Inhibition of ER stress-mediated apoptosis in macrophages by nuclear-cytoplasmic relocalization of eEF1A by the HIV-1 Nef protein

HIV-1 Nef protein has key roles at almost all stages of the viral life cycle. We assessed the role of the Nef/eEF1A (eukaryotic translation elongation factor 1-alpha) complex in nucleocytoplasmic shuttling in primary human macrophages. Nuclear retention experiments and inhibition of the exportin-t (Exp-t) pathway suggested that cytoplasmic relocalization of eEF1A, mediated by Exp-t, occurs in Nef-treated monocyte-derived macrophages (MDMs). We observed the presence of tRNA in the Nef/eEF1A complexes. Nucleocytoplasmic relocalization of the Nef/eEF1A complexes prevented stress-induced apoptosis of MDMs treated with brefeldin-A. Blockade of stress-induced apoptosis of MDMs treated with HIV-1 Nef resulted from enhanced nucleocytoplasmic transport of eEF1A with decreased release of mitochondrial cytochrome c, and from increased tRNA binding to cytochrome c, ultimately leading to an inhibition of caspase activation. Our results indicate that HIV-1 Nef, through the nucleocytoplasmic relocalization of eEF1A and tRNAs, enhances resistance to stress-induced apoptosis in primary human macrophages

Mutations in the IkBa gene in Hodgkin's disease suggest a tumour suppressor role for IkBa

The NF-kappa B/Rel family of transcription factors regulates wide variety of genes whose products play a fundamental role in inflammatory and immune responses. The implication of NF-kappa B/Rel proteins and their I kappa B regulatory subunits in the control of cellular growth and oncogenesis, was suggested by the induction of fatal lymphomas in birds by the v-rel oncoprotein, and the rearrangement and amplification of several genes encoding the NF-kappa B/Rel/I kappa B signal transduction factors in human malignancies, primarily of lymphoid origin. Hodgkin's disease (HD) is a lymphoma characterized by a low frequency of malignant Hodgkin and Reed-Sternberg (H/RS) cells in a reactive background of nonneoplastic cells. The peculiar activated phenotype of Hodgkin and Reed-Sternberg cells and their pattern of cytokine secretion are believed to be a consequence of constitutive activation of the NF-kappa B transcription factor. Here, we report the detection of mutations of the 1k Ba gene, in two HD-derived cell lines and in two out of eight biopsy samples from patients with relapsed Hodgkin's disease. The presence of defective I kappa B alpha is thus likely to explain the constitutive activation of NF-kappa B in these cells and suggests that I kappa B alpha is a tumour suppressor controlling the oncogenic activation of NF-kappa B in Hodgkin and Reed-Sternberg cells.</p

NF-kB inhibits apoptosis in murine mammary epithelia

The transcription factor NF-κB is a key modulator of apoptosis in a variety of cell types, but to date this specific function of NF-κB has not been demonstrated in epithelia. Here, we describe the activation of NF-κB during post-lactational involution of the mouse mammary gland, a period of extensive apoptosis of luminal epithelial cells. Significantly, active NF-κB localized exclusively to nonapoptotic epithelial cells both in vivoand in the mammary epithelial cell line, KIM-2, transduced with an NF-κB-dependent green fluorescent protein reporter. Activation of NF-κB in vitro coincided with a decrease in the cytosolic repressor, IκBα. Furthermore, induction of NF-κB either by extracellular ligands or, more specifically, by inhibition of the IκB repressor with adenoviral constructs expressing antisense mRNA, resulted in enhanced survival of KIM-2 cells. Therefore, although coincident with induction of apoptosis both in vivo and in vitro, NF-κB appeared to exert a selective survival function in epithelial cells. This study highlights for the first time a role for NF-κB in modulating apoptosis in epithelium