?

Phenotypes

Mouse phenotype:

increased circulating alanine transaminase level

Subcellular localization

basal body, Nucleoli, Golgi apparatus

Function

Three heterologously expressed BLOC-1/BORC components (GFP-BLOC1S4/-BLOC1S2/-SNAPIN) could coimmunoprecipitate PC1-BF, but not CD16.7-BF (Fig. 4A). To rule out the possibility of overexpression artefacts from heterologously expressing BLOC-1/BORC subunits, we validated antibodies to BLOC1S1/2 and SNAPIN using CRISPR-mediated knockout or shRNA based knockdown cell lines of the respective subunits (Supplementary Fig. S4). These validated antibodies were then used in a PLA with PC1 and BLOC1S1/SNAPIN in NHPTK RECs (Fig. 4B). A positive PLA reaction was observed with PC1 when paired with BLOC1S1 or SNAPIN, but not when paired with a negative control (LAMINB1), or conducted with no primary antibody (Fig. 4B). Notably, we also find that PC1 specifically interacts with ciliary and lysosomal proteins, including components of the biogenesis of lysosome-related organelles complex (BLOC-1) and BLOC-one-related-complex (BORC). BLOC-1/BORC colocalizes with PC1 at lysosomes and cilia and is required for proper ciliary PC1 localization. In addition, PC1 mutant kidney cells derived from an ADPKD patient display defects in BLOC-1/BORC distribution. Renal cells depleted of PC1 exhibit abnormal lysosomal distribution, similar to those depleted of BLOC-1/BORC components. Finally, shRNA knockdown of BLOC-1/BORC components promoted cystogenesis in a 3D in vitro cyst model, and this could be attenuated by heterologous expression of the C terminus of PC1. This rich dataset thus links the BLOC-1/BORC complex to PC1 function and can be further mined for additional mechanistic insights into the PC1/2 ADPKD proteins(41086943).