MEK overexpression and deletion. (A) DLBCL cells were transduced with wild-type or constitutively active MEK1 using retroviral delivery. After transduction of constitutively active MEK1, cells were treated with PD98059 (100μM) or AZD6244 (200nM for Raji and 300nM for OCI-LY3). Expression of pERK and ERK was determined by Western blot analysis using specific antibodies in OCI-LY3 cells with constitutively active MEK1 in the presence of PD98059 or AZD6244. (B) Raji and OCI-LY3 cells were treated with PD98059 or AZD for 48 hours after transduction with MEK1-CA retrovirus. Apoptosis was measured by annexin V/PI staining followed by flow cytometry. (C) OCI-LY3 and OCI-lY19 cells were transfected with vector alone or dominant negative (DN)–MEK1. After 72-hour transfection, apoptosis was measured by annexin V/PI staining and assessed by flow cytometry. Expression of DN-MEK1 was confirmed by Western blotting using HA antibody. CA indicates constitutively active; wt, wild-type; AZDAZD6244; and PD, PD98059.