Background: The suppressors of cytokine signaling (SOCS) are inhibitors of cytokine signaling; methylation of SOCS-3 has been implicated in the tumorigenesis of liver and head and neck cancer.
Aims: This study was performed to elucidate the role of SOCS-1 and SOCS-3 in Barrett adenocarcinoma and its precursor lesions.
Methods: After microdissection, DNA of 19 Barrett's adenocarcinomas, 56 Barrett's intraepithelial neoplasias (n = 29 low grade [LGIN] and n = 27 high grade [HGIN]), 30 Barrett's mucosa without neoplasia, 20 samples of normal squamous, gastric epithelium as well as four cell lines were studied by using methylation- specific PCR (MSP) for the SOCS-1 and SOCS-3 promoter. The presence of SOCS-3 mRNA transcripts was confirmed by semiquantitative real-time PCR, and the SOCS-3 protein was analyzed immunohistochemically.
Results: In normal squamous epithelium and normal gastric mucosa, neither SOCS-3 nor SOCS-1 methylation was observed. In Barrett's mucosa without intraepithelial neoplasia, SOCS-3 methylation occurred in 4/30 cases (13%) whereas SOCS-1 was unmethylated. A hypermethylated SOCS-3 promotor was found in 14/19 Barrett's adenocarcinoma (74%) and in 20/29 high and 6/27 low grade intraepithelial neoplasias (69% and 22%, respectively). SOCS-1 promoter hypermethylation occurred in 8/19 adenocarcinoma (42%) and in 6/29 high grade and 1/27 low grade intraepithelial neoplasias (21% and 4%, respectively). Methylation of the SOCS-3 promoter correlated with downregulation of SOCS-3 transcripts and protein expression in these tumors and various cell lines. In the cell lines tested, SOCS-3 and SOCS-1 transcripts increased upon treatment with the demethylation compound 5-aza-2-deoxycytidine (5-AZA- DC).
Conclusions: These data indicate, that promoter methylation and subsequent transcript downregulation of SOCS-3 transcripts and, to a much lesser extent, SOCS-1 are involved in the multistep carcinogenesis of Barrett's adenocarcinoma.