L-leucine increases total number of erythroid (Gly A⁺ and CD71⁺) cells in RPS14 and RPS19 shRNA transduced CD34⁺ progenitor cells. (A-D) CD34⁺ hematopoietic progenitor cells were targeted with short hairpin RNAs (shRNAs) against RPS19 (B), RPS14 (D), and a control (luciferase; A-C) Transduced cells were treated with 100μM and 1mM L-leucine or no treatment and continuously selected with 1 μg/mL puromycin starting at day 2. Cells were transferred to high EPO containing medium (2 U/mL) on day 7 and harvested on day 10. The number of erythroid cells was determined by flow cytometry after staining for CD71 and glycophorin A. The experiments were performed in triplicate and repeated 3 times with similar results (***P < .001; *P < .02; Student t test).