| dc.description.abstract | Singleminded-2s (Sim2s) is a member of the basic helix-loop-helix Per-Arnt-Sim (bHLH-PAS) family of transcription factors. Members of this family play important roles in sensing and responding to environmental changes, controlling circadian rhythms, and development. Previous work in our laboratory found that Sim2s is down-regulated in human breast cancer patients and cell lines and over-expression of Sim2s in highly invasive breast cancer cells blocks their proliferative and invasive potentials. Additionally, when Sim2s is knocked-down in MCF7 breast cancer cells, this normally relatively non-aggressive cell line becomes highly invasive and metastatic.
In the studies presented here, we found that over-expression of Sim2s in MCF7 cells caused these cells to have a significant decrease in proliferative ability. Propidium iodide flow cytometry showed more Sim2s cells in the G2/M and S phases of the cell cycle as compared to Empty controls. While we observed no changes in cyclin or CDK levels between Empty controls and Sim2s cells, the regulatory protein p21 was found to be significantly up-regulated in Sim2s cells at both the RNA and protein levels. Additionally, we confirmed a cellular senescence phenotype in the Sim2s cells through markers such as β-galactosidase staining, and Western blot analysis of Ki67 and H3K9Me2. Based on these results, we hypothesize that over-expression of Sim2s triggers an up-regulation of p21, resulting in cellular senescence and cell cycle arrest. We also found that Sim2s cells are more highly sensitized to DNA damage through clonogenic survival assays. Together, these studies support the idea that Sim2s is involved in cell cycle control by up-regulation of p21 resulting in cellular senescence and the DNA damage response by sensitizing cells to genotoxic reagents. | en |
