MAP kinases mediate phagocytosis and melanization via prophenoloxidase activation in medfly hemocytes

E. coli phagocytosis by medfly hemocytes, in contrast to mammalian macrophages, associates with E. coli-challenged hemocyte secretion by mitogen activating protein (MAP) kinases. In the present work, we examined whether this system links with the proteolytic activation of prophenoloxidase (proPO). P...

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Published in:Biochimica et biophysica acta 2005-06, Vol.1744 (2), p.145-156
Main Authors: Mavrouli, Maria D., Tsakas, Sotiris, Theodorou, Georgios L., Lampropoulou, Maria, Marmaras, Vassilis J.
Format: Article
Language:English
Subjects:
Animals
Ceratitis capitata - cytology
Enzyme Activation
Hemocytes - enzymology
Insect immunity
Melanins - physiology
Mitogen activating protein kinase
Mitogen-Activated Protein Kinases - classification
Mitogen-Activated Protein Kinases - metabolism
Monophenol Monooxygenase - metabolism
Phagocytosis
Prophenoloxidase
Prophenoloxidase-activating proteinase
Protein Precursors - metabolism
Signal Transduction
Signalling
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Summary:E. coli phagocytosis by medfly hemocytes, in contrast to mammalian macrophages, associates with E. coli-challenged hemocyte secretion by mitogen activating protein (MAP) kinases. In the present work, we examined whether this system links with the proteolytic activation of prophenoloxidase (proPO). ProPO and prophenoloxidase-activating proteinases (PAPs) were initially identified within freshly isolated medfly hemocytes. Moreover, flow cytometry and immunocytochemical analysis revealed the constitutive expression of proPO and its stable association with hemocyte surface. The expression level of hemocyte surface proPO is not affected by E. coli infection. In addition, flow cytometry analysis in freshly isolated hemocytes showed that E. coli phagocytosis is markedly blocked by antibodies against proPO or PAPs, as well as by several serine protease inhibitors, strongly supporting the involvement of proPO cascade in the phagocytosis process. Similarly, it was shown that melanization process depends on proPO activation. MAP kinases appeared to control both phagocytosis and melanization, since they regulate PAPs secretion, a prerequisite for the conversion of proPO to active PO. From this and previous studies, hemocytes appear to be central to immune response in medfly.
ISSN:0167-4889
0006-3002
1879-2596
DOI:10.1016/j.bbamcr.2005.04.011