Homer proteins mediate the interaction between STIM1 and Cav1.2 channels

STIM1 is a ubiquitous Ca2+ sensor of the intracellular, agonist-sensitive, Ca2+ stores that communicates the filling state of the Ca2+ compartments to plasma membrane store-operated Ca2+ (SOC) channels. STIM1 has been presented as a point of convergence between store-operated and voltage-operated Ca2+ influx, both inducing activation of SOC channels while suppressing Ca(v)1.2 channels. Here we report that Homer proteins play a relevant role in the communication between STIM1 and Ca(v)1.2 channels. HEK-293 cells transiently expressing Ca(v)1.2 channel subunits alpha(1), beta(2) and alpha(2)delta-1 exhibited a significant Ca2+ entry upon treatment with a high concentration of KCl. In Ca(v)1.2-expressing cells, treatment with thapsigargin (TG), to induce passive discharge of the intracellular Ca2+ stores, resulted in Ca2+ influx that was significantly greater than in cells not expressing Ca(v)1.2 channels, a difference that was abolished by nifedipine and diltiazem. Treatment with TG induces co-immunoprecipitation of Homer1 with STIM1 and the Ca(v)1.2 alpha(1) subunit. Impairment of Homer function by introduction of the synthetic PPKKFR peptide into cells, which emulates the praline-rich sequences of the PPXXF motif, or using siRNA Homer1, reduced the association of STIM1 and the Ca(v)1.2 alpha(1) subunit. These findings indicate that Homer is important for the association between both proteins. Finally, treatment with siRNA Homer1 or the PPKKFR peptide enhanced the nifedipine-sensitive component of TG response in Ca(v)1.2-expressing cells. Altogether, these findings provide evidence for a new role of Homer1 supporting the regulation of Ca(v)1.2 channels by STIM1. (C) 2015 Elsevier B.V. All rights reserved.