Effects of mastoparan and related peptides on phosphoinositide breakdown in HL-60 cells and cell-free preparations.

In differentiated HL-60 cells the amphiphilic peptide mastoparan induces a dose-dependent stimulation of phosphoinositide breakdown with an EC50 value of 9μM. Such stimulation can be markedly reduced by pretreatment of the cells with pertussis toxin (100 ng/ml, 2h). In membranes obtained from differentiated HL-60 cells, guanine nucleotides stimulate the formation of IP2 and IP3. Calcium ions also induce phosphoinositide breakdown in this preparation independent of the presence of guanine nucleotides. In HL-60 cell membranes, mastoparan inhibited GTPγS-stimulation of phosphoinositide breakdown with an IC50 value of 3 μM. Such inhibitory activity of mastoparan also was present in membranes from cells pretreated with pertussis toxin. Calcium-induced stimulation of phosphoinositide breakdown was not significantly inhibited by mastoparan. The analogs mastoparan-X and polistes mastoparan had similar inhibitory activity, whereas the analog des-Ile1-Asn2-mastoparan was inactive. In permeabilized HL-60 cells mastoparan also inhibited phosphoinositide breakdown. Another amphiphilic peptide, melittin, was inactive in HL-60 intact cells, but similar to mastoparan, inhibited guanine nucleotide-induced phosphoinositide breakdown in HL-60 cell membranes and permeabilized cells. Thus, mastoparan peptides can stimulate phosphoinositide breakdown in intact HL-60 cells, probably through the interaction with a guanine nucleotide binding protein. In permeabilized cells an in cell membranes, mastoparan induces inhibition of guanine nucleotide-mediated phosphoinositide breakdown presumably through an interaction with an intracellular site. The inhibitory action of mastoparan and melittin is probably related to the amphiphilic character of these peptides.