PI3K activation interferes with cell surface trafficking and radioiodide uptake conferred by exogenous Flag-tagged hNIS gene expression. (A) MCF-7 and MCF-7/PI3K p110αCAAX cells were transiently transfected with pcDNA3/Flag-hNIS and subjected to Flag immunofluorescence 48 hours later. While Flag-hNIS is detectable on the cell surface in parental MCF-7 cells (arrows), it is retained intracellularly in MCF-7/PI3K p110αCAAX cells. Magnification = 63×. (B) MCF-7 and MCF-7/PI3K p110αCAAX cells were transiently transfected with pcDNA3/Flag-hNIS and subjected to 125I uptake assay 48 hours later. A nearly 4-fold increase in 125I uptake resulting from exogenous NIS expression is present in parental MCF-7 cells as compared to MCF-7/PI3K p110αCAAX. **p < .001.