Characterization of proteins secreted by pancreatic cancer cells with anticancer drug treatment in vitro.

Pancreatic cancer is one of the most lethal cancers, with an incidence equaling mortality. It is a heterogeneous group of neoplasms in which pancreatic ductal adenocarcinoma is most common. Pancreatic cancer cannot be cured even if detected early. When treatment is initiated, a suitable method of administration of anticancer drugs must be chosen. Anticancer drugs kill tumor cells. However, side effects including initiation are problematic in anticancer drug therapy. Improved methods for the diagnosis of side effects of pancreatic cancer by using sensitive and specific tumor markers are highly desirable. Therefore, efficient strategies for biomarker discovery are urgently needed. Here, we present an approach based on direct experimental access to proteins released by PANC-1 human pancreatic cancer cells in vitro. A two-dimensional (2-D) map and catalog of this subproteome, herein termed the secretome, were established comprising more than 1,000 proteins observed by '2-D difference in-gel electrophoresis analysis using cyanine dye'. We investigated 22 spots that were 1.20-fold upregulated and 31 spots that were 0.66-fold downregulated by gemcitabine chloride treatment. Proteins in these spots were identified by nano-high-performance liquid chromatography electrospray ionization time of flight mass spectrometry/mass spectrometry. Most secretome constituents were nominally cellular proteins. By mass spectrometry screening, 14-3-3 protein sigma (14-3-3 σ), protein S100-A8, protein S100-A9, galectin-7, lactotransferrin (lactoferrin, LF) precursor, serotransferrin (transferrin) precursor, and vitamin D binding protein precursor were identified. Western blotting confirmed the presence of 14-3-3 σ and LF. We found that upregulation of 14-3-3 σ was associated with apoptosis, and downregulation of LF was found to suppress tumorigenesis.