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D. Deretic, V. Traverso, E. Rodriguez de Turco, N. Ransom; Phospholipid Modulation That Inactivates Ezrin/Moesin and Rac1 Inhibits Fusion of Rhodopsin-Bearing Post-Golgi Transport Carriers in Retinal Photoreceptors . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4261.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We have previously reported (ARVO 2001) that budding and fusion of rhodopsin-bearing transport carriers (RTCs) are the most sensitive transport steps affected by the changes in phospholipid metabolism in propranolol (Ppl) treated retinas. Ppl increased membrane content of newly synthesized PA and PI, and decreased PI(4,5)P2. EM analysis revealed that Ppl caused accumulation of RTCs at the base of the ROS, around the cilium. In the present study, we searched for the potential fusion regulators affected by phospholipid modulation. Methods: Frog retinas were treated with 0.5 mM Ppl and subjected to subcellular fractionation to prepare RTCs, or examined by confocal microscopy. Results: Proteomic analysis of RTCs following Ppl treatment revealed an absence of a 75 kD protein. Sequence analysis by tandem mass spectrometry of this protein excised from the control sample showed four tryptic fragments of moesin and two of ezrin. Ezrin and moesin are highly homologous proteins that regulate membrane-cytoskeleton interactions. Their membrane association and activity are regulated by PI(4,5)P2. Ppl caused inactivation of ezrin/moesin and redistribution from the RTCs and the RIS plasma membrane into the cytosol. This further caused dissociation of their downstream effectors, rho-GDI and small GTPase rac1 from the membranes. Confocal microscopy showed that ezrin/moesin and rac1 are localized on RTCs at the sites of their fusion with the plasma membrane. Ppl profoundly affects this localization and therefore potentially disrupts the fusion sites. Conclusions: Our data suggest that in Ppl treated photoreceptors the lack of functional ezrin/moesin and rac1 on fusion sites is the primary cause for the inability of RTCs to fuse with the RIS plasma membrane and deliver rhodopsin and newly synthesized phospholipids to the ROS.
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