Figure 5.

Overexpression of CALNUC increases ⁴⁵Ca²⁺ uptake. (A) Nontransfected HeLa cells (N.T.), or those stably transfected with GFP alone, or transiently expressing CALNUC-GFP or CALNUC-GFP deletion mutants were incubated with 2 μCi/ml ⁴⁵Ca²⁺ for 48 h to reach ⁴⁵Ca²⁺ equilibrium. ⁴⁵Ca²⁺ uptake by cells overexpressing CALNUC-GFP was 2.5-fold (2,500 vs. 1,000 cpm) greater than that found in nontransfected cells or those expressing GFP alone. Truncated CALNUC in which both EF-1 [CN(ΔEF-1)-GFP] or EF-1 and EF-2 [CN(ΔEF-1, 2)-GFP] were deleted completely lost Ca²⁺-binding capability. (B) EcR-CHO cells stably transfected with CALNUC cDNA (EcR-CHO-CALNUC) were loaded with ⁴⁵Ca²⁺ as in A. ⁴⁵Ca²⁺ uptake in induced cells (10 μM muristerone A) was threefold that found in noninduced cells (7,400 vs. 2,500 cpm). Results (mean ± SD) represent the average of values obtained in three separate experiments performed in duplicate.