Sodium butyrate inhibits the self-renewal capacity of endometrial tumor side-population cells by inducing a DNA damage response.

We previously isolated side-population (SP) cells from a human endometrial cancer cell line, Hec1, and determined that Hec1-SP cells have cancer stem-like cell features. In this study, we isolated SP cells and non-SP (NSP) cells derived from a rat endometrial cell line expressing human [(12)Val] KRAS (RK12V cells) and determined the SP phenotype. RK12V-SP cells showed self-renewal capacity, the potential to develop into stromal cells, reduced expression levels of differentiation markers, long-term proliferating capacity in cultures, and enhanced tumorigenicity, indicating that RK12V-SP cells have cancer stem-like cell features. RK12V-SP cells also display higher resistance to conventional chemotherapeutic drugs. In contrast, treatment with a histone deacetylases (HDAC) inhibitor, sodium butyrate (NaB), reduced self-renewal capacity and completely suppressed colony formation of RK12V-SP cells in a soft agar. The levels of intracellular reactive oxygen species (ROS) and the number of γH2AX foci were increased by NaB treatment of both RK12V-SP cells and RK12V-NSP cells. The expression levels of γH2AX, p21, p27, and phospho-p38 mitogen-activated protein kinase were enhanced in RK12V-SP cells compared with RK12V-NSP cells. These results imply that treatment with NaB induced production of intracellular ROS and DNA damage in both RK12V-SP and RK12V-NSP cells. Following NaB treatment, DNA damage response signals were enhanced more in RK12V-SP cells than in RK12V-NSP cells. This is the first article on an inhibitory effect of NaB on proliferation of endometrial cancer stem-like cells. HDAC inhibitors may represent an attractive antitumor therapy based upon their inhibitory effects on cancer stem-like cells.

Induction of senescence by progesterone receptor-B activation in response to cAMP in ovarian cancer cells.

OBJECTIVE: Progesterone receptor (PR) expression is a favorable prognostic marker in ovarian cancer. We previously demonstrated that the induction of PR-B by treatment with cAMP was associated with G0/G1 arrest of the cell cycle and growth inhibition in NIH 3T3 cells. In this study, we examined the effect of cAMP treatment on cell growth in Ras-transformed NIH3T3 cells and ovarian cancer cells. METHODS: 1) The levels of PR-B and cell cycle associated proteins (p21, p27 and Rb) following treatment with cAMP in the Ras-transformed NIH3T3 cells (K12V) and ovarian cancer cell lines (SKOV cells) were investigated by Western blots. 2) The effects of PR overexpression following treatment with cAMP or after infection of an adenovirus expressing PR-B on cell growth and tumorigenicity in a soft agar culture were examined. RESULTS: 1) Treatment with cAMP increased PR-B and p27 levels in K12V cells and inhibited cell growth by inducing premature senescence. Induction of senescence was specific to the transformed cells. 2) In SKOV cells, treatment with cAMP induced PR-B, p27 and p21 expression, reduced the level of phosphorylated Rb, caused accumulation of cells in the G0/G1 fraction of the cell cycle, and induced senescence. 3) Both anchorage-dependent and -independent SKOV cell growths were inhibited by cAMP treatment. 4) Induction of both the expression and transcriptional activity of PR-B is critical for the induction of senescence and suppression of tumorigenicity. CONCLUSION: Treatment of cAMP, through activation of PR-B, induced senescence and suppressed tumorigenicity in ovarian cancer cells.