Rapid activation of post-hepatectomy factor/nuclear factor kappa B in hepatocytes, a primary response in the regenerating liver

The liver represents one of the few organs in the intact animal that has the capacity to regenerate following injury or partial hepatectomy. One of the earliest responses that has been detected in the remnant liver is the activation of post-hepatectomy factor(s) (PHF), a kappa B site DNA binding activity. We reasoned that understanding the molecular nature of PHF might provide insight into what triggers liver regeneration. We found that PHF is rapidly activated and turned over in the regenerating liver, demonstrating peak activity at 30 min post-hepatectomy and virtual disappearance by 1 h. As determined by supershift, cross-linking, and cross-linking/immunoprecipitation analyses, PHF contains intact p50/p65nuclear factor kappa B (NF-kappa B) subunits. To explore the basis for activation of PHF/NF-kappa B in the regenerating liver, we determined the level of individual Rel family subunits in the nuclei of normal and regenerating liver cells. We found evidence for nuclear translocation of p65/RelA, but other Rel family proteins including p50/NF-kappa B1 and p52/NF-kappa B2 are present at a low level in the nuclei of cells at a constitutive level pre- and post-hepatectomy and appear not to form DNA binding homodimers. The level of I kappa B-alpha falls slightly then increases at 3 h post-hepatectomy in concert with the induction of its mRNA. As demonstrated by the induction of I kappa B-alpha mRNA in hepatocytes in situ and identification of PHF/NF-kappa B in cultured hepatocytes, PHF/NF-kappa B is localized primarily in hepatocytes in the regenerating liver. This represents one of the few examples of NF-kappa B activation in the intact animal in a non-hematopoietic cell type. The activation of PHF/NF-kappa B suggests a mechanism by which hepatocytes regulate their mitogenic program during liver regeneration.     

Regulation of nuclear factor-kappa B and its inhibitor I kappa B-alpha/MAD-3 in monocytes by Mycobacterium tuberculosis and during human tuberculosis

Blood monocytes from patients with active tuberculosis are activated in vivo, as evidenced by an increase in the stimulated release of proinflammatory cytokines, such as TNF-alpha, and the spontaneous expression of IL-2R. Further, monocytes from patients demonstrate an augmented susceptibility to a productive infection with HIV-1 in vitro. Mycobacterium tuberculosis and its components are strong signals to activate monocytes to production of cytokines. In this study we examined the basis of activation of monocytes during active tuberculosis and by M. tuberculosis. We found a constitutive degradation of I kappa B-alpha, the major cytoplasmic inhibitor of nuclear factor kappa B (NF-kappa B), in freshly isolated PBMC and monocytes from patients with tuberculosis. In contrast, I kappa B-alpha levels in PBMC and monocytes from healthy subjects or from patients with nontuberculous pulmonary conditions were intact. Further, by electrophoretic mobility shift assay, NF-kappa B was activated in monocytes from tuberculous patients. The expression of I kappa B-alpha gene, which is responsive to activation by NF-kappa B, was up-regulated in PBMC and monocytes from patients, but not in mononuclear cells from healthy subjects or those with nontuberculous lung diseases. By contrast, the expression of other adherence-associated early genes, such as IL-8 and IL-1 beta, was not up-regulated in PBMC of tuberculous patients. Further, M. tuberculosis and its tuberculin, purified protein derivative, induced the degradation of I kappa B-alpha and the expression of I kappa B-alpha mRNA, and purified protein derivative induced the activation of NF-kappa B in monocytes.     

Nuclear targeted suppression of NF-kappa B activity by the novel quinone derivative E3330

The activation of NF-kappa B consists of at least three steps: degradation of I kappa B alpha, translocation of NF-kappa B into the nucleus, ai post-translational modification of NF-kappa B (e.g., phosphorylation of p65). In the present study, we found that a novel quinone derivative E3330 selectively inhibited NF-kappa B-mediated gene expression without affecting any of these steps. E3330, when included in the culture medium, suppressed NF-kappa B DNA-binding activity in PMA-induced Jurkat cell nuclear extracts, suggesting that the inhibition by E3330 of NF-kappa B-mediated gene expression was due to its ability to suppress NF-kappa B DNA-binding activity. Fractionation of the nuclear extracts by column chromatography revealed that a nuclear factor enhanced NF-kappa B DNA-binding activity and that this enhancing activity was interrupted after treatment with E3330. Moreover, a major polypeptide with a molecular mass of 40 kDa was found to be in the highly purified fraction containing the NF-kappa B-enhancing activity and predominantly bind E3330. Taken together, these results suggest that the NF-kappa B activity, after dissociation from I kappa B, is enhanced by a nuclear factor that is active irrespective of PMA treatment, and the nuclear factor-mediated enhancement is selectively inhibited by E3330. Thus, we conclude that E3330 may belong to a novel class of anti-NF-kappa B drugs.     

Role of unphosphorylated, newly synthesized I kappa B beta in persistent activation of NF-kappa B

Stimulation with inducers that cause persistent activation of NF-kappa B results in the degradation of the NF-kappa B inhibitors, I kappa B alpha and I kappa B beta. Despite the rapid resynthesis and accumulation of I kappa B alpha, NF-kappa B remains induced under these conditions. We now report that I kappa B beta is also resynthesized in stimulated cells and appears as an unphosphorylated protein. The unphosphorylated I kappa B beta forms a stable complex with NF-kappa B in the cytosol; however, this binding fails to mask the nuclear localization signal and DNA binding domain on NF-kappa B, and the I kappa B beta-NF-kappa B complex enters the nucleus. It appears therefore that during prolonged stimulation, I kappa B beta functions as a chaperone for NF-kappa B by protecting it from I kappa B alpha and allowing it to be transported to the nucleus.