase TRAIL-R2 receptor expression and decrease the cellular FLICE-inhibitory protein (cFLIP) in human lung cancer cell lines. Perifosine and TRAIL both induced cell death by apoptosis in the THP-1 AML cell line, which is characterized by constitutive PI3K/Akt activation, but lacks functional p53. Perifosine, at concentrations below IC(50), dephosphorylated Akt and increased TRAIL-R2 levels, as shown by Western blot, reverse transcription-PCR, and flow cytometric analysis. Perifosine also decreased the long isoform of cFLIP (cFLIP-L) and the X-linked inhibitor of apoptosis protein (XIAP) expression. Perifosine and TRAIL synergized to activate caspase-8 and induce apoptosis, which was blocked by a caspase-8-selective inhibitor. Up-regulation of TRAIL-R2 expression was dependent on a protein kinase Calpha/c-Jun-NH(2)-kinase 2/c-Jun signaling pathway activated by perifosine through reactive oxygen species production. Perifosine also synergized with TRAIL in primary AML cells displaying constitutive activation of the Akt pathway by inducing apoptosis, Akt dephosphorylation, TRAIL-R2 up-regulation, cFLIP-L and XIAP down-regulation, and c-Jun phosphorylation. The combined treatment negatively affected the clonogenic activity of CD34(+) cells from patients with AML. In contrast, CD34(+) cells from healthy donors were resistant to perifosine and TRAIL treatment. Our findings suggest that the combination of perifosine and TRAIL might offer a novel therapeutic strategy for AML.

Sparc localizes to the blebs of hobit cells and human primary osteoblasts

Secreted protein acidic and rich in cystein (SPARC) is a secreted glycoprotein involved in several biological processes such as tissue remodeling, embryonic development, cell/extracellular matrix interactions, and cell migration. In particular, SPARC affects bone remodeling through the regulation of both differentiation/survival of osteoblasts and bone extracellular matrix synthesis/turnover. Here, we investigated SPARC subcellular localization in the human osteoblastic HOBIT cell line by immunocytochemistry and western blot analysis. We show that, under normal exponential cell growth conditions, SPARC localized both to cell nucleus and to cytoplasm, with no co-localization on actin stress fibers. However, in colchicine-treated HOBIT cells and human primary osteoblasts undergoing blebs formation, SPARC showed a different cellular distribution, with an additional marked compartmentalization inside the blebs, where it co-localized with globular actin and actin-binding proteins such as alpha-actinin, cortactin, and vinculin. Moreover, we demonstrate by an in vitro assay that the addition of SPARC to actin and alpha-actinin inhibited the formation of cross-linked actin filaments and disrupted newly formed filaments, most likely due to a direct interaction between SPARC and alpha-actinin, as indicated by immunoprecipitation assay. The specific silencing of SPARC RNA expression markedly decreased the ability of colchicine-treated HOBIT cells to undergo blebbing, suggesting a direct role for SPARC in cell morphology dynamics during cytoskeletal reorganization.

Effects of neridronic acid on osteoclasts derived by physiological dual-cell cultures

Increased osteoclastic activity is observed in many osteopathic disorders - including postmenopausal osteoporosis, Paget's disease, primary bone tumours, lytic bone metastases, multiple myeloma and rheumatoid arthritis - that involve increased bone resorption and a loss of bone mass. Bisphosphonates are highly effective inhibitors of bone resorption that selectively affect the osteoclasts. The aim of this study was to obtain more information about the mechanism of action of bisphosphonates such as neridronic acid using a dual-cell culture model. As a model of osteoclastogenesis we used a murine monocyte/macrophage cell line RAW 264.7 type CRL 2278 co-cultured with murine osteoblasts. The monocyte-osteoblast system allows physiological experimentation of bone anti-resorption drugs, simulating bone turnover in pathologies such as osteoporosis. The direct actions of neridronic acid on cell proliferation and functionality in the co-culture model were examined using tartrate-resistant acid phosphatase (TRAP) assay, immunohistochemical localization of actin, and transmission and scanning electron microscopy (SEM). Results showed that the percentage of TRAP-positive cells, an early marker of osteoclastic differentiation, was significantly higher in control cultures than in co-cultures treated with variable concentrations of neridronic acid. Neridronic acid induced dramatic morphological changes, characterized by the loss of the ruffled border. The actin ring associated with the plasma membrane of the cells treated with neridronic acid was shown to break down. The tissue-specific targeting of neridronic acid to bone mineral suggests that it may inhibit bone resorption by direct effects on osteoclasts or other bone cells in the immediate microenvironment of the osteoclasts. From our study, we conclude that structural alterations induced by neridronic acid in our co-culture system lead to decreased osteoclast function. This may encourage the use of neridronic acid to reduce bone resorption in the therapy of demineralizing metabolic bone disorders.

Increased OPG expression and impaired OPG/TRAIL ratio in the aorta of diabetic rats

Despite accumulating evidence showing that TNF-related apoptosis inducing ligand (TRAIL) plays a role in vascular biology and that its decoy receptor osteoprotegerin (OPG) is expressed in the vessel wall, modulation of these TNF and TNF-R family members in the early phases of diabetes mellitus has not been investigated. The expression of TRAIL and of OPG was examined both at the mRNA and protein levels in control and streptozotocin (SZT)-induced diabetic rats at early time points after the induction of diabetes mellitus. No differences in the steady-state mRNA levels of TRAIL were noticed by quantitative RT-PCR among the two groups of animals. On the other hand, diabetic rats showed a rapid and significant increase of the steady-state mRNA levels of OPG in the aortic wall of diabetic animals with respect to vehicle-treated (control) animals. These findings were confirmed at the protein level by analysing the amount of TRAIL and OPG proteins in aortic lysates by either Western blot or immunohistochemistry. Thus, an abnormal elevation of the OPG/TRAIL ratio in the vessel wall characterizes the early onset of diabetes mellitus and might represent a molecular mechanism involved in the vascular dysfunction characterizing diabetes mellitus.

In vitro exposure of human chondrocytes to pulsed electromagnetic fields

The effect of pulsed electromagnetic fields (PEMFs) on the proliferation and survival of matrix-induced autologous chondrocyte implantation (MACI)-derived cells was studied to ascertain the healing potential of PEMFs. MACI-derived cells were taken from cartilage biopsies 6 months after surgery and cultured. No dedifferentiation towards the fibro- blastic phenotype occurred, indicating the success of the surgical implantation. The MACI-derived cultured chondrocytes were exposed to 12 h/day (short term) or 4 h/day (long term) PEMFs exposure (magnetic field intensity, 2 mT; frequency, 75 Hz) and proliferation rate determined by flow cytometric analysis. The PEMFs exposure elicited a significant increase of cell number in the SG2M cell cycle phase. Moreover, cells isolated from MACI scaffolds showed the presence of collagen type II, a typical marker of chondrocyte functionality. The results show that MACI membranes represent an optimal bioengineering device to support chondrocyte growth and proliferation in surgical implants. The surgical implant of MACI combined with physiotherapy is suggested as a promising approach for a faster and safer treatment of cartilage traumatic lesions.

Nuclear diacylglycerol kinases: emerging downstream regulators in cell signaling networks

There exists an active lipid metabolism in the nucleus, which is regulated differentially from the lipid metabolism taking place elsewhere in the cell. Evidence has been accumulated that nuclear lipid metabolism is closely involved in a variety of cell responses, including proliferation, differentiation, and apoptosis. A fundamental lipid second messenger which is generated in the nucleus is diacylglycerol, that is mainly known for its role as an activator of some protein kinase C isoforms. Diacylglycerol kinases attenuate diacylglycerol signaling by converting this lipid to phosphatidic acid, which also has signaling functions. Ten mammalian diacylglycerol kinase isoforms have been cloned so far, and some of them are found also in the nucleus, either as resident proteins or after migration from cytoplasm in response to various agonists. Experiments using cultured cells have demonstrated that nuclear diacylglycerol kinases have prominent roles in cell cycle regulation and differentiation. In this review, the emerging roles played by diacylglycerol kinases in the nucleus, such as the control of G1/S phase transition, are discussed.

The insulin-like growth factor-I receptor kinase inhibitor NVP-AEW541 induces apoptosis in acute myeloid leukemia cells exhibiting autocrine insulin-like growth factor-I secretion

Insulin-like growth factor-I (IGF-I) and its receptor (IGF-IR) have been implicated in the pathophysiology of many human cancers, including those of hematopoietic lineage. We investigated the therapeutic potential of the novel IGF-IR tyrosine kinase activity inhibitor, NVP-AEW541, on human acute myeloid leukemia (AML) cells. NVP-AEW541 was tested on a HL60 cell subclone, which is dependent on autocrine secretion of IGF-I for survival and drug resistance, as well as primary drug resistant leukemia cells. NVP-AEW541 treatment (24 h) induced dephosphorylation of IGF-IR. NVP-AEW541 also caused Akt dephosphorylation and changes in the expression of key regulatory proteins of the cell cycle. At longer incubation times (48 h), NVP-AEW541-induced apoptotic cell death, as demonstrated by caspase-3 cleavage. Apoptosis was accompanied by decreased expression of anti-apoptotic proteins. NVP-AEW541 enhanced sensitivity of HL60 cells to either cytarabine or etoposide. Moreover, NVP-AEW541 reduced the clonogenic capacity of AML CD34(+) cells cultured in the presence of IGF-I. Chemoresistant AML blasts displayed enhanced IGF-I secretion, and were sensitized to etoposide-induced apoptosis by NVP-AEW541. Our findings indicate that NVP-AEW541 might be a promising therapeutic agent for the treatment of those AML cases characterized by IGF-I autocrine secretion.

Phosphoinositide 3-kinase/Akt signaling pathway and its therapeutical implications for human acute myeloid leukemia

The phosphoinositide 3-kinase (PI3K)/Akt signaling pathway is crucial to many aspects of cell growth, survival and apoptosis, and its constitutive activation has been implicated in the both the pathogenesis and the progression of a wide variety of neoplasias. Hence, this pathway is an attractive target for the development of novel anticancer strategies. Recent studies showed that PI3K/Akt signaling is frequently activated in acute myeloid leukemia (AML) patient blasts and strongly contributes to proliferation, survival and drug resistance of these cells. Upregulation of the PI3K/Akt network in AML may be due to several reasons, including FLT3, Ras or c-Kit mutations. Small molecules designed to selectively target key components of this signal transduction cascade induce apoptosis and/or markedly increase conventional drug sensitivity of AML blasts in vitro. Thus, inhibitory molecules are currently being developed for clinical use either as single agents or in combination with conventional therapies. However, the PI3K/Akt pathway is important for many physiological cellular functions and, in particular, for insulin signaling, so that its blockade in vivo might cause severe systemic side effects. In this review, we summarize the existing knowledge about PI3K/Akt signaling in AML cells and we examine the rationale for targeting this fundamental signal transduction network by means of selective pharmacological inhibitors.

Nuclear phosphoinositide specific phospholipase C (PI-PLC)-beta 1: a central intermediary in nuclear lipid-dependent signal transduction

Several studies have demonstrated the existence of an autonomous intranuclear phospho-inositide cycle that involves the activation of nuclear PI-PLC and the generation of diacylglycerol (DG) within the nucleus. Although several distinct isozymes of PI-PLC have been detected in the nucleus, the isoform that has been most consistently highlighted as being nuclear is PI-PLC-beta1. Nuclear PI-PLC-beta1 has been linked with either cell proliferation or differentiation. Remarkably, the activation mechanism of nuclear PI-PLC-beta1 has been shown to be different from its plasma membrane counterpart, being dependent on phosphorylation effected by p44/42 mitogen activated protein (MAP) kinase. In this review, we report the most up-dated findings about nuclear PI-PLC-beta1, such as the localization in nuclear speckles, the activity changes during the cell cycle phases, and the possible involvement in the progression of myelodisplastic syndrome to acute myeloid leukemia.

Nuclear expression of diacylglycerol kinases: possible involvement in DNA replication

The existence of intranuclear lipid-dependent signal transduction systems has been demonstrated by several independent groups. Remarkably, intranuclear lipid-dependent signal transduction pathways are regulated independently from their membrane/cytosolic counterparts. A sizable body of evidence suggests that nuclear lipid signaling controls critical biological functions such as cell proliferation, differentiation, and apoptosis. Diacylglycerol (DG) is a fundamental lipid second messenger which is produced in the nucleus. Since the levels of nuclear DG fluctuate during the cell cycle progression, it has been suggested that this lipid second messenger has important regulatory roles. Most likely, nuclear DG serves as a chemoattractant for some isoforms of protein kinase C that migrate to the nucleus in response to a variety of agonists. The nucleus also contains diacylglycerol kinases (DGKs), i.e. the enzymes that, by converting DG into phosphatidic acid (PA), terminate DG-dependent events. This review aims at highlighting the different isozymes of DGKs present within the nucleus as well as at discussing their potential functions with particular emphasis placed on DNA replication.

Phosphoinositide 3-kinase/Akt inhibition increases arsenic trioxide-induced apoptosis of acute promyelocytic and T-cell leukaemias

Recent studies suggest that the prosurvival signal transduction pathway involving phosphoinositide 3-kinase (PI3K)/Akt can confer an aggressive, apoptosis-resistant phenotype to acute leukaemia cells. We have investigated the effect of modulating this signalling pathway on the sensitivity of leukaemic cell lines (NB-4, CEM, Jurkat, MOLT-4) and acute promyelocytic primary blasts to apoptosis induced by 1 micromol/l As2O3. Whereas parental NB-4 cells did not display any phosphorylated (active) Akt, CEM, Jurkat and MOLT-4 cells exhibited high levels of Akt activation. Consistently, treatment of NB-4 cells with pharmacological inhibitors of the PI3K/Akt pathway (LY294002, wortmannin) did not increase sensitivity of these cells to arsenic trioxide (As2O3), whereas siRNA knock-down of Akt enhanced As2O3-induced apoptosis of CEM, Jurkat and MOLT-4 cells. Overexpression of a constitutively active Akt cDNA rendered NB-4 cells less susceptible to As2O3. Upon prolonged exposure to As2O3, we isolated a NB-4 cell clone that was resistant to As2O3 and displayed high levels of active Akt. LY294002 treatment of acute promyelocytic primary blasts with elevated Akt phosphorylation levels resulted in an increased sensitivity to As2O3. These results may provide a rationale for the development of combined or sequential treatment with PI3K/Akt inhibitors to improve the efficacy of As2O3 on acute leukaemias and also to overcome As2O3 resistance.

Deguelin, A PI3K/AKT inhibitor, enhances chemosensitivity of leukaemia cells with an active PI3K/AKT pathway

Activation of the phosphoinositide 3 kinase (PI3K)/Akt signalling pathway has been linked with resistance to chemotherapeutic drugs, and its downregulation, by means of PI3K inhibitors, lowers resistance to various types of therapy in tumour cell lines. Recently, it has been reported that deguelin, a naturally occurring rotenoid, is a powerful inhibitor of PI3K. We investigated whether or not deguelin could enhance the sensitivity to chemotherapeutic drugs of human U937 leukaemia cells and acute myeloid leukaemia (AML) blasts with an activated PI3K/Akt network. Deguelin (10 nmol/l) induced S phase arrest with interference of progression to G2/M, and at 100 nmol/l significantly increased apoptotic cell death of U937. At 10-100 nmol/l concentrations, deguelin downregulated Akt phosphorylation of leukaemia cells and markedly increased sensitivity of U937 cells to etoposide or cytarabine. A 10 nmol/l concentration of deguelin did not negatively affect the survival rate of human cord blood CD34+ cells, whereas it increased sensitivity of AML blasts to cytarabine. Deguelin was less toxic than wortmannin on erythropoietin- and stem cell factor-induced erythropoiesis from CD34+ progenitor cells. Overall, our results indicate that deguelin might be used in the future for increasing sensitivity to therapeutic treatments of leukaemia cells with an active PI3K/Akt signalling network.

Involvement of the phosphoinositide 3-kinase/Akt signaling pathway in the resistance to therapeutic treatments of human leukemias

A major factor undermining successful cancer treatment is the occurrence of resistance to conventional treatments such as chemotherapy and ionizing radiation. Evidence accumulated over the recent years has indicated the phosphoinositide 3-kinase/Akt signal transduction pathway as one of the major factors implicated in cancer resistance to conventional therapies. Indeed, the phosphoinositide 3-kinase/Akt axis regulates the expression and/or function of many anti-apoptotic proteins which strongly contributes to cancer cell survival. As a result, small molecules designed to specifically target key components of this signaling network are now being developed for clinical use as single therapeutic agents and/or in combination with other forms of therapy to overcome resistance. Initially, the phosphoinositide 3-kinase/Akt signal transduction pathway has been mainly investigated in solid tumors. Recently, however, this network has also been recognized as an important therapeutic target in human leukemias. Specific inhibition of this signalling pathway may be a valid approach to treat these diseases and increase the efficacy of standard types of therapy.

Different levels of the neuronal nitric oxide synthase isoform modulate the rate of osteoclastic differentiation of TIB-71 and CRL-2278 RAW 264.7 murine cell clones

It has been clearly established that osteoclasts, which play a crucial role in bone resorption, differentiate from hematopoietic cells belonging to the monocyte/macrophage lineage in the presence of macrophage-colony stimulating factor (M-CSF) and receptor activator of NF-kappaB ligand (RANKL). We have here investigated the M-CSF- and RANKL-induced osteoclastic differentiation of two distinct clones of the murine monocytic/macrophagic RAW 264.7 cell line, known as TIB-71 and CRL-2278, the latter cell clone being defective for the expression of the inducible nitric oxide synthase isoform in response to interferon-gamma or lipopolysaccharide. CRL-2278 cells demonstrated a more rapid osteoclastic differentiation than TIB-71 cells, as documented by morphology, tartrate-resistant acid phosphatase positivity, and bone resorption activity. The enhanced osteoclastic differentiation of CRL-2278 was accompanied by a higher rate of cells in the S/G2-M phases of cell cycle as compared to TIB-71. The analysis of nitric oxide synthase (NOS) isoforms clearly demonstrated that only neuronal NOS was detectable at high levels in CRL-2278 but not in TIB cells under all tested conditions. Moreover, the broad inhibitor of NOS activity L-NAME significantly inhibited osteoclastic differentiation of CRL-2278 cells. Altogether, these results demonstrate that a basal constitutive neuronal NOS activity positively affects the RANKL/M-CSF-related osteoclastic differentiation.

Novel 2′-substituted, 3′-deoxy-phosphatidyl-myo-inositol analogues reduce drug resistance in human leukaemia cell lines with an activated phosphoinositide 3-kinase/Akt pathway

Activation of the phosphoinositide 3-kinase (PI3-K)/Akt signalling pathway has been linked with resistance to chemotherapeutic drugs, and its down-regulation, by means of pharmacological inhibitors of PI3-K, considerably lowers resistance to various types of therapy in cell lines derived from solid tumours. Recently, a new class of Akt inhibitors, referred to as phosphatidylinositol ether lipids (PIAs), have been synthesized. We tested whether two new PIAs could lower the sensitivity threshold to chemotherapeutic drugs of human leukaemia cell lines with an activated PI3-K/Akt network. We used HL60AR (for apoptosis resistant), K562 and U937 cells. The two pharmacological inhibitors, used at 5 micromol/l, down-regulated Akt kinase activity and phosphorylation. Neither of the two chemicals affected the activity of other signalling proteins in the Akt pathway, such as phosphoinositide-dependent protein kinase-1 or PTEN. When employed at 5 micromol/l, the Akt inhibitors markedly reduced the resistance of the leukaemic cell lines to etoposide or cytarabine. Remarkably, a 5 micromol/l concentration of the inhibitors did not negatively affect the survival rate of human cord blood CD34(+) cells. Overall, our results indicate that new selective Akt pharmacological inhibitors might be used in the future for overcoming Akt-mediated resistance to therapeutic treatments of acute leukaemia cells.

The phosphoinositide 3-kinase/Akt pathway regulates cell cycle progression of HL60 human leukemia cells through cytoplasmic relocalization of the cyclin-dependent kinase inhibitor p27(Kip1) and control of cyclin D1 expression

The serine/threonine protein kinase Akt, a downstream effector of phosphoinositide 3-kinase (PI3K), plays a pivotal role in tumorigenesis because it affects the growth and survival of cancer cells. Several laboratories have demonstrated that Akt inhibits transcriptional activation of a number of related forkhead transcription factors now referred to as FoxO1, FoxO3, and FoxO4. Akt-regulated forkhead transcription factors are involved in the control of the expression of both the cyclin-dependent kinase (cdk) inhibitor p27(Kip1) and proapoptotic Bim protein. Very little information is available concerning the importance of the PI3K/Akt pathway in HL60 human leukemia cells. Here, we present our findings showing that the PI3K/Akt axis regulates cell cycle progression of HL60 cells through multiple mechanisms also involving the control of FoxO1 and FoxO3. To this end, we took advantage of a HL60 cell clone (HL60AR cells) with a constitutively activated PI3K/Akt axis. When compared with parental (PT) HL60 cells, HL60AR cells displayed higher levels of phosphorylated FoxO1 and FoxO3. In AR cells forkhead factors localized predominantly in the cytoplasm, whereas in PT cells they were mostly nuclear. AR cells proliferated faster than PT cells and showed a lower amount of the cdk inhibitor p27(Kip1), which was mainly found in the cytoplasm and was hyperphosphorylated on threonine residues. AR cells also displayed higher levels of cyclin D1 and phosphorylated p110 Retinoblastoma protein. The protein levels of cdk2, cdk4, and cdk6 were not altered in HL60AR cells, whereas the activities of both ckd2 and cdk6 were higher in AR than in PT cells. These results show that in HL60 cells the PI3K/Akt signaling pathway may be involved in the control of the cell cycle progression most likely through mechanisms involving the activation of forkhead transcription factors.

Intranucleolar localization of DNA topoisomerase II? is a distinctive feature of necrotic, but not of apoptotic, Jurkat T-cells

Two distinct types of cell death have been described: apoptosis and necrosis. However, it is becoming increasingly clear that the differences between these two types are far less numerous than initially thought. Morphological analyses might provide important information to distinguish apoptotic from necrotic samples. We recently reported that in necrotic, but not apoptotic, HL-60 human myeloid leukaemia cells, the nuclear protein topoisomerase IIalpha concentrated in nucleoli. In order to ascertain whether or not this phenomenon was restricted to a peculiar cell type or could be detected also in cells of lymphoid lineage, we performed an investigation aimed at defining the localization of topoisomerase IIalpha in apoptotic and necrotic Jurkat human T lymphoblastoid cells. Immunofluorescence staining demonstrated that topoisomerase IIalpha was excluded from the condensed chromatin of apoptotic cells, whereas in necrotic cells it was localized in discrete nuclear dots. Immuno-electron microscopy analysis showed that topoisomerase IIalpha was undetectable in nucleoli of normal and apoptotic cells, whereas it was present in the nucleolus of necrotic cells irrespectively of the type of inducer used (ethanol, H(2)O(2), HgCl(2)). Taken together, our findings identify topoisomerase IIalpha as a potential morphological marker useful to discriminate between apoptotic and necrotic cells.

A new selective AKT pharmacological inhibitor reduces resistance to chemotherapeutic drugs, TRAIL, all-trans-retinoic acid, and ionizing radiation of human leukemia cells

It is now well established that the reduced capacity of tumor cells of undergoing cell death through apoptosis plays a key role both in the pathogenesis of cancer and in therapeutic treatment failure. Indeed, tumor cells frequently display multiple alterations in signal transduction pathways leading to either cell survival or apoptosis. In mammals, the pathway based on phosphoinositide 3-kinase (PI3K)/Akt conveys survival signals of extreme importance and its downregulation, by means of pharmacological inhibitors of PI3K, considerably lowers resistance to various types of therapy in solid tumors. We recently described an HL60 leukemia cell clone (HL60AR cells) with a constitutively active PI3K/Akt pathway. These cells were resistant to multiple chemotherapeutic drugs, all-trans-retinoic acid (ATRA), and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Treatment with two pharmacological inhibitors of PI3K, wortmannin and Ly294002, restored sensitivity of HL60AR cells to the aforementioned treatments. However, these inhibitors have some drawbacks that may severely limit or impede their clinical use. Here, we have tested whether or not a new selective Akt inhibitor, 1L-6-hydroxymethyl-chiro-inositol 2(R)-2-O-methyl-3-O-octadecylcarbonate (Akt inhibitor), was as effective as Ly294002 in lowering the sensitivity threshold of HL60 cells to chemotherapeutic drugs, TRAIL, ATRA, and ionizing radiation. Our findings demonstrate that, at a concentration which does not affect PI3K activity, the Akt inhibitor markedly reduced resistance of HL60AR cells to etoposide, cytarabine, TRAIL, ATRA, and ionizing radiation. This effect was likely achieved through downregulation of expression of antiapoptotic proteins such as c-IAP1, c-IAP2, cFLIP(L), and of Bad phosphorylation on Ser 136. The Akt inhibitor did not influence PTEN activity. At variance with Ly294002, the Akt inhibitor did not negatively affect phosphorylation of protein kinase C-zeta and it was less effective in downregulating p70S6 kinase (p70S6K) activity. The Akt inhibitor increased sensitivity to apoptotic inducers of K562 and U937, but not of MOLT-4, leukemia cells. Overall, our results indicate that selective Akt pharmacological inhibitors might be used in the future for enhancing the sensitivity of leukemia cells to therapeutic treatments that induce apoptosis or for overcoming resistance to these treatments.

Diacylglycerol kinase-theta is localized in the speckle domains of the nucleus

It is well established that the nucleus is endowed with enzymes that are involved in lipid-dependent signal transduction pathways. Diacylglycerol (DAG) is a fundamental lipid second messenger that is produced in the nucleus. Previous reports have shown that the nucleus contains diacylglycerol kinases (DGKs), i.e., the enzymes that, by converting DAG into phosphatidic acid (PA), terminate DAG-dependent events. Here, we show, by immunofluorescence staining and confocal analysis, that DGK-theta localizes mainly to the nucleus of various cell lines, such as MDA-MB-453, MCF-7, PC12, and HeLa. Nuclear DGK-theta co-localizes with phosphatidylinositol 4,5-bisphosphate (PIP(2)) in domains that correspond to nuclear speckles, as revealed by the use of an antibody to the splicing factor SC-35, a well-established marker for these structures. The spatial distribution of nuclear DGK-theta was dynamic in that it was affected by inhibition of mRNA transcription with alpha-amanitin. Immuno-electron microscopy analysis demonstrated that DGK-theta, PIP(2), and phosphoinositide-specific phospholipase Cbeta1 (PLCbeta1) associated with electron-dense particles within the nucleus that correspond to interchromatin granule clusters. Cell fractionation experiments performed in MDA-MB-453, HeLa, and PC12 cells showed a preferential association of DGK-theta with the nucleus. Western blots demonstrated that DGK-theta was enriched in the nuclear matrix fraction prepared from MDA-MB-453 cells. Immunoprecipitation experiments with an antibody to PLCbeta1 revealed in MDA-MB-453 cells an association between this enzyme and both DGK-theta and phosphatidylinositol phosphate kinase Ialpha (PIPKIalpha). Our findings strengthen the contention that speckles represent a crucial site for the nuclear-based inositol lipid cycle. We may speculate that nuclear speckle-located DGK-theta, on cell stimulation with an agonist, converts to PA the DAG derived from PLCbeta1-dependent PIP(2) hydrolysis.

Flow cytometric detection of total and serine 473 phosphorylated Akt

The evaluation of regulatory proteins is important for biological studies and is also established as a prognostic marker for cancer diagnosis. Very recently, it has been highlighted that the serine/threonine kinase Akt plays a fundamental role in survival pathways and is also involved in the onset of resistance to anti-neoplastic drugs and ionizing radiation in cell lines derived from solid tumors. For its full activation Akt needs to be phosphorylated on Serine 473 residue. Molecules that are fundamental in determining resistance to therapeutic treatments might serve in the future as clinical markers to tailor therapy and/or predict treatment response. The aim of this study was to ascertain whether or not flow cytometric analysis of total Akt and of its form phosphorylated on Serine 473 could be related to standard techniques such as Western blotting with phosphospecific antibodies and in vitro kinase assay. To this end, we employed as experimental models HL-60 and PC-12 lines in which there is an enhancement of Akt activity. Our results showed that flow cytometry analysis, performed on fixed and permeabilized cells, correlated well with the results provided by in vitro activity assays and Western blots. Therefore, our findings might indicate that flow cytometric study of Akt (both total and phosphorylated) content may be applied in routine work for phenotyping of hematological and non-hematological neoplasias, and allow for its use as a useful marker for the classification and the prognosis of neoplastic diseases.

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.

Constitutively active Akt1 protects HL60 leukemia cells from TRAIL-induced apoptosis through a mechanism involving NF-kappaB activation and cFLIP(L) up-regulation

TRAIL is a member of the tumor necrosis factor superfamily which induces apoptosis in cancer but not in normal cells. Akt1 promotes cell survival and blocks apoptosis. The scope of this paper was to investigate whether a HL60 human leukemia cell clone (named AR) with constitutively active Akt1 was resistant to TRAIL. We found that parental (PT) HL60 cells were very sensitive to a 6 h incubation in the presence of TRAIL and died by apoptosis. In contrast, AR cells were resistant to TRAIL concentrations as high as 2 microg/ml for 24 h. Two pharmacological inhibitors of PI3K, Ly294002 and wortmannin, restored TRAIL sensitivity of AR cells. AR cells stably overexpressing PTEN had lower Akt1 activity and were sensitive to TRAIL. Conversely, PT cells stably overexpressing a constitutive active form of Akt1 became TRAIL resistant. TRAIL activated caspase-8 but not caspase-9 or -10 in HL60 cells. We did not observe a protective effect of Bcl-X(L) or Bcl-2 against the cytotoxic activity of TRAIL, even though TRAIL induced cleavage of BID. There was a close correlation between TRAIL sensitivity and intranuclear presence of the p50 subunit of NF-kappaB. Higher levels of the FLICE inhibitory protein, cFLIP(L), were observed in TRAIL-resistant cells. Both the cell permeable NF-kappaB inhibitor SN50 and cycloheximide lowered cFLIP(L)expression and restored sentivity of AR cells to TRAIL. Our results suggest that Akt1 may be an important regulator of TRAIL sensitivity in HL60 cells through the activation of NF-kappaB and up-regulation of cFLIP(L) synthesis.

The phosphoinositide 3-kinase/AKT1 pathway involvement in drug and all-trans-retinoic acid resistance of leukemia cells

Disruption of the apoptotic pathways may account for resistance to chemotherapy and treatment failures in human neoplastic disease. To further evaluate this issue, we isolated a HL-60 cell clone highly resistant to several drugs inducing apoptosis and to the differentiating chemical all-trans-retinoic acid (ATRA). The resistant clone displayed an activated phosphoinositide 3-kinase (PI3K)/AKT1 pathway, with levels of phosphatidylinositol (3,4,5) trisphosphate higher than the parental cells and increased levels of both Thr 308 and Ser 473 phosphorylated AKT1. In vitro AKT1 activity was elevated in resistant cells, whereas treatment of the resistant cell clone with two inhibitors of PI3K, wortmannin or Ly294002, strongly reduced phosphatidylinositol (3,4,5) trisphosphate levels and AKT1 activity. The inhibitors reversed resistance to drugs. Resistant cells overexpressing either dominant negative PI3K or dominant negative AKT1 became sensitive to drugs and ATRA. Conversely, if parental HL-60 cells were forced to overexpress an activated AKT1, they became resistant to apoptotic inducers and ATRA. There was a tight relationship between the activation of the PI3K/AKT1 axis and the expression of c-IAP1 and c-IAP2 proteins. Activation of the PI3K/AKT1 axis in resistant cells was dependent on enhanced tyrosine phosphorylation of the p85 regulatory subunit of PI3K, conceivably due to an autocrine insulin-like growth factor-I production. Our findings suggest that an up-regulation of the PI3K/AKT1 pathway might be one of the survival mechanisms responsible for the onset of resistance to chemotherapeutic and differentiating therapy in patients with acute leukemia.

Molecular characterization of protein kinase C-alpha binding to lamin A

Previous results from our laboratory have identified lamin A as a protein kinase C (PKC)-binding protein. Here, we have identified the regions of PKC-alpha that are crucial for this binding. By means of overlay assays and fusion proteins made of glutathione-S-transferase (GST) fused to elements of rat PKC-alpha, we have established that binding occurs through both the V5 region and a portion of the C2 region (i.e., the calcium-dependent lipid binding (CaLB) domain) of the kinase. In particular, we have found that amino acid 200-217 of the CaLB domain are essential for binding lamin A, as a synthetic peptide corresponding to this stretch of amino acids prevented the interaction between the CaLB domain and lamin A. We also show that the presence of four lysine residues of the CaLB domain (K205, K209, K211, and K213) was essential for the binding. We have determined that binding of elements of PKC-alpha to lamin A does not require the presence of cofactors such as phosphatidylserine (PS) and Ca(2+). We have also found that the binding site of lamin A for the CaLB domain of PKC-alpha is localized in the carboxyl-terminus of the lamin, downstream of amino acid 499. Our findings may prove to be important to clarify the mechanisms regulating PKC function within the nucleus and may also lead to the synthesis of isozyme-specific drugs to attenuate or reverse PKC-dependent nuclear signaling pathways important for the pathogenesis of cancer.

Nuclear inositol lipid signaling and its potential involvement in malignant transformation

Growth, differentiation, and apoptosis of eukaryotic cells are mediated by extremely complex signaling pathways and a high degree of coordination is required for regulating cell proliferation. In multicellular organisms homeostasis is achieved through signal transduction events. If these homeostatic mechanisms are interrupted, a disease, such as cancer, may ensue. Lipid second messengers, particularly those derived from polyphosphoinositide cycle, play a pivotal role in several cell signaling networks. Evidence accumulated over the past 15 years has highlighted the presence of an autonomous nuclear inositol lipid metabolism, and suggests that lipid signaling molecules are important components of signaling pathways operating within the nucleus. Recent findings are starting to elucidate how the nuclear phosphoinositide cycle is regulated and what down-stream molecules are targeted through this cycle. In this review, we shall summarize the most updated data about inositol lipid-dependent nuclear signaling pathways that might have a relevance for the development of cancer. In the near future, this knowledge might also prove to have relevance for the diagnosis and treatment of the neoplastic disease.

Binding of elements of protein kinase C-alpha regulatory domain to lamin B1

Previous results from our laboratory have demonstrated that lamin B1 is a protein kinase C (PKC)-binding protein. Here, we have identified the regions of PKC-alpha that are important for this binding. By means of overlay assays and fusion proteins made of glutathione-S-transferase (GST) fused to elements of the regulatory domain of rat PKC-alpha, we have established that binding occurs through both the V1 region and a portion of the C2 region (i.e., the calcium-dependent lipid binding [CaLB] domain) of the kinase. In particular, we have found that amino acids 200-217 of the CaLB domain are essential for binding lamin B1, as a synthetic peptide corresponding to this stretch of amino acids prevented the interaction between the CaLB domain of PKC-alpha and lamin B1. In agreement with the results of other investigators, we have determined that binding of regulatory elements of PKC-alpha to lamin B1 does not require the presence of cofactors such as PS and Ca(2+). We have also found that the binding site of lamin B1 for PKC-alpha is localized in the carboxyl-terminus of the lamin. Our findings may prove to be important in shedding more light on the mechanisms that regulate PKC functions within the nuclear compartment and may also lead to the synthesis of isozyme-specific pharmacological tools to attenuate or reverse PKC-dependent nuclear signalling pathways important for the pathogenesis of cancer.

The controversial nuclear matrix: a balanced point of view

The nuclear matrix is defined as the residual framework after the removal of the nuclear envelope, chromatin, and soluble components by sequential extractions. According to several investigators the nuclear matrix provides the structural basis for intranuclear order. However, the existence itself and the nature of this structure is still uncertain. Although the techniques used for the visualization of the nuclear matrix have improved over the years, it is still unclear to what extent the isolated nuclear matrix corresponds to an in vivo existing structure. Therefore, considerable skepticism continues to surround the nuclear matrix fraction as an accurate representation of the situation in living cells. Here, we summarize the experimental evidence in favor of, or against, the presence of a diffuse nucleoskeleton as a facilitating organizational nonchromatin structure of the nucleus.

Localization of the small monomeric GTPases Rab3D and Rab3A in the AtT-20 rat pituitary cell line

We investigated the cellular localization of the small GTPases Rab3D and Rab3A in AtT-20 cells treated with the drug Brefeldin A. Brefeldin A induces the redistribution of the Golgi complex into the endoplasmic reticulum and tubulation of endosomes. However, in Brefeldin A-treated wild-type AtT-20 cells, both Rab3D and Rab3A retained their distribution, indicating that they belong to a nonendosomal, post-Golgi compartment. Immunoelectron microscopy experiments indicated that both Rab3D and Rab3A localized to the ACTH-containing, large dense core granules. In contrast, in cell clones overexpressing a mutated form of Rab3D (Rab3D N135I), Rab3A did not localize to the dense core granules. Moreover, since our previous results showed that overexpression of Rab3D N135I severely impaired regulated ACTH secretion in AtT-20 cells, we sought to determine whether the impairment could depend on a redistribution of two key components of the regulated exocytosis machinery, synaptotagmin and SNAP-25. As far as synaptotagmin was concerned, in cell clones overexpressing Rab3D N135I, the protein did not localize close to the plasma membrane, in agreement with the previously reported defective docking of dense core granules to the plasma membrane. Immunofluorescence experiments showed that SNAP-25 did not change its localization in these cell clones. All in all, our findings strengthen the notion that both Rab3D and Rab3A are associated with the dense core granule compartment of AtT-20 cells, and that the impairment in the ACTH secretion caused by overexpression of a mutated Rab3D form is likely to be due to a lacking of granule docking to the plasma membrane, possibly because Rab3A fails to associate with the granules.

Diacylglycerol kinases in nuclear lipid-dependent signal transduction pathways

Several independent groups have shown that lipid-dependent signal transduction systems operate in the nucleus and that they are regulated independently from their membrane and cytosolic counterparts. A sizable body of evidence suggests that nuclear lipid signaling controls critical biological functions such as cell proliferation and differentiation. Diacylglycerol is a fundamental lipid second messenger which is produced in the nucleus. The levels of nuclear diacylglycerol fluctuate during the cell cycle progression, suggesting that such a molecule has important regulatory roles. Most likely, nuclear diacylglycerol serves as a chemoattractant for some isoforms of protein kinase C that migrate to the nucleus in response to a variety of agonists. The nucleus also contains diacylglycerol kinases, i.e. the enzymes that, by converting diacylglycerol into phosphatidic acid, terminate diacylglycerol-dependent events. A number of diacylglycerol kinases encoded by separate genes are present in the mammalian genome. This review aims at highlighting the different isotypes of diacylglycerol kinases identified at the nuclear level as well as at discussing their potential function and regulation.

Phosphoinositide-specific phospholipase Cbeta1 expression is not linked to nerve growth factor-induced differentiation, cell survival or cell cycle control in PC12 rat pheocromocytoma cells

Recent reports have highlighted that phosphoinositide-specific phospholipase Cbeta1 expression is linked to neuronal differentiation in different experimental models. We sought to determine whether or not this is also true for nerve growth factor (NGF)-induced neuronal differentiation of rat PC12 cells. However, we did not find differences in the expression of both the forms of phosphoinositide-specific phospholipase Cbeta1 (a and b) during sympathetic differentiation of these cells. Also, PC12 cell clones stably overexpressing phosphoinositide-specific phospholipase Cbeta1 were not more susceptible to the differentiating effect of NGF. Furthermore, since it is well established that phosphoinositide-specific phospholipase Cbeta1 affects cell proliferation, we investigated whether or not PC12 cell clones stably overexpressing phosphoinositide-specific phospholipase Cbeta1 showed differences in survival to serum deprivation and cell cycle, when compared to wild type cells. Nevertheless, we did not find any differences in these parameters between wild type cells and the overexpressing clones. Interestingly, in PC12 cells the overexpressed phosphoinositide-specific phospholipase Cbeta1 did not localize to the nucleus, but by immunofluorescence analysis, was detected in the cytoplasm. Therefore, our findings may represent another important clue to the fact that only when it is located within the nucleus phosphoinositide-specific phospholipase Cbeta1 is able to influence cell proliferation.

Proliferating or differentiating stimuli act on different lipid-dependent signaling pathways in nuclei of human leukemia cells

Previous results have shown that the human promyelocytic leukemia HL-60 cell line responds to either proliferating or differentiating stimuli. When these cells are induced to proliferate, protein kinase C (PKC)-beta II migrates toward the nucleus, whereas when they are exposed to differentiating agents, there is a nuclear translocation of the alpha isoform of PKC. As a step toward the elucidation of the early intranuclear events that regulate the proliferation or the differentiation process, we show that in the HL-60 cells, a proliferating stimulus (i.e., insulin-like growth factor-I [IGF-I]) increased nuclear diacylglycerol (DAG) production derived from phosphatidylinositol (4,5) bisphosphate, as indicated by the inhibition exerted by 1-O-octadeyl-2-O-methyl-sn-glycero-3-phosphocholine and U-73122 (1-[6((17 beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione), which are pharmacological inhibitors of phosphoinositide-specific phospholipase C. In contrast, when HL-60 cells were induced to differentiate along the granulocytic lineage by dimethyl sulfoxide, we observed a rise in the nuclear DAG mass, which was sensitive to either neomycin or propranolol, two compounds with inhibitory effect on phospholipase D (PLD)-mediated DAG generation. In nuclei of dimethyl sulfoxide-treated HL-60 cells, we observed a rise in the amount of a 90-kDa PLD, distinct from PLD1 or PLD2. When a phosphatidylinositol (4,5) bisphosphate-derived DAG pool was generated in the nucleus, a selective translocation of PKC-beta II occurred. On the other hand, nuclear DAG derived through PLD, recruited PKC-alpha to the nucleus. Both of these PKC isoforms were phosphorylated on serine residues. These results provide support for the proposal that in the HL-60 cell nucleus there are two independently regulated sources of DAG, both of which are capable of acting as the driving force that attracts to this organelle distinct, DAG-dependent PKC isozymes. Our results assume a particular significance in light of the proposed use of pharmacological inhibitors of PKC-dependent biochemical pathways for the therapy of cancer disease.

Erythropoietin-induced erythroid differentiation of K562 cells is accompanied by the nuclear translocation of phosphatidylinositol 3-kinase and intranuclear generation of phosphatidylinositol (3,4,5) trisphosphate

D-3 phosphorylated inositides are a peculiar class of lipids, synthesized by phosphatidylinositol 3-kinase (PtdIns 3-K), which are also present in the nucleus. In order to clarify a possible role for nuclear D-3 phosphorylated inositides during human erythroid differentiation, we have examined the issue of whether or not, in K562 human erythroleukemia cells, erythropoietin (EPO) may generate nuclear translocation of an active PtdIns 3-K. Immunoprecipitation with an anti-p85 regulatory subunit of PtdIns 3-K, revealed that both the intranuclear amount and the activity of the kinase increased rapidly and transiently in response to EPO. Enzyme translocation was blocked by the specific PtdIns 3-K pharmacological inhibitor, LY294002, which also inhibited erythroid differentiation. In vivo, intranuclear synthesis of phosphatidylinositol (3,4,5) trisphosphate (PtdIns (3,4,5)P(3)) was stimulated by EPO. Almost all PtdIns 3-K that translocated to the nucleus was highly phosphorylated on tyrosine residues of the p85 regulatory subunit. These findings strongly suggest that an important step in the signaling pathways that mediate EPO-induced erythroid differentiation may be represented by the intranuclear translocation of an active PtdIns 3-K.

Nuclear apoptotic changes: an overview

Apoptosis is a form of active cell death essential for morphogenesis, development, differentiation, and homeostasis of multicellular organisms. The activation of genetically controlled specific pathways that are highly conserved during evolution results in the characteristic morphological features of apoptosis that are mainly evident in the nucleus. These include chromatin condensation, nuclear shrinkage, and the formation of apoptotic bodies. The morphological changes are the result of molecular alterations, such as DNA and RNA cleavage, post-translational modifications of nuclear proteins, and proteolysis of several polypeptides residing in the nucleus. During the last five years our understanding of the process of apoptosis has dramatically increased. However, the mechanisms that lead to apoptotic changes in the nucleus have been only partially clarified. Here, we shall review the most recent findings that may explain why the nucleus displays these striking modifications. Moreover, we shall take into consideration the emerging evidence about apoptotic events as a trigger for the generation of autoantibodies to nuclear components.

Nuclear changes in necrotic HL-60 cells

Cell death in eukaryotes can occur by either apoptosis or necrosis. Apoptosis is characterized by well-defined nuclear changes which are thought to be the consequence of both proteolysis and DNA fragmentation. On the other hand, the nuclear modifications that occur during necrosis are largely less known. Here, we have investigated whether or not nuclear modifications occur during ethanol-induced necrotic cell death of HL-60 cells. By means of immunofluorescence staining, we demonstrate that the patterns given by antibodies directed against some nuclear proteins (lamin B1, NuMA, topoisomerase IIalpha, SC-35, B23/nucleophosmin) changed in necrotic cells. The changes in the spatial distribution of NuMA strongly resembled those described to occur during apoptosis. On the contrary, the fluorescent pattern characteristic for other nuclear proteins (C23/nucleolin, UBF, fibrillarin, RNA polymerase I) did not change during necrosis. By immunoblotting analysis, we observed that some nuclear proteins (SAF-A, SATB1, NuMA) were cleaved during necrosis, and in the case of SATB1, the apoptotic signature fragment of 70 kDa was also present to the same extent in necrotic samples. Caspase inhibitors did not prevent proteolytic cleavage of the aforementioned polypeptides during necrosis, while they were effective if apoptosis was induced. In contrast, lamin B1 and topoisomerase IIalpha were uncleaved in necrotic cells, whereas they were proteolyzed during apoptosis. Transmission electron microscopy analysis revealed that slight morphological changes were present in the nuclear matrix fraction prepared from necrotic cells. However, these modifications (mainly consisting of a rarefaction of the inner fibrogranular network) were not as striking as those we have previously described in apoptotic HL-60 cells. Taken together, our results indicate that during necrosis marked biochemical and morphological changes do occur at the nuclear level. These alterations are quite distinct from those known to take place during apoptosis. Our results identify additional biochemical and morphological criteria that could be used to discriminate between the two types of cell death. J. Cell. Biochem. Suppl. 36: 19-31, 2001.

Re-examination of the mechanisms regulating nuclear inositol lipid metabolism

Although inositol lipids constitute only a very minor proportion of total cellular lipids, they have received immense attention by scientists since it was discovered that they play key roles in a wide range of important cellular processes. In the late 1980s, it was suggested that these lipids are also present within the cell nucleus. Albeit the early reports about the intranuclear localization of phosphoinositides were met by skepticism and disbelief, compelling evidence has subsequently been accumulated convincingly showing that a phosphoinositide cycle is present at the nuclear level and may be activated in response to stimuli that do not activate the inositol lipid metabolism localized at the plasma membrane. Very recently, intriguing new data have highlighted that some of the mechanisms regulating nuclear inositol lipid metabolism differ in a substantial way from those operating at the cell periphery. Here, we provide an overview of recent findings regarding the regulation of both nuclear phosphatidylinositol 3-kinase and phosphoinositide-specific phospholipase C-beta1.

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.

Behavior of nucleolar proteins during the course of apoptosis in camptothecin-treated HL60 cells

By means of immunofluorescence and immunoelectron microscopy we have studied the fate of different nucleolar components during the apoptotic process in camptothecin-treated HL60 cells. We have found that RNA polymerase I disappeared while UBF was associated with previously described fibrogranular threaded bodies. In contrast, fibrillarin, C23/nucleolin, and B23/nucleophosmin remained detectable in granular material present amid micronuclei of late apoptotic cells. Double immunolabeling experiments showed colocalization of both C23 and B23 with fibrillarin. Immunoblotting analysis showed that UBF was proteolytically degraded, whereas fibrillarin, C23/nucleolin, and B23/nucleophosmin were not. These results may help explain the presence of anti-nucleolar antibodies seen in various pathological disorders.

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.

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.