| Moreover , we demonstrate that p38alpha and its upstream activator , MKK 6 , phosphorylate STAT 4 on serine 721 , and are required for STAT 4 full transcriptional activity induced by IL 12 , establishing the MKK6 / p38alpha / STAT4 pathway as an important mediator of IL 12 actions . ( Blood . 2000 ; 96 : 1844 1852 ) . ^^^ |