Abstract 625: DNA mismatch repair protein MLH1 induces apoptosis in human prostate cancer.
Authors: Fukuhara Shinichiro , Chang Inik , Chiyomaru Takeshi , Majid Shahana , Saini Sharanjot , Yamamura Soichiro , Arora Sumit , Shahryari Varahram , Ueno Koji , Hirata Hiroshi , Deng Guoren , Dahiya Rajvir , Tanaka Yuichiro 
Published: August 2014

Prostate cancer is one of the most common malignancies in men and ranks the second most common cause of cancer-related deaths. Mismatch repair (MMR) enzymes act as proofreading complexes that maintain the genomic integrity and MMR-deficient cells show an increased mutation rate. MMR is essential to the survival of the cell and health of the individual. Recent studies have shown that MMR influence the regulation of tumor development in various cancers, such as colon, ovarian, and others, but their impact on prostate cancer growth has not been investigated thus far. One important gene in the MMR complex is MutL homolog 1 (MLH1). The aim of the present study was to investigate the effect of MLH1 on growth properties of prostate cancer. MLH1 levels were characterized in patients with prostate cancer. Immunohistochemical analysis was done on tissue microarrays (TMAs) by using a monoclonal antibody for MLH1. TMAs consisted of cores sampled from the center of donor tissue blocks from 36 prostate cancer cases of various Gleason's grades. Staining intensity was measured to estimate the expression level of MLH1 proteins in each core and compared. As MLH1 levels differed between grades of cancer, we then evaluated the functional effects of MLH1 on prostate cancer cells. Expression of MLH1 was initially measured in normal and cancerous prostate cell lines by real-time PCR and western blotting. Cancerous cells displaying the lowest levels of MLH1 as compared to normal cells was then transfected with MLH1 to determine gene effects on cell proliferation by utilizing the MTS assay, and apoptosis by flow cytometry. Immunohistochemical analysis showed patients with high Gleason's score to have reduced expression of MLH1 compared to those with low grade prostate cancer. To determine the role of MLH1 on prostate cancer cell growth, gene transfection studies were then performed. Of the various prostate cell lines, DU145 cells had dramatically reduced expression levels of MLH1 as measured by real-time PCR with no protein detected by western blotting, whereas levels were high in normal prostate cell lines. Interestingly, over-expressing the MLH1 gene in DU145 cells decreased cell proliferation and increased apoptosis compared to vector control. These results demonstrate MLH1 to protect against prostate cancer progression and to have a functional role by affecting apoptosis of prostate cancer cells.

Citation Format: Shinichiro Fukuhara, Inik Chang, Takeshi Chiyomaru, Shahana Majid, Sharanjot Saini, Soichiro Yamamura, Sumit Arora, Varahram Shahryari, Koji Ueno, Hiroshi Hirata, Guoren Deng, Rajvir Dahiya, Yuichiro Tanaka. DNA mismatch repair protein MLH1 induces apoptosis in human prostate cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 625. doi:10.1158/1538-7445.AM2013-625