Macrophages are key regulators of immune system connecting innate and specific immune responses. Macrophages proliferate in presence of their growth factor, M-CSF. The addition of bacterial lipopolysacharide, LPS, induces macrophage activation and stops their proliferation engaging a pro-inflammatory response. The activation of ERK MAPK is required for both macrophage proliferation and activation. However, different time-course of ERK activation is displayed. Proliferation is a process dependent on early and short ERK activation, whereas LPS addition delays and elongates ERK activation inducing an inflammatory response. Proliferating or activating responses are balanced by the extent and duration of ERK phosphorylation that is regulated by mitogen kinase phosphatase MKP1 (DUSP1). MKP1 is induced by both M-CSF and LPS and its kinetics of induction is correlated with those of inactivation of MAPKs. The induction of MKP-1 by M-CSF or LPS is mediated by PKC-epsilon.Our studies in primary cultures of murine bone marrow derived macrophages, show that MKP-1 expression by both M-CSF and LPS is dependent on activation of Raf-1 kinase, and its interaction with PKC Õ. The time-course of activation of ERK is correlated with that of Raf-1 and MEK-1/2. The use of specific inhibitors and RNA of interference, has shown that ERK activation during proliferation is dependent on Raf-1 activation, whereas in response to inflamatory stimuli such as LPS an alternative pathway to Raf-1 to direct the activation of these kinases. Inhibition of Raf-1 activity causes a growth arrest. The cell cycle blockage at G1 phase correlated with increased expression of cyclin-dependent kinase (Cdks) inhibitors, p21Waf1 and p27Kip1. On the other hand, no effects were observed during macrophage activation as assessed by pro-inflammatory cytokine expression and induction of nitric oxide synthase following LPS stimulation. In addition, the transcriptional induction of MKP-1 phosphatase by both M-CSF and LPS is independent of ERK and p38 activation, but dependent on JNK activation as assessed using inhibitors. In consequence to inactivation of MKP-1, an elongation of other MAPKs activity, ERK and p38, is observed. Macrophages constitutively express JNK1 and JNK2 isoforms, while no JNK3 is detected. JNK1 is the main isoform involved in JNK activity. Using single knock-out mice for jnk1 and jnk2 genes, we have demonstrated that MKP-1 induction is mediated by JNK1 isoform. Moreover, JNK1 is also required for biosynthesis of proinflammatory cytokines (TNF-alpha, IL-1beta and IL-6) and for induction of nitric oxide synthase. This requirement is independent on JNK1 function as regulator of MKP-1 induction, as shown using knock-out mice for this phosphatase. These data indicate that Raf-1 is critical in ERK MAPK activation during macrophage proliferation whereas its absence does not compromise macrophage activation. Furthermore, Raf-1 is involved in the expression of MKP-1 phosphatase implicated in MAPK deactivation, through interaction with PKC-epsilon isoform. In addition, MKP-1 phosphatase expression is also dependent on JNK activity suggesting a selfregulation of MAPKs through induction of phosphatases. From different JNK isoforms, JNK1 is involved both in the expression of MKP-1 phosphatase and displays a direct role in the LPS-dependent macrophage activation.
Identifer | oai:union.ndltd.org:TDX_UB/oai:www.tdx.cat:10803/1811 |
Date | 18 May 2006 |
Creators | Sánchez Tilló, Ester |
Contributors | Celada Cotarelo, Antonio, Lloberas Cavero, Jorge, Universitat de Barcelona. Departament de Fisiologia (Biologia) |
Publisher | Universitat de Barcelona |
Source Sets | Universitat de Barcelona |
Language | English |
Detected Language | English |
Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/publishedVersion |
Format | application/pdf |
Source | TDX (Tesis Doctorals en Xarxa) |
Rights | info:eu-repo/semantics/openAccess, ADVERTIMENT. L'accés als continguts d'aquesta tesi doctoral i la seva utilització ha de respectar els drets de la persona autora. Pot ser utilitzada per a consulta o estudi personal, així com en activitats o materials d'investigació i docència en els termes establerts a l'art. 32 del Text Refós de la Llei de Propietat Intel·lectual (RDL 1/1996). Per altres utilitzacions es requereix l'autorització prèvia i expressa de la persona autora. En qualsevol cas, en la utilització dels seus continguts caldrà indicar de forma clara el nom i cognoms de la persona autora i el títol de la tesi doctoral. No s'autoritza la seva reproducció o altres formes d'explotació efectuades amb finalitats de lucre ni la seva comunicació pública des d'un lloc aliè al servei TDX. Tampoc s'autoritza la presentació del seu contingut en una finestra o marc aliè a TDX (framing). Aquesta reserva de drets afecta tant als continguts de la tesi com als seus resums i índexs. |
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