Transfected plasmids have reduced expression in cells deficient in SEPTIN 9 or ESCRT proteins

Transfection of cells with DNA plasmids typically involves the uptake of lipoparticles by endocytosis, followed by the inefficient escape of these particles from endosomes into the cytoplasm. We found that the expression of transfected plasmids was reduced in cells depleted of either SEPTIN 9 or proteins in the endosomal sorting complexes required for transport (ESCRT) pathway. The reduction in plasmid expression could not be fully explained by effects on endocytosis. SEPTIN 9 depletion appeared to reduce the acidification of plasmid-containing compartments, suggesting that it primarily affects the pH-sensitive escape of plasmids from endosomes. Depletion of the ESCRT proteins VPS36 or ALIX resulted in especially dramatic reductions in transfected plasmid expression, which were accompanied by reduced colocalization between the transfected DNA and CHMP4, an ESCRT protein important for endosomal membrane remodeling during intraluminal vesicle formation. Finally, transfected plasmid DNA was strongly colocalized with LC3B, suggesting that the default pathway for transfected material is autophagy.