Epithelial–mesenchymal transition (EMT) has a major role in cancer progression and metastasis. However, the specific mechanism of transcriptional repression involved in this process remains largely unknown. Dachshund homologue 1 (DACH1) expression is lost in invasive breast cancer with poor prognosis, and the role of DACH1 in regulating breast cancer metastasis is poorly understood. In this study, significant correlation between the expression of DACH1 and the morphology of breast cancer cells was observed. Subsequent investigation into the relationship between DACH1 and EMT showed that overexpression of DACH1 in ZR-75-30 cells induced a shift towards epithelial morphology and cell–cell adhesion, as well as increased the expression of the epithelial marker E-cadherin and suppressed cell migration and invasion. In contrast, silencing DACH1 in MCF-7 and T47D cells disrupted the epithelial morphology and cell–cell contact, reduced the expression of E-cadherin, and induced cell migration and invasion. DACH1 also specifically interacted with SNAI1, but not SNAI2, to form a complex, which could bind to the E-box on the E-cadherin promoter in an SNAI1-dependent manner. DACH1 inhibited the transcriptional activity of SNAI1, leading to the activation of E-cadherin in breast cancer cells. Furthermore, the level of DACH1 also correlated with the extent of metastasis in a mouse model. DACH1 overexpression significantly decreased the metastasis and growth of 4T1/Luc cells in BALB/c mice. Analysis of tissue samples taken from human breast cancers showed a significant correlation between the expression of DACH1 and E-cadherin in SNAI1-positive breast cancer. Collectively, our data identified a new mechanistic pathway for the regulation of EMT and metastasis of breast cancer cells, one that is based on the regulation of E-cadherin expression by direct DACH1–SNAI1 interaction.

Disruption of the circadian rhythm is now believed to associate with a number of hormone-related cancers, such as breast cancer, in which aberrant estrogen receptor-α (ERα) signaling is a major contributor. However, the molecular mechanisms underlying the function of core clock proteins in cancer are still largely undefined. In this study, we showed that circadian locomotor output cycles kaput (CLOCK), a key circadian protein, can interact with ERα. Furthermore, this interaction was enhanced by estrogen. We also showed that CLOCK can be sumoylated and sumoylation of CLOCK, which is also stimulated by estrogen, had two consequences: (1) it increased the transcriptional activity of CLOCK; and (2) it increased the CLOCK-modulated transcriptional activity of ERα, as shown by increased transcription of cyclin D1. Sumoylation of CLOCK occurred at two lysine residues, K67 and K851. The enhancement of ERα transcriptional activity exerted by wild-type but not mutant (2K/2R) CLOCK in response to estrogen indicated that sumoylation of CLOCK may have an important role in estrogen-dependent signaling. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay conducted with breast cancer cell lines (MCF-7 and T47D) demonstrated that sumoylation of CLOCK stimulated cell growth and increased the proportion of S phase cells in the cell cycle. The results of this study uncovered new insight into the connection between a major circadian protein and a major estrogen-dependent transcription factor, providing the basis for further research into the involvement of circadian proteins in breast cancer.

Breast cancer that is accompanied by a high level of cyclin E expression usually exhibits poor prognosis and clinical outcome. Several factors are known to regulate the level of cyclin E during the cell cycle progression. The transcription factor DEC1 (also known as STRA13 and SHARP2) plays an important role in cell proliferation and apoptosis. Nevertheless, the mechanism of its role in cell proliferation is poorly understood. In this study, using the breast cancer cell lines MCF-7 and T47D, we showed that DEC1 could inhibit the cell cycle progression of breast cancer cells independently of its transcriptional activity. The cell cycle-dependent timing of DEC1 overexpression could affect the progression of the cell cycle through regulating the level of cyclin E protein. DEC1 stabilized cyclin E at the protein level by interacting with cyclin E. Overexpression of DEC1 repressed the interaction between cyclin E and its E3 ligase Fbw7α, consequently reducing the level of polyunbiquitinated cyclin E and increased the accumulation of non-ubiquitinated cyclin E. Furthermore, DEC1 also promoted the nuclear accumulation of Cdk2 and the formation of cyclin E/Cdk2 complex, as well as upregulating the activity of the cyclin E/Cdk2 complex, which inhibited the subsequent association of cyclin A with Cdk2. This had the effect of prolonging the S phase and suppressing the growth of breast cancers in a mouse xenograft model. These events probably constitute the essential steps in DEC1-regulated cell proliferation, thus opening up the possibility of a protein-based molecular strategy for eliminating cancer cells that manifest a high-level expression of cyclin E.