RPGR protein complex regulates proteasome activity and mediates store-operated calcium entry
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Sarita Rani Patnaik1,2, Xun Zhang1, Lincoln Biswas1, Saeed Akhtar3, Xinzhi Zhou1, Deva Krupakar Kusuluri2, James Reilly1, Helen May-Simera2, Susan Chalmers4, John G. McCarron4 and Xinhua Shu1
1Department of Life Sciences, Glasgow Caledonian University, Glasgow G4 0BA, Scotland
2Institute of Molecular Physiology, Johannes Gutenberg-Universität Mainz, D-55128 Mainz, Germany
3Cornea Research Chair, Department of Optometry, King Saud University, Riyadh 11433, Kingdom of Saudi Arabia
4Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow G4 0RE, Scotland
Xinhua Shu, email: Xinhua.Shu@gcu.ac.uk
Keywords: ciliopathy; RPGR complex; actin cytoskeleton; endoplasmic reticulum; store-operated Ca2+ entry
Received: December 11, 2017 Accepted: April 07, 2018 Published: May 01, 2018
Ciliopathies are a group of genetically heterogeneous disorders, characterized by defects in cilia genesis or maintenance. Mutations in the RPGR gene and its interacting partners, RPGRIP1 and RPGRIP1L, cause ciliopathies, but the function of their proteins remains unclear. Here we show that knockdown (KD) of RPGR, RPGRIP1 or RPGRIP1L in hTERT-RPE1 cells results in abnormal actin cytoskeleton organization. The actin cytoskeleton rearrangement is regulated by the small GTPase RhoA via the planar cell polarity (PCP) pathway. RhoA activity was upregulated in the absence of RPGR, RPGRIP1 or RPGRIP1L proteins. In RPGR, RPGRIP1 or RPGRIP1L KD cells, we observed increased levels of DVl2 and DVl3 proteins, the core components of the PCP pathway, due to impaired proteasomal activity. RPGR, RPGRIP1 or RPGRIP1L KD cells treated with thapsigargin (TG), an inhibitor of sarcoendoplasmic reticulum Ca2+- ATPases, showed impaired store-operated Ca2+ entry (SOCE), which is mediated by STIM1 and Orai1 proteins. STIM1 was not localized to the ER-PM junction upon ER store depletion in RPGR, RPGRIP1 or RPGRIP1L KD cells. Our results demonstrate that the RPGR protein complex is required for regulating proteasomal activity and for modulating SOCE, which may contribute to the ciliopathy phenotype.
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