Curcumin Induces Downregulation of E2F4 Expression and Apoptotic Cell Death in HCT116 Human Colon Cancer Cells; Involvement of Reactive Oxygen Species

E2F transcription factors and their target genes have been known to play an important role in cell growth control. We found that curcumin, a polyphenolic phytochemical isolated from the plant Curcuma longa, markedly suppressed E2F4 expression in HCT116 colon cancer cells. Hydrogen peroxide was also found to decrease E2F4 protein level, indicating the involvement of reactive oxygen species (ROS) in curucmin-induced downregulation of E2F4 expression. Involvement of ROS in E2F4 downregulation in response to curcumin was confirmed by the result that pretreatment of cells with N-acetylcystein (NAC) before exposure of curcumin almost completely blocked the reduction of E2F4 expression at the protein as well as mRNA level. Anti-proliferative effect of curcumin was also suppressed by NAC which is consistent to previous reports showing curcumin-superoxide production and induction of poly (ADP-ribose) polymerase (PARP) cleavage as well as apoptosis. Expression of several genes, cyclin A, p21, and p27, which has been shown to be regulated in E2F4-dependent manner and involved in the cell cycle progression was also affected by curcumin. Moreover, decreased (cyclin A) and increased (p21 and p27) expression of these E2F4 downstream genes by curcumin was restored by pretreatment of cells with NAC and E2F4 overexpression which is induced by doxycycline. In addition, E2F4 overexpression was observed to partially ameliorate curcumin-induced growth inhibition by cell viability assay. Taken together, we found curcumin-induced ROS down-regulation of E2F4 expression and modulation of E2F4 target genes which finally lead to the apoptotic cell death in HCT116 colon cancer cells, suggesting that E2F4 appears to be a novel determinant of curcumin-induced cytotoxicity.

Expressions of E2F4 and E2F2 Transcription Factors in Breast Carcinoma

BACKGROUND: The E2F family (E2F1 to E2F6) of transcription factors plays a key role in cell cycle progression. Some act as oncogenes and others act as tumor suppressor genes (TSG) in a tissue-specific manner. E2F4 may function as a TSG. However, the role of E2F4 in breast carcinogenesis remains controversial. Also the clinical impact of E2F2 expression on breast cancer remains unknown. METHODS: Expressions of E2F4 and E2F2 were assessed immunohistochemically in 113 breast carcinomas and were compared with clinicopathological variables, expressions of G1/S checkpoint proteins (p16, cyclin D1 and Rb), and DNA ploidy to identify their possible role and to assess their prognostic value in breast cancer. RESULTS: Expressions of E2F4 and E2F2 were detected in 48 cases (42.5%) and 66 cases (58.4%), respectively. Expressions of E2F4 and E2F2 were significantly correlated with large tumor size (p<0.001) and lymph node metastasis (p<0.001). There was no correlation between expressions of E2F4 or E2F2 and any other variables, including age, histologic grade, DNA ploidy and expressions of p16, cyclin D1 and Rb. CONCLUSIONS: These results suggest that expressions of E2F4 and E2F2 are associated with growth and spread of breast cancer and indicate poor prognosis.