Secretome mapping of the human gut and microbiome from colorectal cancer patients

Abstract

In Malaysia, colorectal cancer (CRC) was the second most common cancer among men and women. The human gut is home to trillions of gut flora that thrive in delicate balance, which has helped maintain host’s gut homeostasis and mutually benefited both parties tremendously. However, a drastic perturbation of microbial composition has hampered gut homeostasis initiating tumour microenvironment for development of CRC. Hitherto, the study of human gut secretome is still scarce with gap of knowledge to be filled. The objective of this study was to profile secreted proteins released from the human gut and microbial of CRC patients and control with healthy colon morphology by assessing the secretome in stool samples, using mass spectrometry technology. Stool samples from 26 CRC and 20 controls were collected, homogenized and filtered prior to protein extraction and analysis. Samples were subjected for in solution digestion, followed by protein identification and quantification. Bioinformatics tools such as SPSS, MaxQuant, DAVID and String were used for statistical analysis, data visualization, functional annotations and prediction of protein interactions and pathways. We identified more human origin proteins in CRC as compared to control and inversely for proteins from microbial origin. The identified human proteins that are exclusive for CRC were mostly related to cell adhesion, intracellular signal transduction and angiogenesis functions and the top identified proteins were mapped to Stage I and II of CRC. The best prediction model for CRC was built upon the combination of human Huntingtin and RNA exonuclease 5 proteins. The model was sensitive but not specific in discriminating the control from CRC. Meanwhile, the top annotated KEGG pathway for human CRC-exclusive proteins was Hypoxia-inducible factor-1 (HIF-1). In addition, yeast proteins were topping the microbial CRC-exclusive proteins list, with the predicted protein interactions mapped to DNA repair, transcription regulation and ATP binding. In conclusion, gut flora and human colon released abundance of microbial proteins to the external environment possibly mediating various host-microbe reactions and responses in CRC.