Purchase this article with an account.
Hemangi Patil, Paulo A. Ferreira; The Components of the Ocular-Renal Disease Interactome Comprised of RPGR, RPGRIP1α1 and NPHP4 Perform Complementary Roles in Its Exit from the Endoplasmic Reticulum. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1619.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The Retinitis Pigmentosa GTPase Regulator Protein 1 (RPGRIP1) forms a scaffolding complex with the Retinitis Pigmentosa GTPase Regulator (RPGR) and nephrocystin-4 (NPHP4). Mutations affecting the RPGRIP1 interactome cause syndromic retinal dystrophies, but the molecular and subcellular processes mediated by this interactome are not understood. RPGR1-19 and RPGRORF15 isoforms determine the subcellular localization of RPGRIP1α1 to the endoplasmic reticulum (ER) and cytosolic compartments, respectively (Patil, H. et al. 2011 Biology Open, in press). However, the role(s) of NPHP4 in these subcellular targeting processes and the roles of RPGRIP1 and RPGR isoforms in allied NPHP4 function(s) are lacking. We seek to test the hypothesis that the interplay between RPGR, RPGRIP1α1 and NPHP4, modulate their subcellular targeting and sorting.
We performed microscopy analysis of cultured cells ectopically expressing RPGR, RPGRIP1α1 or NPHP4, singly or in combination, and with and without disease mutations known to uncouple the formation of binary complexes, to determine interdependent subcellular roles between wild-type and mutant proteins.
NPHP4 alone is targeted to the ER, where, like RPGR1-19, it interfaces with restricted ER domains labeled with calreticulin. Co-expression of NPHP4 or RPGR1-19 with RPGRIP1α1 promotes the clearance of intracellular deposits of RPGRIP1α1 and its targeting and co-localization with NPHP4 or RPGR1-19 to the ER. In contrast, RPGRORF15 promotes the exit of NPHP4 from the ER and its dispersion and co-localization with RPGRORF15 throughout the cytosolic compartment. Co-expression of RPGRORF15 with NPHP4 and RPGRIP1α1 has a similar subcellular targeting effect on the triad complex. Co-expression of NPHP4 with mutant RPGRORF15 and wild-type RPGRIP1α1, wild-type RPGRORF15 and mutant RPGRIP1α1 or mutant RPGRORF15 and mutant RPGRIP1α1 causes the sequestration or buildup of the RPGRORF15-RPGRIP1α1-NPHP4 complex in the ER with the double and single mutations having the strongest and weakest effects, respectively.
NPHP4 recruits RPGRIP1α1 to the ER, whereas RPGRORF15 retrieves the NPHP4-RPGRIP1α1 complex from the ER. Mutations uncoupling RPGRORF15 from RPGRIP1α1 down-modulate synergisticaly the ability of RPGRORF15 to promote the exit of the RPGRIP1 interactome from the ER. A model emerges in which deficits in subcellular events priming the formation and exit of preciliary complexes from the ER and mediated by the RPGRIP1 interactome impair the tethering and targeting of such complexes to the cilium and the elaboration of outer segments of photoreceptors.
This PDF is available to Subscribers Only