Supplementary Material for: Dysregulated MDR1 by PRDM1/Blimp1 Is Involved in the Doxorubicin Resistance of Non-Germinal Center B-Cell-Like Diffuse Large B-Cell Lymphoma

<b><i>Introduction:</i></b> The chemoresistance mechanism of diffuse large B-cell lymphoma (DLBCL) is still poorly understood, and patient prognosis remains unsatisfactory. This study aimed to investigate drug resistance mechanisms in non-germinal center B-cell-like (non-GCB) DLBCL. <b><i>Methods:</i></b> Doxorubicin (DOX)-resistant OCI-Ly3 cells were generated through long-term incubation of cells in a medium with gradually increasing DOX concentrations. The expression levels of genes related to drug metabolism were determined using a functional gene grouping polymerase chain reaction (PCR) array. Drug-resistant proteins were identified using bioinformatics, and molecular association networks were subsequently generated. The association and mechanism of key genes were determined using a dual-luciferase reporter assay System and chromatin immunoprecipitation (ChIP). The expression of drug-resistant genes and target genes was then measured using Western blotting and immunohistochemistry. The correlation between gene expressions was analyzed using Spearman’s rank correlation coefficient. <b><i>Results:</i></b> Using the PCR array, <i>MDR1</i> was identified as the key gene that regulates DOX resistance in OCI-Ly3/DOX-A100, a non-GCB DLBCL cell line. The dual-luciferase reporter assay system demonstrated that <i>MDR1</i> transcription could be inhibited by PRDM1. ChIP results showed that PRDM1 had the ability to bind to the promoter region (−1,132 to −996) of <i>MDR1</i>. In OCI-Ly3/DOX cells, NF-κB activity and PRDM1 expression decreased with an increase in drug-resistant index, whereas <i>MDR1</i> expression increased with enhanced drug resistance. Immunohistochemical analysis revealed that relative <i>MDR1</i> expression was higher than that of PRDM1 in human DLBCL tissue samples. A negative correlation was observed between MDR1 and PRDM1. <b><i>Conclusion:</i></b> In non-GCB DLBCL cells, NF-κB downregulates PRDM1 and thereby promotes <i>MDR1</i> transcription by terminating PRDM1-induced transcriptional inhibition of <i>MDR1</i>. Such a mechanism may explain the reason for disease recurrence in non-GCB DLBCL after R-CHOP or combined CHOP with bortezomib treatment. Our findings may provide a potential therapeutic strategy for reducing drug resistance in patients with DLBCL.