Epithelial-mesenchymal transition (EMT) is a series of events in which fully differentiated epithelial cells undergo transition to a mesenchymal phenotype giving rise to fibroblasts and myofibroblasts. EMT is increasingly recognized as important process not only in development, but also in adult life: in wound healing, fibrosis, and the invasion and metastasis of tumor cells. The phenotypic conversion involves loss of epithelial polarity, loss of epithelial markers, loss of adherens and gap junctions, cytoskeletal reorganization, and transition to a spindle-shaped morphology concomitant with acquisition of mesenchymal markers and an invasive phenotype.
Cyclic nucleotide phosphodiesterases (PDE) comprise a family of related proteins, which can be subdivided into 11 families (PDE1-PDE11) based on their amino acid sequences, sensitivity to different activators and inhibitors and their ability to preferentially hydrolyze either cAMP (PDE4, 7, 8) or cGMP (PDE5, 6, 9) or both (PDE1, 2, 3, 10, 11). cAMP and cGMP are ubiquitous second messengers and consequently PDEs propagate many signaling pathways, including proliferation, migration, and differentiation.The present study was undertaken to evaluate the potential role of phosphodiesterases (PDE) in TGF-beta11 induced EMT in the human alveolar epithelial type-II cell line-A549. TGF-beta1 induced EMT was characterized by morphological alterations and by expression changes of EMT specific markers. TGF-beta1 treatment decreased expression of epithelial phenotype markers such as E-cadherin, cytokeratin-18, zona occludens-1 and increased expression of mesenchymal phenotype markers such as collagen I, fibronectin-EDA and alpha;-smooth muscle actin. Interestingly, a 2-fold increase in total cAMP-PDE activity following TGF-beta1 stimulation was found and attributed to increased PDE3 and PDE4 activities. Further mRNA and protein expression demonstrated upregulation of PDE4A and PDE4D isoforms in TGF-beta1 stimulated cells. Most importantly, treatment of TGF- beta1 stimulated epithelial cells with the PDE4 selective inhibitor Rolipram potently inhibited EMT changes in a Smad-independent manner by decreasing reactive oxygen species (ROS). Rolipram pre-treatment resulted in E-Cad restoration as well as in Fibronectin abolishement.
In addition, Rho kinase signaling activated by TGF- beta1 during EMT demonstrated as a positive regulator of PDE4. Our findings suggest that TGF-beta mediated up-regulation of PDE4 promotes EMT in alveolar epithelial cells.
Thus, targeting PDE4 isoforms may be a novel approach to attenuating EMT-associated lung diseases, such as pulmonary fibrosis and lung cancer.
Verknüpfung zu Publikationen oder weiteren Datensätzen
