Conformation-dependent binding of a Tetrastatin peptide to αvβ3 integrin decreases melanoma progression through FAK/PI3K/Akt pathway inhibition

Tetrastatin, a 230 amino acid sequence from collagen IV, was previously demonstrated to inhibit melanoma progression. In the present paper, we identified the minimal active sequence (QKISRCQVCVKYS: QS-13) that reproduced the anti-tumor effects of whole Tetrastatin in vivo and in vitro on melanoma cell proliferation, migration and invasion. We demonstrated that QS-13 binds to SK-MEL-28 melanoma cells through the alpha(v)beta(3) integrin using blocking antibody and beta 3 integrin subunit siRNAs strategies. Relevant QS-13 conformations were extracted from molecular dynamics simulations and their interactions with alpha(v)beta 3 integrin were analyzed by docking experiments to determine the binding areas and the QS-13 amino acids crucial for the binding. The in silico results were confirmed by in vitro experiments. Indeed, QS-13 binding to SK-MEL-28 was dependent on the presence of a disulfide-bound as shown by mass spectroscopy and the binding site on alpha(v)beta(3) was located in close vicinity to the RGD binding site. QS-13 binding inhibits the FAK/PI3K/Akt pathway, a transduction pathway that is largely involved in tumor cell proliferation and migration. Taken together, our results demonstrate that the QS-13 peptide binds alpha(v)beta(3) integrin in a conformation-dependent manner and is a potent antitumor agent that could target cancer cells through alpha(v)beta(3).