Proteome Analysis Of Colorectal Carcinoma

Colorectal Cancer is one of the most common malignancies and the second leading cause of cancer death in western developed countries. In China, colorectal carcinoma, among other malignant diseases, occupies the fifth position in the mortality. And with the changes of life style and diet structure, the incidence of colorectal carcinoma still continues to increase.Colorectal carcinogenesis is a multistep process involving numerous gene alterations leading to the activation of oncogenes and the loss of function of tumor suppressor genes. In recent years, although considerable progresses in screening, diagnosis and treatment of colorectal carcinoma have been made, corresponding improvements in outcome of patients are not yet apparent. The main reason is to lack of the effective ways for early detection, prevention and treatments.The identification of tumor markers suitable for the early detection and diagnosis of cancer holds great promise to improve the clinical outcome of patients. Currently, there are many techniques available to screen the gene expression at thetranscriptional levels, such as mRNA differential display and cDNA microarray, etc.Although these methods can provide high-throughput information about the differential gene expression, there were no cost-effective biomarkers for early detection and evaluation of prognosis developed. There are several reasons why the numerous and extensive previous transcriptomic analyses of cancer may not haverevealed all tumor-associated proteins. These include (1) a lack of linear correlation between transcription and disease-associated protein levels; (2) translocation of a protein in the disease state rather than simply differential levels of the transcript; (3) levels of transcript cannot predict post-translational modification and interaction with other proteins.The analysis of cellular proteins expressed by a genome, by a cell or by a tissue, termed proteomics, represents a powerful analytic technology to enhance the study of the diagnosis, treatment and prevention of human disease. Combination of techniques including two dimensional gel electrophoresis (2-DE), mass spectrometry (MS), and bioinformatics, proteomics can be expected to show the changes in the protein expression profile during tumor development and progression, thus leading to the identification of new molecular markers and potential therapeutic targets. So, in the present study, we used proteomics-based techniques to analyze protein expression patterns of colorectal carcinoma and matched normal colorectal mucosa in order to detect the proteins whose expressions are associated with malignant transformation of colorectal mucosa. It is hoped that this information will yield further insight into the molecular mechanisms and signaling pathways underlying colorectal carcinogenesis and lead to the identification of key proteins that can be used for diagnostic, prognostic and therapeutic purposes.Total proteins from 10 cases of colorectal carcinoma and their matched normal mucosa are separated by 2-DE and visualized by silver staining. The digitized images then were analyzed with PDQuest software in order to establish the differential expression profiles between the carcinoma and normal tissues.The differential expressed protein spots were cut from the gels using proteomework spot cutter and subjected to in-gel digestion with trypsin. The digested peptides' separation was conducted by a Finnigan LTQ MS coupled with a Surveyor HPLC system. And based on the MS/MS raw data, protein identification was performed by application of theSEQUEST search program to the SWISS PROT human non-redundant protein database (filter parameters: the Xcorr 1+≥1.9, 2+≥2.2, 3+≥3.7 and DelCN≥0.1).In the results, 35 protein spots showed significant changes in colorectal carcinoma compared to normal colorectal carcinoma. 15 proteins were found to be up-regulated and 20 proteins were down-regulated in the tumour tissues (expression regulation more than 5-fold). 14 of these proteins were identified by tandem mass spectrometry...