Electroporation of extraneous proteins into CHO cells: increased efficacy by utilizing centrifugal force and microsecond electrical pulses

Applying Antibodies Inside Cells: Principles and Recent Advances in Neurobiology, Virology and Oncology

To interfere with cell function, many scientists rely on methods that target DNA or RNA due to the ease with which they can be applied. Proteins are usually the final executors of function but are targeted only indirectly by these methods. Recent advances in targeted degradation of proteins based on proteolysis-targeting chimaeras (PROTACs), ubiquibodies, deGradFP (degrade Green Fluorescent Protein) and other approaches have demonstrated the potential of interfering directly at the protein level for research and therapy. Proteins can be targeted directly and very specifically by antibodies, but using antibodies inside cells has so far been considered to be challenging. However, it is possible to deliver antibodies or other proteins into the cytosol using standard laboratory equipment. Physical methods such as electroporation have been demonstrated to be efficient and validated thoroughly over time. The expression of intracellular antibodies (intrabodies) inside cells is another way to interfere with intracellular targets at the protein level. Methodological strategies to target the inside of cells with antibodies, including delivered antibodies and expressed antibodies, as well as applications in the research areas of neurobiology, viral infections and oncology, are reviewed here. Antibodies have already been used to interfere with a wide range of intracellular targets. Disease-related targets included proteins associated with neurodegenerative diseases such as Parkinson's disease (α-synuclein), Alzheimer's disease (amyloid-β) or Huntington's disease (mutant huntingtin [mHtt]). The applications of intrabodies in the context of viral infections include targeting proteins associated with HIV (e.g. HIV1-TAT, Rev, Vif, gp41, gp120, gp160) and different oncoviruses such as human papillomavirus (HPV), hepatitis B virus (HBV), hepatitis C virus (HCV) and Epstein-Barr virus, and they have been used to interfere with various targets related to different processes in cancer, including oncogenic pathways, proliferation, cell cycle, apoptosis, metastasis, angiogenesis or neo-antigens (e.g. p53, human epidermal growth factor receptor-2 [HER2], signal transducer and activator of transcription 3 [STAT3], RAS-related RHO-GTPase B (RHOB), cortactin, vascular endothelial growth factor receptor 2 [VEGFR2], Ras, Bcr-Abl). Interfering at the protein level allows questions to be addressed that may remain unanswered using alternative methods. This review addresses why direct targeting of proteins allows unique insights, what is currently feasible in vitro, and how this relates to potential therapeutic applications.

Transduction and utility of the granulocyte-macrophage colony-stimulating factor gene into monocytes and dendritic cells by adeno-associated virus

The genetic manipulation of antigen-presenting dendritic cells (DC) offers promise for stimulating the immune response, in particular for anticancer and antiviral protocols. As adeno-associated virus (AAV) has shown promise as a gene delivery vector for transducing a variety of hematopoietic cell types, we have investigated AAV's ability to genetically alter DC. In this analysis, we modified the standard granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) treatment of adherent monocytes to generate DC. In our protocol, adherent monocytes were first infected with an AAV/GM-CSF/Neo vector, and the addition of IL-4 was delayed for 2 days to allow for a brief period of monocyte proliferation. AAV-mediated transduction of the GM-CSF and Neo genes into monocytes/DC precursors was demonstrated by G418 selection, GM-CSF secretion, GM-CSF RNA expression (reverse transcriptase-polymerase chain reaction amplification [RT-PCR]), and cell proliferation. Cells resulting from infection with AAV/GM-CSF/Neo virus, and subsequent IL-4 and tumor necrosis factor-alpha (TNF-alpha) treatment, displayed multiple classic markers consistent with mature DC. Finally, chromosomal integration of the AAV vector was also demonstrated in sorted CD83+ DC. These data strongly suggest that AAV vectors will be useful for the genetic manipulation of DC and suggest that the transduction of the GM-CSF gene was able to fully replace the need for exogenous GM-CSF in the production of mature DC.

Electric pulse-induced precipitation of biological macromolecules in electroporation

We found that electric discharge through solution of biological macromolecules (DNA, RNA and proteins) causes precipitation of significant portions of these macromolecules. This precipitation is a consequence of the interaction of biological macromolecules with the metal ions solubilized from the anode plate by the electric pulse, and occurs in both absence and presence of the cells in poration medium. Precipitated fractions of macromolecules sediments at the centrifugation speed used to pellet eukaryotic cells and does not dissolve when washed with buffer. Our data indicate a complication of the direct evaluation of electroporation efficiency based on the assumption that electroporated biological macromolecules which remain associated with the cells after several washes, are successfully electroinjected into the cytoplasm of cells.

Excess protein in nuclei isolated from heat-shocked cells results from a reduced extractability of nuclear proteins

An excellent correlation has been established between the quantity of protein associated with nuclei isolated from heat-shocked cells and the level of hyperthermic cell killing. However, controversy remains about whether increases in nuclear-associated protein result from a heat-induced migration of cytoplasmic proteins into the nucleus or because hyperthermia reduces the solubility of nuclear proteins in the detergent buffers commonly used to isolate nuclei. To address this controversy, the nuclear protein content was measured in whole and detergent-extracted cells before and following hyperthermia. It was found that hyperthermia caused no significant change in the nuclear protein content of whole, unextracted cells, and when fluorescently labeled proteins were microinjected into the cytoplasm no gross change in the selective permeability of the nuclear membrane to soluble proteins was observed during or following hyperthermia. Measurements in extracted cells showed that the detergent buffers removed protein from both the nucleus and cytoplasm of control, nonheated cells and that hyperthermia reduced the extractability of both nuclear and cytoplasmic proteins. The amount of protein found in nuclei isolated from heated cells approached that observed in nuclei within nonheated whole cells as the hyperthermic exposure was increased. Thus, the dose-dependent, two- to threefold increase in the protein content of nuclei isolated from heated cells represents a heat-induced reduction in the extractability of proteins normally present within cell nuclei and does not result from a mass migration of cytoplasmic proteins into the nucleus, although some specific proteins (e.g., the 70 KDa heat shock protein) do migrate to the nucleus following heat shock. Differential scanning calorimetry (DSC) measurements of whole cells, isolated nuclei, cytoplasts, and karyoplasts supported these conclusions and suggested that most of the detergent-insoluble proteins remaining in the nuclei and cytoplasm of heated cells are in their native state. Thus, a relatively small amount of denatured protein may be sufficient to initiate and sustain insoluble protein aggregates comprised of mostly native proteins. Analyses of the DSC data also implied that the previously identified critical target proteins, predicted to have a Tm of 46.0 degrees C, are present in both the nucleus and cytoplasm.

Electroporation and commercial liposomes efficiently deliver soluble protein into the MHC class I presentation pathway. Priming in vitro and in vivo for class I-restricted recognition of soluble antigen

Class I major histocompatibility complex (MHC)-restricted cytotoxic T lymphocyte responses to ovalbumin (OVA) were evaluated following delivery of soluble antigen mixed with commercial liposomes or by electroporation of soluble protein into target cells. Splenic antigen presenting cells (APC) and transfected L cell lines were sensitised for recognition by OVA-specific, class I-restricted T hybridomas when antigen was introduced by either method into live cells. Delivery of soluble OVA by both electroporation and commercial liposomes proved more efficient than osmotic loading in sensitising for class I presentation. OVA-specific cytotoxic T lymphocytes (CTL) were effectively primed in naive mice following reinjection of spleen cells pulsed with soluble OVA encapsulated by liposomes or electroporated in vitro. These CTL recognised the well defined OVA257-264 determinant in association with H-2Kb and were derived under conditions where CTL activity obtained from cross priming by soluble OVA alone was undetectable. In addition, using electroporation and commercial liposomes, the loading of APC for OVA recognition required intact MHC-linked antigen presentation genes deleted in the T2-Kb cell line. Antigen delivery to APC by electroporation and commercial liposomes provides a simple and efficient way of studying class I-restricted T cell recognition of soluble protein antigens.