The genetic make-up of a cell resides entirely in its DNA. Now that the nucleotide sequence of several genomes has been determined, the major challenging problem is to understand how cell ...differentiation, proliferation or death are controlled. Major steps include analysis of the determinants of the cell cycle, the unravelling of RNAs and proteins involved in the control of gene expression and the dissection of the protein-destruction machinery. The successive steps to be considered are transcription of RNA on the DNA template, mRNA stabilization or degradation, and mRNA translation and protein localization in the right cell compartment. Gene expression or gene silencing is the result of many DNA-RNA-protein interactions and chromatin is among the key regulators of gene expression. Open chromatin (euchromatin) allows expression of the DNA message. This chromatin structure is generally characterized by the presence on the gene promoters of transcription complexes associated with histone acetyltransferases (HATs). On the contrary, closed chromatin (heterochromatin) is poorly acetylated and more condensed. It contains histone deacetylases (HDACs), potentially associated with DNA methyltransferases (DNMTs). DNMT activity leads to methylation and silencing of the DNA. Thus, a major problem in the field of gene regulation resides in understanding chromatin structure at each promoter, a formidable task for the years to come.
NF-kappaB is a crucial transcription factor tightly regulated by protein
interactions and post-translational modifications, like phosphorylation
and acetylation. A previous study has shown that ...trichostatin
A (TSA), a histone deacetylase inhibitor, potentiates
tumor necrosis factor (TNF) alpha-elicited NF-kappaB activation and
delays IkappaBalpha cytoplasmic reappearance. Here, we demonstrated
that TSA also prolongs NF-kappaB activation when induced by the
insulino-mimetic pervanadate (PV), a tyrosine phosphatase inhibitor
that initiates an atypical NF-kappaB signaling. This extension is
similarly correlated with delayed IkappaBalpha cytoplasmic reappearance.
However, whereas TSA causes a prolonged IKK activity when
addedtoTNFalpha, it does notwhenaddedtoPV.Instead, quantitative
reverse transcriptase-PCR revealed a decrease of ikappabalphamRNAlevel
after TSA addition to PV stimulation. This synthesis deficit of the
inhibitor could explain the sustained NF-kappaB residence in the
nucleus. In vivo analysis by chromatin immunoprecipitation assays
uncovered that, forPVinduction but not forTNFalpha, the presence of
TSA provokes several impairments on the ikappabalphapromoter: (i) diminution
of RNA Pol II recruitment; (ii) reduced acetylation and
phosphorylation of histone H3-Lys14 and -Ser10, respectively; (iii)
decreased presence of phosphorylated p65-Ser536; and (iv) reduction
of IKKalphabinding. The recruitment of these proteins on the
icam-1 promoter, another NF-kappaB-regulated gene, is not equally
affected, suggesting a promoter specificity of PV with TSA stimulation.
Taken together, these data suggest that TSA acts differently
depending on the NF-kappaB pathway and the targeted promoter in
question. This indicates that one overall histone deacetylase role is
to inhibit NF-kappaB activation by molecular mechanisms specific of
the stimulus and the promoter.
Dissemination of carcinoma cells requires the pericellular degradation of the extracellular matrix, which is mediated by membrane type 1-matrix metalloproteinase (MT1-MMP). In this article, we report ...a co–up-regulation and colocalization of MT1-MMP and atypical protein kinase C iota (aPKCι) in hormone receptor-negative breast tumors in association with a higher risk of metastasis. Silencing of aPKC in invasive breast-tumor cell lines impaired the delivery of MT1-MMP from late endocytic storage compartments to the surface and inhibited matrix degradation and invasion. We provide evidence that aPKCι, in association with MT1-MMP–containing endosomes, phosphorylates cortactin, which is present in F-actin–rich puncta on MT1-MMP–positive endosomes and regulates cortactin association with the membrane scission protein dynamin-2. Thus, cell line-based observations and clinical data reveal the concerted activity of aPKC, cortactin, and dynamin-2, which control the trafficking of MT1-MMP from late endosome to the plasma membrane and play an important role in the invasive potential of breast-cancer cells.
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