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.