MAPK3 and cancer: Promotion of tumor EMT and metastasis through downregulation of E-cadherin and upregulation of mesenchymal markers. Enhancement of chemoresistance via HER2 and p38 MAPK phosphorylation. Maintenance of cancer stem cells through the ERK1/2 pathway. Induction of hepcidin via the SMAD1-5-8 pathway. Promotion of tumor sphere formation.