The DNA transfer efficiency in liposomal versus viral transfection is very low, mainly due to an insufficient nuclear transport of the delivered DNA after its endocytotic uptake to the cell. Ligand activation of intracellular steroid receptors and their subsequent mobilization to the nucleus could result in a co-transport of DNA to the nucleus. The augmentation of nuclear transport of DNA after steroid addition might cause enhanced transfection efficiency. We used cell lines from gynecologic malignoma expressing steroid receptors, such as T47D and Mcf-7 breast cancer cell lines, as well as receptor-negative cell lines, such as Hec1A from endometrium carcinoma or the breast cancer cell line MDA-MB-231. The cells were transfected by the liposomal transfection agent Dotap with the gene for firefly-luciferase as a reporter gene and transfection efficiencies were determined in the luciferase assay. We compared the effect of the addition of cholesterol and steroids in different cell lines on the transfection efficiency. The addition of cholesterol to transfection agents led to an enhancement of the luciferase activity in all cell lines. Steroids enhanced the transfection efficiency only in receptor-positive cell lines. The transfection efficiencies of HEC-1A or MDA-MB-231 cells were not enhanced by steroids. A progesterone preincubation of receptor-positive T47D cells resulted in a decrease of progesterone receptors and afterwards the progesterone enhanced transfection was dramatically diminished. We presume that the transfection enhancement by steroids is dependent on increased nuclear import of the delivered DNA only in the presence of steroid receptors. Steroid enhancement of transfection is different from the benefit of cholesterol for transfection that acts on general cellular properties or the transfection complex as such. Liposomal transfection in combination with steroids might be useful for a cell-specific enhancement of gene transfer for example in gynecological malignoma where subgroups are expressing high levels of steroid receptors.

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