Mnk1 regulates mRNA translation and de novo protein synthesis in human and murine megakaryocytes. (A) Human, cord blood–derived, CD34⁺ megakaryocytes were left alone with vehicle control (DMSO, blue line) or treated with CGP 57380 (10 μM, red line) on culture day 13 and then allowed to adhere on fibrinogen-coated plates for 2 hours. Megakaryocytes were then lysed and sedimented by centrifugation on a 5% to 50% sucrose gradient. Isolated monosome and polysome fractions are indicated. Graphs are representative of n = 3 independent experiments. (B) Human, cord blood–derived, CD34⁺ megakaryocytes were cultured in the presence of CGP 57380 (10 μM) or vehicle control (DMSO) on culture day 13. Megakaryocytes were then resuspended in [³⁵S]-methionine media and allowed to adhere on fibrinogen-coated plates for 2 hours. Protein synthesis was quantified using a scintillation counter (∗P < .05; n = 5 independent experiments). (C) Bone marrow–derived megakaryocytes from either WT or Mnk1 KO mice were resuspended in [³⁵S]-methionine media and allowed to adhere on fibrinogen-coated plates for 2 hours. Protein synthesis was quantified using a scintillation counter (∗P < .05; n = 6 independent experiments).