Functional Analyses of Live-cell Membrane Proteins Using Ion-sensitive Field-effect Transistor

Abstract

Functional analyses of the membrane proteins on live cells using ion-sensitive field effect transistors (ISFETs) are described in this review. Expressions of human epidermal growth factor receptor (HER2) and epidermal growth factor receptor (EGFR) on live cancer cells have been detected using cell-based field effect transistors (FETs) in combination with enzymatic signal amplification. A good correlation could be obtained between the pH values measured with the cell-based FETs and the fluorescence intensities measured using the fluorescence-activated cell sorting (FACS), with a correlation coefficient of 0.976. The interactions between membrane proteins/transporters and ligands at cell membranes using a cell-based FET with an oocyte were monitored non-invasively. Xenopus laevis oocytes were injected with the capped human organic anion transporting peptide C (hOATP-C) cRNA. Estrone-3-sulfate (E3S) was used as a substrate for hOATP-C during the uptake measurements. The transporting kinetics of the substrate when mediated by the wild-type and the mutant-type transporters could be distinguished using the cell-based FETs. It was found that the signal generation mechanism of the cell-based transistor could be explained by direct or indirect proton transport via the transporters. Measurements of expression levels of membrane proteins is important to analyze their signaling pathways and cellular outcomes. Moreover, membrane proteins and transporters constitute one of the most extensively studied classes of drug targets. Therefore, a system based on cell-based FETs would be suitable for rapid and cost-effective identification of biomarkers and high throughput analysis of drug candidates.