MAPK3 and neoplasm: In this study, we show that SIX1 is phosphorylated at serine 225 (S225) by ERK1/2 in response to growth factors and is dephosphorylated by the atypical protein phosphatase eyes absent 4 (EYA4).23 Phosphorylation controls aerobic glycolysis and tumor-promoting activity of SIX1.