Downregulation of EphA7 by hypermethylation in colorectal cancer

Abstract

A significant reduction of EphA7 expression in human colorectal cancers was shown using semiquantitative reverse transcription-polymerase chain reaction analysis in 59 colorectal cancer tissues, compared to corresponding normal mucosas (P ¼ 0.008), and five colon cancer cell lines. To investigate the mechanism of EphA7 downregulation in colorectal cancer, we examined the methylation status of the 5 0 CpG island around the translation start site in five colon cancer cell lines using restriction enzymes, methylation-specific PCR, and bisulfite sequencing and found evidence of aberrant methylation. The expression of EphA7 in colon cancer cell lines was restored after treatment with 5-aza-2 0 -deoxycytidine. Analysis of methylation status in totally 75 tumors compared to clinicopathological parameters revealed that hypermethylation of colorectal cancers was more frequent in male than in female (P ¼ 0.0078), and in moderately differentiated than in well-differentiated adenocarcinomas (P ¼ 0.0361). There was a tendency that hypermethylation in rectal cancers was more frequent than in colon cancers (P ¼ 0.0816). Hypermethylation was also observed in colorectal adenomas. This is the first report describing the downregulation of an Eph family gene in a solid tumor via aberrant 5 0 CpG island methylation. It provides the evidence that EphA7 gene is involved in human colorectal carcinogenesis.

Global DNA methylation profiling reveals silencing of a secreted form of Epha7 in mouse and human germinal center B-cell lymphomas

“…Similar results were obtained with the human embryonic kidney cell line 293T, consistent with a previous report (Wang et al, 2005). In contrast, MS-PCR demonstrated methylation of the EPHA7 promoter in 23 of the 31 informative patient lymphoma samples and the human pre-B-cell line, Nalm-6 (Figure 4a).…”

“…EPHA7 is highly upregulated in hepatocellular and lung carcinomas (Surawska et al, 2004). Conversely, EPHA7 is a target of DNA hypermethylation and silencing in colorectal cancer (Wang et al, 2005). To our knowledge, our results are the first to show that EPHA7 is a target of hypermethylation and silencing in mature B-cell lymphomas.…”

“…Individual clones were then sequenced. MS-PCR for the human EPHA7 promoter was performed as described previously (Wang et al, 2005). Primer sets amplified a 229-bp product located at the same genomic site (forward primers located at À432 to À413 and reverse primers located at À223 to À204, relative to the translational start site).…”

Overexpression of the receptor tyrosine kinase EphA4 in human gastric cancers

“…Overexpression of EphB2, ephrinB1, EphA2, and ephrinA1 has been reported in gastric cancer [11][12][13] . On the other hand, the concept that Eph receptors are oncogenes needs a new look on the basis of recent findings of downregulation of Eph receptors in certain types of cancer [14][15][16][17] . However, because functions of Eph receptors can overlap, loss of one receptor can be partially compensated for by other Eph receptors that have similar ligand-binding specificities and expression patterns [7] .…”

Downregulation of EphA1 in colorectal carcinomas correlates with invasion and metastasis

“…7 A number of Eph receptors and their ephrins ligands are implicated in carcinogenesis. [8][9][10][11][12][13][14][15][16] EphA1, the first member of Eph receptors tyrosine kinase, was isolated from erythropoietin-producing hepatocellular carcinoma cell lines and is located on chromosome 7q34. 17 It is widely expressed in normal tissues including lung, small intestinal, kidney, bladder, thymus, and colon.…”