Membrane localization of FK506‐binding proteins FKBP51 and FKBP52, immunophilins that are part of the endothelial store‐operated calcium entry heterocomplex

Disruption of the endothelium leads to increased vascular permeability. Activation of store‐operated calcium (SOC) entry promotes inter‐endothelial cell gap formation. Canonical transient receptor potential proteins 1 and 4 (TRPC1/4) are subunits of the calcium‐selective SOC entry channel I soc , and rat pulmonary artery endothelial cells (PAECs) and pulmonary microvascular endothelial cells (PMVECs) express the I soc channel subunits. Data from our laboratory have implicated FK506 binding proteins (FKBPs) as regulators of SOC entry with FKBP52 facilitating and FKBP51 inhibiting activation. However, mechanisms by which immunophilins regulate SOC entry are unknown. We first sought to determine whether the immunophilins localize to the endothelial membrane where the TRPC1/4 heterocomplex is found. Membrane‐cytoskeleton preparations of PAECs and PMVECs resolved FKBP51 and FKBP52 in plasma membrane fractions, and immunocytochemistry revealed localization to cell‐cell borders. Next, co‐immunoprecipitation experiments were performed to determine whether these immunophilins contribute to the endothelial TRPC1/4 heterocomplex. We observed that FKBP52 co‐immunoprecipitated with TRPC4. Collectively, these data reveal membrane localization of FKBP51 and FKBP52, suggesting that they might contribute to the endothelial SOC entry heterocomplex. Supported by 5R00HL089361