We previously reported that gelsolin gene expression is reduced in various tumors. In an effort to gain further insights into the mechanism of gelsolin downregulation in tumors, we examined the in vivo properties of the gelsolin promoter in urinary bladder cancer cell lines. Neither mutation nor hypermethylation was responsible for gene silencing at the promoter. After exposure to trichostatin A (TSA), a histone deacetylase inhibitor, gelsolin promoter activity was markedly enhanced in the cancer cells, not in cells derived from normal tissue. Chromatin immunoprecipitation assays revealed that both histones H3 and H4 were hypoacetylated in the promoter region of the cancer cells, and the accumulation of acetylated histones was detected by TSA treatment.
Key words: gelsolin; gene silencing; dimethylsulfate hypersensitivity; bladder cancer; in vivo footprintingCancers occur due to the accumulation of abnormalities in gene function. While many of them are genetic (mutation and deletion), epigenetically mediated changes in gene expression have been increasingly investigated. Hypermethylation of CpG islands, which are GC-rich regions usually located at the 5Ј end of genes, results in alterations in the histone acetylation and methylation status around gene promoter regions. Aberrant cytosine methylation and concomitant histone modifications play important roles in the repression of over half of the tumor suppressor genes during malignant transformation. 1,2Previously, we reported that the expression of gelsolin, an actin-regulatory protein, is frequently silenced in various cancers, including stomach, colon, urinary bladder and lung, and that gelsolin functions as a tumor suppressor. [3][4][5][6][7] These findings were also demonstrated in breast and prostate cancers. 8,9 On the other hand, a subset of non small cell lung cancers is characterized by high expression levels of gelsolin correlated with lymphatic invasion, 10 and there was a gradual increase in gelsolin with an increase in tumor grade and stage in uroepithelial carcinoma. 11 Gelsolin induced invasion of epithelial cells as well as colon adenocarcinoma cells. 12 It is therefore possible that a decrease in expression during a particular stage is followed by an increase during another stage. To understand roles of gelsolin in the whole process of tumorigenesis, mechanisms for both down-and upregulations should be analyzed. In breast cancers, gelsolin genes were not mutated; however, epigenetic changes in the chromatin structure were responsible for the deficiency. 13 Histone deacetylase (HDAC) inhibitors, such as trichostatin A (TSA) and apicidin, selectively induced the expression of gelsolin. 14,15 Recent studies have suggested a new mechanism for cell-specific gene regulation linking nuclear architecture, chromatin structure and functional organization of DNA sequences. 16 In an effort to determine the molecular basis of gelsolin downregulation in urinary bladder cancer and to better understand the carcinogenic process, we investigated the gelsolin prom...