MPL P106L exhibits cellular trafficking defects without inducing ER stress. (A) Human MPL intracellular localization of UT-7 MPL WT and UT-7 MPL P106L: cells were stained with antibodies directed against the ER (anti-CALR), the Golgi apparatus (anti-GM130), the ER-Golgi intermediate compartment (anti-ERGIC), and MPL (anti-HA), and immunofluorescence was analyzed by confocal microscopy. (B) ER stress analysis: UT-7 MPL WT and P106L cells were treated with 1 μM thapsigargin for 30 minutes and analyzed by western blotting. (C) Localization of the murine MPL receptor fused to GFP: cells were transduced with the retroviral vector pREX-IRES-CD4-muMPLHA fused to GFP and directly analyzed without fixation by confocal microscopy. Wheat germ agglutinin served as membrane marker.