THE DUAL-SPECIFICITY PHOSPHATASES M3 6 AND MKP-3 ARE HIGHLY SELECTIVEFOR INACTIVATION OF DISTINCT MITOGEN-ACTIVATED PROTEIN-KINASES/

The mitogen-activated protein (MAP) kinase family includes extracellul ar signal regulated kinase (ERK), c-Jun NH2-terminal kinase/stress-act ivated protein kinase (JNK/SAPK) and p38/RK/CSBP (p38) as structurally and functionally distinct enzyme classes. Here we describe two new du al specificity phosphatases of the CL100/MKP-1 family that are selecti ve for inactivating ERK or JNK/SAPK and p38 MAP kinases when expressed in COS-7 cells. M3/6 is the first phosphatase of this family to displ ay highly specific inactivation of JNK/SAPK and p38 MAP kinases. Altho ugh stress-induced activation of p54 SAPK beta, p46 SAPK gamma (JNK1) or p38 MAP kinases is abolished upon co-transfection with increasing a mounts of M3/6 plasmid, epidermal growth factor-stimulated ERK1 is rem arkably insensitive even to the highest levels of M3/6 expression obta ined. In contrast to M3/6, the dual specificity phosphatase MKP-3 is s elective for inactivation of ERK family MAP kinases. Low level express ion of MKP-3 blocks totally epidermal growth factor-stimulated ERK1, w hereas stress-induced activation of p54 SAPK beta and p38 MAP kinases is inhibited only partially under identical conditions. Selective regu lation by M3/6 and MKP-3 was also observed upon chronic MAP kinase act ivation by constitutive p21(ras) GTPases. Hence, although M3/6 express ion effectively blocked p54 SAPK beta activation by p21(rac) (G12V), E RK1 activated by p21(ras) (G12V) was insensitive to this phosphatase. ERK1 activation by oncogenic p21(ras) was, however, blocked totally by co-expression of MKP-3. This is the first report demonstrating recipr ocally selective inhibition of different MAP kinases by two distinct d ual specificity phosphatases.