Background
Colorectal cancer (CRC) is one of the leading causes of death by cancer worldwide and in need of novel potential diagnostic biomarkers for early discovery.
Methods
We conducted a two-step study. We first employed bioinformatics on data from The Cancer Genome Atlas to obtain potential biomarkers and then experimentally validated some of them on our clinical samples. Our aim was to find a methylation alteration common to all clusters, with the potential of becoming a diagnostic biomarker in CRC.
Results
Unsupervised clustering of methylation data resulted in four clusters, none of which had a known common genetic or epigenetic event, such as mutations or methylation. The intersect among clusters and regulatory regions resulted in 590 aberrantly methylated probes, belonging to 198 differentially expressed genes. After performing pathway and functional analysis on differentially expressed genes, we selected six genes:
CEP55
,
FOXD3
,
FOXF2
,
GNAO1
,
GRIA4
and
KCNA5
, for further experimental validation on our own clinical samples. In silico analysis demonstrated that
CEP55
was hypomethylated in 98.7% and up-regulated in 95.0% of samples. Genes
FOXD3
,
FOXF2
,
GNAO1
,
GRIA4
and
KCNA5
were hypermethylated in 97.9, 81.1, 80.3, 98.4 and 94.0%, and down-regulated in 98.3, 98.9, 98.1, 98.1 and 98.6% of samples, respectively. Our experimental data show
CEP55
was hypomethylated in 97.3% of samples and down-regulated in all samples, while
FOXD3
,
FOXF2
,
GNAO1
,
GRIA4
and
KCNA5
were hypermethylated in 100.0, 90.2, 100.0, 99.1 and 100.0%, and down-regulated in 68.0, 76.0, 96.0, 95.2 and 84.0% of samples, respectively. Results of in silico and our experimental analyses showed that more than 97% of samples had at least four methylation markers altered.
Conclusions
Using bioinformatics followed by experimental validation, we identified a set of six genes that were differentially expressed in CRC compared to normal mucosa and whose expression seems to be methylation dependent. Moreover, all of these six genes were common in all methylation clusters and mutation statuses of CRC and as such are believed to be an early event in human CRC carcinogenesis and to represent potential CRC biomarkers.
Electronic supplementary material
The online version of this article (10.1186/s12920-019-0501-z) contains supplementary material, which is available to authorized users.