[Show abstract][Hide abstract] ABSTRACT: In the present study, we demonstrated the cell cycle periodicity of Erbin expression with the maximal expression of Erbin in G2/M phase. A significant increase in Erbin promoter activity was observed in G2/M phase-synchronized cells. Sequence analysis revealed a c-Myb site in the core promoter region of Erbin. Mutagenesis of c-Myb consensus sequences abrogated the increased Erbin promoter activity in G2/M phase. ChIP and oligonucleotide pull-down assays validated that the recruitment of c-Myb to the consensus sequences was specific. The interaction of c-Myb with c-Myb site in the Erbin promoter was significantly enhanced in G2/M phase. Ectopic overexpression of c-Myb led to the up-regulation of Erbin promoter activity and c-Myb silencing by small interfering RNA significantly decreased Erbin protein level. Transfection of c-Myb rescued Erbin expression that was impaired by c-Myb knockdown. It proves that c-Myb and the c-Myb response element mediate the cell cycle-dependent expression of Erbin. Inactivation of Erbin causes an acceleration of the G1/S transition, the formation of multipolar spindles and abnormal chromosome congression. These results unravel a critical role of c-Myb in promoting Erbin transcription in G2/M phase and also predict an unappreciated function of Erbin in cell cycle progression.
PLoS ONE 08/2012; 7(8):e42903. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fra-1 is overexpressed in a variety of human tumors. Whether MMP-9 expression is regulated by Fra-1 has been contradictory. To clarify the capability of Fra-1 in activating transcription of MMP-9 gene, we analyzed the transcriptional activity of the MMP-9 promoter through the measure of luciferase activities in the MCF-7 cells transiently transfected with Fra-1. The positive regulation of Fra-1 on MMP-9 promoter was not detectable. By the analysis of MMP-9 promoter, a potential Stat3 binding site, just juxtaposed AP-1 consensus sequence, was noticed. The reporter assay showed that MMP-9 promoter was activated remarkably by cotransfection with Fra-1 and Stat3C. DNA affinity precipitation assay confirmed the binding of Stat3 and Fra-1 to the elements of MMP-9 promoter and also revealed c-Jun recruited to Stat3-Fra-1 complex. By immunoprecipitation assay, the Stat3/Fra-1, Stat3/c-Jun and Fra-1/c-Jun complexes were identified in vivo. Our study demonstrated that the activation of MMP-9 promoter is dependent upon interactions of Fra-1/c-Jun with Stat3. A juxtaposed Stat3/AP-1 element plays a crucial role in the manner of enhancersome in the activation of MMP-9 gene. The functional cooperation of the Stat3 and AP-1 transcription factors is required for the transcription of MMP-9 gene.
[Show abstract][Hide abstract] ABSTRACT: In the present study, the sub-cellular localization of ErbB2 and its mutants expressed as GFP-tagged proteins in MCF-7 cells or endogenous ErbB2 in SKBR3 cells was examined. The data presented here demonstrate that the full-length ErbB2 was localized at the cytoplasmic membrane and ErbB2 ICD localized in the nucleus predominantly. The sequence of ErbB2 ICD contains the information supporting its nuclear translocation and cytoplasmic retention. A region (residues 721-970) harboring an arginine triplet is essential for the cytoplasmic trafficking of ErbB2. The results indicate that differential sub-cellular localization of ErbB2 ICD and the full-length ErbB2 is dependent on their structural determinants. The present results give initial clues for further analysis of the mechanism of ErbB2 intracellular localization.
[Show abstract][Hide abstract] ABSTRACT: Human breast cancer cell line SKBR3 expresses high level of the ErbB2 molecule, which has been associated with poor prognosis of breast cancer. Elevated ErbB2 functions as a transactivating co-receptor and promotes the formation of ErbB2 containing heterodimers, which are more mitogenic and transforming, and have a higher ligand affinity and signaling potency by virtue of the potent latent kinase activity of ErbB2. Interestingly, SKBR3 cells are non-tumorigenic in nude mice. By ectopic overexpression of c-Jun in SKBR3 cells, involvement of c-Jun in invasiveness and metastasis in vivo was investigated in this study. The critical role of c-Jun in the tumorigenesis and metastasis is demonstrated in nude mice.
[Show abstract][Hide abstract] ABSTRACT: c-Jun/AP-1 has been linked to invasive properties of aggressive breast cancer. Recently, it has been reported that overexpression of c-Jun in breast cancer cell line MCF-7 resulted in increased AP-1 activity, motility and invasiveness of the cells in vitro and tumor formation in nude mice. However, the role of c-Jun in metastasis of human breast cancer in vivo is currently unknown.
To further investigate the direct involvement of c-Jun in tumorigenesis and metastasis, in the present study, the effects of c-Jun overexpression were studied in both in vitro and in nude mice.
Ectopic overexpression of c-Jun promoted the growth of MCF-7 cells and resulted in a significant increase in the percentage of cells in S phase and increased motility and invasiveness. Introduction of c-Jun gene alone into weakly invasive MCF-7 cells resulted in the transfected cells capable of metastasizing to the nude mouse liver following tail vein injection.
The present study confirms that overexpression of c-Jun contributes to a more invasive phenotype in MCF-7 cells. It indicates an interesting relationship between c-Jun expression and increased property of adhesion, migration and in vivo liver metastasis of MCF-7/c-Jun cells. The results provide further evidence that c-Jun is involved in the metastasis of breast cancer. The finding also opens an opportunity for development of anti-c-Jun strategies in breast cancer therapy.