Cellular internalization of human calcitonin derived peptides in MDCK monolayers:: A comparative study with Tat(47-57) and penetratin(43-58)

Purpose. The objective of this study was to evaluate key motif requirements of human calcitonin (hCT)-derived peptides for the permeation through the plasma membrane of MDCK monolayers, as epithelial model. Methods. Truncated and sequence-modified fluorescent-labeled hCT-derived peptides were synthesized through Fmoc chemistry. Peptide uptake by confluent MDCK was observed by confocal laser scanning microscopy. The cytotoxic effect of the peptides on cellular integrity was followed by LDH release. For direct comparison we covered the cellular uptake of established cell penetrating peptides, Tat(47-57) and penetratin(43-58). Results. Truncated sequences of hCT, from hCT(9-32) to hCT( 1832), penetrated the plasma membrane and demonstrated a sectoral, punctuated cytoplasmic distribution. The uptake process appeared to be temperature-, time- and concentration-dependent. Amino acid modifications of hCT(18-32) indicated that both the proline in position 23 and the positive charge of lysine in position 18 are crucial for peptide uptake. The reverse sequence hCT(32-18) did not penetrate the membrane, indicating the importance of sequence orientation. Tat(47-57) and penetratin(43-58) showed a similar punctuated cytoplasmic distribution in MDCK and HeLa cell lines. No relevant toxicity was observed. Conclusions. Selected hCT-derived peptides have cell penetrating properties. The uptake mechanism seems to involve an endocytic pathway.