CREB and AP‐1 activation regulates MKP‐1 induction by LPS or M‐CSF and their kinetics correlate with macrophage activation versus proliferation

Abstract

MAPK phosphatase-1 (MKP-1) is a protein phosphatase that plays a crucial role in innate immunity. This phosphatase inactivates ERK1/2, which are involved in two opposite functional activities of the macrophage, namely proliferation and activation. Here we found that although macrophage proliferation and activation induce MKP-1 with different kinetics, gene expression is mediated by the proximal promoter sequences localized between À380 and À180 bp. Mutagenesis experiments of the proximal element determined that CRE/AP-1 is required for LPS-or M-CSF-induced activation of the MKP-1 gene. Moreover, the results from gel shift analysis and chromatin immunoprecipitation indicated that c-Jun and CREB bind to the CRE/AP-1 box. The distinct kinetics shown by M-CSF and LPS correlates with the induction of JNK and c-jun, as well as the requirement for Raf-1. The signal transduction pathways that activate the induction of MKP-1 correlate kinetically with induction by M-CSF and LPS.Key words: Activation . Kinases . Macrophage . Phosphatases . Proliferation IntroductionMacrophages perform critical functions during the immune response. These cells are regulators of homeostasis and play an important role in innate and acquired immunity during infection, tumor growth, and wound healing [1]. In response to needs, tissue macrophages proliferate, further differentiate to more specialized macrophagic populations, or become activated. Macrophages, like many other cells of the immune system, are produced in large excess and most undergo apoptosis [2].In the presence of M-CSF, macrophages differentiate and proliferate. However, the proliferation of these cells is blocked when they are activated by Gram-negative LPS or by . Activation causes many biochemical, morphological and functional modifications. Macrophage response to M-CSF and LPS involves the phosphorylation of the three members of the MAPK family [4].MAPK are critical components of signal transduction pathways activated by a range of stimuli and they mediate a number of physiological and pathological changes in cell function [5,6]. MAPK activation requires phosphorylation on a threonine and tyrosine residue located in the activation loop. This process is reversible even in the continued presence of activating stimuli, thereby indicating that protein phosphatases regulate MAPK [7]. Although MAPK are conserved evolutionary pathways present in eukaryotic cells, the kinetics of activation and their subcellular compartmentalization are cell type-specific, and they orchestrate differential cellular responses. For example, in neuronal cells, sustained MAPK phosphorylation of even days is required for cellular activation or differentiation, while in fibroblasts, phosphorylation of this kinase family is very short. In contrast, to Immunol. 2009. 39: 1902-1913 Cristina Casals-Casas et al. 1902 achieve proliferation, extended activation of MAPK is required in these cells [6,7]. The correct spatio-temporal regulation of MAPK signalling is crucial in determining cellular responses to g...

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“…Indeed, several AP-1 family or CREbinding proteins have been shown to translocate to the nucleus during LPS stimulation (Casals-Casas et al, 2009). According to our reporter gene assay, AP-1 appears to be blocked at a high concentration of Pa-EE (200 g/ml) (Fig.…”

“…It is well known that AP-1 and CREB are important transcription factors in LPS-mediated inflammatory responses (Proffitt et al, 1995;Casals-Casas et al, 2009). Indeed, several AP-1 family or CREbinding proteins have been shown to translocate to the nucleus during LPS stimulation (Casals-Casas et al, 2009).…”

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