The GTP binding activity of transglutaminase 2 promotes bone metastasis of breast cancer cells by downregulating microRNA-205.

Previous studies have shown that transglutaminase 2 (TG2) induces epithelial to mesenchymal transition (EMT) in various tumors. Several studies have also demonstrated the critical role of microRNAs (miRNAs) in regulating EMT of various types of tumors. However, the relationship between TG2 and miRNAs is not well understood. In the present study, we investigated if miR-205, which is known to inhibit EMT and is commonly regulated by TG2, contributes to TG2-induced EMT of human breast cancer cells. We have analyzed the expression of miR-205 in TG2-expressing and TG2-non-expressing breast cancer cells by quantitative real-time PCR (qRT-PCR) and the expression of TG2 and EMT related markers, such as ZEB1 and Vimentin, by western blotting. We also have studied the regulation of tumor metastasis by miR-205 and TG2 using matrigel invasion assays, intracardiac injection of breast cancer cells into mice and in vivo bioluminescent imaging. MiR-205 was significantly downregulated in high TG2-expressing or TG2-transfected breast cancer cells than in low TG2-expressing or mock-transfected breast cancer cells. Overexpression of miR-205 reduced the bone metastasis of MCF7/TG2-C277S cells that express transamidase-activity deficient TG2 and inhibits the invasiveness of MDA-MB-231 breast cancer cells that express TG2. Bioluminescent imaging showed that intracardiac injection of MCF7/TG2-C277S cells in mice promoted bone tumors, especially in the knee and jaw, but MCF7/TG2-C277S cells ectopically expressing miR-205 did not metastasize. The GTP binding activity, but not transamidase activity, of TG2, induces EMT in breast cancer cells by inhibiting the expression of miR-205 that suppresses EMT by downregulating the expression of ZEB1, an EMT marker. Moreover, in vivo experiments demonstrate that miR-205 down-regulation by TG2 induces bone metastasis of breast cancer cells.