Effects of miR-224-5p-enhanced downregulation of pannexin-1 on docetaxel-induced apoptosis in amoeboid-like CD44high oral cancer cells

We previously found that microRNAs play major roles in the maintenance of amoeboid-like oral squamous cell carcinoma (OSCC) cells with high expression of CD44 (CD44(high)). However, the roles of microRNAs in chemotherapeutic resistance exhibited by CD44(high) amoeboid-like OSCC cells are unclear. Here, docetaxel-induced apoptosis was examined in CD44(high) OSCC cells (CD44(high) OM-1 cells) cultured on laminin-coated silicone gel. Amoeboid-like CD44(high) OSCC cells exhibited robust resistance to docetaxel-induced apoptosis and significant upregulation of miR-224-5p expression compared with epithelial-like CD44(high) OSCC cells and mesenchymal-like CD44(high) OSCC cells. The expression of pannexin-1 (PANX1), a channel-forming protein that regulates the release of ATP, was significantly upregulated following transfection of amoeboid-like CD44(high) OSCC cells with an miR-224-5p inhibitor. These results suggest that miR-224-5p inhibits PANX1 expression. Furthermore, miR-224-5p inhibitor-transfected amoeboid-like CD44(high) OSCC cells exhibited significant enhancement of the proportion of apoptotic cells; however, this effect was significantly inhibited by knockdown of PANX1 with PANX1 small interfering RNA. Additionally, the miR-224-5p inhibitor-enhanced extracellular ATP levels were significantly reduced by PANX1 knockdown. These findings imply that miR-224-5p plays a vital role in the resistance to docetaxel-induced apoptosis by attenuating PANX1-induced ATP discharge. Moreover, amoeboid-like CD44(high) OSCC cells may be involved in chemotherapeutic resistance of OSCC.