(D) Quantification of the average ratio of nuclear/cytoplasmic fluorescence of GFP-COP1 in (C). Mean values ± S.E.M. are shown for three independent experiments where 50 individual cells per experiment were analyzed. Significance relative to GFP-COP1 with empty vector was calculated using the Student t test (ns, not significant; ***p < 0.0001; ****p < 0.00001). 