Introduction
Colorectal cancer (CRC) is one of the most common malignant tumors worldwide with high morbidity and mortality [
1]. Estimated new cancer cases of CRC rank second and deaths rank the fifth of all cancers in 2022 in China [
2]. Early diagnosis-involved biomarkers may play a crucial role in improving the prognosis of patients with CRC and remain to be explored currently.
“Normal-adenoma-cancer-cancer metastasis” is the main pathway for the occurrence and development of sporadic CRC, during which a series of changes of cumulative genes and epigenetics might occur [
3,
4]. It has been shown in many that abnormal DNA methylation, including hypermethylated and hypomethylated states, is widespread in colorectal adenomas, and many abnormal methylated genes have been found, suggesting that the change of gene epigenetic inheritance, as a frequent early event, may affect the transition of colorectal adenomas to CRC, which may also serve as a biomarker for early diagnosis [
3,
5,
6]. However, traditional research methods are mainly limited to the discovery and detection of a single gene, unable to reveal the methylation status of the whole colorectal adenoma and CRC. There are deficiencies in the pathogenesis, early diagnosis, and risk assessment of colorectal adenoma and cancer [
7]. Therefore, the adoption of a new genomic methylation detection method is more conducive to a comprehensive analysis of the methylation profile of colorectal adenoma, further revealing its mechanism of action in colorectal adenoma and CRC development and discovering new methylation markers that may be used in the early diagnosis of adenoma and CRC.
Illumina Infinium 450K detection technology with powerful detection function, high throughput, and high sensitivity is a genome-wide methylation detection and analysis method. We aimed to find different methylation sites as new methylation markers in CRC and colorectal adenoma compared with the normal group using Illumina Infinium 450K methylation chip to detect and analyze the methylation spectrum of each group. Our results would provide new ideas and clues for investigating of pathogenesis and early diagnosis of colorectal adenoma and CRC.
Discussion
Early diagnosis with markers improves the prognosis of patients with CRC. DNA methylation was concerned to play an essential role in tumors occurrence, development, and metastasis. The characteristic methylation sites are of great significance for the diagnosis, typing, prognosis, and treatment of tumors including CRC. The gene CpG island promoter is often hypermethylated, leading to tumor suppressor gene silencing. DKK2 promoter methylation and related RNA status were suggested as biomarkers of CRC diagnosis [
8]. SDC2 and TFPI2 methylation, which was affected by tumor location, patient age, mutation load, and microsatellite instability (MSI), may be considered methylation markers for CRC detection [
9]. Promoter methylation-mediated repression of UNC5C and UNC5D correlated with poor progression-free and overall survival, which has good relation to diagnosis and prognosis in CRC [
10]. It was reported that many genes in colorectal cancer, such as p14, p16, p53, MGMT, APC, hMLH1, THBS1, E-cadherin, TIMP3, and GSTP1, have the presence of promoter CpG island hypermethylation, which is considered to be an early event in colorectal cancer [
11,
12]. Therefore, the methylation profile of CRC to reveal the correlation may be helpful for early diagnosis and prognosis of CRC.
Adopting a new genomic methylation detection method is more conducive to a comprehensive analysis of the methylation profile of CRC to further reveal its mechanism of action in the canceration process and discover new methylation markers for CRC diagnosis and prognosis. The methylation chip of Illumina Infinium 450K detection technology, covering a detection range of more than 485,000 CpG sites, is a genome-wide methylation detection analysis method with powerful detection function, has high throughput, has high sensitivity, and has the advantages of high accuracy and good repeatability [
13,
14]. Recently, the Illumina Infinium 450K methylation chip has been used to obtain many new methylation markers in CRC detection [
7]. In the present study, the Illumina Infinium 450K methylation chip was used to detect gene methylation in CRC and adenoma compared with the normal group. A large number of different methylation sites were found in CRC, including 65,535 (13.50%) differentially methylated markers in the adenoma group, among which 25,464 (38.86%) were hypermethylated markers and 40,071 (61.14%) were hypomethylated markers, covering a total of 8541 differentially methylated genes as well as 395,571 (8.15%) differential methylation marker probes which were compared between the sporadic colorectal cancer group and the normal group, including 21,710 (54.86%) hypermethylated markers and 17,861 (45.14%) hypomethylated markers, covering a total of 3551 differential methylation genes. 318,208 differential methylation markers were further found in the CRC and adenoma compared with the normal group in our study. The top 20 hypermethylated CpG sites mapping to 15 genes and 20 hypomethylated CpG sites mapping to 20 genes were identified according to Δβ values in the adenoma group, the results of which showed that the hypermethylated CpG sites were mainly located in the CGI region, and the hypomethylated CpG sites were primarily located in the gene body region. Our results suggested that hypermethylation may play a more important role in promoter regions, while hypomethylation may act in gene body regions and CpG off-island regions. Our results were consistent with the previous studies that the majority of methylation including hypomethylation and hypermethylation occurring during adenoma formation may play an essential role in tumorigenesis and progression [
15‐
17]. According to previous studies, some genes as diagnostic markers were selected through screening in colorectal adenoma and colorectal cancer. One hundred eighty-one hypermethylated genes and 28 hypomethylated genes were screened among the methylation markers obtained from the adenoma and normal control, and 151 hypermethylated genes and five hypomethylated genes were screened among the methylation markers of the colon cancer and normal control groups. Moreover, among the typical markers of adenoma and cancer, 61 hypermethylated genes and four hypomethylated genes were screened.
Abnormal methylation of tumor suppressor gene promoter is one of the most essential methylation events; it often leads to the silencing of tumor suppressor genes, which plays a vital role in the occurrence and development of cancer. The distribution of gene promoter structure and CpG island structure were then compared with that of the normal group utilizing microarray data combined with bioinformatics analysis in the present study, the results of which showed that there were a large number of differential methylation markers in colorectal cancer and adenoma. One thousand eight hundred seventy differential methylated markers including 1524 hypermethylated markers and 346 hypomethylated markers were found in the gene promoter region in colorectal adenomas compared with the normal group. Among the top 20 promoter hypermethylated genes, 15 genes have been reported methylated including ten genes detected in bowel cancer and five genes detected in adenoma. Among the top 20 promoter hypomethylated genes, nine genes have been reported methylated, including five genes detected in bowel cancer and four genes detected in adenoma. GO and KEGG pathway analyses of 929 promoter differential methylated genes showed that they covered many different functional communities. GO analysis results showed that promoter differential methylated genes were mainly enriched in chemical synaptic transmission, nervous system development, extracellular matrix organization, extracellular matrix structural components, RNA polymerase II regulatory region sequence-specific DNA binding, sequence-specific DNA binding, plasma membrane, protein extracellular matrix, cell membrane, and other annotation topics. The KEGG pathway analysis showed that promoter differential methylation genes are mainly involved in ligand-receptor interactions, nicotine addiction, calcium signaling, and other signal transduction pathways of neural activity. These results indicate that there are many types of genes involved in the regulation of signal transduction pathways in the occurrence and development of CRC. Still, the specific mechanisms need to be further studied.
Based on the results of the methylation chip of Illumina Infinium 450K detection and bioinformatic analysis, five hypermethylated genes, ZNF471, SND1, SPOCK1, FBLIM1, and OTX1, were selected for further investigation in the colorectal adenoma, CRC, and control normal tissues in our study. Our results showed that all the genes of ZNF471, SND1, SPOCK1, FBLIM1, and OTX1 methylation with the area under receiver operating curve (ROC) more than 0.90 were significantly high in the colorectal adenoma and CRC compared with the normal group. ZNF471 methylation was found in tongue squamous cell carcinoma and may be served as a diagnostic marker in the previous study [
18]. In another study, hypermethylation of the ZNF471 gene promoter was inversely correlated with its expression, and overexpression of ZNF471 inhibited EMT and acted as a tumor suppressor with diagnostic and prognostic significance in cervical cancer [
19]. Our results similarly indicated that ZNF471 methylation level was higher in CRC and colorectal adenoma than the normal group which suggested that our results for ZNF471 appear consistent with the above previous study and indicate this gene might display good diagnostic value as a tumor suppressor for both colorectal cancer and adenomas. As an N6-methyladenosine (m6A) reader, SND1 is associated with methylation and can modify mRNA and regulate target mRNA stability [
20]. SND1 expression was increased in tumors such as bladder cancer [
21], glioma [
22], and ovarian cancer [
23] and correlated with proliferation and metastasis as well as chemoresistance. As previously reported, SND1 hypermethylation was found in CRC, which was consistent with our results of the present study [
7]. SPOCK1 was significantly highly expressed in liver cancer [
24], pancreatic cancer [
25], and colon cancer cells [
26] and correlated with tumor immune infiltrates in colorectal cancer as one of the valuable prognostic biomarkers [
27]. SPOCK1 was reported to connect with tumor immune infiltrates and may be a useful prognostic biomarker and act a carcinogenic gene in CRC. SPOCK1 hypomethylation was found in the placentas of women with the HbSS genotype. The promoter CpG islands of SPOCK1 were hypermethylated and promoted tumor progress in CRC [
26,
28] similar to our research. FBLIM1 was mentioned to enhance oral cancer malignancy in a previous study [
29] and may contribute to the diagnosis of hepatocellular cancer [
30]. FBLIM1 was hypomethylated and could reduce cell proliferation in non-alcoholic fatty liver disease [
31]. In our study, hypermethylated FBLIM1 was first found in CRC and colorectal adenoma and the role of FBLIM1 in tumor development and progress is worth further study. As previously reported [
32,
33], OTX1 was hypermethylated in cancers such as lung, squamous cell carcinomas and breast cancer. Hypermethylated OTX1 was detected in our study, which may be associated with its oncogene function in CRC similar to a previous study that OTX1 promotes CRC progression [
34]. Our results indicated that ZNF471, SND1, SPOCK1, FBLIM1, and OTX1 methylation may be useful in diagnosing colorectal cancer and adenoma. However, the diagnostic value of each marker has been preliminarily analyzed presently. The relationship between the above markers and clinicopathological factors in colorectal cancer and adenoma and the mechanism in the occurrence and development of tumors is still worthy of investigation in our further study.
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