Pattern Recognition Receptors and the Host Cell Death Molecular Machinery

Pattern Recognition Receptors (PRRs) are proteins capable of recognizing molecules frequently found in pathogens (the so-called Pathogen-Associated Molecular Patterns—PAMPs), or molecules released by damaged cells (the Damage-Associated Molecular Patterns—DAMPs). They emerged phylogenetically prior to the appearance of the adaptive immunity and, therefore, are considered part of the innate immune system. Signals derived from the engagement of PRRs on the immune cells activate microbicidal and pro-inflammatory responses required to eliminate or, at least, to contain infectious agents. Molecularly controlled forms of cell death are also part of a very ancestral mechanism involved in key aspects of the physiology of multicellular organism, including the elimination of unwanted, damaged or infected cells. Interestingly, each form of cell death has its particular effect on inflammation and on the development of innate and adaptive immune responses. In this review article, we discuss some aspects of the molecular interplay between the cell death machinery and signals initiated by the activation of PRRs by PAMPs and DAMPs

LUBAC prevents lethal dermatitis by inhibiting cell death induced by TNF, TRAIL and CD95L

The linear ubiquitin chain assembly complex (LUBAC), composed of HOIP, HOIL-1 and SHARPIN, is required for optimal TNF-mediated gene activation and to prevent cell death induced by TNF. Here, we demonstrate that keratinocyte-specific deletion of HOIP or HOIL-1 (E-KO) results in severe dermatitis causing postnatal lethality. We provide genetic and pharmacological evidence that the postnatal lethal dermatitis in HoipE-KO and Hoil-1E-KO mice is caused by TNFR1-induced, caspase-8-mediated apoptosis that occurs independently of the kinase activity of RIPK1. In the absence of TNFR1, however, dermatitis develops in adulthood, triggered by RIPK1-kinase-activity-dependent apoptosis and necroptosis. Strikingly, TRAIL or CD95L can redundantly induce this disease-causing cell death, as combined loss of their respective receptors is required to prevent TNFR1-independent dermatitis. These findings may have implications for the treatment of patients with mutations that perturb linear ubiquitination and potentially also for patients with inflammation-associated disorders that are refractory to inhibition of TNF alone

CD95L downregulation by PGE2 and its impact on T lymphocyte death.

Células apresentadoras de antígeno (APCs) controlam as respostas de linfócitos T por múltiplos mecanismos, que incluem a expressão de moléculas co-estimuladoras, a produção de citocinas e outros mediadores. Estes mecanismos exercem influência não só na proliferação, diferenciação e polarização dos linfócitos T, mas também interferem na sobrevivência destas células. No presente trabalho, foi demonstrado que fator(es) solúvel(eis) produzido(s) por APCs ativadas via receptores do tipo Toll (TLRs) suprimem a morte induzida por ativação (AICD) de linfócitos T. Este efeito foi observado em APCs não estimuladas, porém foi significativamente maior após estimulação das APCs com lipopolissacarídeo (LPS). Através do uso de diferentes camundongos nocautes, foi mostrado que a produção do fator protetor induzida por LPS é dependente da via de TLR4/MyD88 e independente de TLR2 e CD14. Este fator foi identificado como prostaglandina E2 (PGE2) e foi demonstrado que os sobrenadantes derivados de APC e a PGE2 sintética bloqueiam a expressão de CD95L em linfócitos T estimulados via TCR/CD3. A inibição da expressão de CD95L reduz tanto a AICD como a morte de macrófagos, alvos do ataque citotóxico dos linfócitos T ativados. Foi demonstrado também que, ao invés de bloquear a via do CD95, a PGE2 potencializa a morte induzida por anticorpos anti-CD95 agonistas. Os receptores de PGE2, EP2 e EP4, parecem ser os responsáveis por mediar os efeitos supressores da PGE2 na AICD, já que a estimulação farmacológica destes receptores mimetiza o efeito protetor da PGE2 e seus respectivos antagonistas interferem com a proteção conferida pelos sobrenadantes de APCs e pela PGE2 sintética. A ativação do EP2 e do EP4 age sinergicamente na ativação das vias dependentes da PKA e de EPAC, que contribuem para a inibição da AICD. Por fim, a ativação dos principais fatores de transcrição envolvidos com a expressão de CD95L (NFAT, AP-1 e NF-kB) não é bloqueada por PGE2. Por outro lado, PGE2 induziu a expressão de ICER, um repressor transcripcional, através da ativação de CREB. Em conjunto, estes resultados indicam que as APCs podem modular os níveis de expressão de CD95L através da secreção de PGE2 em resposta ao LPS, através de uma via dependente de TLR4 e MyD88, com conseqüências tanto para a morte de linfócitos T quanto para a sua própria sobrevivência.Antigen-presenting cells (APCs) control T-cell responses by multiple mechanisms, including the expression of co-stimulatory molecules and the production of cytokines and other mediators that control T-cell proliferation, survival and differentiation. In this present work, it was demonstrated that soluble factor(s) produced by Toll-like receptor (TLR)-activated APCs suppress activation-induced cell death (AICD). This effect was observed in non-stimulated APCs, but it was significantly increased after lipopolysaccharide (LPS) treatment. Using different KO mice, it was found that the LPS-induced protective factor is dependent on TLR4/MyD88 and independent of TLR2 and CD14. The protective factor was identified as prostaglandin E2 (PGE2) and it was shown that both APC-derived supernatants and PGE2 prevented CD95L upregulation in T cells in response to TCR/CD3 stimulation, thereby avoiding both AICD and activated T cell killing of target macrophages. It was also demonstrated that instead of blocking CD95 pathway, PGE2 enhanced T cell death induced by agonistic anti-CD95 antibodies. The PGE2 receptors, EP2 and EP4, appear to be involved in AICD suppression since pharmacological stimulation of these receptors mimics the protective effect on T cells and their respective antagonists interfere with the protection induced by either APCs derived or synthetic PGE2. The engagement of EP2 and EP4 synergistically activates protein kinase A (PKA) and exchange protein directly activated by cAMP pathways to prevent AICD. Finally, the activation of the main transcription factors involved in CD95L expression (NFAT, AP-1 and NF-kB) is not avoided by PGE2. On the other hand, PGE2 induces the expression of ICER, a transcriptional repressor of CD95L, through CREB activation. Taken together, these results indicate that APCs can regulate T-cell levels of CD95L by releasing PGE2 in response to LPS through a TLR4/MyD88-dependent pathway, with consequences for both T cell and their own survival

Control of death receptor ligand activity by posttranslational modifications

The death receptor ligands are involved in many physiological and pathological processes involving triggering of apoptosis, inflammation, proliferation, and activation. The expression of these molecules is reported to be tightly regulated at the transcriptional level. However, over the last few years, an increasing number of data demonstrated that the control of transcription is only one of the mechanisms that manage the expression of the death receptor ligands. Thus, this review is focused on posttranslational regulation of the three main members of this family, namely FasL, TNF-α, and TRAIL. We discuss here the importance of distribution, storage, and degranulation of these molecules, as well as their shedding by proteases on the control of death receptor ligands expression and activity

Mitochondrial DNA restriction and genomic maps of seven species of Melipona (Apidae: Meliponini)

This paper reports efforts to characterize the mitochondrial genome of Meliponini. Here we describe the restriction and partial genomic map of seven Melipona species (M. bicolor, M. compressipes, M. marginata, M. melanoventer, M. quadrifasciata, M. rufiventris and M. subnitida). The maps were obtained through RFLP and PCR-RFLP using 15 restriction enzymes. The total number of sites mapped ranged from 12 to 19, indicating a high level of genetic diversity among those species. MtDNA total size was estimated to be 18 500 bp

A scientific note on mtDNA gene order rearrangements among highly eusocial bees (Hymenoptera, Apidae)

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Sustained activation of p53 in confluent nucleotide excision repair-deficient cells resistant to ultraviolet-induced apoptosis

p53 activation is one of the main signals after DNA damage, controlling cell cycle arrest, DNA repair and apoptosis. We have previously shown that confluent nucleotide excision repair (NER)-deficient cells are more resistant to apoptosis induced by ultraviolet irradiation (UV). Here, we further investigated the effect of cell confluence on UV-induced apoptosis in normal and NER-deficient (XP-A and XP-C) cells, as well as the effects of treatments with the ATWATR inhibitor caffeine, and the patterns of p53 activation. Strong p53 activation was observed in either proliferating or confluent cells. Caffeine increased apoptosis levels and inhibited p53 activation in proliferating cells, suggesting a protective role for p53. However, in confluent NER-deficient cells no effect of caffeine was observed. Transcription recovery measurements showed decreased recovery in proliferating XPA-deficient cells, but no recovery was observed in confluent cells. The levels of the cyclin/Cdk inhibitor, p21(Waf1/Cip1), correlated well with p53 activation in proliferating cells. Surprisingly, confluent cells also showed similar activation of p21(Waf1/Cip1). These results indicate that reduced apoptosis in confluent cells is associated with the deficiency in DNA damage removal, since this effect is not clearly observed in NER-proficient cells. Moreover, the strong activation of p53 in confluent cells, which barely respond to apoptosis, suggests that this protein, under these conditions, is not linked to UV-induced cell death signaling. (c) 2008 Elsevier B.V. All rights reserved

An oligonucleotide primer set for PCR amplification of the complete honey bee mitochondrial genome

Mitochondrial DNA markers have been widely used to address population and evolutionary questions in the honey bee Apis mellifera. Most of the polymorphic markers are restricted to few mitochondrial regions. Here we describe a set of 24 oligonucleotides that allow PCR amplification of the entire mitochondrial genome of the honey bee A. mellifera in 12 amplicons. These fragments have important applications for the study of mitochondrial genes in different subspecies of A. mellifera and as heterospecific probes to characterize mitochondrial genomes in other bee species