posted on 2012-03-02, 00:00authored byHendrick Loei, Hwee Tong Tan, Teck Kwang Lim, Kiat Hon Lim, Jimmy
Bok-Yan So, Khay Guan Yeoh, Maxey C. M. Chung
Gastric cancer is the second leading cause of cancer
deaths worldwide,
and currently, there are no clinically relevant biomarkers for gastric
cancer diagnosis or prognosis. In this study, we applied a 2D-LC-MS/MS
based approach, in combination with iTRAQ labeling, to study the secretomes
of the gastric cancer cell lines AGS and MKN7. By performing a comparative
analysis between the conditioned media and the whole cell lysates,
our workflow allowed us to differentiate the bona fide secreted proteins from the intracellular contaminants within the
conditioned media. Ninety proteins were found to have higher abundance
in the conditioned media as compared to the whole cell lysates of
AGS and MKN7 cells. Using a signal peptide and nonclassical secretion
prediction tool and an online exosome database, we demonstrated that
up to 92.2% of these 90 proteins can be exported out of the cells
by classical or nonclassical secretory pathways. We then performed
quantitative comparisons of the secretomes between AGS and MKN7, identifying
43 differentially expressed secreted proteins. Among them, GRN was
found to be frequently expressed in gastric tumor tissues, but not
in normal gastric epithelia by immunohistochemistry. Sandwich ELISA
assay also showed elevation of serum GRN levels in gastric cancer
patients, particularly those with early gastric cancer. Receiver operating
characteristic (ROC) curves analysis confirmed that serum GRN can
provide diagnostic discriminations for gastric cancer patients