RESUMO
Understanding function and specificity of de-ubiquitylating enzymes (DUBs) is a major goal of current research, since DUBs are key regulators of ubiquitylation events and have been shown to be mutated in human diseases. Most DUBs are cysteine proteases, relying on a catalytic triad of cysteine, histidine and aspartate to cleave the isopeptide bond between two ubiquitin units in a poly-ubiquitin chain. We have discovered that the two Drosophila melanogaster homologues of human OTUD4, CG3251 and Otu, contain a serine instead of a cysteine in the catalytic OTU (ovarian tumor) domain. DUBs that are serine proteases instead of cysteine- or metallo-proteases have not been described. In line with this, neither CG3251 nor Otu protein were active to cleave ubiquitin chains. Re-introduction of a cysteine in the catalytic center did not render the enzymes active, indicating that further critical features for ubiquitin binding or cleavage have been lost in these proteins. Sequence analysis of OTUD4 homologues from various other species showed that within this OTU subfamily, loss of the catalytic cysteine has occurred frequently in presumably independent events, as well as gene duplications or triplications, suggesting DUB-independent functions of OTUD4 proteins. Using an in vivo RNAi approach, we show that CG3251 might function in the regulation of Inhibitor of Apoptosis (IAP)-antagonist-induced apoptosis, presumably in a DUB-independent manner.
Assuntos
Cisteína/metabolismo , Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Serina/metabolismo , Proteases Específicas de Ubiquitina/genética , Ubiquitina/genética , Sequência de Aminoácidos , Substituição de Aminoácidos , Animais , Apoptose/genética , Sítios de Ligação , Domínio Catalítico , Sequência Conservada , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Evolução Molecular , Regulação da Expressão Gênica , Humanos , Proteínas Inibidoras de Apoptose/antagonistas & inibidores , Proteínas Inibidoras de Apoptose/genética , Proteínas Inibidoras de Apoptose/metabolismo , Dados de Sequência Molecular , Ligação Proteica , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/metabolismo , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Ubiquitina/metabolismo , Proteases Específicas de Ubiquitina/metabolismo , UbiquitinaçãoRESUMO
BACKGROUND & AIMS: Regulatory CD4(+) T cells (Tregs) are considered to affect outcomes of HCV infection, because they increase in number during chronic hepatitis C and can suppress T-cell functions. METHODS: Using microarray analysis, in situ immunofluorescence, ELISA, and flowcytometry, we characterised functional differentiation and localisation of adaptive Tregs in patients with chronic hepatitis C. RESULTS: We found substantial upregulation of IL-8 in Foxp3(+)CD4(+) Tregs from chronic hepatitis C. Activated GARP-positive IL-8(+) Tregs were particularly enriched in livers of patients with chronic hepatitis C in close proximity to areas of fibrosis and their numbers were correlated with the stage of fibrosis. Moreover, Tregs induced upregulation of profibrogenic markers TIMP1, MMP2, TGF-beta1, alpha-SMA, collagen, and CCL2 in primary human hepatic stellate cells (HSC). HSC activation, but not Treg suppressor function, was blocked by adding a neutralizing IL-8 antibody. CONCLUSIONS: Our studies identified Foxp3(+)CD4(+) Tregs as an additional intrahepatic source of IL-8 in chronic hepatitis C acting on HSC. Thus, Foxp3(+)CD4(+) Tregs in chronic hepatitis C have acquired differentiation as regulators of fibrogenesis in addition to suppressing local immune responses.
