The role of homer family adaptor proteins in regulation of store-operated calcium influx in A431 cells

Abstract

332 The major pathways for Ca 2+ influx in nonexcitable cells are store-operated channels (SOC). SOCs are activated by depletion of intracellular calcium stores. In the previous studies we used patch-clamp electrophysiology to describe the properties of store-operated channels I min in human carcinoma A431 cell lines. I min are gated by direct protein-protein interaction with inositol-1,4,5-trisphosphate receptor type 1 (IP 3 R1). We supposed that this interaction might be facilitated by scaffold proteins of Homer family. Homer family proteins specifically bind to unique PPXXF sequence in IP 3 R and in some other proteins. Several isoforms of Homer proteins exist. Homer 1c isoforms have coilcoiled domain, which mediate homooligomerization. That is why Homer 1c oligomers can form macromolecular complexes with partner proteins. Homer 1a isoform lacking coil-coiled domain can disrupt macromolecular complexes of Homer 1c and its partner proteins. The aim of this study was to determine the role of Homer protein in activation of store-operated channels. We applied the Gst-Homer recombinant protein (concentration 100 nM) to inside-out patches excised from A431 cells using 105 mM Ba 2+ in the pipette as a current carrier. Application of Gst-Homer 1c to the cytosolic surface of the patch did not activate channels. Addition of GST Homer 1a to the same patch resulted in an activation of I min channels.