human er u03b2 1 u03bcci u03b3 32 p atp 100 u03bcm atp in 1 u00d7 kinase buffer as above with or without sb 203580 at 0 5 u03bcm and with or without active p38 u03b2 see as above at 50 ng for lane 1 amp 3 100 ng for lane 4 200 ng for lane 5 amp 6 zero for lane 2 under optimized conditions using the in vitro kinase assay of example 3 the present inventors have observed that all forms of p38 mapk alpha beta gamma and delta phosphorylate both er u03b1 and er u03b2 and that the p38 u03b1 and p38 u03b2 induced phosphorylation of er can be inhibited by the p38 specific inhibitor sb 203580 the instant invention provides in vitro data showing that p38 mapk is capable of functionally activating er not only by direct phosphorylation of er but also by phosphorylating the er coactivator amplified in breast cancer 1 aib1 fig4 shows in vitro phosphorylation assay according to example 3 of aib1 by p38 mapk purified recombinant p38 map kinase phosphorylates xenopus oocyte expressed aib1 lanes 3 5 similarly to extracellular signal regulated kinase 2 erk 2 lane 7 the p38 specific inhibitor sb 203580 inhibits aibi phosphorylation by p38 mapk lane 4 lanes 2 and 8 are.