Abstract
Proteins, as executives of genes' instructions, are responsible for cellular phenotypes. Integrating proteomics with gene microarray, we conducted this study to identify potential protein biomarkers of colorectal cancer (CRC). Isobaric tags with related and absolute quantitation (iTRAQ) labeling mass spectrometry (MS) was applied to screen and identify differentially expressed proteins between paired CRC and adjacent normal mucosa. Meanwhile, Affymetrix U133plus2.0 microarrays were used to perform gene microarray analysis. Verification experiments included immunohistochemistry (IHC), western blot and enzyme-linked immunosorbent assay (ELISA) of selected proteins. Overall, 5469 differentially expressed proteins were detected with iTRAQ-MS from 24 matched CRC and adjacent normal tissues. And gene microarray identified 39859 differential genes from 52 patients. Of these, 3083 differential proteins had corresponding differentially expressed genes, with 245 proteins and their genes showed >1.5-fold change in expression level. Gene ontology enrichment analysis revealed that up-regulated proteins were more involved in cell adhesion and motion than down-regulated proteins. In addition, up-regulated proteins were more likely to be located in nucleus and vesicles. Further verification experiments with IHC confirmed differential expression levels of 5 proteins (S100 calcium-binding protein A9, annexin A3, nicotinamide phosphoribosyltransferase, carboxylesterase 2 and calcium activated chloride channel A1) between CRC and normal tissues. Besides, western blot showed a stepwise increase of annexin A3 abundance in normal colorectal mucosa, adenoma and CRC tissues. ELISA results revealed significantly higher serum levels of S100 calcium-binding protein A9 and annexin A3 in CRC patients than healthy controls, validating diagnostic value of these proteins. Cell experiments showed that inhibition of annexin A3 could suppress CRC cell proliferation and aggressiveness. S100 calcium-binding protein A9, annexin A3, nicotinamide phosphoribosyltransferase, carboxylesterase 2 and calcium activated chloride channel A1 were probably potential biomarkers of colorectal cancer. Annexin A3 was a potentially valuable therapeutic target of CRC.
Highlights
According to statistics of World Health Organization (WHO), colorectal cancer (CRC) is the third most common malignancy worldwide, with it being the fourth leading cause of cancer-related deaths [1]
Up-regulated proteins were more likely to be located in nucleus and vesicles
Expression levels of 24 proteins amongst the 245 proteins were significantly different (P
Summary
According to statistics of World Health Organization (WHO), colorectal cancer (CRC) is the third most common malignancy worldwide, with it being the fourth leading cause of cancer-related deaths [1]. Despite diagnostic and therapeutic advancements, CRC survival rate has hardly changed over the last two decades, with over 50% of patients having regional or distant metastasis at the time of diagnosis [1]. 5-year survival rates of patients www.impactjournals.com/oncotarget in different stages vary dramatically, from more than 90% in stage I to less than 10% in stage IV [1, 2]. As a heterogeneous disease, almost every patient of CRC has his/ her specific features. Early detection and individual treatment are of great significance for CRC. Screening and identifying new biomarkers are warranted to better diagnose, treat, predict and monitor recurrence of CRC
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