Jeffrey et al. explored the role of the nuclear-localized dual specificity phosphatase (DUSP) isoform known as phosphatase of activated cells 1 (PAC-1, which is encoded by the DUSP2 gene) in regulation of leukocyte activity and a mouse model of autoimmune arthritis. Surprisingly, cells from Dusp2—/— mice showed decreased induction of inflammatory arthritis (delayed onset of symptoms and diminished histological and clinical features). Stimulated macrophages and bone marrow-derived mast cells (BMMCs) from the Dusp2—/— mice exhibited reduced gene expression and secretion of inflammatory mediators. In addition, the cultured BMMCs from the mutant mice exhibited greater apoptosis and decreased cell survival. Only phosphatase-active forms of PAC-1 rescued the cytokine production phenotype of the mutant cells, and overexpression of a phosphatase-inactive mutant in wild-type cells acted as a dominant-negative inhibitor of cytokine production. Despite in vitro evidence that mitogen-activated protein kinases (MAPKs) of the p38 and ERK are substrates of PAC-1, the activity of these two MAPKs was decreased in the Dusp2—/— mast cells and macrophages. In contrast, phosphorylation of the MAPK c-Jun N-terminal kinase (JNK) was increased in the Dusp2—/— cells. Reporter gene assays indicated the PAC-1 deficiency reduced gene expression by at least two transcriptional regulators, the NFAT-AP1 complex and Elk1. Pharmacological inhibition of JNK in the PAC-1 deficient cells rescued ERK phosphorylation and Elk-mediated transcription, suggesting that the JNK pathway negatively regulates the ERK pathway, such that when JNK activity is high, ERK activity is suppressed. These results have implications for (i) conclusions based on in vitro enzyme assays because the specificity of PAC-1 in vitro did not appear to match its in vivo activity and (ii) therapeutic targeting of PAC-1 as a specific modulator of MAPK signaling in immune cells, especially for treatment of autoimmune disease.
K. L. Jeffrey, T. Brummer, M. S. Rolph, S. M. Liu, N. A. Callejas, R. J. Grumont, C. Gillieron, F. Mackay, S. Grey, M. Camps, C. Rommel, S. D. Gerondakis, C. R. Mackay, Positive regulation of immune cell function and inflammatory responses by phosphatase PAC-1. Nat. Immunol. 7, 274-283 (2006). [PubMed]