| Nur 77 is phosphorylated in cells by RSK in response to mitogenic stimulation . ^^^ In the present study , we show that Nur 77 is phosphorylated on this site by RSK ( ribosomal S 6 kinase ) and MSK ( mitogen and stress activated kinase ) , but not by PKB ( protein kinase B ) or PKA ( protein kinase A ) , in vitro . ^^^ In cells , phosphorylation of Nur 77 in vivo is catalysed by RSK , which is activated downstream of the classical MAPK ( mitogen activated protein kinase ) cascade . ^^^ Phosphorylation of Nur 77 by RSK is able to promote the binding of Nur 77 to 14 3 3 proteins in vitro , however , no evidence could be seen for this interaction in cells . ^^^ |