Identification and characterization of epidermal growth factor receptor ligands in Bombyx mori

Abstract:

Epidermal growth factor receptor (EGFR) is a multi-functional receptor distributed throughout the metazoa. Study on its ligands so far remained mainly on mammals, including how ligands are processed into active forms, their interaction with EGFR, and the signaling pathway they induce. However, in invertebrates, ligands are more divergent among species. Currently, except for Drosophila, less is known about the insect EGFR ligands. Here, we identified two EGFR ligands in Bombyx mori by homology search, domain prediction, analysis of the potential translation initiation sequence and construction of phylogenetic tree, termed as BmEGF-1 and BmEGF-2. BmEGF-1 shows the greatest similarity to Drosophila Spitz and their Rhomboid-recognition motifs are highly identical. BmEGF-2 is a homolog to Drosophila Vein. Then we purified BmEGF-1 extracellular domain expressed in E. coli, and performed pull-down assay with BmEGFR extracellular domain secreted by Sf9 cells. The result confirmed their interaction. Lastly, we found the phosphorylation level of ERK and p38 MAPK was elevated after expression of BmEGF-1 in BmE cells, which suggested that BmEGF-1 is not only able to activate the canonical ERK signaling pathway, but may participate in other cellular processes by inducing p38 MAPK signaling pathway. Our study provides reference to further study of the biological function of BmEGF in silkworm.