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 labeled proteomics of INPP5E to broaden the number of known functional modules that work in 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 rudimentary outer segment membrane of developing photoreceptors in retinal organoids. Dysfunction of INPP5E - either due to pathogenic variants in human fibroblasts or CRISPR/Cas9-generated loss-of-function variants in human retinal organoids - causes the localization of EHBP1 to be altered. Our data suggest 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 pathogenic variants in INPP5E, and suggests that EHBP1 might be a candidate gene for retinal ciliopathies.