Underexpression of LATS1 TSG in colorectal cancer is associated with promoter hypermethylation.

Abstract

To investigate large tumor suppressor 1 (LATS1) expression, promoter hypermethylation, and microsatellite instability in colorectal cancer (CRC). RNA was isolated from tumor tissue of 142 CRC patients and 40 colon mucosal biopsies of healthy controls. After reverse transcription, quantitative polymerase chain reaction (PCR) was performed, and LATS1 expression was normalized to expression of the ACTB and RPL32 housekeeping genes. To analyze hypermethylation, genomic DNA was isolated from 44 tumor CRC biopsies, and methylation-specific PCR was performed. Microsatellite instability (MSI) status was checked with PCR using BAT26, BAT25, and BAT40 markers in the genomic DNA of 84 CRC patients, followed by denaturing gel electrophoresis. Decreased LATS1 expression was found in 127/142 (89.4%) CRC cases with the average ratio of the LATS1 level 10.33 ± 32.64 in CRC patients vs 32.85 ± 33.56 in healthy controls. The lowest expression was found in Dukes' B stage tumors and G1 (well-differentiated) cells. Hypermethylation of the LATS1 promoter was present in 25/44 (57%) CRC cases analyzed. LATS1 promoter hypermethylation was strongly associated with decreased gene expression; methylated cases showed 162× lower expression of LATS1 than unmethylated cases. Although high-grade MSI (mutation in all three markers) was found in 14/84 (17%) cases and low-grade MSI (mutation in 1-2 markers) was found in 30/84 (36%) cases, we found no association with LATS1 expression. Decreased expression of LATS1 in CRC was associated with promoter hypermethylation, but not MSI status. Such reduced expression may promote progression of CRC.