Human Prostate Epithelial Cells Secrete The Tumor Suppressor Maspin As A Soluble And Exosome-Associated Protein.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Maspin, an epithelial-specific member of the serine protease inhibitor superfamily, inhibits tumor invasion and metastasis. Overall maspin expression is downregulated or lost in invasive and metastatic carcinomas. Maspin subcellular distribution among the nuclear, cytoplasmic and extracellular compartments is differentially regulated during tumor progression. Extracellular maspin has been shown to inhibit tumor cell invasion and motility in vitro. Also, recombinant maspin was shown to inhibit endothelial cell tube formation in vitro and tumor-angiogenesis in vivo. To date, the mechanisms governing maspin trafficking remain unclear. In the current study, we aim to investigate the mechanism and biological significance of maspin secretion. Normal and tumor cells known to secrete maspin, were treated with or without drugs targeting classical or non-classical secretory pathways. The CM were collected and analyzed for soluble and exosome-associated proteins. We also utilized atomic force microscopy to characterize the physical characteristics of exosomes. We found maspin as a soluble protein in the CM. Maspin secretion was not inhibited by the drug treatments. In fact, maspin secretion increased under drug treatment targeting the classical secretory pathway. Furthermore, maspin was detected in the exosomes. Under drug treatment, the overall increase in maspin secretion was accompanied by an increase in detection of maspin in the exosomes. Based on the drug treatment-induced changes in maspin's secretion patterns, we speculate that maspin is secreted via a non-classical pathway. In addition, we provide the first evidence that maspin is secreted inclusively as both a free and an exosome-encapsulated molecule in normal and tumor cells. The existence of extracellular maspin as a free and an exosome-associated molecule implies a dual role for maspin in the tumor microenvironment. These novel findings are currently under investigation since the tumor suppressive activity of exosome-associated maspin may be of particular significance in cell-cell communication, and tumor suppressive activity of free maspin may be associated with extracellular matrix remodeling. Citation Format: Ivory S. Dean, Sijana Dzinic, Alexander Kaplun, Yi Zou, Guangzhao Mao, Shijie Sheng. Human prostate epithelial cells secrete the tumor suppressor maspin as a soluble and exosome-associated protein . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5067. doi:10.1158/1538-7445.AM2013-5067