Phosphoinositide 3-kinases (PI3K) have long been considered promising drug targets for the treatment of inflammatory and autoimmune disorders as well as cancer and cardiovascular diseases. But the lack of specificity, isoform selectivity and poor biopharmaceutical profile of PI3K inhibitors have so far hampered rigorous disease-relevant target validation. Here we describe the identification and development of specific, selective and orally active small-molecule inhibitors of PI3Kgamma (encoded by Pik3cg). We show that Pik3cg(-/-) mice are largely protected in mouse models of rheumatoid arthritis; this protection correlates with defective neutrophil migration, further validating PI3Kgamma as a therapeutic target. We also describe that oral treatment with a PI3Kgamma inhibitor suppresses the progression of joint inflammation and damage in two distinct mouse models of rheumatoid arthritis, reproducing the protective effects shown by Pik3cg(-/-) mice. Our results identify selective PI3Kgamma inhibitors as potential therapeutic molecules for the treatment of chronic inflammatory disorders such as rheumatoid arthritis.

MAP kinase phosphatase-3 (MKP-3) dephosphorylates phosphotyrosine and phosphothreonine and inactivates selectively ERK family mitogen-activated protein (MAP) kinases. MKP-3 was activated by direct binding to purified ERK2. Activation was independent of protein kinase activity and required binding of ERK2 to the noncatalytic amino-terminus of MKP-3. Neither the gain-of-function Sevenmaker ERK2 mutant D319N nor c-Jun amino-terminal kinase-stress-activated protein kinase (JNK/SAPK) or p38 MAP kinases bound MKP-3 or caused its catalytic activation. These kinases were also resistant to enzymatic inactivation by MKP-3. Another homologous but nonselective phosphatase, MKP-4, bound and was activated by ERK2, JNK/SAPK, and p38 MAP kinases. Catalytic activation of MAP kinase phosphatases through substrate binding may regulate MAP kinase activation by a large number of receptor systems.Signal transduction pathways that lead to activation of MAP kinases control many diverse and essential functions in yeast, worms, flies, and mammals. Extracellular signal-regulated kinase-1 (ERK1) and ERK2 exemplify one class of MAP kinase that undergoes activation by a range of stimuli including growth factors, cytokines, cell adhesion, tumor-promoting phorbol esters, and oncogenes (1). Specific functions assigned to ERK activity include chemotaxis, neuronal differentiation, and synaptic changes underlying memory and learning, as well as cellular mitogenesis and oncogenic transformation (1, 2).Full activation of ERK requires phosphorylation of threonine and tyrosine residues by a class of MAP kinase/ERK kinase (MEK) exemplified by MEK-1 (1, 3). Conversely, an emerging family of dual-specificity phosphatases that act on both phosphotyrosine and phosphothreonine reverse this process and also appear to be critical regulators of MAP kinase activity. CL100/3CH134 or MAP kinase phosphatase-1 (MKP-1) is the archetypal member of this gene family and has high substrate specificity for MAP kinases (4). Up to nine other mammalian dual-specificity phosphatases have been identified, and several of these are under tight transcriptional control and display distinct tissue, cell, and subcellular expression patterns (5, 6). MKP-3 appears exceptional in that it specifically inactivates ERK as compared with c-Jun NH 2 -terminal kinases/stress-activated protein kinases (JNK/SAPK) or p38 MAP kinases (7). We now show that ERK, but not other MAP kinases, cause substratetriggered activation of MKP-3.We purified various MKP-3 deletion mutants expressed in Escherichia coli and found that the NH 2 -terminal noncatalytic domain (amino acids 1 to 221) binds tightly to its target MAP kinases p44 ERK1 and p42 ERK2 (8). Binding to purified ERK2 (9) stimulates p-nitrophenyl phosphate (p-NPP) phosphatase activity of full-length MKP-3 by up to 30-fold (Fig. 1A) (10). Both glutathione-S-transferase (GST)-ERK2 and ERK2 caused similar activation of either the fusion protein GST-MKP-3, His-tagged MKP-3, or free MKP-3 (11). Activation of MKP-3 was dose-dependent and saturable wit...

We have studied the phosphorylation of the Bcl-2 family of proteins by different mitogen-activated protein (MAP) kinases. Purified Bcl-2 was found to be phosphorylated by the c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) p54-SAPK␤, and this is specific insofar as the extracellular signal-regulated kinase 1 (ERK1) and p38/RK/CSBP (p38) catalyzed only weak modification. Bcl-2 undergoes similar phosphorylation in COS-7 when coexpressed together with p54-SAPK␤ and the constitutive Rac1 mutant G12V. This is seen by both 32 PO 4 labeling and the appearance of five discrete Bcl-2 bands with reduced gel mobility. As anticipated, both intracellular p54-SAPK␤ activation and Bcl-2 phosphorylation are blocked by co-transfection with the MAP kinase specific phosphatase MKP3/PYST1. MAP kinase specificity is also seen in COS-7 cells as Bcl-2 undergoes only weak phosphorylation when co-expressed with enzymatically activated ERK1 or p38. Four critical residues undergoing phosphorylation in COS-7 cells were identified by expression of the quadruple Bcl-2 point mutant T56A,S70A,T74A,S87A. Sequencing phosphopeptides derived from tryptic digests of Bcl-2 indicates that purified GST-p54-SAPK␤ phosphorylates identical sites in vitro. This is the first report of Bcl-2 phosphorylation by the JNK/SAPK class of MAP kinases and could indicate a key modification allowing control of Bcl-2 function by cell surface receptors, Rho family GTPases, and/or cellular stresses.

The mitogen-activated protein (MAP) kinase family includes extracellular signal-regulated kinase (ERK), c-Jun NH 2 -terminal kinase/stress-activated protein kinase (JNK/SAPK) and p38/RK/CSBP (p38) as structurally and functionally distinct enzyme classes. Here we describe two new dual specificity phosphatases of the CL100/MKP-1 family that are selective 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 display highly specific inactivation of JNK/SAPK and p38 MAP kinases. Although stress-induced activation of p54 SAPK␤, p46 SAPK␥ (JNK1) or p38 MAP kinases is abolished upon co-transfection with increasing amounts of M3/6 plasmid, epidermal growth factor-stimulated ERK1 is remarkably insensitive even to the highest levels of M3/6 expression obtained. In contrast to M3/6, the dual specificity phosphatase MKP-3 is selective for inactivation of ERK family MAP kinases. Low level expression of MKP-3 blocks totally epidermal growth factor-stimulated ERK1, whereas stress-induced activation of p54 SAPK␤ and p38 MAP kinases is inhibited only partially under identical conditions. Selective regulation by M3/6 and MKP-3 was also observed upon chronic MAP kinase activation by constitutive p21 ras GTPases. Hence, although M3/6 expression effectively blocked p54 SAPK␤ activation by p21 rac (G12V), ERK1 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 reciprocally selective inhibition of different MAP kinases by two distinct dual specificity phosphatases.The mitogen activated protein (MAP) kinase 1 family comprises the extracellular signal-regulated kinase (ERK), c-Jun NH 2 -terminal kinase/stress-activated protein kinase (JNK/ SAPK), and p38/RK/CSBP (p38) as three structurally and functionally distinct enzyme classes (1-7). ERK family members are activated by a variety of growth and differentiation factors, while MAP kinases of the JNK/SAPK, and p38 class are activated preferentially by cellular stresses, and inflammatory cytokines (1)(2)(3)(4)(5)(7)(8)(9)(10)(11)(12). Activated MAP kinases phosphorylate a range of cellular substrates, including additional kinases and several transcription factors (7,(13)(14)(15)(16). MAP kinase-dependent regulation of diverse targets indicates a critical role orchestrating many varied and important cellular processes. Likely functions include a pivotal role for ERK in mediating neuronal differentiation in PC12 cells as well as growth factor-stimulated proliferation and oncogenic transformation in fibroblasts (17-21). Recent investigations also support the view that activation of JNK/SAPK and p38 MAP kinases are critical in processes mediating platelet aggregation and secretion, in generation of inflammatory cytokines as well as in triggering of apoptotic death in a range of cell types (6,12,(22)(23)(24)(25).Full activation of MAP kinases requires dual phosphorylation on...

Mitogen-activated protein kinases facilitate many cellular processes and are essential for immune cell function. Their activity is controlled by kinases and dual-specificity phosphatases. A comprehensive microarray analysis of human leukocytes identified DUSP2 (encoding the phosphatase PAC-1) as one of the most highly induced transcripts in activated immune cells. We generated Dusp2(-/-) mice and found considerably reduced inflammatory responses in the 'K/BxN' model of rheumatoid arthritis. PAC-1 deficiency led to increased activity of Jun kinase (Jnk) but unexpected impairment of the activity of extracellular signal-regulated kinase (Erk) and the kinase p38, reduced activity of the transcription factor Elk1 and a complex of mobilized transcription factor NFAT and the AP-1 transcription factor and decreased effector immune cell function. Thus, PAC-1 is a key positive regulator of inflammatory cell signaling and effector functions, mediated through Jnk and Erk mitogen-activated protein kinase crosstalk.