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Constitutive nuclear NF kappa B/rel DNA-binding activity of rat thymocytes is increased by stimuli that promote apoptosis, but not inhibited by pyrrolidine dithiocarbamate.

ABSTRACT: Rat thymocytes spontaneously undergo apoptotic death in cell culture, and are also sensitive to the induction of apoptosis by various stimuli. We show that unstimulated thymocytes constitutively express a p50-containing nuclear factor kappa B (NF kappa B)/rel DNA-binding activity in their nuclei. When the cells were fractionated by density-gradient centrifugation this activity was found to be most pronounced in immature CD4+8+ thymocytes, the cell population that undergoes selection by apoptosis in vivo and that is most sensitive to external inducers of apoptosis in vitro. The intensity of the NF kappa B/rel protein-DNA complex was significantly enhanced 30 min after exposing thymocytes to methylprednisolone or etoposide, two agents well known to induce apoptosis in these cells. Expression of this DNA-binding activity therefore correlates with the subsequent occurrence of apoptosis. By analogy to other systems, it has been suggested that antioxidants such as pyrrolidine dithiocarbamate (PDTC) inhibit thymocyte apoptosis by preventing the activation of an NF kappa B/rel transcription factor. However, we have found that etoposide induces a very similar enhancement of the NF kappa B/rel DNA-binding activity in the presence or absence of PDTC, despite a pronounced inhibition of apoptotic DNA fragmentation in the former situation. Dithiocarbamates therefore do not exert their anti-apoptotic activity in thymocytes by inhibiting the activation of this transcription factor.

SUBMITTER: Slater AF

PROVIDER: S-EPMC1136190 | biostudies-other | 1995 Dec

REPOSITORIES: biostudies-other

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Project description:In monocytes, the nuclear factor NF-kappa B has been invoked as an important transcription factor in the expression of cytokine genes, of cell-surface receptors and in the expression of human immunodeficiency virus. In such cells, DNA binding activity of NF-kappa B can be detected without intentional stimulation. In our studies, cells of the human monocytic line Mono Mac 6, cultured in medium containing fetal-calf serum and low levels of lipopolysaccharide (LPS), also exhibit such 'constitutive' NF-kappa B, as demonstrated by mobility-shift analysis of nuclear extracts. This nuclear NF-kappa B was still present when contaminant LPS was removed by ultrafiltration and when serum was omitted. Protein-DNA complexes of constitutive NF-kappa B are similar in mobility to the LPS-induced NF-kappa B and both are recognized by an antibody specific to the p50 subunit of NF-kappa B. By contrast, treatment of cells with pyrrolidine dithiocarbamate (PDTC) will only block LPS-induced NF-kappa B, but not the constitutive binding protein. Using LPS-free and serum-free conditions, constitutive NF-kappa B can be detected in different cell lines of the monocytic lineage (HL60, U937, THP-1, Mono Mac 1 and Mono Mac 6), but not in Molt 4 T cells or K562 stem cells. When ordered according to stage of maturation, the amount of constitutive NF-kappa B was not increased in more mature cell lines. Furthermore, when inducing differentiation in Mono Mac 6 cells, with vitamin D3, no change in constitutive or inducible NF-kappa B can be detected. Analysis of primary cells revealed substantial constitutive NF-kappa B-binding activity in blood monocytes, pleural macrophages and alveolar macrophages. The constitutive NF-kappa B appears to be functionally active, since a low level of tumour necrosis factor (TNF) transcript is detectable in monocytes, and this level can be increased by blocking transcript degradation using cycloheximide. The level of constitutive NF-kappa B in these cells is variable and is frequently found to be lower in the more mature macrophages. Constitutive NF-kappa B was not maintained by autocrine action of cytokines TNF, interleukin 6, interleukin 10, granulocyte-macrophage colony-stimulating factor or macrophage colony-stimulating factor, since neutralizing antibodies did not reduce constitutive DNA-binding activity. Furthermore, blockade of prostaglandin or leukotriene biosynthesis did not affect constitutive NF-kappa B.(ABSTRACT TRUNCATED AT 400 WORDS)

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Constitutive nuclear NF kappa B/rel DNA-binding activity of rat thymocytes is increased by stimuli that promote apoptosis, but not inhibited by pyrrolidine dithiocarbamate.

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