U-0126 is a selective, non-ATP competitive inhibitor of mitogen activated protein kinase kinase (MEK), inhibiting MEK1 and MEK2 with IC50 values of 72 nM and 58 nM, respectively (Favata et al.; Scherle et al.) It shows little or no inhibition at micromolar levels of other kinases such as ERK, protein kinase C (PKC), c-Jun N-terminal kinases (JNK), other MAP kinase kinases (MKK3, MKK4, MKK6), cyclin-dependent kinases (CDK2, CDK4), ABL, and RAF (Favata et al.) 1998)
U-0126 also antagonizes AP-1 transcription and selectively inhibits promoters containing AP-1 response elements (Favata et al.)
