Mutations in the PKD1 gene result in
autosomal dominant polycystic kidney disease (
ADPKD), the most common monogenetic cause of
end-stage renal disease (
ESRD) in humans. Previous reports suggested that PKD1, together with PKD2/
polycystin-2, may function as a receptor-
cation channel complex at cilia and on intracellular membranes and participate in various signaling pathways to regulate cell survival, proliferation and macroautophagy/autophagy. However, the exact molecular function of PKD1 and PKD2 has remained enigmatic. Here we used Pkd1-deficient mouse inner medullary collecting duct cells (mIMCD3) genetically deleted for Pkd1, and tubular epithelial cells isolated from nephrons of
doxycycline-inducible conditional pkd1fl/fl;Pax8rtTA;TetOCre+ knockout mice to show that the lack of Pkd1 caused diminished lysosomal acidification, LAMP degradation and reduced CTSB/
cathepsin B processing and activity. This led to an impairment of autophagosomal-lysosomal fusion, a lower delivery of ubiquitinated cargo from multivesicular bodies (MVB)/exosomes to lysosomes and an enhanced secretion of unprocessed CTSB into the extracellular space. The TFEB-dependent lysosomal biogenesis pathway was however unaffected. Pkd1-deficient cells exhibited increased activity of the
calcium-dependent CAPN (
calpain)
proteases, probably due to a higher
calcium influx. Consistent with this notion CAPN inhibitors restored lysosomal function, CTSB processing/activity and autophagosomal-lysosomal fusion, and blocked CTSB secretion and LAMP degradation in pkd1 knockout cells. Our data reveal for the first time a lysosomal function of PKD1 which keeps CAPN activity in check and ensures lysosomal integrity and a correct autophagic flux.Abbreviations: acCal: acetyl-
calpastatin peptide;
ADPKD:
autosomal dominant polycystic kidney disease; CI-1:
calpain inhibitor-1; CQ:
chloroquine; Dox:
doxycycline; EV: extracellular vesicles; EXO: exosomes; LAMP1/2:
lysosomal-associated membrane protein 1/2;
LGALS1/GAL1/
galectin-1:
lectin, galactose binding, soluble 1; LMP: lysosomal membrane permeabilization; mIMCD3: mouse inner medullary collecting duct cells; MV: microvesicles; MVB: multivesicular bodies; PAX8: paired box 8; PKD1/
polycystin-1:
polycystin 1,
transient receptor potential channel interacting; PKD2/
polycystin-2:
polycystin 2,
transient receptor potential cation channel; Tet:
tetracycline; TFEB:
transcription factor EB; VFM: vesicle-free medium; WT: wild-type.