Morphological changes of BM-N4 cells induced by bombyxin, an insulin-related peptide of Bombyx mori.

Bombyxin is a brain secretory peptide of the silkmoth Bombyx mori whose amino acid sequence shows considerable sequence homology with vertebrate insulin-family peptides. We found that a Bombyx cell line, named BM-N4, showed morphological changes when bombyxin was added to the culture medium at doses as low as 10(-10) M. Bombyxin-treated cells displayed a series of morphological modifications: 1 to 2 weeks after introduction of bombyxin, the cells increased in size, then they trended to aggregate, or took a spindle shape. These changes of the cells were bombyxin specific, not induced by other vertebrate insulin-family peptides. To prove that these modifications of the cells are mediated by receptors on the cell surface of the cells, we performed a receptor binding assay using 125I-labeled bombyxin. Scatchard analysis of the binding assay indicated that this cell line has a single class of receptors for bombyxin with a Kd = 2.36 +/- 0.56 nM and each cell has 15,800 +/- 1400 binding sites on the cell surface.