DHFR and breast cancer: This miRNA confers paclitaxel resistance to breast cancer cells through suppressing the expression of the proapoptotic protein Bcl-2 antagonist killer 1 (Bak1) [22]; in addition, it can reduce the expression of dihydrofolate reductase (DHFR) and thymidylate synthase (TS) to promote the resistance of colon cancer and osteosarcoma to the drugs methotrexate or Tomudex [23].