Effect of PF4 on G1ME cells and expression of LRP1. (A) The effect of PF4 on percentage of CD42⁺ cells after re-expression of GATA-1 by the introduction of a GATA-1-IRES-eGFP MIGR1 retrovirus with and without 25 μg/mL PF4 in serum-free media. Results are for eGFP⁺-transfected cells. On the left are total CD42⁺ cells; middle are small, CD42⁺ cells; and right are large, CD42⁺ cells (based on forward scatter on flow cytometry). Data are shown as mean +1 SD of 4 experiments. *P < .008 comparing with and without PF4 added. (B) LRP1 expression in G1ME cells both before and after transfection with either a MIGR1 empty retrovirus (□) or MIGR1 retrovirus containing GATA-1 (♦). Figure organized as in panel A. Shown is a representative experiment of 3. (C) LRP1 expression on human cultured megakaryocytes derived from adult CD34⁺ bone marrow cells. Open triangles show total CD41⁺ cells, whereas closed triangles show LRP1⁺/CD41⁺ cells. Mean +1 SD is shown for 4 independent experiments. (D) Ploidy analysis in relation to LRP1 expression. The gray line represents cells that are CD41⁻. The broken line is cells that are CD41⁺ but LRP1⁻. The solid, dark line represents the cells that are positive for both LRP1 and CD41. Data are from a single experiment, but are representative of results from 5 independent experiments.