Placenta-specific 9, a putative secretory protein, induces G2/M arrest and inhibits the proliferation of human embryonic hepatic cells

Abstract

Background: Placenta-specific 9 (Plac9) is a putative secreted protein that was first discovered in the context of embryogenesis. The expression pattern of Plac9 during embryogenesis, together with the results of recent reports, suggest that Plac9 may play a role in the liver development. The present study was conducted to investigate the secretory characteristics of Plac9 and its potential role in liver cell physiology. Methods: Immunofluorescence was employed to identify the subcellular distribution of Plac9. Cellular proliferative activity was analyzed by MTT assay and cell colony formation. The cell cycle distribution of Plac9 was analyzed by flow cytometry, and a functional analysis was performed using L02 cells following their stable infection with a lentivirus over-expressing Plac9. Results: Plac9 is a novel protein that is localized to the cytoplasm and may be secreted through the classic endoplasmic reticulum-Golgi route. The overexpression of Plac9 inhibits cell growth and induces G2/M phase arrest. Conclusion: Our findings reveal a novel role for Plac9 in regulating cell growth.

Proteomic analysis reveals that Placenta-specific 9 induces cell proliferation and motility programs in human bronchial epithelial cells

“…Consistently, MTT and colony formation experiments provided clear evidence that the overexpression of Plac9 could inhibit cell proliferation. The result was consistent with that our previous study showing that Plac9 overexpression inhibits proliferation of human embryo liver cell line, L02 [25]. Furthermore, cell cycle distribution data showed that overexpression of Plac9 in 16HBE could increase S phase population and a corresponding decrease of cells in the G1 phase.…”

“…To explore the role of Plac9 in human bronchial epithelial pathogenesis, we constructed a stable Plac9overexpressing cell line (16HBE-GFP-Plac9) by transfecting the lentiviral Plac9 vector, which expressed both GFP and Plac9 under the control of the constitutive CMV promoter, into the 16HBE cells and a control line (16HBE-GFP) stably expressed only GFP as previously described [25]. Figure 2A showed representative photo of the stable cell lines (16HBE-GFP-Plac9 and 16HBE-GFP).…”

“…Cells were treated with 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT, Sigma, St Louis, MO, USA) for cell proliferation assay as described [25,53]. Brie y, the cells were cultured by seeding 1,000 cells/well into a 96-well tissue culture plate.…”

“…This was performed similarly as previously described [25,53]. Brie y, approximately 10 6 16HBE cells were pelleted and xed with 70% ethanol for 1 hour at 4 ˚C.…”

“…Placenta-speci c 9 (Plac9) is a putative secretory protein, which was initially identi ed in human placenta [24,25]. In a previous study, we found that Plac9 could inhibit cell proliferation via altering cell cycle related proteins, phospho-c-Myc, cyclin B1, p21 Waf/Cip1 and phospho-Histone H3 [25]. To investigate if Plac9 play a role in lung epithelial cell function and pathology, we searched public databases for Plac9 and found reduced Plac9 expression in lung cancers.…”