MAPK4 and breast cancer: Moreover, several downstream genes in this reaction, i.e., calcium-dependent protein kinase (CDPK), mitogen-activated protein kinase kinase 4/5 (MAPKK4/5), mitogen-activated protein kinase kinase kinase 1 (MEKK1), WKRY33, WRKY22 and respiratory burst oxidase (Rboh), were upregulated in BC.