Imaging analysis to quantitate the Interplay of membrane and cytoplasm protein dynamics

Plasma membrane proteins are extremely important in cell signaling and cellular functions. Protein expression and localization alter in response to various signals in a way that is dependent on cell type and niche. Compartmental quantification of the expression of particular proteins is a very useful means of understanding their role in cellular processes. Immunofluorescence staining is frequently used to investigate the distribution of proteins of interest. Here, we present an imaging method for quantifying the membrane to cytoplasm ratio (MCR) of proteins analyzed at single-cell resolution. This technique provides a robust quantification of membrane proteins and contributes new insights into membrane expression dynamics. We have developed a protocol that uses immunostaining to assess protein expression according to the fluorescent cellular distribution and to compute the MCR. The method was applied to measure the MCR of glucose transporter 4 (GLUT4) in response to insulin in 3T3-L1 cells, an in-vitro model for adipocyte function and adipogenesis. The results revealed informative changes in the subcellular localization of GLUT4 following insulin induction. MCR analysis is a powerful imaging tool that can be generally applied to membrane proteins to provide a rapid and efficient quantitative analysis of protein distribution and sub-cellular processes in cells.