Involvement of the JNK‐like protein of the Aedes albopictus mosquito cell line, C6/36, in phagocytosis, endocytosis and infection of West Nile virus

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Abstract
We recently cloned a c‐Jun amino‐terminal kinase (JNK) sequence from the C6/36 cell line, derived from the mosquito Aedes albopictus. We showed that SP600125, an inhibitor of JNK proteins, inhibits phagocytosis by C6/36 cells, suggesting that the JNK‐like protein regulates phagocytosis. Here, we show that C6/36 cells constitutively express low levels of mRNA encoding the antibacterial peptides, cecropin and defensin, but that these mRNAs were up‐regulated upon stimulation by lipopolysaccharide (LPS). Thus, the C6/36 cells have properties similar to those of mammalian macrophages. To characterize further the functional properties of C6/36 cells, we have assayed the role of the JNK‐like protein in phagocytosis, endocytosis, and viral infection. C6/36 cells phagocytosed bacteria and artificial beads, and this was only slightly up‐regulated following LPS stimulation, suggesting that newly stimulated JNK‐like protein was not necessary for phagocytosis. SP600125 inhibited the acidification of intracellular compartments, including those involved in the endocytic pathway. Pretreatment of C6/36 cells with SP600125 or bafilomycin A1, but not cytochalasin D, inhibited the entry of West Nile virus (WNV), suggesting that WNV is internalized mainly by endocytosis, and that the JNK signalling pathway is important for endocytic entry. These findings indicate that the JNK‐like protein regulates basic physiological functions, including phagocytosis and endocytosis and infection of WNV.