Abstract 1071: DeltaEF1 promotes breast cancer cell proliferation through down-regulating p21 expression

Background: Deregulation of the cell cycle and abnormal cell proliferation are involved in breast carcinogenesis. Recent evidence suggests that deltaEF1, a zinc finger-homeodomain transcription factor, is a potential regulatory factor at the crossroad between proliferation and differentiation. However, how deltaEF1 mediates its proliferative effects in tumorigenesis has not been recognized yet. Materials and Methods: Quantitative RT-PCR and immunoblotting were used to determine the expressions of deltaEF1, p21, p27, CDK2, CDK4, and CDK6 at the mRNA and the protein levels, respectively, in MCF-7, MDA-MB-231, T47D, and ZR-75-1 breast cancer cells, as well as in 22 breast cancer specimens. Cell proliferation and BrdU incorporation assays as well as flow cytometry were used to determine cell proliferation of MDA-MB-231 cells with deltaEF1-overexpression or deltaEF1 siRNA knockdown. Luciferase assay was used to determine deltaEF1-driven transcriptional activities of the wild-type and mutant human p21 promoters. Quantitative CHIP assay was used to detect the direct association of deltaEF1 with the wild-type human p21 proximal promoter. Results: We found that ectopic expression of deltaEF1 in MDA-MB-231 cells significantly promoted cell proliferation as indicated by an increase of cells in S phase of the cell cycle. As anticipated, deltaEF1 knockdown by RNA interference decreased the cells in S phase, suggesting a role of deltaEF1 in the G1-S transition of breast cancer cells. Importantly, we also demonstrated that deltaEF1 down-regulated p21 with up-regulation of CDK2 and CDK4. Furthermore, our studies revealed that deltaEF1 inhibited p21 transcription after recruited to the E 2 -box element on the p21 promoter. Depletion of endogenous deltaEF1 was sufficient to trigger p21 expression in MDA-MB-231 cells, resulting in the cell cycle arrest. In addition, an inverse correlation of deltaEF1 and p21 expression was detected in both breast cancer cell lines and clinical tumor specimens, further supporting the role of p21 down-regulation in the stimulatory effect of deltaEF1 on cell proliferation. Conclusions: We conclude that deltaEF1 plays a critical role in promoting cell proliferation in breast cancer. Given that higher expression level of deltaEF1 is associated with more progressive phenotype of breast cancer, our collective data suggest that deltaEF1 is a key regulatory factor at the crossroad between proliferation and differentiation, thus underscoring tumor progression and metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1071.