== Anthrax LT treatment blocks the induction of HIF-1 and its target genes.A, differential expression of HIF-1 target genes Byakangelicin in HepG2 cells pretreated for 3 h with (LT) or without (M) LT, and then cultured in normoxic or hypoxic conditions for 20 h. of eIF4B, eIF4E, and rpS6, critical components of the intracellular machinery required for HIF-1 translation. Moreover, blockade of MKK1/2-ERK1/2, but not p38 or JNK signaling, lowers HIF-1 protein levels in both normoxic and hypoxic conditions, consistent with a role for MKK1 and MKK2 as the major targets of LT responsible for the inhibition of HIF-1 translation. The physiological importance of the LT-induced translation blockade is demonstrated by the finding that LT treatment decreases the survival of hepatocyte cell lines grown in hypoxic conditions, an effect that is overcome by preinduction of HIF-1. Taken together, these Byakangelicin data support a role for LT in dysregulating HIF-1 and thereby disrupting homeostatic responses to hypoxia, an environmental characteristic of certain tissues at Byakangelicin baseline and/or during disseminated infection withBacillus anthracis. == Introduction == Anthrax is a life-threatening disease caused by infection withBacillus anthracis(1,2).B. anthracisexpresses lethal factor (LF)2and the receptor-binding protective antigen (PA) on its pXO1 virulence plasmid (3). The combination of LF and PA is termed lethal toxin (LT). LF is a zinc-dependent metalloprotease with specific activity Byakangelicin against mitogen-activated protein kinase kinases (MKKs) (4,5) and NACHT leucine-rich repeat protein 1 (NALP1) (6,7), which are involved in the regulation of metabolism, immunological responses, cellular proliferation, and other critical cellular functions (8,9). Administration of LTin vivoleads to a shock-like clinical syndrome that parallels the clinical features of late-stage anthrax infection (10,11). Although the proximal targets of LT are well described, identification of the downstream mediators of toxicity remains an area of active investigation. Current models support the conclusion that the etiology of LT-induced cardiovascular collapse is multifactorial; LT has direct toxic effects on cardiac and smooth muscle (12), which may be exacerbated by disrupted endothelial cell function (12) and/or abrogation of cell-cell adhesion and barrier function (11,13). These factors combine to induce cardiovascular collapse and death. Other pathological features of LT-treated animals appear to support this scenario. For example, LT administration to mice results in a pattern of pathology that is characterized by cytotoxicity in tissues that are relatively hypoxic, including the metaphyseal bone marrow and centrilobar regions of the liver (14). These findings have been interpreted to suggest that LT induces tissue hypoxia via cardiovascular compromise, which then leads to cell death in susceptible tissues that are characterized by relatively low baseline oxygen concentrations (14). Although hypoxia has been considered as a contributor to LT-induced pathology, it is possible that LT could affect homeostatic responses to hypoxia. In this regard, LT has been shown to block hypoxia-driven retinal neovascularization in a neonatal mouse model (15). Byakangelicin The master transcription factor that regulates these protective responses is hypoxia-inducible factor (HIF)-1. HIF-1 is composed of two subunits, the O2-labile subunit (HIF-1) and the stable subunit (HIF-1) (16,17). The heterodimeric HIF-1 complex binds hypoxia-responsive elements (HREs) containing a conserved RCGTG core sequence. Rabbit polyclonal to PC HIF-1 directly controls expression of genes crucial for adaptation to hypoxia, encoding proteins regulating angiogenesis, glucose metabolism, cell growth and survival, tumor metastasis, and immune responses (18,19). HIF-1 activity is controlled primarily through post-translational modification and stabilization of the HIF-1 subunit (16,20,21). Under normoxic conditions, HIF-1 undergoes post-translational hydroxylation of two proline residues (Pro-402 and Pro-564) within its oxygen-dependent degradation domain, mediated by prolyl hydroxylases (22). Hydroxylated HIF-1 is subsequently.