Biochemical Fractionation of Membrane Receptors in the Nucleus

Fractionation of cytoplasmic and nuclear proteins is a well-recognized biochemical technique to detect the intracellular distribution and expression level of proteins of interest. In the last decade, accumulating evidence shows that various types of cell surface receptors, such as receptor tyrosine kinases (RTKs), peptide hormone receptors, and cytokine receptors, are detected in the nuclei. Therefore, subcellular fractionation, including nonnuclear/nuclear extraction and the subsequent subnuclear fractionation without detectable crosscontamination during the process, is critical for studying membrane receptors that transit from the cell surface to the nucleus. Here, we utilize the epidermal growth factor receptor (EGFR) tyrosine kinase as an example of a comprehensive biochemical protocol for isolating membrane receptors in the nuclei of cancer cells.