The membrane-lytic peptides K8L9 and melittin enter cancer cells via receptor endocytosis following subcytotoxic exposure.

We investigate the cell entry mechanism of the membrane-lytic peptides K8L9 and melittin in cancer cell lines. K8L9 and melittin interacted with the highly expressed endocytic receptors neuropilin-1, low-density lipoprotein-related protein receptor 1 (LRP1), and transferrin receptor. Silencing of these receptors by small interfering RNAs (siRNAs) attenuated the cytotoxic activity of K8L9 in four cancer cell lines. Intracellular K8L9 and melittin triggered enlargement of the lysosomal compartments and cytosolic translocation of cathepsin B. Hsc70 was identified as a melittin-interactive molecule using coimmunoprecipitation and mass spectrometry, and Hsc70-siRNA attenuated the cellular uptake of K8L9 and cytotoxic activity by K8L9 and melittin. These findings suggest that K8L9 and melittin can enter cancer cells via receptor endocytosis following subcytotoxic treatment and subsequently affect lysosomal compartments.