SIRT1 is expressed in prostatic adenocarcinomas and increases tumor cell invasion when overexpressed in DU145 cells

3509

SIRT1 is an NAD-dependent histone deacetylase that has been associated with salutary effects such as antiaging, neuroprotective, and cardioprotective actions. However SIRT1 may also have tumorigenic effects since SIRT1 has been reported to cause deactivation of p53 (Vaziri et al Cell 2001), activation of MAPK (Ota et al Oncogene 2005), and some of the epigenetic changes that occur in neoplasms appear to result from a tumor specific association of SIRT1 with Ezh2 in a histone modifying complex called PRC4 (Kuzmichev et al PNAS 2005). In an immunohistologic survey of 29 human prostate tumors, intranuclear staining of SIRT1 was present in all cases, however SIRT1 staining was also present in benign gland epithelial cells. Immunostaining of tissues from prostate carcinoma-prone transgenic mice (the TRAMP strain) showed that SIRT1 was present in about half of the epithelial cells in normal glands, in an increased fraction of cells in PIN lesions, and in essentially all the cells in the carcinomas. In vitro assays for invasion of collagen matrix (Matrigel) by DU145 cells are often used as a measure for malignant alterations involving this human prostate tumor cell line. Using Lipofectamine, DU145 cells were transfected with an expression vector containing SIRT1 tagged at the C-terminus with GFP. G418-selected subclones of stably transfected SIRT1-GFP-vector and empty-GFP-vector subclones were obtained. These cells were tested in transwell two chamber assays of Matrigel invasion stimulated by the chemokine SDF-1α. The percent invasion (Mean ± StanDev of triplicate tests) seen in this Matrigel invasion assay was: nonvector transfected DU145 cells (15 ± 3%), SIRT1-GFP- vector transfected DU145 cells (31 ± 5%), and empty-GFP-vector transfected DU145 cells (12 ± 4%). Work in progress will further examine the effects of modulating SIRT1 activity on the DU145 cell Matrigel invasion assay by using chemical activators and inhibitors of SIRT1 and by overexpression of a dominant negative mutant of SIRT1. In conclusion, our in vitro assay results indicate that SIRT1 overexpression can induce prostate cancer cell invasion and this suggests that SIRT1 could represent a therapeutic target for drugs aimed at blocking tumor progression.