A non-invasive technique for quantifying and isolating fused cells

Precise Detection on Cell-Cell Fusion by a Facile Molecular Beacon-Based Method

Cell-cell fusion studies provide an experimental platform for evaluating disease progression and investigating cell infection. However, to realize sensitive and quantitative detection on cell-cell fusion is still a challenge. Herein, we report a facile molecular beacon (MB)-based method for precise detection on cell-cell fusion. By transfection of the spike protein (S protein) and enhanced green fluorescent protein (EGFP) in HEK 293 cells, the virus-mimicking fusogenic effector cells 293-S-EGFP cells were constructed to interact with target cells. Before mixing the effector cells with the target cells, the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression in 293-S-EGFP cells was silenced, and the MB for GAPDH mRNA detection was delivered into the GAPDH silenced 293-S-EGFP cells. Once cell-cell fusion occurred, MB migrated from the GAPDH silenced effector cells to the target cells and hybridized with GAPDH mRNA in the target cells to induce fluorescence emission. The cell-cell fusion can be easily visualized and quantitated by fluorescence microscopy and flow cytometry. The fluorescence intensity is strongly dependent on the number of fused target cells. This MB-based method can easily identify the differences in the cell fusions for various target cells with different angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2) expression levels, resulting in dramatically different fluorescence intensities in fused target cells. Our study provides a convenient and efficient quantitative detection approach to study cell-cell fusion.

Characterization of the plasma membrane localization and orientation of HPV16 E5 for cell-cell fusion

Human papillomavirus (HPV) is a non-enveloped DNA virus with an approximately 8000 base pair genome. Infection with certain types of HPV is associated with cervical cancer, although the molecular mechanism by which HPV induces carcinogenesis is poorly understood. Three genes encoded by HPV16 are regarded as oncogenic - E5, E6, and E7. The role of E5 has been controversial. Expression of HPV16 E5 causes cell-cell fusion, an event that can lead to increased chromosomal instability, particularly in the presence of cell cycle checkpoint inhibitors like HPV16 E6 and E7. Using biochemical and cell biological assays to better understand HPV16 E5, we find that HPV16 E5 localizes to the plasma membrane with an intracellular amino terminus and an extracellular carboxyl-terminus. Further, HPV16 E5 must be expressed on both cells for cell fusion to occur. When the extracellular epitope of HPV16 E5 is targeted with an antibody, the number of bi-nucleated cells decreases.