Abstract
The mammalian SWI/SNF chromatin remodeling complex, an essential epigenetic regulator, contains either a single Brm or BRG1 molecule as its catalytic subunit. We observed frequent loss of Brm expression but not of BRG1 in human gastric cancer cell lines. Treatment with histone deacetylase inhibitor rescued Brm expression, indicating epigenetic regulation of this gene, and an RNA interference-based colony formation assay revealed antioncogenic properties of Brm. Brm immunostaining of 89 primary gastric cancers showed an obvious reduction in 60 cases (67%) and a severe decrease in 37 cases (42%). Loss of Brm is frequent in the major gastric cancer types (well- or moderately-differentiated tubular adenocarcinoma and poorly-differentiated adenocarcinoma) and positively correlates with the undifferentiated state. Among the minor gastric cancer types, Brm expression persists in signet-ring cell carcinoma and mucinous adenocarcinoma, but a marked decrease is observed in papillary adenocarcinoma. Intestinal metaplasia never shows decreased expression, indicating that Brm is a valid marker of gastric oncogenesis. In contrast, BRG1 is retained in most cases; a concomitant loss of BRG1 and Brm is rare in gastric cancer, contrary to other malignancies. We further show that Brm is required for villin expression, a definitive marker of intestinal metaplasia and differentiation. Via regulating such genes important for gut differentiation, Brm should play significant roles in determining the histologic features of gastric malignancy.
Highlights
The incidence and mortality of gastric cancer has gradually fallen over the past few decades
We examined the expression of three major components of SWI/SNF (Brm, BRG1, and Ini1) in 27 gastric and colorectal cancer cell lines and found that 7 of 17 of the gastric cell types were strongly deficient in Brm (Fig. 1A)
It is intriguing that a deficiency in Brm is much more frequent in stomach cancer than in any other tumor type and is noteworthy that the BRG1 expression levels are mostly unaffected in the Brm-deficient gastric cancers, unlike other cancer types
Summary
The incidence and mortality of gastric cancer has gradually fallen over the past few decades. The development and progression of many cancers have been shown to involve a number of epigenetic disorders in addition to genetic defects. In this regard, it has been well established that. Global DNA hypomethylation is thought to occur during the early stages of tumor development in gastric as well as other tissues [3]. The roles of other factors involved in epigenetic regulation, such as histone modification and chromatin remodeling, remain largely unknown in relation to the development of gastric cancer
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