IRF8 is a transcriptional activator of CD37 expression in diffuse large B-cell lymphoma

Abstract

Diffuse large B-cell lymphoma (DLBCL) represents the most common form of non-Hodgkin lymphoma that is still incurable in a large fraction of patients. Tetraspanin CD37 is highly expressed on mature B lymphocytes and multiple CD37-targeting therapies are under clinical development for non-Hodgkin lymphoma. However, CD37 expression is non-detectable in ~50% of DLBCL patients which correlates with inferior treatment outcome, but the underlying mechanisms for differential CD37 expression in DLBCL are still unknown. Here, we investigated the regulation of the CD37 gene in human DLBCL at the (epi-)genetic and transcriptional level. No differences were observed in DNA methylation within the CD37 promoter region between CD37-positive and CD37-negative primary DLBCL patient samples. On the contrary, CD37-negative DLBCL cells specifically lacked CD37 promoter activity, suggesting differential regulation of CD37 gene expression. Using an unbiased quantitative proteomic approach, we identified transcription factor IRF8 to be significantly higher expressed in nuclear extracts of CD37-positive as compared to CD37-negative DLBCL. Direct binding of IRF8 to the CD37 promoter region was confirmed by DNA pull-down assay combined with mass spectrometry, and targeted chromatin immunoprecipitation. Functional analysis indicated that IRF8 overexpression enhanced CD37 protein expression, while CRISPR/Cas9 knock-out of IRF8 decreased CD37 levels in DLBCL cell lines. Immunohistochemical analysis in a large cohort of primary DLBCL (n=206) revealed a significant correlation of IRF8 expression with detectable CD37 levels. Together, this study provides new insight into the molecular mechanisms underlying differential CD37 expression in human DLBCL, and reveals IRF8 as transcriptional regulator of CD37 in B-cell lymphoma.

CD20 expression regulates CD37 levels in B-cell lymphoma – implications for immunotherapies

“…Moreover, our study sheds new light on the regulation of CD37 expression. Decrease in CD37 expression has been reported to affect patients’ prognosis negatively, and according to the studies by other groups (31) and ours, up to 50% of DLBCL patients show undetectable CD37 protein expression by immunohistochemistry. However, it needs to be emphasized that in the IHC stainings performed by us and others a clone of anti-CD37 mAb (2B8) used does not correspond to the clone used for CAR construct (HH1 clone).…”

IRF8: Mechanism of Action and Health Implications

“…IRF8 was necessary for CD20 transcription and anti-CD20 therapy efficacy [ 192 ]. Additionally, IRF8 is a transcriptional regulator of CD37 in DLBCL and regulates the efficacy of anti-CD37 pharmacotherapies [ 55 ]. Continued investigation on anti-PD-L1 therapy has shown that, in hepatocellular carcinoma, IRF8 enhances the response to treatment and suppressed progression [ 18 ].…”

“…IRF8 has weak DNA-binding affinity and its transcription regulatory activity therefore depends on its IAD association with other transcriptional factors to form a transcription complex which renders IRF8 specific and high affinity to bind to the unique DNA motifs at gene promoters [ 23 , 34 , 49 , 50 ]. IRF8 functions as either a transcriptional activator or repressor and it is the IAD-associated transcription factor(s) that dictates IRF8 bindingand transcriptional activity [ 20 , 23 , 33 , 51 , 52 , 53 , 54 , 55 ].…”

IRF8 regulates efficacy of therapeutic anti‐CD20 monoclonal antibodies

“…It will be worth determining whether lymphoma cells carrying IRF8 mutations or downregulating this protein could be selected by anti-CD20 treatment. IRF8 has recently been shown to be a transcriptional regulator of CD37 in DLBCLs [59] and CD37 loss is associated with CD20 downregulation and predicts worse survival [60]. Anti-CD20 antibodies are also widely used to treat autoimmune diseases such as rheuma- toid arthritis (RA), MS, and systemic lupus erythematosus (SLE) [61].…”