IRF4-Dependent Cell Proliferation Is a Potential Therapeutic Target in Peripheral T-Cell Lymphomas
AL Feldman, RA Wilcox, J Porcher, A Dogan, SM Ansell. Mayo Clinic, Rochester, MN
Background: Peripheral T-cell lymphomas (PTCLs) are fatal in the majority of patients. Conventional chemotherapy is largely ineffective, and novel targeted therapeutic strategies are needed. We recently identified PTCLs with novel translocations between the T-cell receptor alpha gene (TRA@) and the transcription factor gene, IRF4 (Feldman et al. Leukemia 2009). Since genes involved in translocations with TRA@ often are oncogenic, we aimed to determine whether IRF4 represents a potential therapeutic target in PTCLs.
Design: To assess the functional role of IRF4 in vitro, SUDHL-1 anaplastic large cell lymphoma (ALCL) cells were transfected with 3 IRF4-specific small interfering RNAs (siRNAs, 100nM), a control siRNA, or no siRNA. Cells were assayed at 48 h for IRF4 mRNA (real-time PCR, normalized to GAPDH), IRF4 and c-MYC protein (Western blot, normalized to beta-actin), and proliferation (3H-thymidine incorporation). Immunohistochemistry for IRF4 and CD30 and fluorescence in situ hybridization for IRF4 were evaluated in 293 PTCL biopsies in 273 patients (M: 157, F: 116; mean age, 58 y).
Results: SUDHL-1 cells expressed IRF4 and CD30 proteins, but lacked an IRF4 translocation. IRF4 siRNA reduced IRF4 mRNA by 51% compared to control siRNA, and decreased IRF4 protein by 71%. In addition, IRF4 siRNA decreased c-MYC protein by 88%, and reduced 3H-thymidine incorporation by 47% compared to control siRNA (p=1.0 x 10-8, t-test). Of 293 PTCLs, 51% were positive for IRF4, and 8% had IRF4 translocations. IRF4 was positive in most ALCLs (88%) and CD30-positive PTCLs, NOS (72%), but in the minority of CD30-negative PTCLs, NOS (13%), angioimmunoblastic T-cell lymphomas (4%), and other PTCLs (17%). IRF4 was strongly associated with CD30 expression both overall (p=7.9 x 10-37, χ2 test) and among PTCLs, NOS (p=3.2 x 10-8, χ2 test).
Conclusions: IRF4 siRNA reduced not only IRF4 mRNA and IRF4 protein in SUDHL-1 cells, but also expression of the proto-oncogene c-MYC and cell proliferation. c-MYC is a key driver of cancer cell growth, and is implicated in the functional role of IRF4 in multiple myeloma. Although IRF4 translocations are rare in PTCLs, IRF4 protein is expressed in about half of cases, and is strongly associated with expression of CD30. These data represent the first evidence for IRF4-dependent cell proliferation in PTCLs, suggesting a oncogenic role for IRF4. Given that IRF4 is overexpressed in approximately 50% of PTCLs, evaluation of IRF4 inhibition as a therapeutic strategy for PTCLs is warranted.
Monday, March 22, 2010 11:15 AM
Platform Session: Section B, Monday Morning