Tyrosine kinase‐mediated cell signalling in the activation of Mytilus hemocytes: possible role of STAT‐like proteins

Abstract

In bivalve molluscs, cell-mediated immunity is carried out by circulating hemocytes, resembling the monocyte/macrophage lineage of vertebrates, that can kill the microbes through phagocytosis and various cytotoxic reactions. Previous data demonstrated that activation of MAPKs (Mitogen Activated Protein Kinases) is involved in the response of mussel hemocytes (Mytilus galloprovincialis Lam.) to bacterial challenge. In this work, the possibility that modulation of components of tyrosine kinase-mediated cell signalling may participate in the activation of mussel hemocytes was investigated. Cell pre-treatment with the macrophage activator IFNc significantly increased the bactericidal activity of mussel hemocytes towards E. coli. Human recombinant IFNc stimulated tyrosine phosphorylation of different members of STAT-like proteins (Signal Transducers and Activators of Transcription), as evaluated by Western blotting of hemocyte protein extracts with specific anti-phospho-STAT antibodies. A similar increase in phosphorylation of immunoreactive STATs was observed in hemocytes incubated with E. coli, this indicating that tyrosine phosphorylation of STAT-like members represents a physiological step in hemocyte activation. IFNc lead to persistent phosphorylation of immunoreactive STAT1, a transcription factor that plays a critical role in innate immunity towards Gram negative bacteria in mammalian systems; moreover, hemocyte pretreatment with IFNc significantly increased bacteria-induced STAT1 phosphorylation, whereas IFNa did not. IFNc also transiently affected the phosphorylation state of different MAPKs. The extent and time course of MAPK phosphorylation induced by IFNc were distinct from those elicited by either IFNa or bacterial challenge. Overall, the results indicate that the hemocyte function can be modulated by heterologous cytokines and bacterial signals that act in concert through tyrosine kinase-mediated transduction pathways converging on STAT-and MAPK-like members.

Effects of tumour necrosis factor α (TNFα) on Mytilus haemocytes: role of stress‐activated mitogen‐activated protein kinases (MAPKs)

“…In particular, Mytilus haemocytes were shown to be responsive to heterologous TNFα and to produce TNFα‐like molecules in response to bacterial components (Hughes et al, 1990, 1993; Ottaviani et al, 1995). We have recently investigated the transduction pathways involved in the immune function of Mytilus haemocytes: a key role for tyrosine kinase‐mediated cell signalling, in particular of MAPKs, has been demonstrated (Canesi et al, 2002b, 2002c, 2003a, 2005). Moreover, in Mytilus haemocytes, like in mammalian macrophages, full activation was induced by both bacterial stimuli and heterologous IFNγ (interferon γ) converging on STAT (signal transducer and activator of transcription) members, STAT1 in particular (Canesi et al, 2003a).…”

“…We have recently investigated the transduction pathways involved in the immune function of Mytilus haemocytes: a key role for tyrosine kinase‐mediated cell signalling, in particular of MAPKs, has been demonstrated (Canesi et al, 2002b, 2002c, 2003a, 2005). Moreover, in Mytilus haemocytes, like in mammalian macrophages, full activation was induced by both bacterial stimuli and heterologous IFNγ (interferon γ) converging on STAT (signal transducer and activator of transcription) members, STAT1 in particular (Canesi et al, 2003a). In the present study, we investigated the possible effects and signalling pathways of heterologous TNFα in Mytilus haemocytes, with particular regard to the role of stress‐activated MAPKs.…”

Molecular cloning and characterization of the STAT gene in Hyphantria cunea haemocytes

“…(2005) reported that Drosophila melanogaster (D)‐STAT was transcribed in all haemocyte samples but did not show upregulation of expression upon infection in Drosophila melanogaster larvae. Incubation of mussel haemocytes with interferon (IFN)γ and E. coli has been shown to result in a rapid and time‐dependent increase in a phosphorylated STAT‐like protein, indicating a physiological role for STAT‐like proteins in mediating immune functions in the haemocytes of bivalve molluscs (Canesi et al ., 2003). The JAK/STAT pathway may have an independent role in various organs, although its activation in these organs occurs through a common mechanism.…”

Still waiting for the toll?

“…In bivalve molluscs, innate cell immunity is mediated by circulating hemocytes that resemble the vertebrate monocyte/macrophage lineage that destroys microbes by phagocytosis and cytotoxic reactions [21]. According to earlier results, activation of Mitogen Activated protein Kinases (MAPKs) is involved in mussel hemocyte responses to bacterial challenge.…”