[PubMed] [Google Scholar] 31. of p38 MAPK significantly reduced the H5N1/97-induced TNF- expression in macrophages. Taken together, our findings suggest that H5N1/97-mediated hyperinduction of cytokines entails the p38 MAPK signaling pathway. These results may provide insights into the pathogenesis of H5N1 disease and rationales for the development of novel therapeutic strategies. The bird flu outbreak in Hong Kong in 1997 caused by influenza A computer virus subtype H5N1 (H5N1/97) was the first documented instance of a purely avian influenza computer virus causing respiratory disease and death in humans. It was associated with an overall mortality rate of 33% (6 of 18 patients; 4, 30, 36). The clinical features were those of a viral pneumonia progressing to acute respiratory distress and multiple organ dysfunction syndromes associated with lymphopenia and hemophagocytosis (36). These clinical features have been associated with cytokine dysregulation (8, 13, 33). From 2001 onward, the precursor ML204 H5N1 viruses continued to reassort and gave rise to novel computer virus genotypes. One of these H5N1 genotypes Dnmt1 was associated with the re-emergence of human ML204 disease in 2003 (12, 27) and led to a common outbreak in Asia with transmission to humans in Vietnam and Thailand in 2004 (34; World Health Business avian influenza information at http://www.who.int/csr/disease/avian_influenza/en/). This situation poses a ML204 significant threat to human health and the potential for the emergence of a pandemic influenza computer virus. We previously showed that in contrast to human influenza computer virus subtypes H3N2 and H1N1, the H5N1 viruses causing human disease in 1997 (H5N1/97) and 2003 (H5N1/03) induce high levels of tumor necrosis factor alpha (TNF-) and other proinflammatory cytokines and chemokines in monocyte-derived macrophages in vitro (3, 12). Viral factors associated with the H5N1-induced hyperinduction of TNF- and related cytokines remain to be fully defined. Using reverse genetics, we exhibited that this nonstructural (NS) gene of the H5N1/97 influenza computer virus contributes, in part, to this effect. However, the human H5N1 computer virus isolates of 1997 and 2003 do not share common NS genes (12) and therefore other viral genes may play an important role in TNF- induction. The cellular transcription factors and signaling pathways associated with H5N1-associated cytokine hyperinduction also remain to be investigated. Putative targets for investigation include the pathways associated with transcription factor NF-B and the mitogen-activated protein kinases (MAPK) together with their downstream signaling cascades. Transcription factor NF-B plays a critical role in gene activation in response to contamination, inflammation, and stress signals. Overexpression of influenza computer virus hemagglutinin, nucleoprotein, or matrix protein in infected cells triggers the NF-B signaling pathway through activation of the inhibitor of NF-B (IB) kinase (IKK) (9). NF-B belongs to the Rel family of dimeric transcription factors including p65 (RelA), RelB, c-Rel, p100, and p105 (16). ML204 Activation of NF-B requires sequential phosphorylation, ubiquitination, and ultimately degradation of IB. IB degradation is usually brought on by activation of a complex of multiple kinases that is composed of IKK and IKK and a structural regulatory subunit, IKK or NEMO. Phosphorylation of IKK and IKK is usually activated by their upstream kinases including NF-B-inducing kinase (16). MAPK and their downstream signaling cascades also play crucial functions in immunological and cellular responses to external stimuli. Three well-characterized users of the MAPK superfamily are p38 MAPK, extracellular signal-regulated kinases 1 and 2 (ERK1/2), and c-jun NH2-terminal kinases (JNK). These kinases regulate gene expression at both the transcription and posttranscription levels by different mechanisms (7). Recent studies by using specific kinase inhibitors and/or dominant-negative mutant forms of kinases have demonstrated the functions of MAPK signaling pathways in influenza A computer virus infection. For example, it has been shown that p38 MAPK and JNK, but not ERK1/2, regulate RANTES expression in influenza virus-infected bronchial epithelial cells (20). Viral RNA induction.
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- Abbreviations: CON, control; CANA, canagliflozin; AMPK, AMP-activated proteins kinase; ACC, acetyl-CoA carboxylase
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