Abstract
Purpose In most cases, the carcinogenesis of colorectal cancer (CRC) follows the normal-adenoma-carcinoma (N-A-C) sequence. In this study, we aimed to identify the key proteins in the N-A-C sequence. Methods Differentially expressed proteins (DEPs) in normal, adenoma, and carcinoma tissues were identified using the Tandem Mass Tag- (TMT-) based quantitative proteomics approach. The landscape of proteomic variation in the N-A-C sequence was explored using gene set enrichment analysis (GSEA) and Proteomaps. Key proteins in the N-A-C sequence were identified, verified, and validated based on our proteomic data, external proteomic data, and external transcriptomic data in the ProteomeXchange, CPTAC, GEO, and TCGA databases. The prognostic value of the key proteins in our database was evaluated by univariate and multivariate Cox regression analysis. The effects of the key proteins on adenoma organoids and colorectal cancer cells were explored in functional studies. Results Based on our proteomic profiles, we identified 1,294 DEPs between the carcinoma (CG) and normal (NG) groups, 919 DEPs between the adenoma group (AG) and NG, and 1,030 DEPs between the CG and AG. Ribosome- and spliceosome-related pathways were mainly enriched in the N-A process. Extracellular matrix- and epithelial-mesenchymal transition- (EMT-) related pathways were mainly enriched in the A-C process. RRP12 and SERPINH1 were identified, verified, and validated as candidate key proteins in the N-A and A-C processes, respectively. Furthermore, RRP12 and SERPINH1 knockdown impeded the viability and proliferation of adenoma organoids. SERPINH1 was validated as a risk factor for disease-free survival (DFS) based on the TCGA and our database, whereas RRP12 did not show prognostic value. SERPINH1 knockdown was accompanied by EMT-related protein variation, increased apoptosis, and reduced proliferation, invasion, and migration of CRC cells in vitro. Conclusions RRP12 and SERPINH1 may play an important role in the N-A and A-C processes, respectively. Furthermore, SERPINH1 showed favorable prognostic value for DFS in CRC patients. We speculate that SERPINH1 might promote not only the A-C process but also the development of CRC.
Highlights
Colorectal cancer (CRC) is the second leading cause of cancer deaths, accounting for approximately 9.2% of all cancer deaths annually [1]
It is widely accepted that the normal mucosa to adenoma (N-A) and adenoma to carcinoma (A-C) processes represent two phases of colorectal carcinogenesis driven by different events in a sequential manner [5]. erefore, we explored the proteomic variation enrichment in the two phases separately using the following methods: (1) paired comparison of the proteomic profiles between NA and adenoma group (AG) and between AG and carcinoma group (CG) by gene set enrichment analysis (GSEA) and (2) identification of the biological processes and pathways enriched in the Differentially expressed proteins (DEPs) associated with the N-A and A-C processes
EMT is one of the most crucial processes in the metastasis of colorectal cancer. erefore, we explored the correlation between SERPINH1 expression levels and the EMT phenotype based on the clinical proteomic tumor analysis consortium (CPTAC) database. e expression level of SERPINH1 was shown to be significantly higher in the EMTgroup compared with that in the epithelial group (Figure 6(g))
Summary
Colorectal cancer (CRC) is the second leading cause of cancer deaths, accounting for approximately 9.2% of all cancer deaths annually [1]. 85% of CRC cases evolve following the normal-adenoma-carcinoma (N-A-C) sequence, which is based on the accumulation of genetic mutations and chromosomal instability (CIN) [2]. E canonical model of the colorectal carcinogenesis requires chronological gene mutations. Inactivation of the adenomatous polyposis coli (APC) initiates the progression from normal mucosa to adenoma, and Kras and TP53 mutation occurs followed by multiple additional gene mutations [3]. Journal of Oncology cannot be accounted for by the fundamental rate of genetic changes but require the development of intrinsic genomic instability for the new mutations to arise [4]. Based on the major principle of carcinogenesis, the majority of studies on colorectal cancer have employed a genomic analysis approach to explore the N-A-C sequence [6,7,8,9,10,11]. 2.5% to 5.6% of cases progress to advanced adenoma (≥1 cm in size, tubulovillous or villous adenoma, high grade dysplasia), which is associated with a high risk of malignant transformation [14, 15]
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