Most
antimicrobial peptides have been shown to have antitumoral activity.
Cecropin A, a linear 37-residue antimicrobial
polypeptide produced by the cecropia moth, has exhibited cytotoxicity in various human
cancer cell lines and inhibitory effects on
tumor growth. In this study, we investigated the apoptosis induced by
cecropin A in the promyelocytic cell line HL-60. Treatment of cells with
cecropin A was characterized by loss of viability in a dose-dependent manner,
lactate dehydrogenase (LDH) leakage, and modest attenuation of lysosomal integrity measured by
neutral red assay. An increase of
reactive oxygen species (ROS) generation, DNA fragmentation, and
phosphatidylserine externalization were quantified following
cecropin A exposure at a concentration of 30 microM, whereas
cecropin A-induced apoptosis was independent of
caspase family members, because the activity of
caspase-8 and -9 were irrelevant. Nevertheless,
caspase-3 activity showed a significant increase at concentrations of 20-40 microM, but a considerable reduction at 50 microM. Flow cytometry analysis revealed a dissipation of the mitochondrial transmembrane potential (Deltapsi(m)), and the accumulation of cells at sub-G1 phase measured by FACS analysis of
propidium iodide (PI) stained nuclei suggested induction of apoptosis. Morphological changes measured by
Hoechst 33342 or
acridine orange/
ethidium bromide staining showed nuclear condensation, corroborating the apoptotic action of
cecropin A. Overall, these data indicate that
cecropin A is able to induce apoptosis in HL-60 cells through a signaling mechanism mediated by ROS, but independently of
caspase activation.