Analysis of somatostatin receptors and somatostatin promoter methylation in human gastric cancer

Somatostatin (SST) is a gut peptide that is able to inhibit the growth of tumor cells in gastric cancer and other types of cancer. The present study investigated the mRNA and protein levels of SST and SST receptors (SSTRs) in human gastric cancer, and detected the DNA methylation of the SST promoter. The protein levels of SST were detected using a radioimmunoassay in 102 human gastric tissue specimens (51 pairs of samples from 51 gastric cancer patients, each pair of samples included a cancer tissue and a normal tissue sample). SST and SSTR mRNA expression was assessed by reverse transcription-PCR (RT-PCR), while SST promoter methylation was examined using quantitative methylation-specific PCR (qMSP) in 51 pairs of tissues. The association between SST protein and RNA levels and SST methylation and gastric cancer were also analyzed. The protein levels of SST were decreased in the gastric cancer group compared with those of the normal group (5.091±0.994 vs. 7.399±0.956 pg/mg; P<0.01). The RT-PCR analysis indicated that the mRNA levels of SST (0.218±0.183 vs. 0.456±0.331; P<0.001) and SSTRs in the gastric cancer group were lower compared with those of the normal gastric tissue group. The methylation proportion of SST was 45.1% (23/51) in the carcinoma group and 3.9% (2/51) in the normal group. In conclusion, SST promoter methylation is a common event in human gastric cancer and is connected with a decrease in SST protein and RNA levels and associated with gastric carcinogens.