The EH Binding protein EHBP1 operates in a ciliary functional module affected by INPP5E dysfunction.

Inositol polyphosphate-5-phosphatase E (INPP5E) encodes the ciliary protein INPP5E, which plays an important role in regulating the phospholipid membrane makeup of the primary cilium. Here we utilize proximity labelled proteomics of INPP5E to broaden the functional modules working within close proximity to the protein. In doing so, we identified the EH binding protein EHBP1 as a ciliary protein that localizes to the basal body and ciliary compartment of the primary cilium in human-derived fibroblasts and RPE cells. Additionally, we show that EHBP1 localizes to the outer membrane of developing photoreceptors in mature retinal organoids. Dysfunction of INPP5E - either due to patient-specific mutations in fibroblasts or a CRISPR/Cas9 generated knock-out in retinal organoids - causes the localization of EHBP1 to be altered. This suggests that EHBP1 functions at the primary cilium and photoreceptors where it is regulated by INPP5E. This provides further insights into the disease pathogenesis of retinal ciliopathies caused by mutations in INPP5E, and suggests that EHBP1 might be a candidate protein for retinitis pigmentosa and retinal ciliopathies.