fibroblasts has revealed a variety of roles for these cytokines in the regulation of the fibrotic process, such as mitogenic activity, stimulation of extracellular matrix and alpha-smooth muscle actin gene expression, alteration of the contractile phenotype, production of proteases, protease inhibitors, chemokines, cytokines and growth 16494499 factors. Recently, microRNAs have emerged as a major class of gene expression regulators linked to many biological functions. Since the first miRNA was identified in Caenorhabditis elegans as an important factor for timing of larval development, thousands of miRNAs have been characterized including about 700 miRNAs in the human genome. MiRNAs are derived from a primary transcript called pri-miRNAs. The current model of maturation includes primary nuclear cleavage of pri-miRNAs by the RNase III endonuclease Drosha, which liberates pre-miRNA hairpins. Hairpins are exported from the nucleus to the cytoplasm, where they are AG1024 site cleaved by Dicer, another RNase III endonuclease. Dicer generates short RNA sequences of about 22-nucleotides. MiRNAs are then assembled with proteins of the Argonaute family into a ribonucleoprotein complex: miRNP, which exhibits binding complementarities with sequences usually located in the 39UTR of the target transcript. The formation of a complex between miRNP and a target leads to a repression of protein synthesis, often associated with mRNA degradation. Complex formation follows a set of rules that have been substantiated by experimental evidences. The major determinant of the interaction between the miRNA and its targets corresponds to a short stretch of 68 nucleotides located 59 of the miRNA, called the ��seed”. This implies that one miRNA can theoretically interacts with hundreds of mRNAs. Because several miRNAs can also target the same transcript, the miRNA regulatory network appears amazingly complex. To date, a small proportion of miRNA targets have been validated and the exact function of most miRNAs remains to be elucidated. Dysregulation of these molecules, including miR-155, has been recently identified in the pathogenesis of inflammatory diseases. MiR-155 is contained within the 17984313 only phylogenetically conserved region of BIC RNA. It has been linked to cancer, viral infection and immunity. MiR155 has been shown to be induced by proinflammatory stimuli such as lipopolysaccharides, Toll-like receptors, IL-1 and TNF-a in macrophages and dendritic cells. It has also been detected in synovial fibroblasts and rheumatoid synovial tissue. Multiple targets for miR-155 have been identified in several cell types and linked with the regulation of B and T cell differentiation, TLR signalling in inflammatory cells, or cellular adhesion in epithelial malignancies. To date, the putative function of miR-155 in fibroblasts remains poorly documented. The aim 
of the present study was to identify the repertoire of miRNA expressed in fibroblasts and to characterize their potential regulation by inflammatory cytokines. The detection of miR-155 into these cells led us to investigate its relationship with keratinocyte growth factor, a central factor in tissue repair that we are establishing as a direct target of miR155. Results miRNA expressed in normal lung fibroblast cells and their modulation by inflammatory cytokines We first analyzed the miRNA expression profile of normal human pulmonary fibroblasts and compared it with the miRNome of the alveolar epithelial cell line A549. Large differences d