Intracellular localization of the WT and mutant R43L, R280C and L101P ABCA3 proteins. A549 cells were transiently transfected with pEYFP-N1/ABCA3 vectors expressing WT or one of the three mutations. YFP fluorescence of ABCA3-YFP fusions (green) was used to detect ABCA3 WT and R43L, R280C and L101P proteins. Colocalization of the ABCA3-YFP signal with the fluorescent signal of (A) the lysosomal/lamellar body protein LAMP3 and (B) the ER protein calnexin (both red) are shown. WT and R43L localized in LAMP3+ vesicles, R280C partially in LAMP3+ vesicles and partially in the ER and L101P completely in the ER. (C) Partial ER localization of HA-tagged R280C in A549 cells transfected with pUB6/HA-R280C plasmid confirms the partial R280C ER retention as independent on the type of the plasmid or protein tag. Representative pictures are shown; scale bars: 5 μm.