Loss-of-function mutations in the OCRL gene, which encodes the
phosphatidylinositol [PI] 4,5-bisphosphate [PI(4,5)P2] 5-phosphatase OCRL, cause defective endocytosis and proximal tubule dysfunction in
Lowe syndrome and
Dent disease 2. The defect is due to increased levels of PI(4,5)P2 and aberrant actin polymerization, blocking endosomal trafficking. PI 3-phosphate [PI(3)P] has been recently identified as a coactivator with PI(4,5)P2 in the actin pathway. Here, we tested the hypothesis that
phosphoinositide 3-kinase (PI3K) inhibitors may rescue the endocytic defect imparted by OCRL loss, by rebalancing
phosphoinositide signals to the actin machinery. The broad-range PI3K inhibitor
copanlisib and class IA p110α PI3K inhibitor
alpelisib reduced aberrant actin polymerization in OCRL-deficient human kidney cells in vitro. Levels of PI 3,4,5-trisphosphate, PI(4,5)P2 and PI(3)P were all reduced with
alpelisib treatment, and
siRNA knockdown of the PI3K catalytic subunit p110α phenocopied the actin phenotype. In a humanized OcrlY/- mouse model,
alpelisib reduced endosomal actin staining while restoring stress fiber architecture and levels of
megalin at the plasma membrane of proximal tubule cells, reflected by improved endocytic uptake of low molecular weight
proteins in vivo. Thus, our findings support the link between
phosphoinositide lipids, actin polymerization and endocytic trafficking in the proximal tubule and represent a proof-of-concept for repurposing
alpelisib in
Lowe syndrome/Dent disease 2.