PTPRJ knockdown results in inhibition of SDF1-driven migration of the megakaryocytic Dami cell line, as well as in reduced thrombopoietin and phorbol-induced maturation of Dami cells. Using lentiviral transduction of a pool of shRNA, we generated Dami cells expressing <10% PTPRJ protein (PTPRJ KO) compared with cells transduced with the negative control vector. (A-B) SDF1-driven migration of Dami cells was investigated using a Transwell assay. Transwell systems having a polycarbonate membrane with an 8-µm pore size were coated with fibrinogen (A) or type I collagen (B). Aliquots of 1 × 10⁵ cells were seeded in the upper chamber of the Transwell system, whereas medium with 300 ng/mL SDF1 (+) or without SDF1 (–) (negative control conditions) was added to the lower chamber. After incubation for 16 hours at 37°C and 5% CO₂, the percentage of cells that migrated to the lower chamber with respect to the number of cells put in the upper chamber at the beginning of the experiment was calculated. Each experiment was performed in duplicate, and data represent the mean of 3 separate experiments. *P < .01, 2-tailed Student t test. (C) Dami cells knocked down for PTPRJ (PTPRJ KO) or transduced with a scramble shRNA were treated for 48 hours with thrombopoietin and phorbol 12-myristate 13-acetate to induce maturation toward the megakaryocytic lineage. Maturation was then quantified as the increase in surface expression of the megakaryocyte-specific markers CD61, CD41, and CD42b with respect to untreated cells (ie, cells incubated in parallel with medium alone). Surface expression of each antigen was evaluated by flow cytometry as the mean fluorescence intensity (MFI). PTPRJ-KO Dami cells exhibited a similar increase in CD61 and CD41 expression compared with control cells but a defective increase in the late megakaryocyte maturation marker CD42b. Data represent the mean ± SD of 3 independent experiments. *P < .05, 2-tailed Student t test.