Expression of MUM1/IRF4 correlates with clinical outcome in patients with B-cell chronic lymphocytic leukemia

The dynamic functions of IRF4 in B cell malignancies

The trajectory of B cell development goes through subsequent steps governed by complex genetic programs, strictly regulated by multiple transcription factors. Interferon regulatory factor 4 (IRF4) regulates key points from pre-B cell development and receptor editing to germinal center formation, class-switch recombination and plasma cell differentiation. The pleiotropic ability of IRF4 is mediated by its “kinetic control”, allowing different IRF4 expression levels to activate distinct genetic programs due to modulation of IRF4 DNA-binding affinity. IRF4 is implicated in B cell malignancies, acting both as tumor suppressor and as tumor oncogene in different types of precursors and mature B cell neoplasia. Here, we summarize the complexity of IRF4 functions related to different DNA-binding affinity, multiple IRF4-specific target DNA motif, and interactions with transcriptional partners. Moreover, we describe the unique role of IRF4 in acute leukemias and B cell mature neoplasia, focusing on pathogenetic implications and possible therapeutic strategies in multiple myeloma and chronic lymphocytic leukemia.

IRF4 drives clonal evolution and lineage choice in a zebrafish model of T-cell lymphoma

IRF4 is a master regulator of immunity and is also frequently overexpressed in mature lymphoid neoplasms. Here, we demonstrate the oncogenicity of IRF4 in vivo, its potential effects on T-cell development and clonal evolution using a zebrafish model. IRF4-transgenic zebrafish develop aggressive tumors with massive infiltration of abnormal lymphocytes that spread to distal organs. Many late-stage tumors are mono- or oligoclonal, and tumor cells can expand in recipient animals after transplantation, demonstrating their malignancy. Mutation of p53 accelerates tumor onset, increases penetrance, and results in tumor heterogeneity. Surprisingly, single-cell RNA-sequencing reveals that the majority of tumor cells are double-negative T-cells, many of which express tcr-γ that became dominant as the tumors progress, whereas double-positive T-cells are largely diminished. Gene expression and epigenetic profiling demonstrates that gata3, mycb, lrrn1, patl1 and psip1 are specifically activated in tumors, while genes responsible for T-cell differentiation including id3 are repressed. IRF4-driven tumors are sensitive to the BRD inhibitor.

IRF4 and IRF8 expression are associated with clinical phenotype and clinico-hematological response to hydroxyurea in essential thrombocythemia

The morbidity and mortality of myeloproliferative neoplasms (MPNs) are primarily caused by arterial and venous complications, progression to myelofibrosis, and transformation to acute leukemia. However, identifying molecular-based biomarkers for risk stratification of patients with MPNs remains a challenge. We have previously shown that interferon regulatory factor-8 (IRF8) and IRF4 serve as tumor suppressors in myeloid cells. In this study, we evaluated the expression of IRF4 and IRF8 and the JAK2V617F mutant allele burden in patients with MPNs. Patients with decreased IRF4 expression were correlated with a more developed MPN phenotype in myelofibrosis (MF) and secondary AML (sAML) transformed from MPNs versus essential thrombocythemia (ET). Negative correlations between the JAK2V617F allele burden and the expression of IRF8 (P < 0.05) and IRF4 (P < 0.001) and between white blood cell (WBC) count and IRF4 expression (P < 0.05) were found in ET patients. IRF8 expression was negatively correlated with the JAK2V617F allele burden (P < 0.05) in polycythemia vera patients. Complete response (CR), partial response (PR), and no response (NR) were observed in 67.5%,10%, and 22.5% of ET patients treated with hydroxyurea (HU), respectively, in 12 months. At 3 months, patients in the CR group showed high IRF4 and IRF8 expression compared with patients in the PR and NR groups. In the 12-month therapy period, low IRF4 and IRF8 expression were independently associated with the unfavorable response to HU and high WBC count. Our data indicate that the expression of IRF4 and IRF8 was associated with the MPN phenotype, which may serve as biomarkers for the response to HU in ET.

IRF4 modulates the response to BCR activation in chronic lymphocytic leukemia regulating IKAROS and SYK

Interferon regulatory factor 4 (IRF4) is a transcriptional regulator of immune system development and function. Here, we investigated the role of IRF4 in controlling responsiveness to B-cell receptor (BCR) stimulation in chronic lymphocytic leukemia (CLL). We modulated IRF4 levels by transfecting CLL cells with an IRF4 vector or by silencing using small-interfering RNAs. Higher IRF4 levels attenuated BCR signaling by reducing AKT and ERK phosphorylation and calcium release. Conversely, IRF4 reduction improved the strength of the intracellular cascade activated by BCR engagement. Our results also indicated that IRF4 negatively regulates the expression of the spleen tyrosine kinase SYK, a crucial protein for propagation of BCR signaling, and the zinc finger DNA-binding protein IKAROS. We modulated IKAROS protein levels both by genetic manipulation and pharmacologically by treating CLL cells with lenalidomide and avadomide (IMIDs). IKAROS promoted BCR signaling by reducing the expression of inositol 5-phosphatase SHIP1. Lastly, IMIDs induced IRF4 expression, while down-regulating IKAROS and interfered with survival advantage mediated by BCR triggering, also in combination with ibrutinib. Overall, our findings elucidate the mechanism by which IRF4 tunes BCR signaling in CLL cells. Low IRF4 levels allow an efficient transmission of BCR signal throughout the accumulation of SYK and IKAROS.

Identification BCL6 and miR-30 family associating with Ibrutinib resistance in activated B-cell-like diffuse large B-cell lymphoma

Ibrutinib has clear efficacy for activated B-cell-like diffuse large B cell lymphoma (ABC-DLBCL) in previous clinical researches. However, the resistance of Ibrutinib has limited its therapeutic benefit and the potential mechanism remains unclear. This study was aimed to identify potential candidate genes and miRNA targets to overcome Ibrutinib resistance in ABC-DLBCL. First, two expression profiles were downloaded from the GEO database, which used to identify the DEGs related to Ibrutinib resistance in ABC-DLBCL cell lines by GEO2R analysis separately. And the common DEGs were obtained though Venn diagram. Then Gene ontology (GO) and pathway enrichment analysis were conducted by DAVID database. From STRING database, BCL6, IL10, IL2RB, IRF4, CD80, PRDM1and GZMB were determined to be the hub genes by protein-protein interaction (PPI) network. Through miRNA-mRNA targeting network, we found that BCL6, IRF4, CD80, and PRDM1 were common target genes of miR-30 family. The cBioPortal database showed that BCL6 had the highest level of genetic alterations among DLBCL. In addition, another expression profile from GEO database showed that BCL6 was significantly high expression in no responsive patients after Ibrutinib treatment, and the receiver operating characteristic (ROC) curve which was used to evaluate the relationship between BCL6 expression and its effect was 0.67. MTT assay showed that treatment with FX1 (a BCL6 inhibitor) can enhance the sensitivity of Ibrutinib in C481S BTK HBL-1 cells. The results suggested that BCL6 and miR-30 family maybe associate with Ibrutinib resistance in ABC-DLBCL.

Prognostic significance of interferon regulating factor 4 in esophageal squamous cell carcinoma

BACKGROUND

Aberrant expression of interferon regulatory factor 4 (IRF4) has been reported in several hematologic malignancies. However, the prognostic significance of IRF4 expression in esophageal squamous cell carcinoma (ESCC) remains unknown.

METHODS

IRF4 protein expression in ESCC tumor specimens was determined immunohistochemically. The correlation of IRF4 expression with clinico-pathological features was assessed from a cohort of 100 patients with primary ESCC. Kaplan-Meier and Cox proportional regression analyses were used to evaluate the association between IRF4 expression and patient survival.

RESULTS

A Kaplan-Meier analysis indicated that patients with high IRF4 expression had a significantly longer overall survival rate than those with low IRF4 expression (p = 0.0006). Furthermore, multi-variate analyses revealed that IRF4 protein expression is an independent prognostic indicator for ESCC patients.

CONCLUSION

Our results suggest that increased IRF4 protein expression correlates with improved outcome in ESCC. IRF4 may therefore represent a promising prognostic biomarker and potential immuno-therapeutic target for patients with ESCC.

Prognostic significance of interferon regulating factor 4 (IRF4) in node-negative breast cancer

PURPOSE

The transcription factor IRF4 regulates immunoglobulin class switch recombination as well as plasma cell differentiation. We examined the prognostic significance of IRF4 expression in node-negative breast cancer (BC).

METHODS

IRF4 expression was evaluated by immunostaining in a cohort of 197 node-negative BC patients not treated in adjuvant setting, referred to as Mainz cohort. The prognostic significance of immunohistochemically determined IRF4 expression for metastasis-free survival (MFS) was examined by Kaplan-Meier survival analysis as well as univariate and multivariate Cox analysis adjusted for age, pT stage, histological grade, ER, and HER2 status. For verification of immunohistochemical results, IRF4 mRNA expression was evaluated using microarray-based gene expression profiling in four previously published cohorts (Mainz, Rotterdam, Transbig, Yu) consisting of 824 node-negative breast cancer patients in total, who were not treated with adjuvant therapy. The prognostic significance of IRF4 mRNA expression on metastasis-free survival (MFS) was examined by univariate and multivariate Cox analysis in the Mainz cohort and by a meta-analysis of all node-negative BC patients and different molecular subtypes. IRF4 mRNA levels were compared to immunohistochemically determined IRF4 expression in 140 patients of the Mainz cohort using Spearman correlation.

RESULTS

Immunohistochemically determined high IRF4 expression was associated with higher MFS in univariate Cox regression (HR 0.178, 95% CI 0.070-0.453, p < 0.001). IRF4 maintained its significance independently of established clinical factors for MFS (HR 0.088, 95% CI 0.033-0.232, p < 0.001). Immunohistochemically, determined IRF4 correlated moderately with IRF4 mRNA expression (ρ = 0.589). Higher expression of IRF4 was associated with better MFS in a meta-analysis of the total cohort (HR 0.438, 95% CI 0.307-0.623, p < 0.001). Prognostic significance was more pronounced in the HER2⁺ molecular subtype (HR 0.215, 95% CI 0.090-0.515, p = 0.001) as compared to the luminal A (HR 0.549, 95% CI 0.248-1.215, p = 0.139), luminal B (HR 0.444, 95% CI 0.215-0.916, p = 0.028), and basal-like subtypes (HR 0.487, 95% CI 0.269-0.883, p = 0.018). Further, IRF4 expression showed independent prognostic significance in a multivariate analysis of the Mainz cohort (HR 0.236, 95% CI 0.105-0.527, p < 0.001).

CONCLUSIONS

IRF4 had independent prognostic significance in node-negative BC. Higher expression of IRF4 was associated with improved outcome. The prognostic impact differed between diverse molecular subtypes and was most pronounced in HER2⁺ breast cancer.

LMP1 signaling pathway activates IRF4 in latent EBV infection and a positive circuit between PI3K and Src is required

Interferon (IFN) regulatory factors (IRFs) have crucial roles in immune regulation and oncogenesis. We have recently shown that IRF4 is activated through c-Src-mediated tyrosine phosphorylation in virus-transformed cells. However, the intracellular signaling pathway triggering Src activation of IRF4 remains unknown. In this study, we provide evidence that Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) promotes IRF4 phosphorylation and markedly stimulates IRF4 transcriptional activity, and that Src mediates LMP1 activation of IRF4. As to more precise mechanism, we show that LMP1 physically interacts with c-Src, and the phosphatidylinositol 3 kinase (PI3K) subunit P85 mediates their interaction. Depletion of P85 by P85-specific short hairpin RNAs disrupts their interaction and diminishes IRF4 phosphorylation in EBV-transformed cells. Furthermore, we show that Src is upstream of PI3K for activation of both IRF4 and Akt. In turn, inhibition of PI3K kinase activity by the PI3K-speicfic inhibitor LY294002 impairs Src activity. Our results show that LMP1 signaling is responsible for IRF4 activation, and further characterize the IRF4 regulatory network that is a promising therapeutic target for specific hematological malignancies.

Immunohistochemical Detection of Multiple Myeloma 1/Interferon Regulatory Factor 4 (MUM1/IRF-4) in Canine Plasmacytoma: Comparison with CD79a and CD20

Multiple myeloma oncogene 1/interferon regulatory factor 4 (MUM1/IRF4) is involved in lymphoid cell differentiation, particularly in the production of plasma cells. We examined the immunoreactivity of mouse monoclonal antibody Mum-1p to MUM1/IRF4 and compared it with expression of CD79a and CD20 in 109 plasmacytomas in 107 dogs. Tissues had been fixed in formalin and embedded in paraffin. One hundred one of 109 (93.5%) tumors were positive for MUM1/IRF4. The staining was nuclear with weak cytoplasmic reaction. Fifty-nine of 105 (56.2%) plasmacytomas were positive for CD79a; only 21 of 108 (19.4%) cases were positive for CD20. MUM1/IRF4 staining was performed on 139 other tumors including B- and T-cell lymphomas, histiocytic proliferations, mast cell tumors, and melanocytic tumors. The only MUM1/IRF4-positive nonplasmacytic tumors were 10 B-cell lymphomas and 1 anaplastic lymphoma. We conclude the following: 1) Antibody Mum-1p is very specific for canine plasmacytomas, 2) antibody Mum-1p is superior in sensitivity and specificity to CD79a and CD20 for the identification of canine plasmacytomas in formalin-fixed, paraffin-embedded tissues, 3) canine lymphomas that express MUM1/IRF4 are few and usually of B-cell origin, 4) other canine leukocytic and melanocytic tumors do not express MUM1/IRF4, and 5) prospective studies are needed to determine whether the expression of MUM1/IRF4, particularly in lymphomas, has prognostic significance.

Gene expression profiling identifies IRF4-associated molecular signatures in hematological malignancies

The lymphocyte-specific transcription factor Interferon (IFN) Regulatory Factor 4 (IRF4) is implicated in certain types of lymphoid and myeloid malignancies. However, the molecular mechanisms underlying its interactions with these malignancies are largely unknown. In this study, we have first profiled molecular signatures associated with IRF4 expression in associated cancers, by analyzing existing gene expression profiling datasets. Our results show that IRF4 is overexpressed in melanoma, in addition to previously reported contexts including leukemia, myeloma, and lymphoma, and that IRF4 is associated with a unique gene expression pattern in each context. A pool of important genes involved in B-cell development, oncogenesis, cell cycle regulation, and cell death including BATF, LIMD1, CFLAR, PIM2, and CCND2 are common signatures associated with IRF4 in non-Hodgkin B cell lymphomas. We confirmed the correlation of IRF4 with LIMD1 and CFLAR in a panel of cell lines derived from lymphomas. Moreover, we profiled the IRF4 transcriptome in the context of EBV latent infection, and confirmed several genes including IFI27, IFI44, GBP1, and ARHGAP18, as well as CFLAR as novel targets for IRF4. These results provide valuable information for understanding the IRF4 regulatory network, and improve our knowledge of the unique roles of IRF4 in different hematological malignancies.

Chronic lymphocytic leukaemia: could immunological tolerance mechanisms be the origin of lymphoid neoplasms?

Immunological tolerance theory in chronic lymphocytic leukaemia (CLL): we suggest that B cells that express B-cell receptors (BCR) that recognize their own BCR epitopes are viewed by immune system as 'dangerous cells'. BCR autonomous signalling may induce constant receptor editing and mistakes in allelic exclusion. The fact that whole BCR recognizes a self-antigen or foreing antigen may be irrelevant in early B cell development. In early B cells, autonomous signalling induced by recognition of the BCR's own epitopes simulates an antigen-antibody engagement. In the bone marrow this interaction is viewed as recognition of self-molecules and induces receptor editing. In mature B cells autonomous signalling by the BCR may promote 'reversible anergy' and also may correct self-reactivity induced by the somatic hypermutation mechanisms in mutated CLL B cells. However, in unmutated CLL B cells, BCR autonomous signalling in addition to self-antigen recognition augments B cell activation, proliferation and genomic instability. We suggest that CLL originates from a coordinated normal immunologic tolerance mechanism to destroy self-reactive B cells. Additional genetic damage induced by tolerance mechanisms may immortalize self-reactive B cells and transform them into a leukemia.

IRF4 and IRF8: Governing the virtues of B Lymphocytes

Interferon Regulatory Factor 4 (IRF4) and IRF8 are critical regulators of immune system development and function. In B lymphocytes, IRF4 and IRF8 have been shown to control important events during their development and maturation including pre-B cell differentiation, induction of B cell tolerance pathways, marginal zone B cell development, germinal center reaction and plasma cell differentiation. Mechanistically, IRF4 and IRF8 are found to function redundantly to control certain stages of B cell development, but in other stages, they function nonredundantly to play distinct roles in B cell biology. In line with their essential roles in B cell development, deregulated expressions of IRF4 and IRF8 have been associated to the pathogenesis of several B cell malignancies and diseases. Recent studies have elucidated diverse transcriptional networks regulated by IRF4 and IRF8 at distinct B cell developmental stages and related malignancies. In this review we will discuss the recent advances for the roles of IRF4 and IRF8 during B cell development and associated diseases.

Murine genetically engineered and human xenograft models of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a genetically complex disease, with multiple factors having an impact on onset, progression, and response to therapy. Genetic differences/abnormalities have been found in hematopoietic stem cells from patients, as well as in B lymphocytes of individuals with monoclonal B-cell lymphocytosis who may develop the disease. Furthermore, after the onset of CLL, additional genetic alterations occur over time, often causing disease worsening and altering patient outcomes. Therefore, being able to genetically engineer mouse models that mimic CLL or at least certain aspects of the disease will help us understand disease mechanisms and improve treatments. This notwithstanding, because neither the genetic aberrations responsible for leukemogenesis and progression nor the promoting factors that support these are likely identical in character or influences for all patients, genetically engineered mouse models will only completely mimic CLL when all of these factors are precisely defined. In addition, multiple genetically engineered models may be required because of the heterogeneity in susceptibility genes among patients that can have an effect on genetic and environmental characteristics influencing disease development and outcome. For these reasons, we review the major murine genetically engineered and human xenograft models in use at the present time, aiming to report the advantages and disadvantages of each.

Implication of IRF4 aberrant gene expression in the acute leukemias of childhood

The most frequent targets of genetic alterations in human leukemias are transcription factor genes with essential functions in normal blood cell development. The Interferon Regulatory Factor 4 (IRF4) gene encodes a transcription factor important for key developmental stages of hematopoiesis, with known oncogenic implications in multiple myeloma, adult leukemias and lymphomas. Very few studies have reported an association of IRF4 with childhood malignancy, whereas high transcript levels have been observed in the more mature immunophenotype of ALL. Our aim was to investigate the expression levels of IRF4 in the diagnostic samples of pediatric leukemias and compare them to those of healthy controls, in order to determine aberrant gene expression and whether it extends to leukemic subtypes other than the relatively mature ALL subpopulation. Quantitative real-time RT-PCR methodology was used to investigate IRF4 expression in 58 children with acute leukemias, 4 leukemic cell lines and 20 healthy children. We show that aberrant IRF4 gene expression is implicated in a variety of leukemic subtypes; higher transcript levels appear in the more immature B-common ALL subtype and in T-cell than in B-cell leukemias, with the highest expression levels appearing in the AML group. Interestingly, we show that childhood leukemia, irrespective of subtype or cell maturation stage, is characterised by a minimum of approximately twice the amount of IRF4 gene expression encountered in healthy children. A statistically significant correlation also appeared to exist between high IRF4 expression and relapse. Our results show that ectopic expression of IRF4 follows the reverse expression pattern of what is encountered in normal B-cell development and that there might be a dose-dependency of childhood leukemia for aberrantly expressed IRF4, a characteristic that could be explored therapeutically. It is also suggested that high IRF4 expression might be used as an additional prognostic marker of relapse at diagnosis.

A role for IRF4 in the development of CLL

Interferon regulatory factor 4 (IRF4) is a critical transcriptional regulator of B-cell development and function. A recent genome-wide single-nucleotide polymorphism (SNP) association study identified IRF4 as a major susceptibility gene in chronic lymphocytic leukemia (CLL). Although the SNPs located in the IRF4 gene were linked to a downregulation of IRF4 in CLL patients, whether a low level of IRF4 is critical for CLL development remains unclear. In rodents, CLL cells are derived from B1 cells whose population is dramatically expanded in immunoglobulin heavy chain Vh11 knock-in mice. We bred a Vh11 knock-in allele into IRF4-deficient mice (IRF4(-/-)Vh11). Here, we report that IRF4(-/-)Vh11 mice develop spontaneous early-onset CLL with 100% penetrance. Further analysis shows that IRF4(-/-)Vh11 CLL cells proliferate predominantly in spleen and express high levels of Mcl-1. IRF4(-/-)Vh11 CLL cells are resistant to apoptosis but reconstitution of IRF4 expression in the IRF4(-/-)Vh11 CLL cells inhibits their survival. Thus, our study demonstrates for the first time a causal relationship between low levels of IRF4 and the development of CLL. Moreover, our findings establish IRF4(-/-)Vh11 mice as a novel mouse model of CLL that not only is valuable for dissecting molecular pathogenesis of CLL but could also be used for therapeutic purposes.

Accelerated development of chronic lymphocytic leukemia in New Zealand Black mice expressing a low level of interferon regulatory factor 4

A recent genome-wide SNP association study identified IRF4 as a major susceptibility gene for chronic lymphocytic leukemia (CLL). Moreover, the SNPs located in the 3' UTR of the IRF4 gene have been linked to a down-regulation of IRF4. However, whether a low level of IRF4 is critical for CLL development remains unclear. New Zealand Black (NZB) mice are a naturally occurring, late-onset mouse model of CLL. To examine the role of a reduced level of IRF4 in CLL development, we generated, through breeding, IRF4 heterozygous mutant mice in the NZB background (NZB IRF4(+/-)). Our results show that CLL development is accelerated dramatically in the NZB IRF4(+/-) mice. The average onset of CLL in NZB mice is 12 months, but CLL cells can be detected in NZB IRF4(+/-) mice at 3 months of age. By 5 months of age, 80% of NZB IRF4(+/-) mice developed CLL. CLL cells are derived from B1 cells in mice. Interestingly, NZB IRF4(+/-) B1 cells exhibit prolonged survival, accelerated self-renewal, and defects in differentiation. Although NZB IRF4(+/-) CLL cells are resistant to apoptosis, high levels of IRF4 inhibit their survival. High levels of IRF4 also reduce the survival of MEC-1 human CLL cells. Our analysis further reveals that high levels of IRF4 suppress Akt activity and can do so without the IRF4 DNA binding domain. Thus, our findings reveal a causal relationship between a low level of IRF4 and the development of CLL and establish IRF4 as a novel regulator in the pathogenesis of CLL.

Interferon regulatory factor 4 is activated through c-Src-mediated tyrosine phosphorylation in virus-transformed cells

The importance of the oncogenic transcription factor interferon regulatory factor 4 (IRF4) in hematological malignancies has been increasingly recognized. We have previously identified the B cell integration cluster (BIC), the gene encoding miR-155, as the first microRNA (miRNA)-encoding gene transcriptionally targeted by IRF4 in virus-transformed cancer cells. Activation of IRFs is prerequisite for their functions. However, how IRF4 is activated in cancer is an open question. Our phosphoproteome profiling has identified several tyrosine phosphorylation sites on IRF4 in Epstein-Barr virus (EBV)-transformed cells. Further, we show here that c-Src dramatically stimulates IRF4 phosphorylation and activity and that Y61 and Y124 are two key sites responding to c-Src-mediated activation. Consistently, c-Src is constitutively expressed and active in EBV-transformed cells. However, c-Src is unlikely to be a direct kinase for IRF4. Furthermore, we have a polyclonal antibody specific to phospho-IRF4(Y121/124) developed in rabbit. We have further shown that inhibition of c-Src activity reduces p-IRF4(Y121/124) and significantly represses transcription of the IRF4 target BIC in EBV-transformed cells. Our results therefore, for the first time, demonstrate that IRF4 is phosphorylated and activated through a c-Src-mediated pathway in virus-transformed cells. These findings will improve our understanding of IRF4 in neoplasia and will provide profound insights into the interaction of oncogenic viruses with IRF4 in the development of hematological malignancies.

A Japanese case of chronic lymphocytic leukemia with t (1;6)

Chronic lymphocytic leukemia (CLL) rarely exhibits an aggressive clinical course and its patients often have chromosomal deletions or additions. Furthermore, reciprocal translocations are barely observed in CLL. There have only been a few reports of CLL with t(1;6), and here we report the first Asian case of CLL with reciprocal translocation t(1;6). Since our case and previously reported CLL patients with t(1;6) consistently showed aggressive clinical course, t(1;6) may define a distinct type of CLL.

IRF4 mutations in chronic lymphocytic leukemia

Interferon regulatory factor 4 (IRF4) is a member of the interferon regulatory factor family of transcription factors and has been shown to have critical functions at several stages of B-cell development. Genome-wide association study identified a polymorphism in the 3' untranslated region of IRF4 as a chronic lymphocytic leukemia risk locus. In this study, we report a recurrent heterozygous somatic mutation in the DNA-binding domain of IRF4 detected in 7 of 457 chronic lymphocytic leukemia patients (1.5%). Patients with IRF4 mutation have a good prognosis, and 4 of 6 have a trisomy 12. We also found that IRF4 mRNA expression is higher in the patients with the mutation.

Lenalidomide downregulates the cell survival factor, interferon regulatory factor-4, providing a potential mechanistic link for predicting response

Overexpression of the transcription factor interferon regulatory factor-4 (IRF4), which is common in multiple myeloma (MM), is associated with poor prognosis. Patients with higher IRF4 expression have significantly poorer overall survival than those with low IRF4 expression. Lenalidomide is an IMiD immunomodulatory compound that has both tumouricidal and immunomodulatory activity in MM. This study showed that lenalidomide downregulated IRF4 levels in MM cell lines and bone marrow samples within 8 h of drug exposure. This was associated with a decrease in MYC levels, as well as an initial G1 cell cycle arrest, decreased cell proliferation, and cell death by day 5 of treatment. In eight MM cell lines, high IRF4 levels correlated with increased lenalidomide sensitivity. The clinical significance of this observation was investigated in 154 patients with MM. Among MM patients with high levels of IRF4 expression, treatment with lenalidomide led to a significantly longer overall survival than other therapies in a retrospective analysis. These data confirm the central role of IRF4 in MM pathogenesis; indicate that this is an important mechanism by which lenalidomide exerts its antitumour effects; and may provide a mechanistic biomarker to predict response to lenalidomide.

MUM1/IRF4: A Review

MUM1/IRF4 protein is a member of the interferon regulatory factor (IRF) family of transcriptional factors initially described as downstream regulators of interferon signaling. The quantity of this factor varies within the hematopoietic system in a lineage and stage-specific way. It is considered to be a key regulator of several steps in lymphoid, myeloid, and dendritic cell differentiation and maturation. MUM1/IRF4 expression is observed in many lymphoid and myeloid malignancies, and may be a promising target for the treatment of some of these neoplasms. We reviewed the literature on MUM1/IRF4, with emphasis on the pathologic aspects of this marker in reactive and malignant hematologic and nonhematologic conditions.

Fine-scale mapping of the 6p25.3 chronic lymphocytic leukaemia susceptibility locus

A recent genome-wide association study of chronic lymphocytic leukaemia (CLL) has identified a susceptibility locus on 6p25.3 associated with a modest but highly significant increase in CLL risk. Using a set of single nucleotide polymorphism (SNP) markers, we generated a fine-scale map and narrowed the association signal to a 18 kb DNA segment within the 3'-untranslated region (UTR) of the IRF4 (interferon regulatory factor 4) gene. Resequencing this segment in European subjects identified 55 common polymorphisms, including 13 highly correlated candidate causal variants. In a large case-control study, it was shown that all but four variants could be excluded with 95% confidence. These four SNPs map to a 3 kb region of the 3'-UTR of IRF4, consistent with the causal basis of the association being mediated through differential IRF4 expression.

A mouse model for chronic lymphocytic leukemia based on expression of the SV40 large T antigen

The simian virus 40 (SV40) T antigen is a potent oncogene able to transform many cell types and has been implicated in leukemia and lymphoma. In this report, we have achieved sporadic SV40 T-antigen expression in mature B cells in mice, by insertion of a SV40 T antigen gene in opposite transcriptional orientation in the immunoglobulin (Ig) heavy (H) chain locus between the D and JH segments. SV40 T-antigen expression appeared to result from retention of the targeted germline allele and concomitant antisense transcription of SV40 large T in mature B cells, leading to chronic lymphocytic leukemia (CLL). Although B-cell development was unperturbed in young mice, aging mice showed accumulation of a monoclonal B-cell population in which the targeted IgH allele was in germline configuration and the wild-type IgH allele had a productive V(D)J recombination. These leukemic B cells were IgDlowCD5+ and manifested nonrandom usage of V, D, and J segments. VH regions were either unmutated, with preferential usage of the VH11 family, or manifested extensive somatic hypermutation. Our findings provide an animal model for B-CLL and show that pathways activated by SV40 T antigen play important roles in the pathogenesis of B-CLL.

New transcription factors in diagnostic hematopathology

The transcription factors (TFs) that controls the intricate machinery of multistep differentiation and activation programs of the lymphoid system, represent a complex array of proteins, whose identification and function has only in part been completed. TFs are usually expressed during specific differentiation or activation cellular programs, making them interesting tools in diagnostic immunohistochemistry. In fact, the specificity of some of these TFs for lineage or activation/differentiation passages or their abnormal expression in specific disease entity, represents a feature that has been exploited in diagnostic/prognostic immunohistochemistry. Bcl-6 was the prototype of this class of markers. Currently, the expanding knowledge of the TFs involved in the differentiation programs and in the activation processes of T-lymphocyte and B-lymphocyte in normal and neoplastic conditions and the availability of antibodies able to efficiently recognize these TFs in histologic material, represent a powerful tool in diagnostic hematopathology. In this review we will consider the basic biologic aspects and the applications in hematopathology of some of the lymphocyte-related TFs, including Pax5/BSAB, MUM1/IRF4, BOB1, Oct-2, T-bet, and FOXP3. This field is rapidly evolving, as witnessed by the ongoing growing number of novel TFs with possible diagnostic applications appearing in the literature.

Detection of the JAK2(V617F) mutation in myeloproliferative disorders by melting curve analysis using the LightCycler system

CONTEXT

A specific mutation, JAK2(V617F), was recently recognized as having diagnostic value for myeloproliferative disorders. No practical assay is currently available for routine use in a clinical laboratory.

OBJECTIVE

We report the development of a real-time polymerase chain reaction melting curve analysis assay that is appropriate for molecular diagnostics testing.

DESIGN

Specific primers and fluorescence resonance energy transfer probes were designed, and patients with a previously diagnosed myeloproliferative disorder, de novo acute myeloid leukemia, or reactive condition were selected. The DNA was extracted from fresh and archived peripheral blood and bone marrow specimens, and real-time polymerase chain reaction melting curve analysis was performed on the LightCycler platform (Roche Applied Science, Indianapolis, Ind).

RESULTS

The JAK2 region was successfully amplified, and wild-type amplicons were reproducibly discriminated from JAK2(V617F) amplicons. Titration studies using homozygous wild-type and mutant cell lines showed the relative areas under a melting curve were proportional to allele proportion, and the assay reliably detected one mutant in 20 total cells. JAK2(V617F) was identified in patients previously diagnosed with a myeloproliferative disorder or acute myeloid leukemia transformed from myeloproliferative disorder, whereas a wild-type genotype was identified in patients with reactive conditions or de novo acute myeloid leukemia.

CONCLUSIONS

These findings demonstrate the suitability of this assay for identifying JAK2(V617F) in a clinical laboratory setting. Furthermore, the semiquantitative detection of JAK2(V617F) in archived specimens provides a new tool for studying the prognostic significance of this mutation.

The proliferation center microenvironment and prognostic markers in chronic lymphocytic leukemia/small lymphocytic lymphoma

Prognostication in chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) based, in part, on ZAP-70 and CD38 expression, and to a lesser extent, on MUM1/IRF4 expression, is currently of great interest. The more aggressive type of CLL/SLL is reportedly characterized by neoplastic cells that are more responsive to B-cell signaling with proliferation centers (PCs), a potentially important site of neoplastic cell stimulation. To study the relationship of these markers to each other and to the pattern of PCs, immunohistochemical stains for ZAP-70 and MUM1/IRF4 were performed and the PC patterns assessed (where possible) in 29 tissue biopsies with CLL/SLL. CD38 expression was assessed in 18 cases using flow cytometry. Ten evaluable cases had a typical PC pattern and 16 an atypical pattern with larger or more confluent PCs and/or more numerous paraimmunoblasts/transformed cells. ZAP-70 was positive in 14 of 28 cases, including 3 with atypical PCs and enhanced PC staining. All 29 cases showed MUM1/IRF4 expression in PCs. Seven cases, none with atypical PC, also showed uniform positivity throughout, 14 showed weaker staining of surrounding lymphocytes, and 8 had PC staining only. CD38 was positive in 14 of 18 cases. The only significant association identified was between uniform MUM1/IRF4 positivity and typical PCs (P = .004). These findings highlight the complex interrelationship of prognostic markers in CLL/SLL and demonstrate potentially important microenvironmental variations in their expression. They support the hypothesis that PCs are a site for B-cell receptor signaling, which helps explain reported site-dependent antigenic variation in CLL/SLL, and suggest that PC morphology may correlate with other biological features.

Immunophenotyping of lymphoproliferative disorders: state of the art

Immunophenotyping was introduced into diagnostic pathology over 30 years ago to assist in the diagnosis and classification of lymphoproliferative disorders. Today the role of immunophenotyping has been expanded beyond this to include the detection of markers of prognosis, determination of disease phenotypes associated with specific chromosomal abnormalities, detection of targets for immunotherapy and to monitor residual disease. Immunoperoxidase detection methods remain the most popular in histopathology, whilst flow cytometry is most commonly applied for haematological samples. The range of monoclonal antibodies available, including those which work in routinely performed tissue specimens, continues to increase. This is in part a result of gene expression studies identifying precise genetic signatures for certain lymphoproliferative disorders and the generation of new protein markers to gene products of upregulated genes. This review summarises the current status and applications of immunophenotyping in the assessment of many of the lymphoid malignancies.

Multiple myeloma oncogene 1 (MUM1)/interferon regulatory factor 4 (IRF4) upregulates monokine induced by interferon-γ (MIG) gene expression in B-cell malignancy

MUM1 (multiple myeloma oncogene 1)/IRF4 (interferon regulatory factor 4) is a transcription factor that is activated as a result of t(6;14)(p25;q32) in multiple myeloma. MUM1 expression is seen in various B-cell lymphomas and predicts an unfavorable outcome in some lymphoma subtypes. To elucidate its role in B-cell malignancies, we prepared MUM1-expressing Ba/F3 cells, which proliferated until higher cellular density than the parental cells, and performed cDNA microarray analysis to identify genes whose expression is regulated by MUM1. We found that the expression of four genes including FK506-binding protein 3 (FKBP3), the monokine induced by interferon-gamma(MIG), Fas apoptotic inhibitory molecule (Faim) and Zinc-finger protein 94 was altered in the MUM1-expressing cells. We then focused on MIG since its expression was immediately upregulated by MUM1. In reporter assays, MUM1 activated the MIG promoter in cooperation with PU.1, and the interaction between MUM1 and the MIG promoter sequence was confirmed. The expression of MIG was correlated with that of MUM1 in B-CLL cell lines, and treatment with neutralizing antibodies against MIG and its receptor, CXCR3, slightly inhibited the proliferation of two MUM1-expressing lines. These results suggest that MUM1 plays roles in the progression of B-cell lymphoma/leukemia by regulating the expression of various genes including MIG. Leukemia (2005) 19, 1471-1478. doi:10.1038/sj.leu.2403833; published online 16 June 2005.

Plasmacellular differentiation in extranodal marginal zone B cell lymphomas of the ocular adnexa: an analysis of the neoplastic plasma cell phenotype and its prognostic significance in 136 cases

AIM

To determine (a) the expression of plasma cell related antigens in extranodal marginal zone B cell lymphomas (EMZL) of the ocular adnexa; and (b) the prognostic value of plasmacellular differentiation in these tumours.

METHODS

A consecutive case series of 136 ocular adnexal EMZL obtained from three ocular pathology centres over 20 years was analysed retrospectively. An extensive immunohistochemical panel, including the plasma cell related antigens VS38c, CD38, CD138, multiple myeloma oncogene-1-protein (MUM1/IRF4), and CREB binding protein (CBP) was performed. EMZL were defined as "plasmacellular differentiated" on the basis of morphological features, evidence of cytoplasmic immunoglobulin, negativity for BSAP/PAX5, and expression of at least one of the investigated plasma cell related antigens. Controls included normal or hyperplastic lymphatic tissues. Detailed clinical data were collected for most patients, and compared with the results of immunohistochemistry. The end points considered for statistical analysis were development of local tumour recurrence, development of systemic disease, and lymphoma related death.

RESULTS

57 (42%) of the 136 ocular adnexal EMZL showed a plasmacellular differentiation; 45 of these plasmacytoid cases were primary tumours. In contrast with most admixed normal plasma cells, which displayed co-expression of MUM1/IRF4, Vs38c, CD38, CD138, and CBP, the plasmacellular differentiated EMZL tumour cells demonstrated co-expression of all five plasma cell related antigens in only six of 57 (11%) plasmacellular differentiated ocular adnexal EMZL. The most commonly expressed plasma cell related antigen was MUM1/IRF4, immunoreactivity being seen in 56/57 (98%) plasmacellular differentiated EMZL examined. Although the association of plasmacellular differentiation in primary ocular adnexal EMZL and disseminated disease was statistically significant on univariate analysis (p = 0.042), this was weaker on multivariate analysis.

CONCLUSION

Plasmacellular differentiated tumour cells in EMZL demonstrate an aberrant immune profile for plasma cell related antigens when compared with normal plasma cells. On multivariate analysis, plasmacellular differentiation in ocular adnexal EMZL was not significantly associated with local recurrence, the development of systemic disease, or with lymphoma related death.

Tissue microarray: A valuable method in diagnosis and prognosis of hematological malignances

BACKGROUND: The novel technology of tissue microarray (TMA) allows rapid and cost-effective analysis of hundreds of markers on the same set of specimens. Limited amount of tissue that could be analyzed and problem of tissue heterogeneity, are the major drawbacks of TMA technique for immunohistochemical characterization of lymphomas. METHODS: In this paper 65 cases of lymphomas were analyzed using TMA with following panel of antibodies: BOB1, Oct2, Bcl2, Bcl6, CD20, CD21, CD23, CD3, CD5, CD10, CD43, CD79a, CD138, Cyclin D1, Ki67, MUM1, Pax5, p53. RESULTS: In 14 patients with diffuse large B-cell lymphoma (DLBCL), 5 were classified as germinative center and 3 as non-germinative center cases according to the Bcl6, CD10, and MUM1 positivity. Other 2 patients were identified as T cell rich B cell lymphoma based on morphology and Oct2 and BOB1 positivity of pleomorphic B lymphocytes. DLBCL with Bcl6+ immunophenotype had better overall survival than Bcl6- cases. All cases of classic mantle cell lymphoma had significantly lower Ki-67 proliferation index than blastoid subtypes. There were 14 cases of chronic lymphocytic leukemia/small cell lymphocytic lymphoma, 6 cases with follicular lymphoma, 5 cases of marginal zone lymphoma, and 7 cases of lymphoplazmacitoid lymphoma. In the indolent lymphoma group, survival of patients with p53+/- was poorer comparing to p53- group. CONCLUSION: We conclude that TMA technique is a valuable method in diagnosis and prognosis of lymphomas, which are considered very heterogeneous group of hematological neoplasms.

Histopathology of B-cell chronic lymphocytic leukemia

Histologic and immunohistologic findings of B-cell chronic lymphocytic leukemia/small lymphocytic leukemia are revised in the light of the more recent knowledge on the pathobiology of the disease. The guidelines for the optimal handling of the bioptic samples are provided. The relevance of the examination of trephines and surgical specimens is outlined with special reference to the identification of risk factors in individual patients.

Distinct types of primary cutaneous large B-cell lymphoma identified by gene expression profiling

In the European Organization for Research and Treatment of Cancer (EORTC) classification 2 types of primary cutaneous large B-cell lymphoma (PCLBCL) are distinguished: primary cutaneous follicle center cell lymphomas (PCFCCL) and PCLBCL of the leg (PCLBCL-leg). Distinction between both groups is considered important because of differences in prognosis (5-year survival > 95% and 52%, respectively) and the first choice of treatment (radiotherapy or systemic chemotherapy, respectively), but is not generally accepted. To establish a molecular basis for this subdivision in the EORTC classification, we investigated the gene expression profiles of 21 PCLBCLs by oligonucleotide microarray analysis. Hierarchical clustering based on a B-cell signature (7450 genes) classified PCLBCL into 2 distinct subgroups consisting of, respectively, 8 PCFCCLs and 13 PCLBCLsleg. PCLBCLs-leg showed increased expression of genes associated with cell proliferation; the proto-oncogenes Pim-1, Pim-2, and c-Myc; and the transcription factors Mum1/IRF4 and Oct-2. In the group of PCFCCL high expression of SPINK2 was observed. Further analysis suggested that PCFCCLs and PCLBCLs-leg have expression profiles similar to that of germinal center B-cell-like and activated B-cell-like diffuse large B-cell lymphoma, respectively. The results of this study suggest that different pathogenetic mechanisms are involved in the development of PCFCCLs and PCLBCLs-leg and provide molecular support for the subdivision used in the EORTC classification.