The investigation of HOXB5 putative target genes and regulation mechanisms in MCF7 breast cancer cells

Abstract

HOX genes are transcription factors that play important roles in body patterning and cell fate specification during normal development. Among them, HOXB5, is involved in a variety of developmental processes, particularly during the enteric nervous system (ENS) development, and thus, abnormalities in HOXB5 function during embryonic stages lead to Hirschsprung’s disease. Importantly, many HOX enes, including HOXB5, are expressed not only during embryogenesis, but also in adults and are deregulated in various cancers. In a previous study, we found aberrant overexpression of HOXB5 in breast cancer tissues and cell lines and demonstrated that HOXB5 is important in the regulation of cell proliferation in breast cancer cells. Also, HOXB5 induces invasive potential of cancer cells through epithelial-mesenchymal transition (EMT). The relationship between HOXB5 and phenotypic changes in MCF7 breast cancer cells has been studied; however, the functions of HOXB5 as a transcription factor and its involvement in signaling pathways remain unclear. In this study, we selected putative downstream target genes of HOXB5, such as interleukin (IL)-6, Snail2 and epidermal growth factor receptor (EGFR) by PCR array analysis. These genes have been reported to be involved in cancer progression, which is characterized by increased growth speed and invasiveness of the tumor cells. Here, we discovered that HOXB5 transcriptionally up-regulated the expression of these genes by directly binding to the promoter regions. Kaplan-Meier analysis of the distant metastasis free survival (DMFS) for ERα-positive patients with breast cancer showed the correlation of high HOXB/EGFR expression with a poor survival. Mechanistic investigations showed that HOXB5 activated the MAPK/Src pathway, not Akt, via EGFR phosphorylation to promote cancer invasiveness. Taking all into consideration, our results establish that HOXB5 up-regulates IL-6, Snail2, and EGFR expression via direct binding to the promoter regions and increases cell invasion through activating EGFR/MAPK/Src pathway. We expect that these data would help diagnose and contribute to personalized therapy in breast cancer patients.