Periostin promotes cell cycle in lung fibroblasts

Idiopathic pulmonary fibrosis (IPF) is a devastating disease with only three to five years of the median survival. Fibroblast proliferation is a hallmark of IPF as well as secretion of extracellular matrix proteins from fibroblasts. However, it is still uncertain how IPF fibroblasts acquire the ability to progressively proliferate. Periostin is a matricellular protein that is highly expressed in the lung tissues of IPF patients and plays a critical role in the pathogenesis of pulmonary fibrosis. However, it remains undetermined whether periostin affects proliferation of lung fibroblasts. In this study, we first comprehensively tried to identify periostin-dependently expressed genes in lung fibroblasts finding that many cell-cycle–related genes are involved in the gene profile. We confirmed that periostin silencing downregulates expression of several cell-cycle–related molecules including the cyclin family, the CDK family, the E2F family, and the transcriptional factors such as B-MYB and FOXM1 in lung fibroblasts. Accordingly, periostin silencing slowed proliferation of lung fibroblasts and affects the distribution of cell cycle particularly at the G1/S checkpoint and drives the cells into G1 arrest. Lung fibroblasts derived from IPF patients also required periostin for maximum proliferation. Moreover, CP4715, a potent inhibitor against integrin V3, a periostin receptor, downregulated proliferation along with expression of cell-cycle–related genes in IPF lung fibroblasts as well as normal lung fibroblasts. These results demonstrate that periostin plays a critical role in proliferation of lung fibroblasts and provide us a beneficial basis to apply the inhibitors against the periostin/integrin V3 interaction to IPF patients. To comprehensively identify genes expressed dependently on periostin in lung fibroblasts, we compared the gene expression profiles with or without knockdown of periostin in lung fibroblasts (MRC-5 cells). MRC-5 cells were transfected with 10 nM periostin siRNA for 48 h.