Identification Of Heat‐Shock Protein HSC70 As A Binding‐Partner Interacting With The Intracellular C‐Terminal Domain Of The Angiotensin II Receptor AT1aR In Proximal Tubules

The main physiological effects of Angiotensin II are related to its binding to Angiotensin II type I receptors (AT1) that are present in both apical and basolateral membranes of proximal tubule cells, where they are known to show functional differences. Little is known about the protein‐protein interactions that regulate the trafficking of this receptor, although its carboxy‐terminal cytoplasmic domain has recently been shown to interact with several classes of cytoplasmic and transmembrane proteins that regulate different aspects of its physiology. The present study aimed to identify interacting proteins with the cytoplasmic tail of AT1R in renal cortex, in an attempt to elucidate mechanisms involved in specific functions of apical and basolateral receptors. Employing GST pull‐down assay with the carboxy‐terminal domain of rat AT1a receptor as a fusion protein and mass spectrometry, we have isolated HSC70 as a binding‐partner interacting protein. The HSC70‐AT1a receptor association was confirmed by affinity chromatography, coimmunoprecipitation, immunofluorescence and confocal microscopy, showing co‐localization of these proteins in proximal tubules. In conclusion, we have isolated a novel binding‐partner with the cytoplasmic domain of the AT1a receptor that might affect its signaling, trafficking and/or ligand‐receptor affinity with relevant physiological consequences.