Periostin is a secretory protein that has been suggested to function as a cell adhesion molecule and promote the invasiveness or growth rate of tumors. However, little is known about the association of its expression and epithelial to mesenchymal transition (EMT), which is considered to play a crucial role in cancer cell metastasis. Thus, the authors investigated whether periostin could be involved in the process of EMT and the role of this gene in pancreatic cancer development. The expression of periostin was observed mainly in stromal cells but very little in cancer cells by immunohistochemistry and real-time RT-PCR. In vitro, pancreatic stellate cells (PSCs) exhibited a much higher basal expression of periostin compared with cancer cells. Periostin secreted in the supernatant from 293T cells that expressed periostin (approximately 150 ng/ml) inhibited the migration of pancreatic cancer cells. Coculture assay revealed that periostin expression in PSC was induced by pancreatic cancer cells. To assess the direct role of periostin in pancreatic cancer cells, the authors generated pancreatic cancer cell lines that stably express periostin. The induced expression of periostin (to 150 ng/ml) altered the morphology of cancer cells, changing them from mesenchymal to epithelial phenotypes with the induction of epithelial markers and a reduction of mesenchymal markers, and showed reduced cell migration in vitro and formed smaller tumors as well as suppressed metastasis in vivo. On the other hand, high concentration of recombinant periostin (1 lg/ml) promoted cell migration with AKT activation. The findings suggest that periostin has biphasic effect on the development of pancreatic cancer. ' 2008 Wiley-Liss, Inc.Key words: pancreatic cancer; periostin; EMT; pancreatic stellate cell Pancreatic adenocarcinoma is one of the most malignant gastrointestinal tumors. Once pancreatic cancer is clinically evident, it progresses rapidly to develop metastatic lesions, frequently by the time of diagnosis. The pathogenic mechanisms that regulate the aggressive behavior of this cancer still remain to be clarified.Tumor metastasis is a multistep pathological process involved in the final phase of tumor development. During this process, epithelium-derived tumor cells undergo fibroblast-like transformation, referred to as epithelial-mesenchymal transition (EMT). 1,2 EMT is the process by which an epithelial cell shows transitory changes in cell structure and becomes a more motile mesenchymal cell with migratory properties during embryogenesis. This transition is considered to be an important event during malignant tumor progression and metastasis. [3][4][5] Periostin is a secretory protein that has been suggested to function as a cell adhesion molecule for preosteoblasts and to participate in osteoblast recruitment, attachment and spreading. 6,7 Recently, the expression of periostin has been implicated in the development of variety of carcinomas such as neuroblastoma, 8 epithelial ovarian cancer 9 and non-small cell lung carcinoma. 10 P...