IRF4 contributes to chemoresistance in IGH::BCL2-positive diffuse large B-cell lymphomas by mediating BCL2-induced...

Diffuse large B-cell lymphoma (DLBCL), an aggressive type of non-Hodgkin's lymphoma, has a high relapse/refractory rate. We previously identified sex-determining region Y (SRY)-box transcription factor (SOX9) as a transcription factor that serves as a prognostic biomarker, particularly in BCL2-overexpressing DLBCL, and plays a vital role in lymphomagenesis. However, the molecular mechanisms that modulate the aberrant expression of SOX9 in this DLBCL subset remain unknown.

Cell viability, apoptosis and cell cycle assays were performed to determine whether SOX9 contributes to DLBCL chemoresistance and rescues silencing IRF4-induced phenotypes. Protein‒protein interactions and protein ubiquitination were elucidated using immunoprecipitation, immunohistochemistry, immunofluorescence and immunoblotting. Chromatin immunoprecipitation sequencing (ChIP-seq), ChIP and dual-luciferase reporter assays were used to investigate IRF4 binding to the SOX9 promoter. The therapeutic potential of IRF4 inhibition was evaluated in vitro and in a mouse model of DLBCL xenografts.

SOX9 enhanced the resistance of the BCL2-overexpressing DLBCL subset to chemotherapy or a BCL2 inhibitor. Moreover, BCL2 inhibition downregulated SOX9 in an immunoglobulin heavy chain/BCL2-positive DLBCL subset. We further identified IRF4 as a key regulator of BCL2-induced SOX9 expression, and ChIP-seq confirmed that IRF4 is a key transcription factor for SOX9 in DLBCL. In addition, BCL2 promotes IRF4 entry into the nucleus by enhancing protein stability and downregulating proteasomal ubiquitination, thereby enforcing SOX9-mediated phenotypes. Finally, in a DLBCL cell line and xenografted mouse model, in vivo inhibition of IRF4 with an hIRF4 antisense oligonucleotide repressed lymphomagenesis and DLBCL chemoresistance.

Our data support the conclusion that IRF4 plays an essential role in BCL2-induced upregulation of SOX9 expression, and targeting IRF4 may represent a promising therapeutic strategy to cure relapsed and refractory DLBCL.

BCL2 activated IRF4 by enhancing its nuclear activity to induce sex-determining region Y (SRY)-box 9 protein (SOX9) aberrant expression, which is a critical pathway for drug resistance in BCL2-overexpressing diffuse large B-cell lymphoma (DLBCL). Targeting IRF4 may be worth investigating further regarding its potential to overcome the chemoresistance of BCL2-overexpressing DLBCL to standard therapies.