INVESTIGATION OF EPIDERMAL GROWTH FACTOR RECEPTOR IN LIVE CELLS BY VARIOUS FLUORESCENCE CROSS-CORRELATION SPECTROSCOPY MODALITIES

Abstract

The epidermal growth factor receptor (EGFR) is a prototypical receptor tyrosine kinase involved in cell growth and proliferation and associated with various cancers. It is commonly assumed that after activation by binding of epidermal growth factor (EGF) to the extracellular domain it dimerizes followed by auto-phosphorylation of tyrosine residues at the intracellular domain. However, its oligomerization state before activation is controversial. In the absence of ligands, EGFR has been found in various, inconsistent amounts of monomeric, inactive dimeric and oligomeric forms. In addition, evidence suggests that the active conformation is not a simple dimer but contains higher oligomers. As experiments in the past have been conducted at different conditions, we investigate here the influence of cell lines (HEK293, COS-7 and CHO-K1), temperature (room temperature and 37°C) and membrane localization on the quantitation of preformed dimers using SW-FCCS, DC-FCCS, quasi PIE-FCCS, and imaging FCCS. While measurement modality, temperature, and localization on upper or lower membrane have only a limited influence on the dimerization amount observed, cell line, and location to periphery versus centre of the cell can change dimerization results significantly. The observed dimerization amount is strongly dependent on the expression level of endogenous EGFR in a cell line and also shows a strong cell-to-cell variability even within the same cell line. In addition, using imaging FCCS, we find that dimers have a tendency to be found at the periphery of cells compared to central positions.