Subcellular localization of FGFR1 in 2D culture. (A) FGF-10 stimulation (60 min) resulted in increased nuclear FGFR1 localization in serum-starved MCF-7 cells, confirmed by examining confocal z-stack sections. The effect was abolished in the presence of PD173074. The green, purple, and red boxes represent the x-z and y-z scan perspectives from the confocal z stack. Bars, 25 µm. (B) Subcellular fractionation revealed that FGF-10 treatment increased nuclear FGFR1 localization in MCF-7 cells. Over a time course of FGF-10 stimulation (0–60 min), there was a significant increase in accumulation of a truncated 55-kD C-terminal fragment of FGFR1 in the nuclear fraction (highlighted in black box), but there was no change in full-length FGFR1 levels. Immunoblotting with anti-TOPOIIa and anti-BIP antibodies confirmed the specificity of the cell fractionation protocol, and pERK confirmed the efficiency of FGF-10 stimulation. Nuclear FGFR1 was normalized to the nuclear marker TOPOIIa, confirming the significance of the accumulation (graph; *, P ≤ 0.05; **, P ≤ 0.01 [Student’s t test]). Error bars show means ± SEM. A.U., arbitrary unit; PM, plasma membrane.