Abstract
The endoplasmic reticulum (ER) was investigated as the initial oligomerization site for the envelope glycoproteins H and F of measles virus (MV), a clinically relevant member of the Paramyxoviridae family, and consequences of this interaction for viral replication were studied. Both proteins were tagged at their cytosolic tails with RRR and KKXX motifs, respectively, resulting in their efficient retention in the ER. Co-transfection of the retained constructs with transport competent MV glycoproteins revealed a dominant negative effect on their biological activity indicating intracellular complex formation and thus retention. Pulse-chase analysis and co-immunoprecipitation experiments demonstrated that this effect is based on both homo- and hetero-oligomerization in the ER. Recombinant viruses additionally expressing ER-retained F showed an altered cytopathic phenotype accompanied by greatly reduced particle release. Similar mutant viruses additionally expressing ER-retained H could not be rescued indicating an even greater negative effect of this protein on virus viability. Our study suggests that both homo- and hetero-oligomerization of MV glycoproteins occur in the ER and that these events are of significance for early steps of particle assembly.
Highlights
The measles virus (MV) envelope consists of hemagglutinin (H) and fusion (F) glycoproteins
Our study suggests that both homo- and heterooligomerization of MV glycoproteins occur in the endoplasmic reticulum (ER) and that these events are of significance for early steps of particle assembly
The mechanism of MV-induced membrane fusion may involve receptor-induced conformational changes in H and F, pointing to a dynamic interaction between these proteins. This was first supported through studies showing that expression of H or hemagglutinin neuraminidase (HN) and F from the same paramyxovirus is necessary for efficient fusion, inferring their type-specific interaction (8 –10)
Summary
Cell Culture, Generation of MV Stocks, and Virus Growth Kinetics— Vero (African green monkey kidney), HT1080 (human bone fibrosarcoma), and PA317 (mouse hybridoma) cells were maintained in Dulbecco’s modified Eagle’s medium containing 10% fetal bovine serum, penicillin, and streptomycin at 37 °C and 5% CO2. Cells were lysed in radioimmunoprecipitation assay buffer (10 mM Tris, pH 7.4; 1% deoxycholate; 1% Triton X-100; 0.1% SDS; 150 mM sodium chloride) containing protease inhibitors and 1 mM PMSF for 15 min at 4 °C and centrifuged for 25 min at 20,000 ϫ g and 4 °C. After absorption of immune complexes to protein G-agarose (Life Technologies, Inc.), samples were washed in buffer 1 (100 mM Tris, pH 7.6; 500 mM lithium chloride; 0.1% Triton X-100; 1 mM dithiothreitol) and in buffer 2 (20 mM Hepes, pH 7.2; 2 mM EGTA; 10 mM magnesium chloride; 0.% Triton X-100; 1 mM dithiothreitol), resuspended in urea buffer for 25 min at 50 °C, and subjected to Western analysis using antibodies specific for F tail. Of recombinant viruses was verified by reverse transcriptase-polymerase chain reaction and DNA sequencing
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