Distinct methylation patterns of two APC gene promoters in normal and cancerous gastric epithelia

Abstract

The adenomatous polyposis coli (APC) tumor suppressor gene is mutationally inactivated in both familial and sporadic forms of colorectal cancers. In addition, hypermethylation of CpG islands in the upstream portion of APC, a potential alternative mechanism of tumor suppressor gene inactivation, has been described in colorectal cancer. Because a subset of both gastric and colorectal cancers display the CpG island methylator phenotype, we hypothesized that epigenetic inactivation of APC was likely to occur in at least some gastric cancers. APC exhibits two forms of transcripts from exons 1A and 1B in the stomach. Therefore, we investigated CpG island methylation in the sequences upstream of exons 1A and 1B, i.e., promoters 1A and 1B, respectively. We evaluated DNAs from 10 gastric cancer cell lines, 40 primary gastric cancers, and 40 matching non-cancerous gastric mucosae. Methylated alleles of promoter 1A were present in 10 (100%) of 10 gastric cancer cell lines, 33 (82.5%) of 40 primary gastric cancers, and 39 (97.5%) of 40 noncancerous gastric mucosae. In contrast, promoter 1B was unmethylated in all of these same samples. APC transcripts from exon 1A were not expressed in nine of the 10 methylated gastric cancer cell lines, whereas APC transcripts were expressed from exon 1B. Thus, expression from a given promoter correlated well with its methylation status. We conclude that in contrast to the colon, methylation of promoter 1A is a normal event in the stomach; moreover, promoter 1B is protected from methylation in the stomach and thus probably does not participate in this form of epigenetic APC inactivation.

Aberrant promoter methylation of multiple genes during multistep pathogenesis of colorectal cancers

“…13 In the present study, we determined the methylation status profile of 19 TSGs including RUNX3, 3OST2 and SOCS1 genes in nonmalignant colonic epithelia (NME), CAs and CRCs. The 19 genes were chosen for study because of their presumed or known roles in various cellular functions related to cancer development, including cell cycle regulation, tissue invasion and metastasis, JAK-STAT and TGF-b signal pathways, key components of retinoid activity, signal transduction, apoptosis, angiogenesis, putative cytokine, mitotic stress checkpoint, methyltransferase superfamily and O-sulfotransferase [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] and were selected from the 6 ''hallmarks of cancer'' 32,33 (Table I). The aims of our study were as follows: (i) to clarify the methylation status of TSGs not previously studied in detail in CRC and correlate methylation with gene expression; and (ii) to investigate the role of methylation during the multistage pathogenesis of CRC, comparing the tumor profile with that of CAs and NME.…”

The relationship between aberrant methylation and survival in non-small-cell lung cancers

“…The methylation status of five genes reported to be frequently methylated and silenced in tumour but not in nonmalignant lung tissues (p16 INK4a , RASSF1A, APC, RARb and CDH13) (Toyooka et al, 2003(Toyooka et al, , 2004 was determined by methylation-specific PCR (polymerase chain reaction) (MSP) assay using gene-specific primers (Herman et al, 1996;Cote et al, 1998;Tsuchiya et al, 2000;Burbee et al, 2001;Toyooka et al, 2001a). Briefly, 1 mg of genomic DNA was modified by sodium bisulphite, which converts all unmethylated cytosines to uracils residues while methylated cytosines remain unchanged.…”

Promoter Methylation and Silencing of PTEN in Gastric Carcinoma

“…Promoter methylation is a representative example of the transcriptional silencing of tumor suppressor genes (Baylin et al, 1998;Herman, 1999). Cancer-related genes, such as APC, p16, p15, E-cadherin, hMLH1, and TIMP3, have been inactivated by aberrant promoter methylation in gastric carcinoma (Leung et al, 2001;Tsuchiya et al, 2000). The role of PTEN in gastric carcinogenesis has not been reported to date.…”