BioProject

Using the orthotopic breast cancer xenograft model of basal-like breast cancer MDA-MB-231 line, we have found that the expression of miRNAs encoded by MIR17HG was significantly decreased in cells isolated from spontaneous lung metastases compared to cells from primary tumors grown in orthotopic sites. More...

Using the orthotopic breast cancer xenograft model of basal-like breast cancer MDA-MB-231 line, we have found that the expression of miRNAs encoded by MIR17HG was significantly decreased in cells isolated from spontaneous lung metastases compared to cells from primary tumors grown in orthotopic sites. We investigated the role of a MIR17HG family member, miR-18a, in primary tumor growth and pulmonary metastasis from the orthotopic site. We demonstrated that enforced expression of exogenous miR-18a, significantly limited continuous growth of primary tumors in mammary gland fat pads and reduced spontaneous lung metastasis. Further investigation on the mechanism of miR-18a action led to the finding that the expression of HIF1A, a key regulator of tumor metastasis, was regulated by miR-18a. Enforced miR-18a expression significantly decreased HIF1A expression at both mRNA and protein levels, resulting in altered transcriptional response and decreased survival of cells in response to Cobalt(II) chloride (CoCl2), a hypoxia-mimicking agent. Conversely, miR-18a knockdown significantly increased HIF1A expression levels and enhanced cell survival in response to CoCl2. Analysis of expression data of human breast tumor tissues showed that miR-18a expression is inversely correlated with HIF1A expression in basal-like breast tumors, supporting a role of miR-18a in restricting HIF1A expression in this subtype of breast cancer. In addition, we demonstrated that hypoxia inhibits miR-18a expression, likely through MYC inactivation. Furthermore, gene expression and functional analysis revealed that miR-18a also plays a role in regulating cell adhesion, migration and invasion. Taken together, this study provides evidence for a novel role of miR-18a to inhibit breast cancer metastasis. Our results suggest that miR-18a downregulation might provide tumor cells survival/growth advantage under hypoxic pressure in basal-like breast cancer. Overall design: A lung metastatic subline, designated as MB231RN-LM, was derived from MDA-MB-231 breast cancer cells through in vivo selection. The MB231RN-LM cells were stably transfected with has-miR-18a or control vector and treated with 200uM Cobalt(II) chloride (CoCl2, a hypoxia-mimicking agent) for 4 hr. A total of 8 samples were subjected to microarray analysis, with two biological repeats for each experiment condition. Less...