Bcl-2 and Bcl-XL serve an anti-inflammatory function in endothelial cells through inhibition of NF-kappaB.
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To maintain the integrity of the vascular barrier, endothelial cells (EC) are resistant to cell death. The molecular basis of this resistance may be explained by the function of antiapoptotic genes such as bcl family members. Overexpression of Bcl-2 or Bcl-XL protects EC from tumor necrosis factor (TNF)-mediated apoptosis. In addition, Bcl-2 or Bcl-XL inhibits activation of NF-kappaB and thus upregulation of proinflammatory genes. Bcl-2-mediated inhibition of NF-kappaB in EC occurs upstream of IkappaBalpha degradation without affecting p65-mediated transactivation. Overexpression of bcl genes in EC does not affect other transcription factors. Using deletion mutants of Bcl-2, the NF-kappaB inhibitory function of Bcl-2 was mapped to bcl homology domains BH2 and BH4, whereas all BH domains were required for the antiapoptotic function. These data suggest that Bcl-2 and Bcl-XL belong to a cytoprotective response that counteracts proapoptotic and proinflammatory insults and restores the physiological anti-inflammatory phenotype to the EC. By inhibiting NF-kappaB without sensitizing the cells (as with IkappaBalpha) to TNF-mediated apoptosis, Bcl-2 and Bcl-XL are prime candidates for genetic engineering of EC in pathological conditions where EC loss and unfettered activation are undesirable. (+info)
Decreased expression of the pro-apoptotic protein Par-4 in renal cell carcinoma.
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Par-4 is a widely expressed leucine zipper protein that confers sensitization to apoptosis induced by exogenous insults. Because the expression of genes that promote apoptosis may be down-regulated during tumorigenesis, we sought to examine the expression of Par-4 in human tumors. We present here evidence that Par-4 protein levels were severely decreased in human renal cell carcinoma specimens relative to normal tubular cells. Replenishment of Par-4 protein levels in renal cell carcinoma cell lines conferred sensitivity to apoptosis. Because apoptosis may serve as a defense mechanism against malignant transformation or progression, decreased expression of Par-4 may contribute to the pathophysiology of renal cell carcinoma. (+info)
Gene expression profiles in HTLV-I-immortalized T cells: deregulated expression of genes involved in apoptosis regulation.
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Human T-cell leukemia virus type I (HTLV-I) is the etiologic agent of adult T-cell leukemia, an acute and often fatal T-cell malignancy. A key step in HTLV-I-induced leukemigenesis is induction of abnormal T-cell growth and survival. Unlike antigen-stimulated T cells, which cease proliferation after a finite number of cell division, HTLV-I-infected T cells proliferate indefinitely (immortalized), thus facilitating occurrence of secondary genetic changes leading to malignant transformation. To explore the molecular basis of HTLV-I-induced abnormal T-cell survival, we compared the gene expression profiles of normal and HTLV-I-immortalized T cells using 'gene array'. These studies revealed a strikingly altered expression pattern of a large number of genes along with HTLV-I-mediated T-cell immortalization. Interestingly, many of these deregulated genes are involved in the control of programmed cell death or apoptosis. These findings indicate that disruption of the cellular apoptosis-regulatory network may play a role in the HTLV-I-mediated oncogenesis. (+info)
Activation of IkappaB kinase beta by protein kinase C isoforms.
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The atypical protein kinase C (PKC) isotypes (lambda/iotaPKC and zetaPKC) have been shown to be critically involved in important cell functions such as proliferation and survival. Previous studies have demonstrated that the atypical PKCs are stimulated by tumor necrosis factor alpha (TNF-alpha) and are required for the activation of NF-kappaB by this cytokine through a mechanism that most probably involves the phosphorylation of IkappaB. The inability of these PKC isotypes to directly phosphorylate IkappaB led to the hypothesis that zetaPKC may use a putative IkappaB kinase to functionally inactivate IkappaB. Recently several groups have molecularly characterized and cloned two IkappaB kinases (IKKalpha and IKKbeta) which phosphorylate the residues in the IkappaB molecule that serve to target it for ubiquitination and degradation. In this study we have addressed the possibility that different PKCs may control NF-kappaB through the activation of the IKKs. We report here that alphaPKC as well as the atypical PKCs bind to the IKKs in vitro and in vivo. In addition, overexpression of zetaPKC positively modulates IKKbeta activity but not that of IKKalpha, whereas the transfection of a zetaPKC dominant negative mutant severely impairs the activation of IKKbeta but not IKKalpha in TNF-alpha-stimulated cells. We also show that cell stimulation with phorbol 12-myristate 13-acetate activates IKKbeta, which is entirely dependent on the activity of alphaPKC but not that of the atypical isoforms. In contrast, the inhibition of alphaPKC does not affect the activation of IKKbeta by TNF-alpha. Interestingly, recombinant active zetaPKC and alphaPKC are able to stimulate in vitro the activity of IKKbeta but not that of IKKalpha. In addition, evidence is presented here that recombinant zetaPKC directly phosphorylates IKKbeta in vitro, involving Ser177 and Ser181. Collectively, these results demonstrate a critical role for the PKC isoforms in the NF-kappaB pathway at the level of IKKbeta activation and IkappaB degradation. (+info)
Prevention of collagen-induced arthritis by gene delivery of soluble p75 tumour necrosis factor receptor.
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Collagen type II-induced arthritis (CIA) in DBA/1 mice can be passively transferred to SCID mice with spleen B- and T-lymphocytes. In the present study, we show that infection ex vivo of splenocytes from arthritic DBA/1 mice with a retroviral vector, containing cDNA for the soluble form of human p75 receptor of tumour necrosis factor (TNF-R) before transfer, prevents the development of arthritis, bone erosion and joint inflammation in the SCID recipients. Assessment of IgG subclass levels and studies of synovial histology suggest that down-regulating the effector functions of T helper-type 1 (Th1) cells may, at least in part, explain the inhibition of arthritis in the SCID recipients. In contrast, the transfer of splenocytes infected with mouse TNF-alpha gene construct resulted in exacerbated arthritis and enhancement of IgG2a antibody levels. Intriguingly, infection of splenocytes from arthritic DBA/1 mice with a construct for mouse IL-10 had no modulating effect on the transfer of arthritis. The data suggest that manipulation of the immune system with cytokines, or cytokine inhibitors using gene transfer protocols can be an effective approach to ameliorate arthritis. (+info)
Systemic administration of rIL-12 synergistically enhances the therapeutic effect of a TNF gene-transduced cancer vaccine.
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Interleukin-12 (IL-12) is a potent antitumor cytokine, which induces and enhances the activity of natural killer (NK) cells, lymphokine activated killer (LAK) cells and cytotoxic T lymphocytes (CTL). IL-12 also stimulates IFN-gamma production from both T cells and NK cells. In this study, we transfected methylcholanthrene-induced fibrosarcoma (MCA-D) with TNF gene and investigated the therapeutic effect of TNF gene-transduced cancer vaccine and whether the vaccination effect is enhanced by systemic administration of recombinant IL-12 (rIL-12), in a murine model. TNF gene-transduced cancer vaccine or systemic administration of rIL-12 showed slight or moderate inhibition of pre-established tumor. However, simultaneous application of the vaccine and rIL-12 resulted in complete eradication. The cytotoxicity of CTL against parental tumor cells was enhanced with the combination of the vaccine and rIL-12, and IFN-gamma production from spleen cells also increased synergistically. Our findings show that synergistic enhancement of CTL activity and IFN-gamma production could play an important role in the antitumor effect of combination therapy using TNF gene-transduced cancer vaccine and rIL-12. (+info)
Differential expression and translocation of protein tyrosine phosphatase 1B-related proteins in ME-180 tumor cells expressing apoptotic sensitivity and resistance to tumor necrosis factor: potential interaction with epidermal growth factor receptor.
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Tumor necrosis factor (TNF)-induced apoptosis can be inhibited by overexpression of specific tyrosine kinases or activation of tyrosine kinase cascades, suggesting potential antagonism between apoptotic and tyrosine kinase signaling processes. In this report, the effects of TNF on EGF receptor tyrosine phosphorylation in ME-180 cell variants selected for apoptotic sensitivity (Sen) or resistance (Res) to TNF, previously shown to differentially express EGFr, were examined. Prior to the onset of apoptosis, TNF caused a significant reduction in the level of EGFr tyrosine phosphorylation in Sen cells but mediated only limited suppression of EGFr tyrosine phosphorylation in apoptotically resistant Res cells. In vitro incubation of cellular membranes with TNF derived from Sen cells stimulated a resident protein tyrosine phosphatase (PTP) activity which was able to dephosphorylate EGFr or tyrosine phosphopeptides mimicking an EGFr autophosphorylation site. In membrane preparations, PTPIB complexed with tyrosine phosphorylated EGFr and this association was disrupted by TNF through an apparent stimulation of PTP activity and turnover of phosphotyrosine. Intrinsic enzymatic activity of PTP1B was 2-3-fold higher in Sen versus Res cell lysates and a family of PTP1B-related proteins with altered C-termini was found to be highly expressed in Sen cells but absent or expressed at reduced levels in Res cells. Cytoplasmic extracts of Sen cells contained PTP1B-like proteins and TNF incubation resulted in the time dependent accumulation of PTP1B-like proteins in Sen cells but did not effect these proteins in Res cells. Together, these results suggest that specific changes in expression and subcellular distribution of phosphotyrosine modulatory proteins may play a role in conveying intrinsic apoptotic sensitivity to TNF in some tumor cell types. (+info)
Protective effect of bactericidal/permeability-increasing protein (rBPI21) in baboon sepsis is related to its antibacterial, not antiendotoxin, properties.
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OBJECTIVE AND SUMMARY BACKGROUND DATA: The recombinant fragment of bactericidal/permeability-increasing protein, rBPI21, has potent bactericidal activity against gram-negative bacteria as well as antiendotoxin (lipopolysaccharide [LPS]) action. On the basis of these activities, the authors sought to discover whether rBPI21 would be protective in baboons with live Escherichia coli-induced sepsis and whether the potential protective effects of rBPI21 (together with antibiotics) would be more closely related to its antibacterial or LPS-neutralizing effects. METHODS: In a prospective, randomized, placebo-controlled subchronic laboratory study, the efficacy of rBPI21 or placebo was studied over 72 hours in chronically instrumented male baboons infused with live E. coli under antibiotic therapy. RESULTS: Intravenous rBPI21 attenuated sepsis-related organ failure and increased survival significantly. Bacteremia was significantly reduced in the rBPI21 group at 2 hours after the start of the E. coli infusion, whereas circulating LPS was less affected. The in vivo formation of tumor necrosis factor was significantly suppressed by the rBPI21 treatment regimen. Microcirculation and organ function were improved. CONCLUSIONS: In baboon live E. coli sepsis, the salutary effect of rBPI21 results from a more prevalent antibacterial than antiendotoxin activity. (+info)