Fig. 4.

Akt phosphorylation mediates Aly's effect in cell proliferation. (A) Aly phosphorylation does not alter Aly nuclear speckle residency. (B and C) Akt phosphorylation on Aly T219 is required for mRNA export activity (B). Quantitative analysis of mRNA export is shown in C. (D) Akt phosphorylation regulates Aly's cell proliferation activity. T219 phosphorylation mimetic mutants enhanced BrdU incorporation, whereas unphosphorylated mutant T219A displayed decreased cell proliferation activity. Results are expressed as mean ± SEM from three independent experiments. *, P < 0.05; **, P < 0.01; ***, P < 0.005 (Student's t test). (E) Cell proliferation assay. HeLa cells, transfected with various Aly phosphorylation mutants, grew in six-well plates. The cell numbers were counted at the indicated time points.