| Twenty years following the identification of nuclear factor-κB (NF-κB) as a regulator of expression of theκB light chain in B cells, research into the function and regulation of the NF-κB family continues at a blistering pace. Advances in understanding how the immune system senses pathogens and processes this information through the activation of NF-κB, as well as an ever-expanding list of diseases in which dysregulation of NF-κB has been implicated, have continued to invite broad interest into the regulation of this inducible transcription factor. Part of the answer lies in these numbers themselves. The sheer volume of work in this area has allowed the field of NF-κB research to be both a source of signaling paradigms that have been broadly applied to other systems, as well as a melting pot in which ideas from disparate fields have merged, been modified, and matured into new concepts. The inducible regulation of gene expression is a central element of normal physiology and is the key to the ability of multicellular organisms to adapt to environmental, mechanical, chemical, and microbiological stresses. Owing to its amenability to experimentation and its importance in disease, NF-κB has served as a model of cell, tissue, and organism level responses that are orchestrated through inducible transcription factors.RNA binding protein QKI encoded by the quaking gene locus was designated from the quaking viable mice. Quaking viable (qkv) is an autosomal recessive mutation due to a deletion of the 5'flanking region of the QKI gene, leading to diminished expression of the selective RNA-binding protein QKI in myelin producing cells and subsequently dysmyelination in the CNS. QKI harbors amino acid domains characteristic of RNA-binding and interaction with Src homology 3 (SH3)-containing signaling molecules, therefore belongs to a fast-growing family denoted as signal transduction activators of RNA (STAR). Currently, all the findings related with QKI are mainly focused on CNS, esp. related with MBP and MAG mRNA stability, splicing, translocation and translational repression during oligodentrocytes differentiation. As RNA-binding protein, its interaction with target mRNA is mainly through binding with cis-element in target mRNA 3'UTR (Quaking Response Element, QRE).Characterization of the expression and the underlying mechanism would shed light on the function of a protein or gene. To this end, we would like to explore the transcription of QKI. By bioinformatics analysis, we found a putative NF-κB binding site at 710bp upstream of atg in QKI gene promoter region, rasising the possibility that NF-κB signal pathway would regulate QKI expression. To confirm the regulation, firstly we constructed the QKI promoter luciferase reportor system. From the reportor assay, both ectopic expression of the constitutively activative subunit of NF-κB (P65) and extracelluar treatment of TNFαcould blunt the transcriptional activity of QKI promoter. These results suggested that the NF-κB signal pathway may transcriptionally down-regulate QKI. Then we found that endogenous QKI mRNA decreased in C2C12 cell line when treated with TNF-α, and similar results were also observed in the primary culture of neonate rat skeletal muscle cells. To validate the decrease of QKI by TNF-αis mediated by NF-κB signal pathway, BAY11-7082, a specific inhibitor to block TNFαactivated NF-κB was included in the following study. We found that this inhibitor rescued the expression of QKI, suggesting that NF-κB signal pathway is involved in the TNFαinduced repression of QKI expression. Similar results were also found when we shut down the NF-κB signal pathway by overexpression of dominat negative IκBαor IKKα. Furthermore, the chromatin immunoprecipation result showed that P65, the activated subunit of NF-κB signal pathway, could interact with QKI promotor directly. We assumed that corepressors, such as histone deacetylases, might colocalize with the P65 at the promoter, which cordinatedly inhibit the QKI expression.To uncover the function of the down-regualtion of QKI by NF-κB signal pathway in skeletal muscle, further studies were done. Through overexpression and knock down of QKI in myocyte C2C12, we found that QKI could inhibit myoblast proliferation and differentiation. Because of the up-regulation of P130, a reserve cell marker, after QKI overexpression, we propose that QKI could enhance the self-renewaland maintaintenance of these reserve cell group. Moreover, we separated the reserve cells from differentiated C2C12 cell culture, and found a higher expression level of QKI in reserve cells. Because reserve cells are similar to satellite cells in skeletal muscle, we claimed that the transcriptioanal down-regulation of QKI by NF-κB signal pathway may functioned in skeletal muscle regeneration. Extracellular cytokine stimulation, such as TNF-α, activated NF-κB signal pathway in satellite cells, then promoted satellite cells to enter cell cycle from resting stage, and finally repair the injured muscle.
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