Placenta-specific 9 () is a putative secreted protein that was first discovered in the context of embryogenesis. The expression pattern of during embryogenesis, together with the results of recent reports, suggest that may play a role in the liver development. The present study was conducted to investigate the secretory characteristics of and its potential role in liver cell physiology. Immunofluorescence was employed to identify the subcellular distribution of Cellular proliferative activity was analyzed by MTT assay and cell colony formation. The cell cycle distribution of was analyzed by flow cytometry, and a functional analysis was performed using L02 cells following their stable infection with a lentivirus over-expressing is a novel protein that is localized to the cytoplasm and may be secreted through the classic endoplasmic reticulum-Golgi route. The overexpression of inhibits cell growth and induces G2/M phase arrest. Our findings reveal a novel role for in regulating cell growth.