Differential effect of OCRL1 patient mutations on protein localization, and sensitivity to FDA‐approved drug suppression of cellular phenotypes associated with Lowe syndrome

Abstract

Lowe Syndrome (LS) is a lethal X‐linked genetic disorder caused by mutations in the OCRL1 gene, which encodes the lipid phosphatase Ocrl1. LS children present with congenital cataracts, low molecular weight proteinuria and mental retardation as characteristic clinical symptoms. Progressive renal dysfunction is the main cause of death. Ocrl1 localizes to the trans Golgi network (TGN), early endosomes and the plasma membrane and has been shown to participate in vesicle trafficking. We established that LS patient cells are defective in fluid phase uptake and ciliogenesis, which are critical processes required for kidney function. Over 100 OCRL1 mutations have been identified in LS, but their specific impact on cellular processes is unknown. However, our results indicate that different mutations have diverse effect on Ocrl1 localization and on triggering cellular phenotypes.We expressed GFP‐Ocrl1 (WT and several patient mutants) in human kidney proximal tubule (HK2) cells and LS fibroblasts lacking endogenous Ocrl1. The co‐localization of WT/mutant Ocrl1 with various organelle markers was quantitatively analyzed and different cellular processes/phenotypes were monitored. Our data indicates that in general, N‐terminal PH domain mutations resulted in redistribution of Ocrl1 to the cytoplasm, ASH‐RhoGAP domain mutations prevented localization of Ocrl1 to TGN and mutations in the phosphatase domain resulted in Golgi apparatus (GA) morphological abnormalities.Importantly, using a drug repurposing approach we identified two FDA‐approved compounds able to differentially suppress LS cellular phenotypes; the ability of these drugs to alleviate defects associated with specific Ocrl1 patient mutants was also analyzed. Our data indicate that while some patient OCRL1 mutations require treatment with both drugs, others only necessitate one for LS cellular phenotype suppression.This study determined for the first time the effect of different patient mutation on the Ocrl1 intracellular localization and on various LS‐associated cellular phenotypes. Further, it explored how different OCRL1 mutations determined the sensitivity of cells to the newly identified FDA‐approved drugs with ameliorating effects on LS phenotypes. It also contributes to expand our understanding of the molecular mechanism of LS pathogenesis and provide the basis for the development of a LS‐specific therapeutic.Support or Funding InformationLowe Syndrome TrustNational Institutes of Health (NIH)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.