MACROPHAGE TRIGGERING WITH CECROPIN-A AND MELITTIN-DERIVED PEPTIDES INDUCES TYPE-II NITRIC-OXIDE SYNTHASE EXPRESSION

Triggering of RAW 264.7 cells with a cecropin A-melittin hybrid peptid e (CA(1-8)M(1-18)) promoted a rapid rise in the intracellular calcium concentration that was followed, after a lag period of 6 h, by nitric oxide synthesis through the expression of the cytokine-inducible form of nitric oxide synthase (type II NOS or iNOS). The maximal effect was obtained at peptide concentrations in the 2 to 5-mu M range. Simultan eous incubation with the peptide and LPS abrogated the nitric oxide sy nthesis elicited after LPS treatment of the cells. CA(1-8)M(1-18) indu ced a rapid activation of nuclear factor KB as evidenced by the presen ce of p50/p65 heterodimers of the nuclear factor kappa B/c-Rel family in the nuclei of activated cells, This peptide also activated the repo rter activity of cells transfected with a plasmid harboring a 1-kb fra gment corresponding to the 5'-flanking region of the murine iNOS gene, CA(1-8)M(1-18) promoted apoptotic cell death at concentrations below 1 to 2 mu M, whereas higher concentrations altered the plasma membrane integrity. These results suggest the involvement of multiple intracel lular signaling pathways in the mechanism by which this peptide elicit s macrophage triggering.