Interestingly, mRNAs have been observed to associate with actin filaments and it has been suggested that this may facilitate translation[7173]. find that cell shape regulates the expression of cytoskeletal proteins by controlling the subcellular localization of myocardin related transcription factor (MRTF)-A. Pharmacological inhibition of cytoskeletal tension or MRTF-A signaling blocks the acquisition of a myofibroblast phenotype in spread cells while overexpression of MRTF-A promotes the expression of cytoskeletal proteins for all cell shapes. These data suggest that cell shape is a critical determinant of myofibroblast development from epithelial cells. == Introduction == Myofibroblasts, specialized cells within the body that exert large contractile forces, mediate wound healing and upon aberrant activation contribute to the development of fibrosis and cancer [14]. The contractility of these cells is governed by specialized matrix adhesions [5] and distinct cytoskeletal organization characterized by contractile bundles of actin and myosin [6]. A hallmark of the myofibroblast phenotype is the expression of alpha smooth muscle actin (SMA), a cytoskeletal protein which promotes increased force production enabling myofibroblasts to close wound sites or to induce tissue contracture during disease. Elucidation of the factors that regulate the evolution and function of myofibroblasts may thus be useful for identification of therapeutic approaches to counteract the development of pathological conditions mediated by myofibroblasts. Epithelial Pindolol cells, if presented with appropriate cues, can transition to a myofibroblast phenotype through an epithelial-mesenchymal transition (EMT). Transforming growth factor (TGF)-1, a potent inducer of EMT, promotes the loss of epithelial features, including apico-basal polarity and intercellular contacts, and the gain of mesenchymal properties including increased migratory capacity and contractility. Furthermore, during EMT cells exhibit dramatic morphological changes. These phenotypic changes are accompanied by changes in gene expression patterns including reduced expression of epithelial markers such as E-cadherin and cytokeratins and upregulation of mesenchymal markers including vimentin [7]. Further progression of EMT can lead to the induction of a myogenic program Pindolol and thede novoexpression of SMA resulting in the development of myofibroblasts [8]. Adhesion to extracellular matrix (ECM) controls cell morphology and adhesion to some ECM components can regulate EMT [912]. Indeed, in some experimental systems cell morphological changes induce features of EMT [13,14]. Cell morphology can also be modulated by physical properties of the microenvironment including matrix rigidity [15]. Biophysical cues are implicated in the regulation of TGF1-induced EMT as rigid matrices promote EMT and compliant matrices block EMT in mammary, kidney, and lung epithelial cells [9,16]. A recent study demonstrated that micropatterned epithelial cells exhibit high expression levels of cytokeratins across a range of cell spread areas and that TGF1 treatment induces downregulation of cytokeratins and upregulation of vimentin across the same range of cell spread areas [17]. However, it is not clear whether TGF signaling and cell shape together regulate the induction of myogenic and cytoskeletal regulatory proteins during the development of myofibroblasts from epithelial cells. Serum response factor (SRF) regulates the transcription of genes associated with adhesion and differentiation [1820] and has been implicated in the control of the myofibroblast phenotype [21,22]. The transcriptional activity of SRF is regulated by a variety of cofactors, including the myocardin-related transcription factor (MRTF) family members MRTF-A and -B (also known as MAL, BSAC, and MKL1/2) [20]. The subcellular localization and activity of MRTFs are in part controlled by their association with monomeric actin (G-actin). Shifts in actin polymerization induce dissociation of MRTFs from G-actin thus allowing for MRTFs to localize to Pindolol the cell nucleus to interact with SRF to promote gene expression. MRTFs play an important role in regulating a variety of cell fates and behaviors including EMT [21,2326], experimental metastasis [27], and myofibroblast activation in response to myocardial infarction [28]. Previous studies have found that the nuclear localization of MRTF-A is sensitive to endogenous RPS6KA6 and exogenous forces [24,2932]. Cell shape can modulate cytoskeletal tension, thus, MRTF signaling during TGF1-induced EMT may be promoted by changes.