08. Histone modification may regulate S100A6 expression in gastric cancer

Background and Objectives: S100A6 has been implicated in a variety of biological functions as well as tumorigenesis. In this study, we investigated the expression status of S100A6 in gastric cancer and explored a possible association of its expression with histone modification.
Materials and methods: S100A6 expression was analyzed by immunohistochemistry to evaluate the prognostic efficacy of clinical outcomes in a cohort of gastric cancer patients. ChIP assay was performed to investigate the modification of histone H3. Moreover, trichostatin A (TSA) was used to detect whether inhibition of histone deacetylation would lead to transcriptional activation of the S100A6 gene promoter.
Results: Our results suggested that S100A6 expression was remarkably increased in 67.5% of gastric cancer tissues as compared with matched noncancerous tissues, and S100A6 is an independent prognostic predictor (P=0.026) significantly related to poor prognosis (P=0.0004). It has become ever more obvious that histone modification can contribute to gene regulation. We further examined whether the histone H3 modification plays a role in the expression of the S100A6 in gastric cancer cell lines and gastric cancer tissues. First, the expression of the S100A6 was detected in AGS, MKN45, KATO3, BGC823, and SGC7901, RF1 and RF48 cells. The real-time PCR and histocytochemistry results showed that the expression of S100A6 mRNA was significantly higher in the AGS, MKN45, KATO3, BGC823, and SGC7901 cells than RF1 and RF48 cells. The levels of acetylated histone H3 and acetylated histone H3 (lysine 9) bound to the S100A6 gene promoter were higher in S100A6 high-expressing cells such as AGS, SGC7901, BGC823, KATO3, and MKN45 than those in low-expressing cells such as RF1 and RF48, while trimethylated histone H3 (lysine 27) and trimethylated histone H3 (lysine 9) modification profiles were not significantly different between high- and low-expressing cells. Moreover, the average percentage of input signal of acetylated histone H3 was significantly different (P=0.043) between matched cancer and nonneoplastic mucosa. More acetylated H3 bound to S100A6 gene promoter was found in cancer tissues than that in matched nonneoplastic mucosa. Moreover, we then examined whether inhibition of histone deacetylation by use of trichostatin A (TSA) would also lead to transcriptional activation of the S100A6 gene promoter. Our results showed treatment of RF1 and RF48 cells with TSA was enough to increase the histone acetylation modification and to stimulate S100A6 expression. Whereas in the MKN45 cells (S100A6 highexpressing), the change of histone acetylation modification was not obvious and the S100A6 expression was increased slightly. The relative quantification of S100A6 mRNA increase in the TSA-treated RF1, RF48 was higher than that in MKN45 cells (P=0.01).
Conclusions: S100A6 is overexpressed in gastric cancer, histone H3 acetylation may regulate the S100A6 overexpression in gastric cancer.