Use of Membrane Potential to Achieve Transmembrane Modification with an Artificial Receptor

Fluorescence Signal Amplification by Using β-Galactosidase for Flow Cytometry; Advantages of an Endogenous Activity-Free Enzyme

We previously proposed using a hydrolysis enzyme for fluorescent signal amplification in flow cytometric detection of antigen proteins, which was named the catalyzed reporter penetration (CARP) method. In this method, antigen proteins are labeled with enzyme-modified antibodies, and then fluorophore-modified substrates stain cells by penetrating the cell membrane upon hydrolysis of the substrate. We proved the concept by using alkaline phosphatase (AP) as the hydrolysis enzyme. However, a required prior inactivation process of endogenous AP activity on the cell surface risked disrupting recognition of antigen proteins by antibodies. In this report, the CARP method was extended to β-galactosidase (β-gal) as an amplification enzyme, which circumvented the requirement of an initial inactivation process because endogenous β-gal activity on the surface of examined cells was found to be negligible. The substrate structure for β-gal was optimized and used for the CARP method. The CARP method showed significantly higher fluorescent signals than a conventional method using fluorophore-modified antibodies. Moreover, the degree of amplification of the fluorescence signal was higher for antigens with low expression levels, showing that the CARP method is a suitable signal amplification method over current conventional approaches.

Signal amplification in flow cytometry for cell surface antigen analysis

Signal enhancing systems have been introduced to enable detection of cell surface antigens by flow cytometry. Cell surface antigens are important targets that describe the function and lineage of cells. Although flow cytometry is an effective tool for analysing cell surface antigens, this technique has poor sensitivity, which prohibits the detection of many important antigens on cell membranes. Thus, signal amplification is essential for developing practical tools for evaluating cell surface antigens by flow cytometry. Using a bright fluorophore or fluorescent polymer incorporated into antibodies is a straightforward strategy to improve flow cytometry sensitivity but may affect the functional characteristics of the labelled antibody. In contrast, enzymatic signal amplification is a more practical and efficient strategy to improve sensitivity that should not affect antibody activity. Although enzymatic signal amplification still has a number of drawbacks, this approach is a promising strategy to analyse cell surface antigens.

Folate receptor-specific cell-cell adhesion by using a folate-modified peptide-based anchor

We report here a folate-modified membrane anchor for cell surface modification to induce cell adhesion to target cells. The membrane anchor region, which was consisted of cationic lysine residues and palmitoyl group-modified residues, was modified with folate through an oligoethlene glycol linker. The peptide anchor was modified on to the cell membrane by using β-cyclodextrin as a solubilizer of the peptide anchor. After modification, the peptide anchor disappeared from the cell membrane via endocytotic uptake or dissociation from the cell membrane. However, the endocytosed peptide was represented on the cell surface via recycling endosome pathway. The obtained folate-modified cells successfully adhered on to target cells which expressed folate receptor α via ligand-receptor specific interaction and adhesion continued at least 4 hours.