New insights into the roles of the <i>FOXO3</i> and <i>P27Kip1</i> genes in signaling pathways

<p><b>Background:</b> The forkhead box O3 (FOXO3) and p27Kip1 are two important genes in breast cancer progression. In the present study we analyzed the effect of simultaneous FOXO3 silencing and p27Kip1 activation on breast cancer cell survival and the potential targets of these changes in cancer molecular pathways.</p> <p><b>Materials and methods:</b> The present study involved the cloning of <i>FOXO3a</i> shRNA and <i>p27Kip1</i> genes under the control of the bidirectional survivin promoter to down- and up-regulate <i>FOXO3</i> and <i>p27Kip1</i> genes, respectively. After transfection of the recombinant expression vector into the breast cancer cell line, the inhibition of cell growth was assessed by MTS and flow cytometry assays. Following the extraction of total mRNA and protein, the expression of target genes was evaluated by qPCR and Western blotting in both treated and untreated cell lines. Then, the downstream protein responses were examined by 2 D electrophoresis. The differentially expressed proteins were also identified by mass spectrometry.</p> <p><b>Results:</b> Rates of cell proliferation were significantly inhibited in the transfected cell line 72 h post-transfection. Proteomic profiling of the cell line resulted in the identification of seven novel protein markers in breast cancer responsive to these changes in expression of <i>FOXO3</i> and <i>p27Kip1</i>. The changes in expression of these markers suggested that certain signaling pathways contribute to the development of breast cancer.</p> <p><b>Conclusion:</b> Simultaneous silencing of <i>FOXO3</i> and activation of <i>p27Kip1</i> in MDA-MB-231 cells caused alterations in the expression level of several genes involved in apoptosis, cell proliferation, cell cycle control, tissue invasion, drug resistance, and metastasis. It seems that the identified genes might serve as useful biomarkers for breast cancer.</p>