title: Polymeric microspheres as protein transduction reagents.
abstract: Discovering the function of an unknown protein, particularly one with neither structural nor functional correlates, is a daunting task. Interaction analyses determine binding partners, whereas DNA transfection, either transient or stable, leads to intracellular expression, though not necessarily at physiologically relevant levels. In theory, direct intracellular protein delivery (protein transduction) provides a conceptually simpler alternative, but in practice the approach is problematic. Domains such as HIV TAT protein are valuable, but their effectiveness is protein specific. Similarly, the delivery of intact proteins via endocytic pathways (e.g. using liposomes) is problematic for functional analysis because of the potential for protein degradation in the endosomes/lysosomes. Consequently, recent reports that microspheres can deliver bio-cargoes into cells via a non-endocytic, energy-independent pathway offer an exciting and promising alternative for in vitro delivery of functional protein. In order for such promise to be fully exploited, microspheres are required that (i) are stably linked to proteins, (ii) can deliver those proteins with good efficiency, (iii) release functional protein once inside the cells, and (iv) permit concomitant tracking. Herein, we report the application of microspheres to successfully address all of these criteria simultaneously, for the first time. After cellular uptake, protein release was autocatalyzed by the reducing cytoplasmic environment. Outside of cells, the covalent microsphere-protein linkage was stable for ≥90 h at 37 °C. Using conservative methods of estimation, 74.3% ± 5.6% of cells were shown to take up these microspheres after 24 h of incubation, with the whole process of delivery and intracellular protein release occurring within 36 h. Intended for in vitro functional protein research, this approach will enable study of the consequences of protein delivery at physiologically relevant levels, without recourse to nucleic acids, and offers a useful alternative to commercial protein transfection reagents such as Chariot™. We also provide clear immunostaining evidence to resolve residual controversy surrounding FACS-based assessment of microsphere uptake.
authors.affiliation: From the ‡School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham, B4 7ET, UK;
authors.forename: David
authors.initials: D
authors.lastname: Nagel
authors.affiliation: §School of Engineering and Applied Science, Aston University, Aston Triangle, Birmingham, B4 7ET, UK;
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Behrendt
authors.affiliation: §School of Engineering and Applied Science, Aston University, Aston Triangle, Birmingham, B4 7ET, UK;
authors.forename: Gwen F
authors.initials: GF
authors.lastname: Chimonides
authors.affiliation: From the ‡School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham, B4 7ET, UK;
authors.forename: Elizabeth E
authors.initials: EE
authors.lastname: Torr
authors.affiliation: From the ‡School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham, B4 7ET, UK; ‖Aston Research Centre for Healthy Aging, Aston University, Aston Triangle, Birmingham, B4 7ET, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: Devitt
authors.affiliation: §School of Engineering and Applied Science, Aston University, Aston Triangle, Birmingham, B4 7ET, UK;
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Sutherland
authors.affiliation: From the ‡School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham, B4 7ET, UK; a.v.hine@aston.ac.uk.
authors.forename: Anna V
authors.initials: AV
authors.lastname: Hine
mesh_terms: D004247:DNA / Q000737:chemistry / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D006801:Humans; D008863:Microspheres; D011108:Polymers / Q000737:chemistry*; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D011108:Polymers; D011506:Proteins; D004247:DNA