Identification of the peptides that stimulate the phosphoinositide hydrolysis in lymphocyte cell lines from peptide libraries

Peptides which stimulate the formation of inositol phosphates (InoPs) in lymphocyte cell lines were identified by screening synthetic peptide libraries composed of random sequences of hexapeptides. The peptides containing the consensus sequence XKYX(P/V)M were found to be most active in the phospholipase C (PLC)-mediated formation of InoPs in a human B myeloma cell line, U266, The peptides also stimulated the phosphoinositide hydrolysis and the release of [Ca2+](i) in HL60 and U937 cell lines, On the other hand, these peptides showed no effect in the following cell lines: NIH3T3, PC12, Daudi, Sp2, Jurkat, H9, Molt-4, SupT-1, K562, and RBL-2H3. The result suggests the possibility that the peptides may have cell type specificity. Experiments with one of the active peptides, WKYMVM-NH2 showed that its action mimics the effect of AlF4- which is a G-protein activator in the InoPs generation, and pertussis toxin partially blocked the InoPs accumulation and [Ca2+](i) release induced by the peptide in the U266 cells, Binding assays with the peptide labeled with I-125 showed that U266 cells have a saturable number of binding sites for the peptide, Taken together, these results suggest that the peptides could activate PLC-mediated signal transduction via a pertussis toxin-sensitive G-protein coupled receptor in certain cell types.