Rabbit Anti-Human IRF4 Monoclonal Antibody, clone CQ7105

We previously reported that PU.1 is downregulated in the majority of myeloma cell lines and primary myeloma cells of certain myeloma patients, and conditional expression of PU.1 in such myeloma cell lines induced cell cycle arrest and apoptosis. We found downregulation of IRF4 protein in the U266 myeloma cell line following induction of PU.1. Previous studies reported that knockdown of IRF4 in myeloma cell lines induces apoptosis, prompting us to further investigate the role of IRF4 downregulation in PU.1-induced cell cycle arrest and apoptosis in myeloma cells. PU. 1 induced downregulation of IRF4 at the protein level, cell cycle arrest and apoptosis in six myeloma cell lines. Chromatin immunoprecipitation (ChIP) revealed that PU.1 directly binds to the IRF4 promoter, whereas a reporter assay showed that PU.1 may suppress IRF4 promoter activity. Stable expression of IRF4 in myeloma cells expressing PU.1 partially rescued the cells from apoptosis induced by PU.1. As it was reported that IRF4 directly binds to the IRF7 promoter and downregulates its expression in activated B cell-like subtype of diffuse large B cell lymphoma cells, we performed ChIP assays and found that IRF4 directly binds the IRF7 promoter in myeloma cells. It is known that IRF7 positively upregulates interferon-beta (IFN beta) and induces apoptosis in many cell types. Binding of IRF4 to the IRF7 promoter decreased following PU.1 induction, accompanied by downregulation of IRF4 protein expression. Knockdown of IRF7 protected PU.1-expressing myeloma cells from apoptosis. Furthermore, IFN beta, which is a downstream target of IRF7, was upregulated in myeloma cells along with IRF7 after PU.1 induction. Finally, we evaluated the mRNA expression levels of PU.1, IRF4 and IRF7 in primary myeloma cells from patients and found that PU.1 and IRF7 were strongly downregulated in contrast to the high expression levels of IRF4. These data strongly suggest that PU.1-induced apoptosis in myeloma cells is associated with IRF4 downregulation and subsequent IRF7 upregulation.

BackgroundTumor-infiltrating lymphocytes influence the prognosis of solid tumors, including ovarian cancer (OC). The immunoregulatory transcription factor (IRF4) is mainly expressed in plasma cells and regulates immunoglobulin class switch recombination as well as plasma cell differentiation. Therefore, we analyzed the impact of IRF4 expression in a consecutive cohort of OC patients.MethodsIRF4 expression was evaluated by immunostaining. Differences in IRF4 expression among the subgroups of the established clinical-pathological features like age, histological subtype, tumor stage, histological grading, postoperative tumor burden, and completeness of chemotherapy were determined by (2) test. The impact of IRF4 expression on progression-free survival (PFS) and overall survival (OS) was examined by univariate and multivariate Cox analysis adjusted for established clinical-pathological factors and Kaplan-Meier survival analysis.Results114 patients entered this study. IRF4 was expressed in 51.7% of the entire cohort. 72.3% patients with high-grade serous OC showed IRF4 expression compared to 37.3% patients with a non-high-grade serous OC (p<0.001). Univariate Cox-regression analysis revealed no prognostic impact of IRF4 expression in terms of PFS (p=0.35) and OS (p=0.98). Kaplan-Meier plots failed to show any prognostic impact for PFS (p=0.35) and OS (p=0.98), too. Established clinical-pathological factors retained their prognostic impact as tumor stage in terms of PFS (<0.001) and as postoperative residual tumor burden (p=0.04), tumor stage (<0.001), histological grade (p=0.02), and completeness of chemotherapy (p<0.001) in terms of OS, respectively.ConclusionImmunohistochemically determined IRF4 expression correlated with high-grade serous OC. However, it failed to show any prognostic impact in this cohort of 114 patients.