Nancy R. Rice

Role of NF-|[kappa]|B in p53-mediated programmed cell death

The tumour suppressor p53 inhibits cell growth through activation of cell-cycle arrest and apoptosis, and most cancers have either mutation within the p53 gene or defects in the ability to induce p53. Activation or re-introduction of p53 induces apoptosis in many tumour cells and may provide effective cancer therapy. One of the key proteins that modulates the apoptotic response is NF-κB, a transcription factor that can protect or contribute to apoptosis. Here we show that induction of p53 causes an activation of NF-κB that correlates with the ability of p53 to induce apoptosis. Inhibition or loss of NF-κB activity abrogated p53-induced apoptosis, indicating that NF-κB is essential in p53-mediated cell death. Activation of NF-κB by p53 was distinct from that mediated by tumour-necrosis factor-α and involved MEK1 and the activation of pp90rsk. Inhibition of MEK1 blocked activation of NF-κB by p53 and completely abrogated p53-induced cell death. We conclude that inhibition of NF-κB in tumours that retain wild-type p53 may diminish, rather than augment, a therapeutic response.

E2F-1 Potentiates Cell Death by Blocking Antiapoptotic Signaling Pathways

The E2F family of transcription factors plays an essential role in promoting cell cycle progression, and one member of the family, E2F-1, is also capable of inducing apoptosis. We show here that E2F-1 can induce apoptosis by a death receptor-dependent mechanism, by downregulating TRAF2 protein levels and inhibiting activation of antiapoptotic signals including NF-kappa B. In this way, E2F-1 expression can lead to the sensitization of cells to apoptosis by a number of agents independently of p53. Deregulation of E2F-1 activity occurs in the majority of human tumors, and the ability of E2F-1 to inhibit antiapoptotic signaling may contribute to the enhanced sensitivity of transformed cells to chemotherapeutic agents.

The PEST-like sequence of I kappa B alpha is responsible for inhibition of DNA binding but not for cytoplasmic retention of c-Rel or RelA homodimers.

In most cells, proteins belonging to the Rel/NF-kappa B family of transcription factors are held in inactive form in the cytoplasm by an inhibitor protein, I kappa B alpha. Stimulation of the cells leads to degradation of the inhibitor and transit of active DNA-binding Rel/NF-kappa B dimers to the nucleus. I kappa B alpha is also able to inhibit DNA binding by Rel/NF-kappa B dimers in vitro, suggesting that it may perform the same function in cells when the activating signal is no longer present. Structurally, the human I kappa B alpha molecule can be divided into three sections: a 70-amino-acid N terminus with no known function, a 205-residue midsection composed of six ankyrin-like repeats, and a very acidic 42-amino-acid C terminus that resembles a PEST sequence. In this study we examined how the structural elements of the I kappa B alpha protein correlate with its functional capabilities both in vitro and in vivo. Using a battery of I kappa B alpha mutants, we show that (i) a dimer binds a single I kappa B alpha molecule, (ii) the acidic C-terminal region of I kappa B alpha is not required for protein-protein binding and does not mask the nuclear localization signal of the dimer, (iii) the same C-terminal region is required for inhibition of DNA binding, and (iv) this inhibition may be accomplished by direct interaction between the PEST-like region and the DNA-binding region of one of the subunits of the dimer.

Kappa B site-dependent activation of the interleukin-2 receptor alpha-chain gene promoter by human c-Rel.

The cis-acting control elements of the interleukin-2 receptor alpha-chain (IL-2R alpha) gene contain a potent kappa B-like enhancer whose activity can be induced by various mitogenic stimuli. Recent cloning of the p50 and p65 subunits of the kappa B-binding protein NF-kappa B complex revealed a striking sequence homology of these proteins with the c-rel proto-oncogene product (c-Rel). On the basis of this homology, we examined the potential role of c-Rel in controlling IL-2R alpha transcription. We now demonstrate that the recombinant human c-Rel protein binds to the kappa B element in the IL-2R alpha promoter and results in alteration of the DNA structure in the adjacent downstream regulatory elements containing the CArG box and the GC box. We found that human c-Rel can activate transcription from the IL-2R alpha promoter, but not the kappa B-containing human immunodeficiency virus type 1 promoter, upon cotransfection into Jurkat T cells. Furthermore, truncation of the carboxyl terminus of c-Rel results in a c-Rel mutant (RelNA) that (i) localizes exclusively in the nucleus and (ii) acts in synergy with wild-type c-Rel in activating transcription from the kappa B site of the IL-2R alpha promoter. Finally, induction of surface IL-2R alpha expression coincides with the induced levels of endogenous c-Rel and induced c-Rel binding to the IL-2R alpha kappa B site. Our study identified c-Rel as one component of the Rel/NF-kappa B-family proteins involved in the kappa B-dependent activation of IL-2R alpha gene expression. Furthermore, our results suggest that a Re1NA-like cellular factor (e.g., NF-kappa B p50 or p49 subunit) acts in synergy with c-Re1 during T-cell activation.

The N-Terminal Domain of IκBα Masks the Nuclear Localization Signal(s) of p50 and c-Rel Homodimers

ABSTRACT Members of the Rel/NF-κB family of transcription factors are related to each other over a region of about 300 amino acids called the Rel Homology Domain (RHD), which governs DNA binding, dimerization, and binding to inhibitor. At the C-terminal end of the RHD, each protein has a nuclear localization signal (NLS). The crystal structures of the p50 and RelA family members show that the RHD consists of two regions: an N-terminal section which contains some of the DNA contacts and a C-terminal section which contains the remaining DNA contacts and controls dimerization. In unstimulated cells, the homo- or heterodimeric Rel/NF-κB proteins are cytoplasmic by virtue of binding to an inhibitor protein (IκB) which somehow masks the NLS of each member of the dimer. The IκB proteins consist of an ankyrin-repeat-containing domain that is required for binding to dimers and N- and C-terminal domains that are dispensable for binding to most dimers. In this study, we examined the interaction between IκBα and Rel family homodimers by mutational analysis. We show that (i) the dimerization regions of p50, RelA, and c-Rel are sufficient for binding to IκBα, (ii) the NLSs of RelA and c-Rel are not required for binding to IκBα but do stabilize the interaction, (iii) the NLS of p50 is required for binding to IκBα, (iv) only certain residues within the p50 NLS are required for binding, and (v) in a p50-IκBα complex or a c-Rel-IκBα complex, the N terminus of IκBα either directly or indirectly masks one or both of the dimer NLSs.

Genetic characterization of human c-rel sequences.

We isolated and sequenced a human genomic-DNA segment that is homologous to a portion of v-rel, the transforming gene of reticuloendotheliosis virus (strain T). We also localized the human rel sequences to human chromosome 2 by screening a panel of rodent X human somatic-cell hybrids with the newly described human rel segment.

Nucleic acid homology between avian and mammalian type C viruses: relatedness of reticuloendotheliosis virus cdna to cloned proviral DNA of the endogenous Colobus virus CPC-1.

Abstract Reverse transcriptase and p30 of the reticuloendotheliosis viruses (REV), which are type C viruses horizontally transmitted among certain avian species, have previously been shown to be related to mammalian rather than to other avian leukosis/sarcoma type C viral proteins. Though the closest homology has been seen between proteins of REV and those of the endogenous macaque viruses (MAC-1 and MMC-1), relatedness of their nucleic acids cannot be detected by routine liquid hybridization. We report here that nucleic acid homology between REV and the colobus monkey endogenous virus (CPC-1), which is highly related to the macaque viruses, can be demonstrated when hybridization is carried out with highly labeled [ 32 P]cDNA and cloned viral DNA immobilized on nitrocellulose. Related regions occur within both the pol and the gag genes of the colobus viral genome. Thus, the REV family of viruses appears to be descended from an ancestral virus which also gave rise to the MAC-1, MMC-1, CPC-1 group of viruses now endogenous in primates.

Bovine Leukemia Virus: Past, Present and Future

Enzootic bovine leukemia has been perceived as an infectious cancer since about 50 years. Appearance of tumor cases has been linked to introduction, in a naive herd, of animals coming from a “tumor case” herd and experimental transmission experiments easily showed that an agent was indeed most probably involved. The exact nature of the agent remained elusive until 1969, when Miller and coworkers (1) observed virus particles in short term cultures of lymphocytes from animals in persistent lymphocytosis, a condition frequently associated with increased risk of leukemia. Since 1969, the virus itself, its host-range and mode of propagation, its interactions with the host and ways of leukemogenesis, ... have been the subject of intense investigation. The nucleotide sequence of several BLV proviruses is now known, thus allowing deep insight to be gained into virus integration and expression and hypotheses to be put forward about putative modes of action. Times are now ripe and the tools are available to undertake a detailed analysis of the chain of events that starts at infection and ends with full blow of the tumor phase. It had been observed, already in 1972 (2), that BLV behaved as a separate entity from the then known retroviruses.