Induction of apoptosis in murine clonal osteoblasts expressed by human T-cell leukemia virus type I tax by NF-kappa B and TNF-alpha

Analysis of the cytotoxicity and bioactivity of CeraSeal, BioRoot™ and AH Plus® sealers in pre-osteoblast lineage cells

BACKGROUND

The objective of the present study was to evaluate in vitro the cytotoxicity and bioactivity of various endodontic sealers (CeraSeal, BioRoot™ and AH Plus®) in pre-osteoblast mouse cells (MC3T3 cells).

METHODS

MC3T3 cells (ATCC CRL-2594) were plated in 1 × 104 cells/well in 96-well plates in contact with endodontic sealers at concentrations of 1:10 and 1:100. Cell viability was evaluated by MTT assay after 24 and 48 h. In addition, sealer bioactivity was measured by RT-PCR for mediator of inflammation (Tnf, Ptgs2) and mineralization (Runx2, Msx1, Ssp1 and Dmp1) after 24 h and by Alizarin Red S Assay of mineralization after 28 days. Data were analyzed using one-way ANOVA followed by the Tukey's post-test at a significance level of 5%.

RESULTS

BioRoot™ presented 24-hour cytotoxicity (p < 0.05) at 1:10 concentration. In the period of 48 h, no endodontic cement was cytotoxic to the cells compared to the control (p > 0.05). TNF-α gene expression was induced by AH Plus® (p < 0.05), while Ptgs2 was induced by the CeraSeal and BioRoot™ (p < 0.05). The expression of Runx2 was stimulated by BioRoot™ and AH Plus® (p < 0.05). In contrast, the expression of Dmp-1 Dmp1 was higher for the CeraSeal and BioRoot™ (p < 0.05). Nonetheless, the sealers did not impact the formation of mineralization nodules (p > 0.05).

CONCLUSION

CeraSeal, BioRoot™ and AH Plus® sealers were not cytotoxic to MC3T3 cells within 48 h, but differentially induced the expression of genes related to inflammation and mineralization without impacting biomineralization by the cells.

Harnessing Tumor Necrosis Factor Alpha to Achieve Effective Cancer Immunotherapy

Tumor necrosis factor alpha (TNFα) is a pleiotropic cytokine known to have contradictory roles in oncoimmunology. Indeed, TNFα has a central role in the onset of the immune response, inducing both activation and the effector function of macrophages, dendritic cells, natural killer (NK) cells, and B and T lymphocytes. Within the tumor microenvironment, however, TNFα is one of the main mediators of cancer-related inflammation. It is involved in the recruitment and differentiation of immune suppressor cells, leading to evasion of tumor immune surveillance. These characteristics turn TNFα into an attractive target to overcome therapy resistance and tackle cancer. This review focuses on the diverse molecular mechanisms that place TNFα as a source of resistance to immunotherapy such as monoclonal antibodies against cancer cells or immune checkpoints and adoptive cell therapy. We also expose the benefits of TNFα blocking strategies in combination with immunotherapy to improve the antitumor effect and prevent or treat adverse immune-related effects.

Functional roles and mechanisms of ginsenosides from Panax ginseng in atherosclerosis

Atherosclerosis (AS) is a leading cause of cardiovascular diseases (CVDs) and it results in a high rate of death worldwide, with an increased prevalence with age despite advances in lifestyle management and drug therapy. Atherosclerosis is a chronic progressive inflammatory process, and it mainly presents with lipid accumulation, foam cell proliferation, inflammatory response, atherosclerotic plaque formation and rupture, thrombosis, and vascular calcification. Therefore, there is a great need for reliable therapeutic drugs or remedies to cure or alleviate atherosclerosis and reduce the societal burden. Ginsenosides are natural steroid glycosides and triterpene saponins obtained mainly from the plant ginseng. Several recent studies have reported that ginsenosides have a variety of pharmacological activities against several diseases including inflammation, cancer and cardiovascular diseases. This review focuses on describing the different pharmacological functions and underlying mechanisms of various active ginsenosides (Rb1,-Rd, -F, -Rg1, -Rg2, and -Rg3, and compound K) for atherosclerosis, which could provide useful insights for developing novel and effective anti-cardiovascular drugs.

Interleukin 6/Wnt interactions in rheumatoid arthritis: interleukin 6 inhibits Wnt signaling in synovial fibroblasts and osteoblasts

Aim

To evaluate the impact of previously unrecognized negative interaction between the Wnt and interleukin (IL) 6 signaling pathways in skeletal tissues as a possible major mechanism leading to age- and inflammation-related destruction of bone and joints.

Methods

Luciferase reporter assays were performed to monitor Wnt pathway activation upon IL-6 and tumor necrosis factor-α (TNFα) treatment. Functional contribution of IL-6 and TNFα interaction to inhibition of bone formation was evaluated in vitro using small hairpin RNAs (shRNA) in mouse mesenchymal precursor cells (MPC) of C2C12 and KS483 lines induced to differentiate into osteoblasts by bone morphogenetic proteins (BMP).

Results

IL-6 inhibited the activation of Wnt signaling in primary human synoviocytes, and, together with TNFα and Dickkopf-1, inhibited the activation of Wnt response. ShRNA-mediated knockdown of IL-6 mRNA significantly increased early BMP2/7-induced osteogenesis and rescued it from the negative effect of TNFα in C2C12 cells, as well as intensified bone matrix mineralization in KS483 cells.

Conclusion

IL-6 is an important mediator in the inhibition of osteoblast differentiation by TNFα, and knockdown of IL-6 partially rescues osteogenesis from the negative control of inflammation. The anti-osteoblastic effects of IL-6 are most likely mediated by its negative interaction with Wnt signaling pathway.

Common pathways regulate Type III TGFβ receptor-dependent cell invasion in epicardial and endocardial cells

Epithelial-Mesenchymal Transformation (EMT) and the subsequent invasion of epicardial and endocardial cells during cardiac development is critical to the development of the coronary vessels and heart valves. The transformed cells give rise to cardiac fibroblasts and vascular smooth muscle cells or valvular interstitial cells, respectively. The Type III Transforming Growth Factor β (TGFβR3) receptor regulates EMT and cell invasion in both cell types, but the signaling mechanisms downstream of TGFβR3 are not well understood. Here we use epicardial and endocardial cells in in vitro cell invasion assays to identify common mechanisms downstream of TGFβR3 that regulate cell invasion. Inhibition of NF-κB activity blocked cell invasion in epicardial and endocardial cells. NF-κB signaling was found to be dysregulated in Tgfbr3(-/-) epicardial cells which also show impaired cell invasion in response to ligand. TGFβR3-dependent cell invasion is also dependent upon Activin Receptor-Like Kinase (ALK) 2, ALK3, and ALK5 activity. A TGFβR3 mutant that contains a threonine to alanine substitution at residue 841 (TGFβR3-T841A) induces ligand-independent cell invasion in both epicardial and endocardial cells in vitro. These findings reveal a role for NF-κB signaling in the regulation of epicardial and endocardial cell invasion and identify a mutation in TGFβR3 which stimulates ligand-independent signaling.

The oncofetal gene survivin promotes cell proliferation and survival in primary human osteoblastic cells

Survivin, the smallest member of the inhibitor of apoptosis gene family, is critical for the regulation of mitosis and maintenance of cell viability during embryonic development and cancer, while not being detectable in most adult differentiated tissues. We know little about whether survivin plays any physiological or pathophysiological role in the adult musculoskeletal system. We studied the expression of survivin in primary human osteoblastic cells and its biological functions in vitro. Survivin was detected by immunoblotting and real-time PCR. Subcellular localization was analyzed by immunofluorescence. Transfection of siRNA and plasmids coding for wild-type survivin was performed to study survivin function, i.e., proliferation and apoptosis assays. Survivin mRNA and protein are expressed in primary human osteoblastic cells. During interphase survivin localizes predominantly to the cytoplasmic compartment, which is relevant for the organization of the spindle apparatus during mitosis. Survivin knockdown resulted in an arrest of the cell cycle at the G(2)/M phase and increased rates of apoptosis. Elevated levels of survivin in primary human osteoblasts enhanced proliferation and cell viability. Taken together, we demonstrate for the first time that survivin is expressed in primary human osteoblastic cells on the mRNA and protein levels. Our results indicate that survivin is a critical factor for cell division and cell viability in primary human osteoblastic cells. Learning more about survivin's role in human osteoblasts could be an important step toward understanding the complex processes involved in bone homeostasis and remodeling.

HTLV-1 Tax: Linking transformation, DNA damage and apoptotic T-cell death

The human T-cell leukemia virus type I (HTLV-1) is the causative agent of adult T-cell leukemia (ATL), an aggressive CD4-positive T-cell neoplasia. The HTLV-1 proto-oncogene Tax, a potent transcriptional activator of cellular and viral genes, is thought to play a pivotal role in the transforming properties of the virus by deregulating intracellular signaling pathways. During the course of HTLV-1 infection, the dysregulation of cell-cycle checkpoints and the suppression of DNA damage repair is tightly linked to the activity of the viral oncoprotein Tax. Tax activity is associated with production of reactive oxygen intermediates (ROS), chromosomal instability and DNA damage, apoptotic cell death and cellular transformation. Changes in the intracellular redox status induced by Tax promote DNA damage. Tax-mediated DNA damage is believed to be essential in initiating the transformation process by subjecting infected T cells to genetic changes that eventually promote the neoplastic state. Apoptosis and immune surveillance would then exert the necessary selection pressure for eliminating the majority of virally infected cells, while escape variants acquiring a mutator phenotype would constitute a subpopulation of genetically altered cells prone to neoplasia. While the potency of Tax-activity seems to be a determining factor for the observed effects, the cooperation of Tax with other viral proteins determines the fate and progression of HTLV-1-infected cells through DNA damage, apoptosis, survival and transformation.

Ubiquitin ligase Smurf1 mediates tumor necrosis factor-induced systemic bone loss by promoting proteasomal degradation of bone morphogenetic signaling proteins

Chronic inflammatory disorders, such as rheumatoid arthritis, are often accompanied by systemic bone loss, which is thought to occur through inflammatory cytokine-mediated stimulation of osteoclast resorption and inhibition of osteoblast function. However, the mechanisms involved in osteoblast inhibition remain poorly understood. Here we test the hypothesis that increased Smad ubiquitin regulatory factor 1 (Smurf1)-mediated degradation of the bone morphogenetic protein pathway signaling proteins mediates reduced bone formation in inflammatory disorders. Osteoblasts derived from bone marrow or long bone samples of adult tumor necrosis factor (TNF) transgenic (TNF-Tg) mice were used in this study. TNF decreased the steady-state levels of Smad1 and Runx2 protein similarly to those in long bones of TNF-Tg mice. In the presence of the proteasome inhibitor MG132, TNF increased accumulation of ubiquitinated Smad1 protein. TNF administration over calvarial bones caused decreases in Smad1 and Runx2 protein levels and mRNA expression of osteoblast marker genes in wild-type, but not in Smurf1(-/-) mice. Vertebral bone volume and strength of TNF-Tg/Smurf1(-/-) mice were examined by a combination of micro-CT, bone histomorphometry, and biomechanical testing and compared with those from TNF-Tg littermates. TNF-Tg mice had significantly decreased bone volume and biomechanical properties, which were partially rescued in TNF-Tg/Smurf1(-/-) mice. We conclude that in chronic inflammatory disorders where TNF is increased, TNF induces the expression of ubiquitin ligase Smurf1 and promotes ubiquitination and proteasomal degradation of Smad1 and Runx2, leading to systemic bone loss. Inhibition of ubiquitin-mediated Smad1 and Runx2 degradation in osteoblasts could help to treat inflammation-induced osteoporosis.

Heme oxygenase-1 induction by (S)-enantiomer of YS-51 (YS-51S), a synthetic isoquinoline alkaloid, inhibits nitric oxide production and nuclear factor-kappaB translocation in ROS 17/2.8 cells activated with inflammatory stimulants

Activation of the inducible nitric oxide synthase (iNOS) pathway contributes to inflammation-induced osteoporosis by suppressing bone formation and causing osteoblast apoptosis. We investigated the mechanism of action by which YS-51S, a synthetic isoquinoline alkaloid, inhibits iNOS expression and nitric oxide (NO) production in ROS 17/28 osteoblast cells activated with the mixture of TNF-alpha, IFN-gamma and LPS (MIX). YS-51S, concentration- and time-dependently, increased heme oxygenase (HO-1) expression. Treatment with YS-51S 1 h prior to MIX significantly reduced MIX-induced NO production and iNOS expression with the IC50 to NO production of 47+/-3.3 microM. Electrophoretic mobility shift assay (EMSA) and western blot analysis showed that YS-51S inhibited MIX-mediated activation and translocation of NF-kappaB to nucleus by suppressing the degradation of its inhibitory protein IkappaBalpha in cytoplasm. YS-51S also reduced NF-kappaB-luciferase activity. In addition, an HO-1 inhibitor ZnPPIX, antagonized the inhibitory effect of YS-51S on iNOS expression and DNA strand break induced by MIX, indicating prevention of NO production by YS-51S is associated with HO-1 activity. Moreover, YS-51S inhibited the oxidation of cytochrome c(2+) by peroxynitrite (PN). Our results indicated that YS-51S may be beneficial in NO-mediated inflammatory conditions such as rheumatoid arthritis by alleviating iNOS expression and NO-mediated cell death of osteoblast with 1) inducing HO-1 expression, 2) interfering the activation of NF-kappaB and 3) quenching of PN.

Bone markers in multiple myeloma

Bone disease, a hallmark of multiple myeloma occurs in the majority of the patients, is associated with bone pain, fractures, hypercalcemia and has major impacts on quality of life. Myeloma is characterized by a unique form of bone disease with osteolytic bone destruction that is not followed by reactive bone formation, resulting in extensive lytic lesions. This review will focus on the pathophysiology of osteoclast activation and osteoblast inhibition in multiple myeloma and on biochemical markers of bone turnover. Since osteolytic lesions do not rapidly heal in myeloma, X-rays cannot reflect the activity of bone disease during antimyeloma treatment. Activity in bone turnover does not parallel changes in monoclonal protein levels. Thus, there is a need for biochemical markers reflecting disease activity in bone. The utility, prognostic implications and limitations of classical and novel markers of bone remodeling (e.g. ICTP, NTx, TRACP-5b, osteoprotegerin, sRANKL) will be discussed in this overview.

Role of macrophages in LPS-induced osteoblast and PDL cell apoptosis

In periradicular lesions and periodontal disease, bacterial invasion leads to chronic inflammation resulting in disruption of the structural integrity of the periodontal ligament and progressive alveolar bone destruction. The pathogenesis of these conditions has been attributed not only to bacterial-induced tissue destruction but also to a defect in periodontal tissue repair. Accumulated data have also shown that lipopolysaccharide (LPS) can directly induce cell death or apoptosis in many cell types, including macrophages, osteoblasts, vascular endothelial cells, hepatocytes and myocytes. The present study hypothesized that bacterial LPS-induced apoptosis in osteoblasts and periodontal ligament fibroblasts (PDL cells) is an important contributing factor to the defect in periodontal tissue repair in periodontal and periapical disease. Macrophages have been shown to respond to bacterial LPS by increasing the production of proinflammatory cytokines. In addition, large numbers of macrophages are present in inflamed periodontal tissue. We speculated that macrophages were a potential candidate cell for mediating apoptosis in osteoblasts and PDL cells in response to bacteria-derived LPS. The macrophage-like cell line, RAW 264.7, was stimulated with LPS, and the conditioned medium was used to treat osteoblasts and PDL cells. Bacterial LPS had no direct apoptotic effect on mouse osteoblasts or PDL cells, whereas the conditioned medium from LPS-activated macrophages was able to induce apoptosis in these cells. To evaluate the contribution of tumor necrosis factor-alpha (TNF-alpha) released from macrophages on osteoblast and PDL cell apoptosis, cells were incubated with conditioned medium from LPS-treated macrophages in the presence and absence of anti-TNF-alpha neutralizing antibodies. TNF-alpha neutralizing antibody pretreatment inhibited the effect of conditioned medium from LPS-treated macrophages on osteoblast and PDL cell apoptosis in a dose-dependent manner. These results suggest that LPS could indirectly induce apoptosis in osteoblasts and PDL cells through the induction of TNF-alpha release from macrophages. These studies provide insight into a potential mechanism by which bacterial-derived LPS could contribute to defective periodontal and bone tissue repair in periodontal and periapical disease.

Quercetin, a bioflavonoid, accelerates TNF-α-induced growth inhibition and apoptosis in MC3T3-E1 osteoblastic cells

The bioflavonoid quercetin is believed to play an important role in preventing bone loss by affecting osteoclastogenesis and regulating many systemic and local factors including hormones and cytokines. This study examined how quercetin acts on tumor necrosis factor-alpha (TNF-alpha)-mediated growth inhibition and apoptosis in MC3T3-E1 osteoblastic cells. Tritium uptake assay showed that a quercetin treatment accelerated TNF-alpha-induced inhibition of DNA synthesis in the cells in a dose-dependent manner. Both the 3-(4,5-dimethylthiazol-2yl-)-2,5-diphenyl tetrazolium bromide and trypan blue staining assays also showed the quercetin-mediated facilitation of TNF-alpha-induced cytotoxicity in the cells. Apoptosis assays revealed an accelerating effect of quercetin on TNF-alpha-induced apoptosis in MC3T3-E1 cells. In addition, Fas activation and poly (ADP ribose) polymerase cleavage are thought to be closely associated with the TNF-alpha-induced apoptosis and its acceleration by the quercetin treatment in the cells. Collectively, this study showed that quercetin accelerates the TNF-alpha-induced growth inhibition and apoptosis in MC3T3-E1 osteoblastic cells.

Tumor necrosis factor promotes Runx2 degradation through up-regulation of Smurf1 and Smurf2 in osteoblasts

Tumor necrosis factor (TNF) plays an important role in the pathogenesis of inflammatory bone loss through stimulation of osteoclastic bone resorption and inhibition of osteoblastic bone formation. Compared with the well established role of TNF in osteoclastogenesis, mechanisms by which TNF inhibits osteoblast function have not been fully determined. Runx2 is an osteoblast-specific transcription factor whose steady-state protein levels are regulated by proteasomal degradation, mediated by the E3 ubiquitin ligases, Smurf1 and Smurf2. We hypothesized that TNF inhibits osteoblast function through Smurf-mediated Runx2 degradation. We treated C2C12 and 2T3 osteoblast precursor cell lines and primary osteoblasts with TNF and found that TNF, but not interleukin-1, significantly increased Smurf1 and Smurf2 expression. TNF increased the degradation of endogenous or transfected Runx2 protein, which was blocked by treating cells with a proteasomal inhibitor or by infecting cells with small interfering (si)RNA against Smurf1 or Smurf2. TNF inhibited the expression of bone morphogenetic protein and transforming growth factor-beta signaling reporter constructs, and the inhibition of each was blocked by Smurf1 siRNA and Smurf2 siRNA, respectively. Overexpression of Smurf1 and/or Smurf2 siRNAs prevented the inhibitory effect of TNF on Runx2 reporter. Consistent with these in vitro findings, bones from TNF transgenic mice or TNF-injected wild type mice had increased Smurf1 and decreased Runx2 protein levels. We propose that one of the mechanisms by which TNF inhibits bone formation in inflammatory bone disorders is by promoting Runx2 proteasomal degradation through up-regulation of Smurf1 and Smurf2 expression.

Regulation of apoptosis in osteoclasts and osteoblastic cells

In postnatal life, the skeleton undergoes continuous remodeling in which osteoclasts resorb aged or damaged bone, leaving space for osteoblasts to make new bone. The balance of proliferation, differentiation, and apoptosis of bone cells determines the size of osteoclast or osteoblast populations at any given time. Bone cells constantly receive signals from adjacent cells, hormones, and bone matrix that regulate their proliferation, activity, and survival. Thus, the amount of bone and its microarchitecture before and after the menopause or following therapeutic intervention with drugs, such as sex hormones, glucocorticoids, parathyroid hormone, and bisphosphonates, is determined in part by effects of these on survival of osteoclasts, osteoblasts, and osteocytes. Understanding the mechanisms and regulation of bone cell apoptosis will enhance our knowledge of bone cell function and help us to develop better therapeutics for the management of osteoporosis and other bone diseases.

Agastache rugosa leaf extract inhibits the iNOS expression in ROS 17/2.8 cells activated with TNF-α and IL-1β

It has been suggested that nitric oxide (NO) derived from inducible nitric oxide synthase (iNOS) may act as a mediator of cytokine-induced effects on bone turn-over. NO is also recognized as an important factor in bone remodeling, i.e., participating in osteoblast apoptosis in an arthritic joint. The components of Agastache rugosa are known to have many pharmacological activities. In the present study, we investigated the effects of Agastache rugosa leaf extract (ELAR) on NO production and the iNOS expression in ROS 17/2.8 cells activated by a mixture of inflammatory cytokines including TNF-alpha and IL-1beta. A preincubation with ELAR significantly and concentration-dependently reduced the expression of iNOS protein in ROS 17/2.8 cells activated with the cytokine mixture. Consequently, the NO production was also significantly reduced by ELAR with an IC50 of 0.75 mg/mL. The inhibitory mechanism of iNOS induction by ELAR prevented the activation and translocation of NF-kappaB (p65) to the nucleus from the cytosol fraction. Furthermore, ELAR concentration-dependently reduced the cellular toxicity induced by sodium nitroprusside, an NO-donor. These results suggest that ELAR may be beneficial in NO-mediated inflammatory conditions such as osteoporosis.

Impaired osteoblastogenesis in myeloma bone disease: role of upregulated apoptosis by cytokines and malignant plasma cells

Bone remodelling is severely affected in myeloma bone disease as a consequence of skeletal metastatization of malignant plasma cells. We investigated whether defective bone replacement is dependent on increased osteoblast apoptosis and/or on deregulated events within the bone microenvironment. Circulating tumour necrosis factor (TNF)-alpha, interferon-gamma, interleukin (IL)-1beta, and IL-6 levels were higher in myeloma patients with overt bone disease, whose osteoblasts constitutively overexpressed Fas, DR4/DR5 complex as receptors to TNF-related apoptosis inducing ligand, intercellular adhesion molecule-1 (ICAM-1), and monocyte chemotactic protein-1 (MCP-1). They were functionally exhausted and promptly underwent apoptosis in vitro, in contrast to the minor tendency to death detected in control osteoblasts from patients without bone involvement and normal donors. Osteoblasts dramatically enhanced their apoptosis in co-cultures with MCC-2 myeloma cells and upregulated both ICAM-1 and MCP-1 in a manner similar to control osteoblasts. Pretreating MCC-2 cells with soluble ICAM-1 led to a striking inhibition of their adhesion to osteoblasts, suggesting that the ICAM-1/lymphocyte function-associated antigen-1 system plays a role in the reciprocal membrane contact to trigger apoptogenic signals. Our data suggest that, in the myeloma bone microenvironment, both high cytokine levels and physical interaction of malignant plasma cells with osteoblasts drive the accelerated apoptosis in these cells leading to defective new bone formation.

Modulation of survival in osteoblasts from postmenopausal women

Osteoblast survival is one of the determinants of postmenopausal osteoporosis development. Recent data from animal experiments suggest that cytokines, in particular Fas ligand (FasL), contribute to postmenopausal osteoporosis. We now address the effect of Fas activation in postmenopausal osteoblast survival and the potential modulatory effect of estrogen and raloxifene analog (LY117018). The expression of Fas mRNA, Fas protein, and the sensitivity to Fas-induced apoptosis were studied in primary cultures of human osteoblasts from postmenopausal women and in osteoblastic MG-63 cells. Human postmenopausal osteoblasts constitutively expressed Fas receptors in the cell surface. TNFalpha increased the expression of Fas mRNA and cell surface Fas expression. Neither estradiol nor raloxifene analog prevented this increase in Fas expression. In addition, activation of Fas receptor resulted in apoptosis of postmenopausal osteoblasts. While TNFalpha did not induce human osteoblast apoptosis, it did increase the lethal effect of Fas activation. Therapeutic concentrations of estradiol or raloxifene analog did not modulate lethal cytokine-induced apoptosis. Both postmenopausal osteoblasts and MG-63 cells express FasL. FasL expression was not modulated by TNFalpha. In conclusion, estrogen and raloxifene analog do not appear to affect the sensitivity of postmenopausal osteoblasts to Fas-mediated apoptosis.

Two discrete events, human T-cell leukemia virus type I Tax oncoprotein expression and a separate stress stimulus, are required for induction of apoptosis in T-cells

Background

It is poorly understood why many transforming proteins reportedly enhance both cell growth (transformation) and cell death (apoptosis). At first glance, the ability to transform and the ability to engender apoptosis seem to be contradictory. Interestingly, both abilities have been widely reported in the literature for the HTLV-I Tax protein.

Results

To reconcile these apparently divergent findings, we sought to understand how Tax might cause apoptosis in a Jurkat T-cell line, JPX-9. Tax expression can be induced equally by either cadmium (Cd) or zinc (Zn) in JPX-9 cells. Surprisingly, when induced by Zn, but not when induced by Cd, Tax-expression produced significant apoptosis. Under our experimental conditions, Zn but not Cd, induced SAPK (stress activated protein kinase)/JNK (Jun kinase) activation in cells. We further showed that transient over-expression of Tax-alone or Jun-alone did not induce cell death. On the other hand, co-expression of Tax plus Jun did effectively result in apoptosis.

Conclusion

We propose that Tax-expression alone in a T-cell background insufficiently accounts for apoptosis. On the other hand, Tax plus activation of a stress kinase can induce cell death. Thus, HTLV-I infection/transformation of cells requires two discrete events (i.e. oncoprotein expression and stress) to produce apoptosis.

The role of ascorbic acid on collagen structure and levels of serum interleukin-6 and tumour necrosis factor-alpha in experimental lathyrism

Lathyrism is characterized by defective collagen synthesis due to inhibition of lysyl oxidase, an enzyme essential for interfibrillar cross-linking. The lathyritic agent beta-aminoproprionitrile (beta-APN) is considered an appropriate agent for studying connective tissue metabolism. We investigated the effects of ascorbic acid on collagen structure and serum cytokine levels in experimentally induced lathyrism. Forty Wistar rats weighing 200-300 g were used in the study: three test groups of 10 rats each (groups 2, 3 and 4) and 10 rats used as a control group (group 1). Experimental lathyrism was induced with daily subcutaneous injections of beta-APN in the test groups for 40 days. On the 40th day, skin biopsies were taken from the control group (group 1) and group 2, to evaluate the effect of beta-APN on dermal collagen. After the 40th day, 10 rats received ascorbic acid 100 mg/kg intraperitoneally daily for 15 days (group 3) and 10 rats (group 4) received no medication and served as a control for group 3. On the 55th day, skin biopsies were taken from groups 3 and 4. Serum concentrations of interleukin-6 and tumour necrosis factor-alpha were assessed in each group by enzyme-linked immunosorbent assay. Ultrastructural examination of the skin biopsies in group 1 revealed normal-appearing epidermal and dermal structures. Group 2 showed disorganization of the epidermis and collagen structure, and vacuolization of the endoplasmic reticulum in fibroblasts. In group 3, ultrastructural examination revealed significant improvement in the structure of dermal collagen after administration of ascorbic acid, whereas the changes in group 4 were unremarkable. Ascorbic acid administration significantly decreased the concentrations of serum cytokines in group 3 compared with group 2 (P < 0.001). Ascorbic acid administration significantly improved dermal collagen structure and serum cytokine levels in experimental lathyrism.

Antibiotic cyclic AMP signaling by "primed" leukocytes confers anti-inflammatory cytoprotection

The mechanism underlying anti-inflammatory effects of macrolide antibiotics remains uncertain. In this study, we first show the evidences concerning the possible link between leukocytic cyclic adenosine monophosphate (cAMP) signaling and the mechanism of anti-inflammatory, cytoprotective actions of macrolides. The clinical range of macrolides (i.e., erythromycin, roxithromycin, and clarithromycin) preferentially inhibited nuclear factor-kappaB activation mediated by reactive oxygen intermediates, inducing cAMP-dependent signaling [i.e., cAMP and cAMP-responsive element-binding protein (CREB)] by "primed" but not "resting" leukocytes. In this context, cAMP/CREB inhibition with adenosine 3':5'-cyclic monophosphothioate, rp-isomer (rp-cAMPs) and CREB decoy oligonucleotides reduced the anti-inflammatory actions of macrolides. These results thus indicate that macrolide-induced cAMP/CREB signaling, selectively by primed leukocytes, plays a major role in the mechanism of anti-inflammatory actions of macrolides.

Human T-cell leukemia virus type 1 tax oncoprotein suppression of multilineage hematopoiesis of CD34+ cells in vitro

Human T-cell leukemia virus type 1 (HTLV-1) and HTLV-2 are highly related viruses that differ in disease manifestation. HTLV-1 is the etiologic agent of adult T-cell leukemia and lymphoma, an aggressive clonal malignancy of human CD4-bearing T lymphocytes. Infection with HTLV-2 has not been conclusively linked to lymphoproliferative disorders. We previously showed that human hematopoietic progenitor (CD34(+)) cells can be infected by HTLV-1 and that proviral sequences were maintained after differentiation of infected CD34(+) cells in vitro and in vivo. To investigate the role of the Tax oncoprotein of HTLV on hematopoiesis, bicistronic lentiviral vectors were constructed encoding the HTLV-1 or HTLV-2 tax genes (Tax1 and Tax2, respectively) and the green fluorescent protein marker gene. Human hematopoietic progenitor (CD34(+)) cells were infected with lentivirus vectors, and transduced cells were cultured in a semisolid medium permissive for the development of erythroid, myeloid, and primitive progenitor colonies. Tax1-transduced CD34(+) cells displayed a two- to fivefold reduction in the total number of hematopoietic clonogenic colonies that arose in vitro, in contrast to Tax2-transduced cells, which showed no perturbation of hematopoiesis. The ratio of colony types that developed from Tax1-transduced CD34(+) cells remained unaffected, suggesting that Tax1 inhibited the maturation of relatively early, uncommitted hematopoietic stem cells. Since previous reports have linked Tax1 expression with initiation of apoptosis, lentiviral vector-mediated transduction of Tax1 or Tax2 was investigated in CEM and Jurkat T-cell lines. Ectopic expression of either Tax1 or Tax2 failed to induce apoptosis in T-cell lines. These data demonstrate that Tax1 expression perturbs development and maturation of pluripotent hematopoietic progenitor cells, an activity that is not displayed by Tax2, and that the suppression of hematopoiesis is not attributable to induction of apoptosis. Since hematopoietic progenitor cells may serve as a latently infected reservoir for HTLV infection in vivo, the different abilities of HTLV-1 and -2 Tax to suppress hematopoiesis may play a role in the respective clinical outcomes after infection with HTLV-1 or -2.

BRCA1 augments transcription by the NF-kappaB transcription factor by binding to the Rel domain of the p65/RelA subunit

BRCA1 is a tumor suppressor gene mutated in cases of hereditary breast and ovarian cancer. BRCA1 protein is involved in apoptosis and growth/tumor suppression. In this study, we present evidence that p65/RelA, one of the two subunits of the transcription factor NF-kappaB, binds to the BRCA1 protein. Treatment of 293T cells with the cytokine tumor necrosis factor-alpha induces an interaction between endogenous p65/RelA and BRCA1. GST-protein affinity assay experiments reveal that the Rel homology domain of the p65/RelA subunit of NF-kappaB interacts with multiple sites within the N-terminal region of BRCA1. Transient transfection of BRCA1 significantly enhances the ability of the tumor necrosis factor-alpha or interleukin-1beta to activate transcription from the promoters of NF-kappaB target genes. Mutation of the NF-kappaB-binding sites in the NF-kappaB reporter blocks the effect of BRCA1 on transcription. Also the ability of BRCA1 to activate NF-kappaB target genes is inhibited by a super-stable inhibitor of NF-kappaB and by the chemical inhibitor SN-50. These data indicate that BRCA1 acts as a co-activator with NF-kappaB. In addition, we show that cells infected with an adenovirus expressing BRCA1 up-regulate the endogenous expression of NF-kappaB target genes Fas and interferon-beta. Together, this information suggests that BRCA1 may play a role in cell life-death decisions following cell stress by modulation of the activity of NF-kappaB.

Upregulation of osteoblast apoptosis by malignant plasma cells: a role in myeloma bone disease

Typical features of multiple myeloma (MM) are osteolytic lesions and severely affected bone regeneration. This study of 53 MM patients demonstrates an enhancement of osteoblast cytotoxicity by malignant myeloma cells via the upregulation of apoptogenic receptors, including Fas ligand (Fas-L) and tumour-necrosis-factor-related apoptosis inducing ligand (TRAIL). Both were significantly increased in the marrow myeloma cells of patients with extensive osteolytic lesions in a fashion similar to the highly malignant human myeloma cell line MCC-2. Osteoblasts from these subjects over-expressed Fas and death receptor (DR) 4/5 and underwent dramatic apoptosis when co-cultured with either MCC-2 or autologous myeloma cells. In osteoblast and myeloma cell co-cultures, monocyte chemoattractant protein 1 (MCP-1) mRNA was upregulated in osteoblasts from patients with severe bone disease in parallel with increased CC-chemokine receptor R2 (CCR2) expression, the ligand of MCP-1, in the myeloma cells. This chemokine was shown to activate malignant cell migration in vitro. An upregulation of ICAM-1 expression occurred in osteoblasts from patients with active skeleton disease. This upregulation appeared to be an effect of malignant plasma cell contact, as MCC-2 co-culture greatly enhanced ICAM-1 production by resting osteoblasts from patients without skeleton involvement. Our results suggest that osteoblasts in active myeloma are functionally exhausted and promptly undergo apoptosis in the presence of myeloma cells from patients with severe bone disease. It is suggested that this cytotoxic effect plays a pivotal role in the pathogenesis of defective bone repair.

Soybean isoflavones inhibit tumor necrosis factor-alpha-induced apoptosis and the production of interleukin-6 and prostaglandin E2 in osteoblastic cells

The effects of individual soybean isoflavones, genistein (4',5,7-trihydroxyisoflavone) and daidzein (4',7-dihydroxyisoflavone), on tumor necrosis factor-alpha (TNF-alpha)-induced apoptosis and the production of local factors in osteoblastic cells has been investigated. Soybean isoflavones increased DNA synthesis and the number of viable cells. When cells were treated with TNF-alpha, the number of viable cells dose-dependently decreased. The decrease in cell number caused by TNF-alpha treatment was due to apoptosis, which was confirmed by TUNEL and cell death ELISA analyses. Soybean isoflavones inhibited apoptosis of osteoblastic cells subjected to TNF-alpha treatment. MC3T3-E1 osteoblastic cells secrete interleukin-6 (IL-6), interleukin-1beta (IL-1beta), nitric oxide (NO) and prostaglandin E(2) (PGE(2)) constitutively, but at low levels. Soybean isoflavones had no effect on the constitutive production of these local factors. When cells were treated with TNF-alpha (10(-10)M), the production of IL-6 and PGE(2), but not that of IL-1beta and NO, significantly increased. Treatment with soybean isoflavones (10(-5)M), in the presence of TNF-alpha (10(-10)M), for 48 h inhibited production of IL-6 and PGE(2), suggesting the antiresorptive action of soy phytoestrogen may be mediated by decreases in these local factors. The findings of this study thus suggest that soybean isoflavones may promote the function of osteoblastic cells and play an important role in bone remodeling.

TGF-beta1 inhibits multiple caspases induced by TNF-alpha in murine osteoblastic MC3T3-E1 cells

Tumor necrosis factor alpha (TNF-alpha) is a proinflammatory cytokine that induces apoptosis in a number of cell systems, including osteoblasts. Transforming growth factor beta1 (TGF-beta1) is an abundant growth factor that is known to stimulate bone formation. This study was designed to examine the role of TGF-beta1 on TNF-alpha-induced apoptosis in murine osteoblastic MC3T3-E1 cells. Total RNA was extracted from MC3T3-E1 cells treated with 20 ng/ml of TNF-alpha, 10 ng/ml of TGF-beta1, or combination, for 6 h. TNF-alpha exerted a variety of effects on the apoptotic gene expression in osteoblasts. Ribonuclease protection assays (RPA) revealed that TNF-alpha upregulated the mRNA levels of caspase-1, -7, -11, -12, and FAS. Western blot analysis showed enhanced processing of caspase-1, -7, -11, and -12, with the appearance of their activated enzymes 24 h after TNF-alpha treatment. In addition, caspase-3-like activity was significantly activated following TNF-alpha treatment. Levels of cleaved poly(ADP-ribose) polymerase and FAS protein were also elevated by TNF-alpha. Finally, Hoechst staining, terminal deoxynucleotidyl-transferase nick-end labeling (TUNEL) assay, and oligonucleosome ELISA all indicated that TNF-alpha induced apoptosis. In contrast, the addition of TGF-beta1 attenuated all of the aforementioned effects of TNF-alpha. Our results demonstrate that TGF-beta1 can decrease TNF-alpha-induced apoptosis in murine osteoblasts at least in part by attenuating TNF-alpha-induced caspase gene expression.

Inhibition of migration of human glioblastoma cells by cerivastatin in association with focal adhesion kinase (FAK)

To investigate the biological effect of cerivastatin on glioblastoma cells, we exposed them to various concentrations of cerivastatin. Cerivastatin exhibited dual effects on glioblastoma cells in a dose-dependent manner. Immunofluorescence microscopy showed disruption of actin stress fibers and focal adhesion plaques even at nanomolar concentrations. Matrigel assay demonstrated marked inhibition of glioblastoma cell invasion. Immunoblot analysis using a phosphospecific antibody against focal adhesion kinase (FAK) showed that inhibition of migration was associated with the down-regulation of tyrosine phosphorylation of FAK. Our data suggest that cerivastatin may be beneficial for combination therapy with conventional anti-cancer drugs by inhibiting the invasion of glioblastoma.

Redox events in HTLV-1 Tax-induced apoptotic T-cell death

A number of studies implicate reactive oxygen intermediates in the induction of DNA damage and apoptosis. Recent studies suggest that the human T-cell leukemia virus type 1 (HTLV-1) Tax protein induces oxidative stress and apoptotic T-cell death. Activation of the T-cell receptor/CD3 pathway enhances the Tax-mediated oxidative and apoptotic effects. Tax-mediated apoptosis and oxidative stress as well as activation of nuclear factor-kappaB can be potently suppressed by antioxidants. This review focuses on Tax-dependent changes in the intracellular redox status and their role in Tax-mediated DNA damage and apoptosis. The relevance of these observations to HTLV-1 virus-mediated T-cell transformation and leukemogenesis are discussed.

p53-independent induction of apoptosis by the HTLV-I tax protein following UV irradiation

Human T cell leukemia virus type 1 (HTLV-1) encodes a transforming protein, Tax. Tax is a promiscuous viral transactivator involved in both cell growth and death control. We have previously shown that Tax sensitizes cells to apoptosis induced by DNA-damaging agents and this report further characterizes the Tax-mediated apoptosis pathway. We found that Tax-mediated apoptosis in response to UV irradiation was inhibited by Bcl-2 and Bcl-X(L) overexpression and by treatment with the caspase inhibitor z-VAd-FMK. Since Tax has been shown to functionally inactivate the apoptosis regulator p53, the effect of Tax on apoptosis in the absence of p53 was examined. In these studies, Tax sensitized p53-negative cells to apoptose, suggesting that Tax can mediate a p53-independent form of apoptosis. In addition, cells expressing both Tax and p53 displayed higher levels of apoptosis than cells expressing either protein alone, suggesting that the apoptosis-inducing activities of Tax and p53 are not completely overlapping. These observations demonstrate that Tax can utilize a p53-independent mechanism to induce apoptotic cell death following UV irradiation.

Estrogen modulates estrogen receptor alpha and beta expression, osteogenic activity, and apoptosis in mesenchymal stem cells (MSCs) of osteoporotic mice

In the mouse, ovariectomy (OVX) leads to significant reductions in cancellous bone volume while estrogen (17beta-estradiol, E2) replacement not only prevents bone loss but can increase bone formation. As the E2-dependent increase in bone formation would require the proliferation and differentiation of osteoblast precursors, we hypothesized that E2 regulates mesenchymal stem cells (MSCs) activity in mouse bone marrow. We therefore investigated proliferation, differentiation, apoptosis, and estrogen receptor (ER) alpha and beta expression of primary culture MSCs isolated from OVX and sham-operated mice. MSCs, treated in vitro with 10(-7) M E2, displayed a significant increase in ERalpha mRNA and protein expression as well as alkaline phosphatase (ALP) activity and proliferation rate. In contrast, E2 treatment resulted in a decrease in ERbeta mRNA and protein expression as well as apoptosis in both OVX and sham mice. E2 up-regulated the mRNA expression of osteogenic genes for ALP, collagen I, TGF-beta1, BMP-2, and cbfa1 in MSCs. In a comparison of the relative mRNA expression and protein levels for two ER isoforms, ERalpha was the predominant form expressed in MSCs obtained from both OVX and sham-operated mice. Cumulatively, these results indicate that estrogen in vitro directly augments the proliferation and differentiation, ERalpha expression, osteogenic gene expression and, inhibits apoptosis and ERbeta expression in MSCs obtained from OVX and sham-operated mice. Co-expression of ERalpha, but not ERbeta, and osteogenic differentiation markers might indicate that ERalpha function as an activator and ERbeta function as a repressor in the osteogenic differentiation in MSCs. These results suggest that mouse MSCs are anabolic targets of estrogen action, via ERalpha activation. J. Cell. Biochem. Suppl. 36: 144-155, 2001.

NF-kappaB, inducible nitric oxide synthase and apoptosis by Helicobacter pylori infection

Oxygen radicals are considered as an important regulator in the pathogenesis of Helicobacter pylori (H. pylori)-induced gastric ulceration and carcinogenesis. Inflammatory genes including inducible nitric oxide synthase (iNOS) may be regulated by oxidant-sensitive transcription factor, nuclear factor-kappaB (NF-kappaB). iNOS induction has been related to gastric apoptosis. We studied the role of NF-kappaB on iNOS expression and apoptosis in H. pylori-stimulated gastric epithelial AGS cells. AGS cells were treated with antisense oligonucleotide (AS ODN) for NF-kappaB subunit p50, an antioxidant enzyme catalase, an inhibitor of NF-kappaB activation pyrrolidine dithiocarbamate (PDTC), iNOS inhibitors N(G)-nitro-L-arginine-methyl ester (L-NAME) and 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT), a peroxynitrite donor SIN-1, and a nitric oxide donor NOC-18 in the presence or absence of H. pylori. H. pylori induced cytotocixity time- and dose-dependently, which occurred with induction in iNOS expression and nitrite production. SIN-1 and NOC-18 induced dose-dependent cytotoxicity in AGS cells. Catalase, PDTC, L-NAME, and AMT prevented H. pylori-induced cytotoxicity and apoptosis. It was related to their inhibition on iNOS expression and nitrite production. The cells treated with AS ODN had low levels of p50 and NF-kappaB and inhibited H. pylori-induced cytotoxicity, apoptosis, iNOS expression, and nitrite production. In conclusion, NF-kappaB plays a novel role in iNOS expression and apoptosis in H. pylori-infected gastric epithelial cells.

Matrix regulation of skeletal cell apoptosis. Role of calcium and phosphate ions

Previously, we noted that inorganic phosphate (P(i)), a major component of bone extracellular matrix, induced osteoblast apoptosis (Meleti, Z., Shapiro, I. M., and Adams, C. S. (2000) Bone (NY) 27, 359-366). Since Ca(2+) along with P(i) is released from bone during the resorption process, we advanced the hypothesis that Ca(2+) modulates P(i)-mediated osteoblast apoptosis. To test this hypothesis, osteoblasts were incubated with both ions, and cell death was determined. We noted that a modest increase in the medium Ca(2+) concentrations ([Ca(2+)](e)) of 0.1-1 mm caused a profound and rapid enhancement in P(i)-dependent death of cultured osteoblasts. An elevation in [Ca(2+)](e) alone had no effect on osteoblast viability, whereas Ca(2+) channel blockers failed to inhibit killing of ion pair-treated cells. These results indicated that P(i)-mediated cell death is not dependent on a sustained increase in the cytosolic Ca(2+) concentration. Terminal dUTP nick-end labeling analysis and measurement of caspase-3 activity of the ion pair-treated cells suggested that death was apoptotic. Apoptosis was confirmed using caspase-3 and endonuclease inhibitors. The mitochondrial membrane potential and cytosolic Ca(2+) status of the treated cells were evaluated. After incubation with [Ca(2+) ](e) and P(i), a decrease in mitochondrial fluorescence was noted, suggesting that the ions decreased the mitochondrial transmembrane potential. Subsequent to the fall in mitochondrial membrane potential, there was a transient elevation in the cytosolic Ca(2+) concentration. Results of the study suggest that the ion pair conspire at the level of the plasma membrane to induce intracellular changes that result in loss of mitochondrial function. The subsequent increase in the cytosolic Ca(2+) concentration may trigger downstream events that transduce osteoblast apoptosis.

PEA3 and AP-1 are required for constitutive IL-8 gene expression in hepatoma cells

Interleukin-8 (IL-8) mRNA was constitutively expressed in human hepatoma cell line, HepG2 and in human hepatocellular carcinoma (HCC), which often form hypervascular tumors. The sequence 5'-AGGAAG-3' at -137 to -132 bp of IL-8 promoter was shown to be polyomavirus enhancer A binding protein-3 (PEA3) binding site, which can cooperate with activator protein-1 (AP-1). Both PEA3 and AP-1 are essential for constitutive IL-8 expression in HepG2 cells, determined by promoter assays. Moreover, PEA3 and IL-8 proteins coexisted in HCC tissues, but not in uninvolved liver tissues. It is possible PEA3 may have important roles in tumor progression and in angiogenesis in HCC.

Etidronate inhibits human osteoblast apoptosis by inhibition of pro-apoptotic factor(s) produced by activated T cells

Humoral factors produced by activated T cells are thought to be important in the development of bone loss in patients with rheumatoid arthritis (RA). We investigated the inhibitory effect of etidronate disodium (EHDP) on apoptosis of human osteoblasts induced by supernatants from in vitro activated T cell cultures. Human osteoblastic cell line MG63 cells and human primary osteoblast-like cells were used in the present study as human osteoblasts. T cells were incubated with interleukin-2 and further activated with 1 2-o-tetradecanoyl-phorbol 13-acetate and ionomycin, either in the presence or absence of EHDP. After we carried out the cultivation, we examined the cytotoxicity of cultured T cell supernatants toward MG63 cells and human primary osteoblast-like cells. Supernatants from activated but not resting T cell cultures efficiently induced apoptosis of MG63 cells and primary osteoblast-like cells. Supernatants from activated T cell cultures, incubated with EHDP, exhibited significantly less cytotoxicity than did supernatants incubated in the absence of EHDP. In contrast, the cytotoxicity of activated T cell culture supernatants was not affected by direct treatment of human osteoblasts with EHDP. The concentration of soluble Fas ligand in activated T cell culture supernatants was actually increased by EHDP. However, EHDP did not influence soluble Fas and tumor necrosis factor-alpha concentrations in the supernatant. Furthermore, treatment of human osteoblasts with EHDP did not alter their expression of Bcl-2/Bcl-xL or their sensitivity to anti-Fas immunoglobulin M-induced apoptosis. Our results suggest that EHDP inhibits the production of soluble factor that induces apoptosis of human osteoblasts and thus exhibits a protective action toward human osteoblast apoptosis induced by activated T cell culture supernatants. Although the exact EHDP-regulated molecule that induces apoptosis of human osteoblasts is unknown at present, our study may explain part of the therapeutic action of bisphosphonates in RA complicated by bone loss.

Inorganic phosphate induces apoptosis of osteoblast-like cells in culture

The major goal of this investigation was to test the hypothesis that one of the major products of bone resorption, inorganic phosphate (Pi), activates osteoblast apoptosis. Osteoblast-like cells were isolated from explants of human bone. In monolayer culture, these cells showed an osteogenic phenotype. Thus, the cells exhibited raised alkaline phosphatase activity, expressed osteogenic messenger RNA transcripts, and formed biological mineral. When these cells were treated with 1-7 mmol/L Pi there was a dose- and time-dependent decrease in cell viability. Accordingly, after 48 h, 5 mmol/L Pi reduced the number of viable osteoblast-like cells by 25%; 7 mmol/L Pi reduced the number of cells by 60%. By 96 h, following treatment with 5 mmol/L Pi, the percentage of viable cells was 30%, whereas 7 mmol/L Pi caused an almost complete loss of osteoblast viability. Osteoblast death was blocked by treating the cells with phosphonoformic acid, an inhibitor of the plasma-membrane Na-Pi transporter. Using morphological and end-labeling procedures, we confirmed that cell death was through apoptosis. To probe the mechanism of cell death, osteoblast-like cells were probed with rhodamine 123, a dye that is responsive to the membrane potential. We noted that Pi-treated cells displayed a profound loss of mitochondrial membrane potential, suggesting that the anion activated the death program through the induction of a mitochondrial membrane permeability transition. We conclude that high levels of osteoblast apoptosis observed at sites of bone resorption may be linked to release of Pi from bone mineral.

Effect of vitamin K2 on osteoblast apoptosis: vitamin K2 inhibits apoptotic cell death of human osteoblasts induced by Fas, proteasome inhibitor, etoposide, and staurosporine

Vitamin K2 is used for the treatment of osteoporosis, but the precise mode of action is still not clear. We investigated the effects of vitamin K2 on apoptosis of human osteoblasts. Human osteoblastic cell line MG63 cells and human primary osteoblast-like cells obtained from bone fragments in corrective surgery were used as human osteoblasts. Cells were cultured with or without various concentrations of vitamin K2 and tumor necrosis factor-alpha (TNF-alpha). We then determined the proliferative response, expression of Fas and Bcl-2-related proteins, and Fas-mediated apoptosis of these cells induced by anti-Fas immunoglobulin M (IgM). In addition, the effect of vitamin K2 in osteoblast apoptosis induced by Z-Leu-Leu-Leu-aldehyde (LLL-CHO), etoposide, or staurosporine was also examined. Human osteoblasts did not show spontaneous apoptosis in culture, even in the presence of vitamin K2 or TNF-alpha. Furthermore, proliferation of the cells was not influenced by vitamin K2 or TNF-alpha. Fas was functionally expressed on human osteoblasts, and the treatment with TNF-alpha significantly enhanced both Fas expression and Fas-mediated apoptosis of osteoblasts. The addition of vitamin K2 to the culture resulted in a dose-dependent inhibition of functional Fas expression on osteoblasts, in the presence or absence of TNF-alpha. Treatment of human osteoblasts with vitamin K2 clearly suppressed Bax expression of the cells, although the expression of Bcl-2 was not influenced by vitamin K2. Fas ligand (FasL) cDNA transformants were cytotoxic against osteoblasts, and the cytotoxicity was increased when osteoblasts were treated with TNF-alpha. The addition of vitamin K2 to osteoblasts significantly decreased the cytotoxic effects of FasL cDNA transformants. Furthermore, apoptosis of human osteoblasts induced by LLL-CHO, etoposide, or staurosporine was also clearly suppressed in vitamin K2-treated osteoblasts. Our results suggest that vitamin K2 inhibits apoptotic cell death of osteoblasts and maintains the number of osteoblasts. These actions may explain the therapeutic efficacy of vitamin K2 in osteoporosis.

Calbindin-D28k is expressed in osteoblastic cells and suppresses their apoptosis by inhibiting caspase-3 activity

The rate of osteoblast apoptosis is a critical determinant of the rate of bone formation. Because the calcium-binding protein calbindin-D(28k) has anti-apoptotic properties in neuronal cells and lymphocytes, we searched for the presence of this protein in osteoblastic cells and investigated whether it can modify their response to proapoptotic signals. Calbindin-D(28K) was expressed at low levels in several osteoblastic cell lines and at high levels in primary cultures of murine osteoblastic cells. Transient transfection of rat calbindin-D(28k) cDNA blocked tumor necrosis factor alpha (TNFalpha)-induced apoptosis in osteoblastic MC3T3-E1 cells, as determined by cell viability and nuclear morphology of cells cotransfected with the green fluorescent protein targeted to the nucleus, whereas transfection of the empty vector had no effect. Calbindin-D(28k) levels in several stably transfected MC3T3-E1 lines were directly related to protection from TNFalpha-induced apoptosis. Purified rat calbindin-D(28k) markedly reduced the activity of caspase-3, a critical molecule for the degradation phase of apoptosis, in a cell-free assay. In addition, cell extracts from MC3T3-E1 cells expressing high levels of calbindin-D(28k) decreased caspase-3 activity, compared with extracts from vector-transfected cells. This effect was apparently unrelated to the calcium binding properties of calbindin, as chelation of calcium by EGTA or addition of other calcium-binding proteins such as calbindin-D(9k), S100, calmodulin, and osteocalcin, did not affect caspase-3 activity. Last, calbindin-D(28k) interacts with the active form of caspase-3 as demonstrated by a GST pull-down assay. These results demonstrate that calbindin-D(28k) is a biosynthetic product of osteoblasts with a role in the regulation of apoptosis. They also reveal that the antiapoptotic properties of calbindin-D(28k) may result not only from calcium buffering but also from the ability of the protein to interact with and to inhibit caspase-3 activity, a property that is independent of its calcium binding capability.

HTLV-1 Tax protein sensitizes cells to apoptotic cell death induced by DNA damaging agents

Transient HTLV-1 Tax expression suppresses cellular nucleotide excision repair, and this effect correlates with Tax transactivation of the proliferating cell nuclear antigen promoter. The inability to repair DNA damage typically induces apoptotic cell death. Therefore, we investigated the effect of Tax-mediated suppression of DNA repair on apoptosis in stable Tax-expressing cells. Constitutive Tax expression reduced cellular nucleotide excision repair activity compared with parental and control cells. Tax-expressing cells were also more sensitive to apoptosis induced by DNA damaging agents than control cells. Even though Tax-expressing cells displayed reduced DNA repair, they showed increased DNA replication following UV damage. These results suggest that Tax suppresses the cell's ability to repair DNA damage and stimulates DNA replication even in the presence of damage. The inability to repair DNA damage is likely to stimulate apoptotic cell death in the majority of Tax-expressing cells while the ability to promote DNA replication may also allow the survival of a small population of cells. We propose that together these effects contribute to the monoclonal nature and low efficiency of HTLV-1 transformation.

Control of apoptosis by Rel/NF-kappaB transcription factors

Apoptosis is a physiological process critical for organ development, tissue homeostasis, and elimination of defective or potentially dangerous cells in complex organisms. Apoptosis can be initiated by a wide variety of stimuli, which activate a cell suicide program that is constitutively present in most vertebrate cells. In diverse cell types, Rel/NF-kappaB transcription factors have been shown to have a role in regulating the apoptotic program, either as essential for the induction of apoptosis or, perhaps more commonly, as blockers of apoptosis. Whether Rel/NF-kappaB promotes or inhibits apoptosis appears to depend on the specific cell type and the type of inducer. An understanding of the role of Rel/NF-kappaB transcription factors in controlling apoptosis may lead to the development of therapeutics for a wide variety of human diseases, including neurodegenerative and immune diseases, and cancer.

Monocyte-Driven Activation-Induced Apoptotic Cell Death of Human T-Lymphotropic Virus Type I-Infected T Cells

We attempted apoptotic cell death induction of T cells infected with human T lymphotropic virus type I (HTLV-I) which induces HTLV-I-associated myelopathy/tropical spastic paraparesis and adult T cell leukemia. T cells acutely infected and expressing HTLV-Igag Ags were killed by cross-linking their TCR with anti-CD3 mAb. Cells in apoptotic process were found by staining with annexin V. The apoptosis was not affected by costimulation through CD28 molecules and was resistant to ligation of Fas molecules. Whereas the virus-infected T cells expressed higher levels of HLA-DR, CD25, CD80, and CD86 Ags than apoptosis-resistant PHA-blasts, the T cell apoptosis was enhanced by addition of exogenous IL-2. Furthermore, in this apoptosis, monocytes played an important role because T cells infected in the absence of monocytes were resistant to the death signals. The apoptosis-sensitive T cells responded to TCR signaling more strongly by proliferating than those apoptosis-resistant cells. Monocytes weakly affected the expression levels of viral Ags on T cells. However, HTLV-I-infected monocytes primed T cells to die by subsequent TCR signaling. T cells primed with the monocytes, subsequently infected in the absence of monocytes, were killed by TCR signaling. These observations suggest that primed and infected T cells could be killed by activation-induced cell death.

Signal transduction of thapsigargin-induced apoptosis in osteoblast

The toxicity of thapsigargin, a selective inhibitor of endoplasmic reticular Ca2+-ATPase, was investigated in osteoblasts. We induced apoptosis in murine osteoblastic MC3T3E1 cells by exposure to the thapsigargin. Thapsigargin transiently increased the phosphotransferase activity of c-Jun N-terminal kinases1 (JNK1), which might in turn activate transcriptional activity of activation protein-1 (AP-1). We then prepared extracts from thapsigargin-treated MC3T3E1 cells and monitored cleavage of acetyl-YVAD-AMC and acetyl-DEVD-AMC, fluorogenic substrates for caspase 1-like and caspase 3-like proteases, respectively. Thapsigargin significantly increased the proteolytic activity of caspase 3-like proteases, but not the activity of caspase 1-like proteases. Furthermore, thapsigargin increased the transcriptional activity of nuclear factor-kappaB (NF-kappaB). These data suggest that thapsigargin-induced apoptosis in osteoblasts may be via activation of JNK1, caspase 3-like family proteases, and transcriptional factors including AP-1 and NF-kappaB.

Tumor necrosis factor-alpha and interleukin-1beta increase the Fas-mediated apoptosis of human osteoblasts

Our recent work demonstrated functional Fas expression on human osteoblasts, and the histologic examination of the periarticular osteoporosis region in patients with rheumatoid arthritis (RA) showed apoptosis in osteoblasts. High concentrations of interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), and IL-6--which are thought to increase bone resorption--have been determined in RA synovium. We investigated the effect of these cytokines on the Fas-mediated apoptosis of human osteoblasts. The human osteoblastic cell line MG63 and human primary osteoblast-like cells from bone biopsy specimens were used as human osteoblasts. Fas expression on these cells was examined by flow cytometry, and Fas-mediated apoptosis induced by anti-Fas immunoglobulin M (IgM) was determined by a chromium 51 release assay, the presence of cells with hypodiploid DNA, staining with Hoechst 33258 dye, and the detection of DNA fragmentation on agarose gel electrophoresis. The proliferation of osteoblasts was analyzed by a tritiated thymidine incorporation assay. Spontaneous apoptosis was not found on cultured osteoblasts. The apoptosis of human osteoblasts was not induced by TNF-alpha, IL-1beta, or IL-6 alone in the absence of anti-Fas IgM. In addition, proliferation of the cells was not affected by these cytokines. Fas was constitutively expressed on unstimulated osteoblasts, and treatment of these cells with IL-1beta or TNF-alpha significantly augmented Fas expression. Human osteoblasts were committed to apoptosis with anti-Fas IgM, and the treatment of both IL-1beta and TNF-alpha markedly increased Fas-mediated apoptosis. TNF-alpha augmented both Fas expression and Fas-mediated apoptosis more efficiently than did IL-1beta. In addition, an additive effect on both Fas expression and Fas-mediated apoptosis was demonstrated when TNF-alpha and IL-1beta were added to osteoblasts. IL-6 influenced neither Fas expression nor the Fas-mediated apoptosis of osteoblasts. Furthermore, no synergistic effect of IL-6 with IL-1beta or TNF-alpha was observed. IL-1beta, TNF-alpha, or IL-6 did not change Bcl-2 expression. Our results suggest that IL-1beta and TNF-alpha regulate osteoblast cell number by up-regulating the Fas-mediated apoptosis of osteoblasts, one of the putative mechanisms inducing periarticular osteoporosis in patients with RA.

Involvement of nitric oxide and biopterin in proinflammatory cytokine-induced apoptotic cell death in mouse osteoblastic cell line MC3T3-E1

We previously demonstrated that the addition of proinflammatory cytokines (tumor necrosis factor-alpha, interleukin-1beta, and interferon-gamma) caused induction of mRNAs for inducible nitric oxide (NO) synthase and GTP cyclohydrolase I, a rate-limiting enzyme for 5,6,7,8-tetrahydrobiopterin (BH4) biosynthesis, and produced their end-products, NO and BH4, in osteoblastic cells. In the present study, we examined whether NO and BH4, biologically active substances produced in response to proinflammatory cytokines, are involved in the effect of these cytokines on cell viability and apoptotic cell death involving DNA fragmentation. Cytokines as well as S-nitroso-N-acetyl-d,l-penicillamine, an NO generator, decreased cell viability, whereas sepiapterin, which was converted intracellularly to BH4, increased it. The examination of cytotoxicity measured in terms of lactate dehydrogenase release and apoptotic cell death assessed by flow cytometric analysis showed that cytokine-induced reduction of cell viability may be based upon cell death by apoptosis, but not lytic death as in necrosis. In the presence of sepiapterin, cytokine treatment resulted in a statistically pronounced reduction in the amount of DNA fragmentation. Furthermore, this fragmentation could be blocked by 2-(4-carboxy-phenyl)-4,4,5,5-tetramethylimidazole-1-oxyl 3-oxide, an NO scavenger. These results suggest that cytokine-induced apoptotic cell death is attributed to NO and is protected by BH4, and that osteoblastic cells in response to proinflammatory cytokines operate both a stimulatory process resulting in NO production and an inhibitory one resulting in BH4 production for apoptotic cell death. Cytokine-induced apoptotic cell death may be a consequence of the predominance of the stimulatory process over the inhibitory process.

Effects of XT-44, a phosphodiesterase 4 inhibitor, in osteoblastgenesis and osteoclastgenesis in culture and its therapeutic effects in rat osteopenia models

We have reported that denbufylline, a phosphodiesterase 4 (PDE4) inhibitor, inhibits bone loss in Walker256/S tumor-bearing rats, suggesting therapeutic potentiality of a PDE4 inhibitor in osteopenia. In the present study, effects of a new PDE4 inhibitor, 1-n-butyl-3-n-propylxanthine (XT-44), in bone were evaluated in cell cultures and animal experiments. In rat bone marrow culture, XT-44 stimulated mineralized-nodule formation, whereas it inhibited osteoclast-like cell formation in mouse bone marrow culture. In Walker256/S-bearing rats (6-week-old female Wistar Imamichi rats), rapid decrease in bone mineral density (BMD) was prominent, and oral administration of XT-44 (0.3 mg/kg, every 2 days) inhibited the decrease in BMD. In the second animal experiment, female Wistar rats (6-week-old) were sciatic neurectomized, and XT-44 was orally administered to these rats every 2 days for 4 weeks. XT-44 administration (0.3 mg/kg) recovered BMD in these neurectomized animals. Furthermore, 19-week-old, female Wistar rats were ovariectomized (OVX), and 15 weeks after surgery, these rats were orally administered XT-44 every 2 days for 8 weeks. XT-44 treatment (1 mg/kg) increased the BMD of OVX rats. These results indicate that XT-44 could be a candidate as a therapeutic drug for treating osteopenia including osteoporosis.

Thrombin receptor mediated signals induce expressions of interleukin 6 and granulocyte colony stimulating factor via NF-kappa B activation in synovial fibroblasts

OBJECTIVE

To clarify the mechanism of thrombin receptor mediated signal transduction and the induction of cytokines by thrombin stimulation in rheumatoid synovial fibroblasts.

METHODS

Cytokines were measured by enzyme linked immunosorbent assay (ELISA) in the supernatants of cultured rheumatoid synovial fibroblasts stimulated by thrombin. To assess the mechanism of thrombin receptor mediated signal transduction in the rheumatoid synovial fibroblasts, electrophoretic mobility gel shift assay (EMSA), immunoglobulin kappa-chloramphenicol acetyltransferase (CAT) assay, and immunostaining for NF-kappa B subunit molecule was performed.

RESULTS

Thrombin stimulation activated the inducible transcription factor NF-kappa B, and then induced subsequent expressions of interleukin 6 (IL6) and granulocyte colony stimulating factor (G-CSF) in the cells.

CONCLUSION

Thrombin receptor mediated signal transduction could induce the expressions of IL6 and G-CSF, and increase inflammatory events in the cavum articulare via NF-kappa B activation.

Insulin-like growth factor I stimulates proliferation and Fas-mediated apoptosis of human osteoblasts

In vitro studies have shown that insulin-like growth factor I (IGF-I) is a potent growth factor for osteoblasts, although both bone formation and resorption are upregulated by IGF-I in vivo. To understand the difference in the action of IGF-I observed in vitro and in vivo experiments, we examined the effect of IGF-I on the proliferation and Fas-mediated apoptosis of human osteoblasts in vitro. Human osteoblastic cell line MG63 and human primary osteoblast-like cells obtained from biopsy specimens were used as human osteoblasts. Cells were cultured with or without various concentrations of IGF-I followed by determination of the proliferative response and Fas-mediated apoptosis. IGF-I dose dependently stimulated the proliferation of cultured human osteoblasts. Both Fas expression and the degree of anti-Fas IgM-induced apoptosis of human osteoblasts was also augmented by IGF-I. Furthermore, the cytotoxicity of Fas ligand (FasL) cDNA transformants against human osteoblasts was increased when IGF-I-stimulated osteoblasts were used as target cells, indicating that stimulation of IGF-I increased functional Fas expression on human osteoblasts as well as their proliferation. The addition of DEVD-CHO, a specific inhibitor of CPP32, to the culture resulted in a significant inhibition of Fas-mediated apoptosis of both unstimulated and IGF-I-stimulated osteoblasts, although it did not affect the proliferative response or Fas expression. Our data suggest that activation of CPP32 is necessary for Fas-mediated apoptosis of human osteoblasts, and treatment of IGF-I increased this signaling pathway. In contrast, regulation of proliferation and Fas expression of the cells were probably not affected by CPP32 activation. Our results suggest that IGF-I acts on cultured human osteoblasts by increasing their proliferation and induction of Fas-mediated apoptosis by neighbouring FasL+ cells such as osteoclasts, thus probably functioning as a local coupling factor in the bone in vivo, stimulating both bone formation and resorption.

Inhibitory effect of glucocorticoid for osteoblast apoptosis induced by activated peripheral blood mononuclear cells

Recent studies suggest a protective effect of glucocorticoid against progression of bone erosion and periarticular osteoporosis in patients with rheumatoid arthritis (RA), although this steroid hormone itself is believed to increase bone loss. To understand the antagonistic effect of glucocorticoid for osteopenic process in RA patients, we examined the effect of dexamethasone on Fas-mediated apoptosis of cultured human osteoblasts induced by either anti-Fas IgM or activated peripheral blood mononuclear cells (PBMC). Human osteoblastic cell line MG63 and primary osteoblast-like cells obtained from biopsy specimens were used in this study. PBMC isolated from healthy donors were cultured with or without recombinant interleukin-2 (rIL-2) followed by 12-O-tetradecanoyl-phorbol 13-acetate (PMA) with ionomycin in the presence or absence of dexamethasone. Fas was functionally expressed on MG63 and primary osteoblast-like cells, and treatment of these cells with dexamethasone affected neither Fas expression nor anti-Fas IgM-induced apoptosis. Activated PBMC expressing membrane-type Fas ligand (mFasL) efficiently killed both MG63 and primary osteoblasts-like cells, and the addition of human Fas chimeric protein (hFas-Fc) significantly diminished the cytotoxicity, indicating that interactions between mFasL of activated PBMC and Fas on human osteoblasts induce apoptosis of the latter. Although dexamethasone did not affect apoptosis of MG63 and primary osteoblast-like cells induced by anti-Fas IgM, treatment of activated PBMC with dexamethasone markedly inhibited both mFasL expression and cytotoxicity of these cells against human osteoblasts, suggesting that dexamethasone preferentially acts not on osteoblasts but PBMC. Cultured supernatants from activated PBMC induced apoptosis of human osteoblasts and the addition of hFas-Fc also inhibited the cytotoxicity of the supernatants. In addition, soluble form FasL (sFasL) was detected in the supernatants of activated PBMC. Furthermore, both the cytotoxicity and sFasL concentration of cultured supernatants of activated PBMC incubated with dexamethasone was significantly lower than that in the absence of dexamethasone. Our data suggest that glucocorticoid suppresses the apoptotic process of osteoblasts by inhibiting the expression of both mFasL and sFasL derived from activated PBMC, mediating a protective effect against periarticular bone loss and bone erosion in inflammatory arthritis such as RA.

Ribozyme-based gene cleavage approach to chronic arthritis associated with human T cell leukemia virus type I: induction of apoptosis in synoviocytes by ablation of HTLV-I tax protein

OBJECTIVE

To develop gene therapy for patients with human T cell leukemia virus type I (HTLV-I)-associated arthropathy (HAAP), we investigated the effects of ribozyme-mediated cleavage of HTLV-I tax/rex messenger RNA (mRNA) on synovial overgrowth.

METHODS

We introduced 2 hammerhead ribozymes targeted against HTLV-I tax/rex mRNA into synovial cells obtained from patients with HAAP and from patients with HTLV-I-negative rheumatoid arthritis (RA) and examined the ribozyme-mediated ablation of Tax expression. Using standard methods, we also determined the cells' ability to stop proliferating and to undergo apoptosis.

RESULTS

The ribozymes successfully cleaved tax/rex mRNA in HAAP patient synoviocytes. Both tax mRNA expression and Tax protein synthesis were inhibited significantly, resulting in inhibition of synovial cell growth and induction of apoptosis. In contrast, synovial cells from RA patients were not affected.

CONCLUSION

In vitro results suggest that ribozyme-mediated gene therapy can inhibit the growth of HTLV-I-infected synovial cells, which is maintained by Tax protein, in HTLV-I-related diseases including HAAP.

Fas and Fas ligand interaction is necessary for human osteoblast apoptosis

We investigated the cellular and humoral interactions between peripheral blood mononuclear cells (PBMCs) and human osteoblasts, leading to apoptosis of osteoblasts. Human osteoblastic cell line MG63 and human primary osteoblast-like cells obtained from biopsy specimens were used in this study. PBMCs were isolated from healthy donors and cultured with or without stimulation by recombinant interleukin-2 followed by 12-o-tetradecanoylphorbol 13-acetate with ionomycin. Fas was functionally expressed on MG63 and primary osteoblast-like cells. Activated PBMCs expressed Fas ligand (FasL) strongly on their surface and killed MG63 and primary osteoblast-like cells. Cultured supernatants of activated PBMCs also induced apoptotic cell death of MG63 and primary osteoblast-like cells. In contrast, both unstimulated PBMCs and cultured supernatants of unstimulated PBMCs did not induce apoptosis of these cells. Furthermore, the cytotoxic effect and induction of apoptosis against MG63 and primary osteoblast-like cells by activated PBMCs and cultured supernatants were inhibited significantly by human Fas chimeric protein. Our data showed that human osteoblasts expressed Fas fuctionally and both membrane-type and soluble form FasL from activated PBMCs induced apoptosis of these cells, providing the one possible mechanism of bone loss in inflammatory diseases such as rheumatoid arthritis.

Nitric oxide acts in conjunction with proinflammatory cytokines to promote cell death in osteoblasts

Proinflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), and interleukin-1 beta are known modulators of bone remodeling in vitro and in vivo. The same cytokines induce the production of nitric oxide (NO) in various cell types, including osteoblasts and osteoclasts, and NO has recently been implicated in the regulation of bone resorption. We investigated the relationship between NO levels and cell viability in MC3T3-E1, a well-characterized osteoblastic cell line. NO donors at high concentrations (> or = 0.5 mM) produce a significant cytotoxic effect over a 48 h period. Various combinations of the three cytokines strongly promote endogenous NO production, and high NO levels are correlated with the loss of cell viability. Although TNF-alpha produces NO-independent cytotoxicity, NO greatly enhances this cytotoxic effect. Human and mouse TNF-alpha differ in their cytotoxic effects, and human TNF-alpha induces lower levels of NO production. In cocultures of RAW 264.7 mouse macrophages stimulated with lipopolysaccharide and IFN-gamma, and untreated MC3T3-E1 osteoblasts, addition of anti-TNF-alpha antibody and inhibition of NO synthesis have additive, protective effects on osteoblast viability. NO cytotoxicity involves an apoptotic mechanism. Our results underline the importance of NO and TNF-alpha as cytotoxic mediators in the osseous microenvironment and might explain the observed deficiency of bone formation in inflammatory sites.