Positive Role In Activation Research Articles

Tenascin-C promotes migration of hepatic stellate cells and production of type I collagen.

Tenascin-C (TN-C) is an extracellular matrix glycoprotein markedly upregulated during liver fibrosis. The study is performed to explore the role of TN-C during the growth and activation of hepatic stellate cells (HSCs). We found that TN-C was accumulated accompanying with the HSC activation. Our data on cell migration assay revealed that the rTN-C treatment enhanced HSC migration in a dose- and time-dependent manner, but did not influence their proliferation. HSCs transfected with pTARGET-TN-C overexpression vector displayed increased the type I collagen (Col I) production. TN-C overexpression enhanced the process of HSC activation through TGF-β1 signaling. Moreover, the anti-α9β1 integrin antibody treatment blocked the TN-C-driven Col I increase in rat HSCs. Collectively, TN-C had a positive role in activation of HSCs mediated by TGF-β1 and α9β1 integrin, manifesting elevation of Col I production and promotion of cell migration. Our results provide a potential insight for the therapy of hepatic fibrosis.

Emodin inhibits coxsackievirus B3 replication via multiple signalling cascades leading to suppression of translation.

CVB3 (coxsackievirus 3) is a primary causal agent of viral myocarditis. Emodin is a natural compound isolated from certain plant roots. In the present study, we found that emodin inhibited CVB3 replication in vitro and in mice, and now we report an unrecognized mechanism by which emodin inhibits CVB3 replication through suppression of viral protein translation via multiple pathways. On one hand, emodin treatment inhibited Akt/mTOR (mammalian target of rapamycin) signalling and activated 4EBP1 (eukaryotic initiation factor 4R-binding protein 1), leading to suppression of translation initiation of ribosomal protein L32 encoded by a 5'-TOP (terminal oligopyrimidine) mRNA. On the other hand, emodin treatment differentially regulated multiple signal cascades, including Akt/mTORC1/p70(S6K) (p70 S6 kinase), ERK1/2 (extracellular-signal-regulated kinase 1/2)/p90(RSK) (p90 ribosomal S6 kinase) and Ca(2+)/calmodulin, leading to activation of eEF2K (eukaryotic elongation factor 2 kinase) and subsequent inactivation of eEF2 (eukaryotic elongation factor 2), resulting in inhibition of CVB3 VP1 (viral protein 1) synthesis. These data imply that eEF2K is a major factor mediating cross-talk of different arms of signalling cascades in this signal network. This notion was verified by either overexpressing eEF2K or treating the cells with siRNAs or eEF2K inhibitor A484954. We showed further that the emodin-induced decrease in p70(S6K) phosphorylation plays a dominant positive role in activation of eEF2K and in turn in conferring the antiviral effect of emodin. This finding was further solidified by expressing constitutively active and dominant-negative Akt. Collectively, our data reveal that emodin inhibits viral replication through impairing translational machinery and suppression of viral translation elongation.

Contribution of the Histone H3 and H4 Amino Termini to Gcn4p- and Gcn5p-mediated Transcription in Yeast

Histone amino termini are post-translationally modified by both transcriptional coactivators and corepressors, but the extent to which the relevant histone modifications contribute to gene expression, and the mechanisms by which they do so, are incompletely understood. To address this issue, we have examined the contributions of the histone H3 and H4 amino termini, and of the coactivator and histone acetyltransferase Gcn5p, to activation of a small group of Gcn4p-activated genes. The histone H3 tail exerts a modest (about 2-fold) but significant effect on activation that correlates with a requirement for Gcn5p and is distributed over multiple lysine residues. The H4 tail also plays a positive role in activation of some of those genes tested, but this does not correlate as closely with Gcn5p coactivation. Microarray experiments did not reveal a close correspondence between those genes activated by Gcn4p and genes requiring the H3 or H4 tail, and analysis of published microarray data indicates that Gcn4p-regulated genes are not in general strongly dependent on Gcn5p. However, a large fraction of genes activated by Gcn4p were found to be repressed by the H3 and H4 amino termini under non-inducing conditions, indicating that one role for Gcn4p is to overcome repression mediated by the histone tails.

FLT3/ITD Mutation Signaling Includes Suppression of SHP-1

Mutations in the FLT3 gene are the most common genetic alteration found in AML patients. FLT3 internal tandem duplication (ITD) mutations result in constitutive activation of FLT3 tyrosine kinase activity. The consequences of this activation are an increase in total phosphotyrosine content, persistent downstream signaling, and ultimately transformation of hematopoietic cells to factor-independent growth. The Src homology (SH)2 domain-containing protein-tyrosine phosphatase (SHP)-1 is involved in the down-regulation of a broad range of growth factor and cytokine-driven signaling cascades. Loss-of-function or deficiency of SHP-1 activity results in a hyperproliferative response of myelomonocytic cell populations to growth factor stimulation. In this study, we examined the possible role of SHP-1 in regulating FLT3 signaling. We found that transformation of TF-1 cells with FLT3/ITD mutations suppressed the activity of SHP-1 by approximately 3-fold. Suppression was caused by decreased SHP-1 protein expression, as analyzed at both the protein and RNA levels. In contrast, protein levels of SHP-2, a phosphatase that plays a stimulatory role in signaling through a variety of receptors, did not change significantly in FLT3 mutant cells. Suppressed SHP-1 protein levels in TF-1/ITD cells were partially overcome after cells were exposed to CEP-701, a selective FLT3 inhibitor. SHP-1 protein levels also increased in naturally occurring FLT3/ITD expressing AML cell lines and in primary FLT3/ITD AML samples after CEP-701 treatment. Furthermore, a small but reproducible growth/survival advantage was observed in both TF-1 and TF-1/ITD cells when SHP-1 expression was knocked down by RNAi. Taken together, these data provide the first evidence that suppression of SHP-1 by FLT3/ITD signaling may be another mechanism contributing to the transformation by FLT3/ITD mutations.

ACE1 regulates expression of the Saccharomyces cerevisiae metallothionein gene.

Copper resistance in Saccharomyces cerevisiae is mediated, in large part, by the CUP1 locus, which encodes a low-molecular-weight, cysteine-rich metal-binding protein. Expression of the CUP1 gene is regulated at the level of transcriptional induction in response to high environmental copper levels. This report describes the isolation of a yeast mutant, ace1-1, which is defective in the activation of CUP1 expression upon exposure to exogenous copper. The ace1-1 mutation is recessive and lies in a genetic element that encodes a trans-acting CUP1 regulatory factor. The wild-type ACE1 gene was isolated by in vivo complementation and restores copper inducibility of CUP1 expression and copper resistance to the otherwise copper-sensitive ace1-1 mutant. Linkage analysis and gene deletion experiments verified that this gene represents the authentic ACE1 locus. ACE1 maps to the left arm of chromosome VII, 9 centimorgans centromere distal to lys5. The ACE1 gene appears to play a direct or indirect positive role in activation of CUP1 expression in response to elevated copper concentrations.

ACE1 regulates expression of the Saccharomyces cerevisiae metallothionein gene.

Copper resistance in Saccharomyces cerevisiae is mediated, in large part, by the CUP1 locus, which encodes a low-molecular-weight, cysteine-rich metal-binding protein. Expression of the CUP1 gene is regulated at the level of transcriptional induction in response to high environmental copper levels. This report describes the isolation of a yeast mutant, ace1-1, which is defective in the activation of CUP1 expression upon exposure to exogenous copper. The ace1-1 mutation is recessive and lies in a genetic element that encodes a trans-acting CUP1 regulatory factor. The wild-type ACE1 gene was isolated by in vivo complementation and restores copper inducibility of CUP1 expression and copper resistance to the otherwise copper-sensitive ace1-1 mutant. Linkage analysis and gene deletion experiments verified that this gene represents the authentic ACE1 locus. ACE1 maps to the left arm of chromosome VII, 9 centimorgans centromere distal to lys5. The ACE1 gene appears to play a direct or indirect positive role in activation of CUP1 expression in response to elevated copper concentrations.