Abstract
The envelope glycoprotein (Env) plays a crucial role in the retroviral life cycle by mediating primary interactions with the host cell. As described previously and expanded on in this paper, Env mediates the trafficking of immature Mason-Pfizer monkey virus (M-PMV) particles to the plasma membrane (PM). Using a panel of labeled RabGTPases as endosomal markers, we identified Env mostly in Rab7a- and Rab9a-positive endosomes. Based on an analysis of the transport of recombinant fluorescently labeled M-PMV Gag and Env proteins, we propose a putative mechanism of the intracellular trafficking of M-PMV Env and immature particles. According to this model, a portion of Env is targeted from the trans-Golgi network (TGN) to Rab7a-positive endosomes. It is then transported to Rab9a-positive endosomes and back to the TGN. It is at the Rab9a vesicles where the immature particles may anchor to the membranes of the Env-containing vesicles, preventing Env recycling to the TGN. These Gag-associated vesicles are then transported to the plasma membrane.
Highlights
Mason-Pfizer monkey virus (M-PMV) is a D-type retrovirus that preassembles its immature particles in the cytoplasm of infected cells [1,2]
It is important in the initiation of envelope glycoprotein (Env) incorporation into the structural polyproteins and cytoplasmic proteins
It is important in the initiation of Env incorporation viralthe particle, it plays a role in anterograde and retrograde trafficking, trafficking, and in the initiation of into viral and particle, and it plays a role in anterograde and retrograde and in the intracellular signaling cascades leading to enhanced viral gene expression initiation of intracellular signaling cascades leading to enhanced viral gene expression [29,30,31,32]
Summary
Mason-Pfizer monkey virus (M-PMV) is a D-type retrovirus that preassembles its immature particles in the cytoplasm of infected cells [1,2]. All three polyproteins initiate synthesis on free polysomes in the cytoplasm, but are co-translationally transported to the microtubule organizing center (MTOC) by the cellular molecular motor dynein This requires the interaction of a cytoplasmic targeting/retention signal (CTRS) in the matrix domain of Gag and a light chain of dynein (Tctex-1) [4,5,6]. We used a panel of endosomal markers based on RabGTPases tagged with enhanced green fluorescent protein (EGFP) to perform colocalization studies with mCherryTM This approach proved that mCherryTM is localized to Rab7a endosomes and to a lesser extent to those positive for. The results allowed us to propose a mode of intracellular trafficking of M-PMV Env and its site(s) of interaction with Gag immature particles
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