Quantitative secretome analysis reveals the interactions between epithelia and tumor cells by in vitro modulating colon cancer microenvironment

In tumor microenvironment, interactions among multiple cell types are critical for cancer progression. Secreted proteins are responsible for crosstalk among these cells within tumor microenvironment. To elucidate the interactions of tumor and epithelia, we co-cultured colon cancer cell line HT29 with normal human colon mucosal epithelial cell line NCM460 to mimic tumor microenvironment in vitro and investigated the differential expression pattern of secretome. A quantitative proteomics approach based on stable isotope labeling by amino acids in cell culture (SILAC) and LC-mass spectrometry was used for secretome analysis. Totally 45 proteins were altered over 2-fold in co-cultured cellular supernatants between equal amounts of NCM460 and HT29 cells, compared with mono-cultured conditions. These differential secreted proteins involve in multiple tumor-associated biological functions. The secretion level and acting pattern of acrogranin, IGFBP6 and vimentin were changed along with different co-cultured cell number ratios between NCM460 and HT29 cells, simulating early, middle or advanced stage of colon cancer. Therefore, a quantitative secretome profiling based on a co-culture system can track secreted protein changes and their associated biological roles between tumor and epithelia, which gives a new insight on communications between tumor and epithelia as well as cancer biotherapy by inhibiting cell interactions. Biological significance Tumor microenvironment is a complex system and comprised of cancer cells and host stromal cells. The growth and progression of tumor have been recognized were affected by multidirectional interactions of secreted proteins (secretome), which were produced by the cells within tumor microenvironment. Focus on general secreted molecules of living cells via proteomic tools, is promising for investigating cell communication. Stable isotope labeling by amino acids in cell culture (SILAC) is a metabolic labeling strategy for quantitative analysis, which is gaining popularity because of its ease of implementation, the high quality of quantitative data obtained, robustness and compatibility with existing experimental workflows. Therefore, SILAC-based quantitative secretome analysis was employed for investigating interactions between epithelia and tumor by in vitro modulating colon cancer microenvironment with established co-culture system, which simplified the complexity of cancer microenvironment also tracked secreted protein changes and their associated biological roles between epithelia and cancer cells. A series of tumor associated secreted proteins was quantitated and investigated in our study. So, the results give a new insight on communications between tumor and epithelia as well as cancer biotherapy by inhibiting interactions of them. (c) 2013 The Authors. Published by Elsevier B.V. All rights reserved.