IRF4 contributes to chemoresistance in IGH-BCL2 positive diffuse large B-cell lymphomas by mediating BCL2 induced SOX9 expression

SOX9 was identified as a prognostic biomarker particularly in IGH-BCL2 translocated germinal center B cell (GCB) subtypes of the diffuse large B cell lymphoma (DLBCL) and plays a vital role in lymphomagenesis. However, the molecular mechanism that modulating the aberrant expression of SOX9 in this DLBCL subset remains unknown. We have demonstrated that SOX9 enhanced IGH-BCL2 positive DLBCL subset resistance to either chemotherapy or BCL2 inhibitor. Moreover, we found that inhibition of BCL2 downregulates SOX9 in IGH-BCL2 positive DLBCL subset. We further identified that IRF4 is a key regulator to mediate BCL2 induced SOX9 expression, alongside with the chip-seq confirmed that IRF4 is a key transcription factor for SOX9 in DLBCL. In addition, BCL2 promote IRF4 entry into the nucleus by enhancing its protein stability, via downregulating of proteosome ubiquitination process, and, therefore, enforce SOX9-mediated phenotypes. Finally, we showed in DLBCL cell lines and xenografted mice model that in vivo inhibition of IRF4 with hIRF4 antisense oligonucleotide (ASO) repressed lymphomagenesis and DLBCL chemoresistance. Altogether, 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 relapse and refractory DLBCL in the future. To identify which genes binds directly to IRF4 and the genes with IRF4-bound transcription sites