Constitutive JAK2 activation in PMBL-derived MedB1 cells. (A) Whole-cell extracts from control (ctrl; TPO activated UT7-mpl, lanes a, f), 1 Burkitt-derived cell line (Ramos, lane b), 2 PMBL-derived cell lines (MedB1, lanes c, g; Karpas 1106, lanes d, h), 2 GC-DLBCL cell lines (SUDHL4, lane i; SUDHL6, lane j), and 2 ABC-DLBCL cell lines (OCI-Ly3, lane k; OCI-Ly10, lane l) were prepared and immunoprecipitated with anti-JAK2 antibodies. Immunoprecipitates were analyzed by Western blot using anti-P-Tyr or anti-JAK2 antibodies. (B) Whole-cell extracts from control (IL-4-treated MedB1 cells) and indicated cell lines were immunoprecipitated with anti-JAK1 or anti-JAK3 antibodies and were analyzed by Western blot using anti-P-Tyr or anti-JAK1 or JAK3 antibodies, as shown in the figure. (C) MedB1 cells were treated with DMSO or 50 μM AG490 for 24 hours. Whole cell extracts were analyzed by Western blot using anti-P-STAT6 or anti-β-actin antibodies as indicated on the right of the figure. The lower panel shows Western blot analysis of JAK2 immunoprecipitates with an anti-P-Tyr antibody.