OCRL1 function in renal epithelial membrane traffic.
The X-linked disorder Lowe syndrome arises from mutations in OCRL1, a lipid phosphatase that hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP(2)). Most patients with Lowe syndrome develop proteinuria very early in life. PIP(2) dynamics are known to modulate numerous steps in membrane trafficking, and it has been proposed that OCRL1 activity regulates the biogenesis or trafficking of the multiligand receptor megalin. To examine this possibility, we investigated the effects of siRNA-mediated OCRL1 knockdown on biosynthetic and postendocytic membrane traffic in canine and human renal epithelial cells. Cells depleted of OCRL1 did not have significantly elevated levels of cellular PIP(2) but displayed an increase in actin comets, as previously observed in cultured cells derived from Lowe patients. Using assays to independently quantitate the endocytic trafficking of megalin and of megalin ligands, we could observe no defect in the trafficking or function of megalin upon OCRL1 knockdown. Moreover, apical delivery of a newly synthesized marker protein was unaffected. OCRL1 knockdown did result in a significant increase in secretion of the lysosomal hydrolase cathepsin D, consistent with a role for OCRL1 in membrane trafficking between the trans-Golgi network and endosomes. Together, our studies suggest that OCRL1 does not directly modulate endocytosis or postendocytic membrane traffic and that the renal manifestations observed in Lowe syndrome patients are downstream consequences of the loss of OCRL1 function.
Cui
Shanshan
S
Renal Electrolyte Division, University of Pittsburgh Medical School, Pittsburgh, Pennsylvania 15261, USA.
Guerriero
Christopher J
CJ
Szalinski
Christina M
CM
Kinlough
Carol L
CL
Hughey
Rebecca P
RP
Weisz
Ora A
OA
D000818:Animals; D002460:Cell Line; D004285:Dogs; D004705:Endocytosis / Q000187:drug effects; D004848:Epithelium / Q000378:metabolism; D018014:Gene Transfer Techniques; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D006867:Hydrolases / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D026561:Low Density Lipoprotein Receptor-Related Protein-2 / Q000378:metabolism*; D008247:Lysosomes / Q000201:enzymology; D008970:Molecular Weight; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects; D011506:Proteins / Q000737:chemistry / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology
D019267:Hemagglutinin Glycoproteins, Influenza Virus; D026561:Low Density Lipoprotein Receptor-Related Protein-2; D011506:Proteins; D034741:RNA, Small Interfering; D006867:Hydrolases; D010744:Phosphoric Monoester Hydrolases; C075695:OCRL protein, human