Abstract LB-375: Inactivation of the deubiquitinase USP44 is an early event in the formation of colorectal cancer

Abstract

Abstract Colorectal cancer (CRC) develops from intraepithelial neoplasms known as adenomas. Genomic profiling of these premalignant lesions presents an opportunity to discover molecular changes that can lead to colorectal cancer. Some of the earliest changes are thought to be epigenetic, including hypermethylation of the promoters of key tumour suppressor genes. To identify such changes in colon cancer we performed whole genome DNA methylation profiling (MBD-Seq) on three adenomas and matched normal mucosa. We then validated epigenetic changes in a cohort of 105 adenomas using COBRA, bisulphite sequencing and quantitative RT-PCR. In each adenoma, we identified 1598, 556 and 331 promoter CpG islands respectively that were hypermethylated when compared with matched normal mucosa. Two of the three adenomas showed CpG island hypermethylation of the USP44 gene, a deubiquitinase previously shown to affect mitotic progression by deubiquitinating Cdc20, a regulator of the Anaphase Promoting Complex. In the absence of USP44, cells prematurely enter anaphase resulting in accelerated mitotic progression. Using COBRA and bisulphite sequencing we show that hypermethylation of USP44 occurred in 100% of 18 CRC cell lines, 79% of 105 adenomas, but in only 10% of 45 matched normal mucosa. In adenomas, USP44 hypermethylation correlated with a >2-fold decrease in gene expression. Reduced expression has also been reported in glioblastoma, B-ALL, breast, colorectal, esophageal, kidney and testicular cancer. We show that treatment of four CRC cell lines with the DNA demethylating agent 5-Aza-2′-deoxycytidine (5azaDC) resulted in a 10-250 fold increase in USP44 expression. In summary, we show that epigenetic inactivation of the deubiquitinase USP44 is a frequent and early event in the formation of colon cancer. Taken together with reports that USP44 expression is reduced in a range of solid organ and haematological malignancies, we propose that epigenetic inactivation of this gene may represent an important yet hitherto unrecognized event in tumour formation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-375. doi:1538-7445.AM2012-LB-375