Deciphering the role of CFTR in osteoblasts

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Background: The cystic fibrosis transmembrane conductance regulator (CFTR) is a protein localised on the apical membrane of epithelial cells where it contributes to their secretory functions by transporting chloride out of the cells. While the physiological role of CFTR as an ion channel is indisputable, recent evidence showing CFTR expression in non-epithelial cells, such as osteoblasts, raises the possibility that it, in addition to channel activity regulation, might have additional roles, apart from its channel activity. Indeed, the punctate intracellular distribution of CFTR in osteoblasts, contrasting with the predominantly apical localization observed in epithelia, is strongly suggestive of distinct cellular functions. Furthermore, work performed in various cell types has revealed that CFTR interacts physically with other proteins through its PDZ-binding motif and that such interactome may regulate downstream signalling pathways involved in cell proliferation and differentiation. Despite these observations, the function of CFTR in osteoblasts has never been thoroughly investigated and remains unclear. Our long-term objective is thus to investigate the function of CFTR in osteoblasts. ******Hypothesis: Guided by our preliminary data showing that CFTR expression increases with osteoblast differentiation, we postulate that CFTR, through its physical interaction with intracellular partners and regulation of downstream signalling pathways, inhibits osteoblast cell-cycle progression and facilitates osteoblast differentiation. ******Experimental approach and Specific Aims: Using murine osteoblasts at various stages of differentiation and experimental approaches combining molecular biology, protein biochemistry, fluorescent microscopy and proteomics, we will pursue the following specific aims:***Aim 1. To investigate whether -catenin interacts with CFTR in osteoblasts;***Aim 2. To identify CFTR-regulated signalling pathways involved in osteoblast proliferation and differentiation;***Aim 3. To identify new interacting partners of CFTR in osteoblasts through the mapping of the CFTR interactome. ******Impact: Collectively, the proposed experiments will advance our understanding of a fundamental cellular process, namely osteoblast differentiation, by establishing that the CFTR, through interactions with other proteins and the regulation of downstream signalling pathways, regulates cell differentiation. We believe this project will shed considerable light on a new function for the CFTR in the control of bone homeostasis.**