title: Optimum modification for the highest cytotoxicity of cationized ribonuclease.
abstract: Cationization of a protein is considered to be a powerful strategy for internalizing a functional protein into cells. Cationized proteins appear to adsorb to the cell surface by electrostatic interactions, then enter the cell in a receptor- and transporter-independent fashion. Thus, in principle, all cell types appear to take up cationized proteins. Since ribonucleases (RNases) have a latent cytotoxic potential, cationized RNases could be useful cancer chemotherapeutics. In this study, we investigated the effect of the degree of cationization on the cytotoxicity of RNase A by modifying carboxyl groups with ethylenediamine. We found that there is an optimum degree of modification for cytotoxicity, in which 5 to 7 out of 11 carboxyl groups in RNase A are modified, toward MCF-7 and 3T3-SV-40 cells. More interestingly, the cytotoxicity of cationized RNase As correlates well with the value of [RNase activity] x [estimated concentration of RNase free from RNase inhibitor], mimicking the practical enzymatic activity of cationized RNase As in cytosol. The results indicate that cationization of a protein to an optimum level is important for maintaining protein function in the cytosol. Sophisticated protein cationization techniques will help to advance protein transduction technology.
authors.affiliation: Department of Bioscience and Biotechnology, Faculty of Engineering, Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan. yamadah@biotech.okayama-u.ac.jp
authors.forename: Junichiro
authors.initials: J
authors.lastname: Futami
authors.forename: Emiko
authors.initials: E
authors.lastname: Nukui
authors.forename: Takashi
authors.initials: T
authors.lastname: Maeda
authors.forename: Megumi
authors.initials: M
authors.lastname: Kosaka
authors.forename: Hiroko
authors.initials: H
authors.lastname: Tada
authors.forename: Masaharu
authors.initials: M
authors.lastname: Seno
authors.forename: Hidenori
authors.initials: H
authors.lastname: Yamada
mesh_terms: D000818:Animals; D002412:Cations / Q000737:chemistry / Q000378:metabolism; D002417:Cattle; D002460:Cell Line; D002470:Cell Survival / Q000502:physiology*; D006801:Humans; D051379:Mice; D021381:Protein Transport / Q000502:physiology; D012259:Ribonuclease, Pancreatic / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D002412:Cations; D012259:Ribonuclease, Pancreatic