Melittin shares certain cellular effects with phorbol ester tumour promoters

Abstract

MELITTIN, a 26-amino acid polypeptide of known sequence, is the major constituent of bee venom¹. Its primary amino acid sequence reveals that the molecule has both basic and hydro-phobic termini, which give the molecule an amphipathic character. Consequently melittin can insert into phospholipid bilayers and exhibits surfactant activity. There is evidence that the association of melittin with cellular membranes results in: (1) disturbance of the acyl groups of phospholipids such that they assume a broader range of angles with respect to each other^2,3; (2) increased phospholipid susceptibility to hydrolysis by phospholipase^4,5; and (3) increased synthesis of prostaglandins from the arachidonic acid released from the phospholipids⁶. Another amphipathic but structurally unrelated group of compounds consists of esters of the diterpene alcohol phorbol. These compounds are well known tumour promoters and have also recently been shown to have the ability to enhance phospholipid deacylation^7,19. It is therefore of interest to determine whether melittin can produce some of the other phenotypic effects that can be induced in cells in culture by phorbol ester tumour promoters^8,9. We report here that both melittin and the phorbol ester, 12-O-tetradecanoyl phorbol-13-acetate (TPA), inhibit differentiation of mouse melanoma cells, enhance anchorage-independent growth of adenovirus-transformed rat embryo cells, and induce arachidonic acid release and prostaglandin synthesis from C3H/10T½ mouse embryo fibroblasts.