The inhibitor of apoptosis (IAP) family of proteins enhances cell survival through mechanisms that remain uncertain. In this report, we show that cIAP1 and cIAP2 promote cancer cell survival by functioning as E3 ubiquitin ligases that maintain constitutive ubiquitination of the RIP1 adaptor protein. We demonstrate that AEG40730, a compound modeled on BIR-binding tetrapeptides, binds to cIAP1 and cIAP2, facilitates their autoubiquitination and proteosomal degradation, and causes a dramatic reduction in RIP1 ubiquitination. We show that cIAP1 and cIAP2 directly ubiquitinate RIP1 and induce constitutive RIP1 ubiquitination in cancer cells and demonstrate that constitutively ubiquitinated RIP1 associates with the prosurvival kinase TAK1. When deubiquitinated by AEG40730 treatment, RIP1 binds caspase-8 and induces apoptosis. These findings provide insights into the function of the IAPs and provide new therapeutic opportunities in the treatment of cancer.

Valproate (VPA)(1) has been used for decades in the treatment of epilepsy, and is also effective as a mood stabilizer and in migraine therapy. It has been shown that VPA is also a histone deacetylase (HDAC) inhibitor. We have previously shown that VPA could trigger active demethylation of ectopically methylated transiently transfected DNA in HEK 293 cells. We therefore tested whether VPA treatment could bring about stable changes in the epigenome by causing changes in the state of DNA methylation of genomic DNA. Using a microarray gene expression analysis we identified the genes whose expression is induced by VPA treatment in HEK 293 cells. We found that a subset of these genes could also be induced by the classical DNA methylation inhibitor 5-aza-2'-deoxy-cytidine (5-aza-CdR) suggesting that VPA can alter the state of expression of genes, which are stably suppressed by DNA methylation. We mapped the state of methylation of three of these genes, MELANOMA ANTIGEN B2 GENE (MAGEB2), METALLOPROTEINASE 2 (MMP2) and WIF1, which are involved in tumor growth and metastasis. A chromatin immunoprecipitation (ChIP) assay revealed that VPA treatment caused as expected a change in the state of acetylation of these genes. Our data supports the concept that chromatin acetylation and DNA methylation are found in a dynamic interrelation and that the consequences of HDAC inhibitors are not limited to changes in histone acetylation but that they also bring about a change in the state of modification of DNA. The implications of our results on the future therapeutic utilities of VPA in cancer will be discussed.

NOD1 {nucleotide-binding oligomerization domain 1; NLRC [NOD-LRR (leucine-rich repeat) family with CARD (caspase recruitment domain) 1]} and NOD2 (NLRC2) are among the most prominent members of the NLR (NOD-LRR) family –proteins that contain nucleotide-binding NACHT domains and receptor-like LRR domains. With over 20 members identified in humans, NLRs represent important components of the mammalian innate immune system, serving as intracellular receptors for pathogens and for endogenous molecules elaborated by tissue injury. NOD1 and NOD2 proteins operate as microbial sensors through the recognition of specific PG (peptidoglycan) constituents of bacteria. Upon activation, these NLR family members initiate signal transduction mechanisms that include stimulation of NF-κB (nuclear factor-κB), stress kinases, IRFs (interferon regulatory factors) and autophagy. Hereditary polymorphisms in the genes encoding NOD1 and NOD2 have been associated with an increasing number of chronic inflammatory diseases. In fact, potential roles for NOD1 and NOD2 in inflammatory disorders have been revealed by investigations using a series of animal models. In the present review, we describe recent experimental findings associating NOD1 and NOD2 with various autoimmune and chronic inflammatory disorders, and we discuss prospects for development of novel therapeutics targeting these NLR family proteins.

Objective The genetic basis of inflammatory bowel disease (IBD) is incompletely understood. The aim of this study was to identify rare genetic variants involved in the pathogenesis of IBD. Design Exome sequencing and immunological profiling were performed in a patient with early onset Crohn's disease (CD). The coding region of the gene encoding X-linked inhibitor of apoptosis protein (XIAP) was sequenced in samples of 275 paediatric IBD and 1047 adult-onset CD patients. XIAP genotyping was performed in samples of 2680 IBD patients and 2864 healthy controls. Functional effects of the variants identified were investigated in primary cells and cultured cell lines. Results Our results demonstrate the frequent occurrence of private variants in XIAP in about four percent of male patients with paediatric-onset CD. While XIAP mutations are known to be associated with the primary immunodeficiency (PID) X-linked lymphoproliferative disease type 2 (XLP2), CD patients described here exhibited intestinal inflammation in the absence of XLP2 and harboured a spectrum of mutations partially distinct from that observed in XLP2. The majority of XIAP variants identified was associated with a selective defect in NOD1/2 signalling, impaired NOD1/2-mediated activation of NF-κB, and altered NF-κB-dependent cytokine production. Conclusions This study reveals the unanticipated, frequent occurrence of XIAP variants in male paediatriconset CD. The link between XIAP and NOD1/2, and the association of XIAP variants with XLP2, support the concept of PID in a subset of IBD patients. Moreover, these studies provide a rationale for the implementation of XIAP sequencing in clinical diagnostics in male patients with severe CD.