Comprehensive genomic profiling of IgM multiple myeloma identifies IRF4 as a prognostic marker

Regulatory network of BLIMP1, IRF4, and XBP1 triad in plasmacytic differentiation and multiple myeloma pathogenesis

Antibody secreting plasma cell plays an indispensable role in humoral immunity. As activated B cell undergoes germinal center reaction and develops into plasma cell, it gradually loses B cell characteristics and embraces functional changes associated with immunoglobulins production. Differentiation of B cell into plasma cell involves drastic changes in cell structure, granularity, metabolism, gene expression and epigenetic regulation that couple with the mounting capacity for synthesis of a large quantity of antigen-specific antibodies. The interplay between three hallmark transcriptional regulators IRF4, BLIMP1, and XBP1, is critical for supporting the cellular reprograming activities during B to plasma cell transition. IRF4 promotes plasma cell generation by directing immunoglobulin class switching, proliferation and survival; BLIMP1 serves as a transcriptional repressor that extinguishes B cell features; whereas XBP1 controls unfolded protein response that relieves endoplasmic reticulum stress and permits antibody release during terminal differentiation. Intriguingly, high expression of IRF4, BLIMP1, and XBP1 molecules have been reported in myeloma cells derived from multiple myeloma patients, which negatively impact treatment outcome, prognosis, and relapse frequency. Despite the introduction of immunomodulatory drugs in recent years, multiple myeloma is still an incurable disease with poor survival rate. An in-depth review of IRF4, BLIMP1, and XBP1 triad molecules in plasma cell generation and multiple myeloma tumorigenesis may provide clues to the possibility of targeting these molecules in disease management.

Avaliação Radiográfica da Maxila e da Mandíbula de Pacientes Diagnosticados com Mieloma Múltiplo: Estudo Retrospectivo

Introdução: O mieloma múltiplo e caracterizado como uma neoplasia maligna plasmocitária com a proliferação anormal de plasmócitos clonais na medula óssea de etiologia desconhecida. Objetivo: Caracterizar os pacientes com mieloma múltiplo atendidos no Setor de Estômato-Odontologia e Prótese do INCA, por meio de dados sociodemográficos, clínicos, laboratoriais e radiográficos. Método: Estudo transversal retrospectivo de pacientes com diagnostico de mieloma múltiplo, no período de 2000 a 2018, que realizaram radiografia panorâmica no período do diagnóstico da doença. Os dados sociodemográficos e clinico-radiográficos da população em estudo foram coletados nos prontuários dos pacientes, armazenados em banco de dados, analisados de forma descritiva e submetidos ao teste não paramétrico X2 (qui-quadrado). Resultados: Na amostra final, foram totalizados 163 casos. A maioria era de homens (56,4%), brancos (55,8%), com idade ≤55 anos (54%), ensino fundamental incompleto (30,7%), não fumantes (54,6%) e não bebedores (54,6%). Havia lesões líticas em 46 pacientes (28,2%) com predileção pela mandíbula (82,6%; p=0,000). Houve maior frequência de margens parcialmente definidas (50,0%), não escleróticas (78,2%) e de aspecto unilocular (43,5%). Dos 46 pacientes que apresentaram lesão lítica maxilomandibular, 27 pacientes tinham >55 anos (p=0,042). Conclusão: Ha maior ocorrência de lesões ósseas na mandíbula quando comparada a maxila.

IgM Plasma Cell Myeloma

OBJECTIVES

Immunoglobulin M plasma cell myeloma (IgMPCM) is a rare entity that is difficult to distinguish from other IgM-related neoplasms. The study aims to characterize the clinicopathologic features of IgMPCM, including MYD88 L265P and CXCR4 mutations.

METHODS

From our institutional archives, bone marrow biopsy specimens from January 1, 2008, to December 1, 2018, with monotypic plasma cells (PCs) expressing IgM that met current International Myeloma Working Group/World Health Organization criteria for PCM were included. Sanger sequencing was used to test for MYD88 L265P and WHIM-like CXCR4 mutations.

RESULTS

Nine cases of IgMPCM were identified. Serum IgM paraproteins were detected in eight cases. CD138-positive PC burden averaged 41.9% (5%-80%). In four cases, PCs had lymphoplasmacytic morphology with cyclin D1 expression by immunohistochemistry. Three of four tested cases were positive for t(11;14) by fluorescence in situ hybridization, one with monosomy 13. The remaining case was positive for del13q14. All were negative for MYD88 L265P and WHIM-like CXCR4 mutations. Eight patients received immunochemotherapy, with four receiving autologous hematopoietic stem cell transplant. Median follow-up was 61 months (range, 11-120). All patients were alive except one.

CONCLUSIONS

Distinguishing IgMPCM from other IgM-related disorders requires correlation with clinical, laboratory, and radiologic findings. Exclusion of MYD88 L265P and WHIM-like CXCR4 mutations may be useful to diagnose IgMPCM.

Exonuclease domain mutants of yeast DIS3 display genome instability

The exosome functions to regulate the cellular transcriptome through RNA biogenesis, surveillance, and decay. Mutations in Dis3, a catalytic subunit of the RNA exosome with separable endonuclease and exonuclease activities, are linked to multiple myeloma. Here we report that a cancer-associated DIS3 allele, dis3^E729K, provides evidence for DIS3 functioning in mitotic fidelity in yeast. This dis3^E729K allele does not induce defects in 7S→5.8S rRNA processing, although it elicits a requirement for P-body function. While it does not significantly influence cell cycle progression alone, the allele reduces the efficiency of cell cycle arrest in strains with defects in kinetochore assembly. Finally, point mutations in the exonuclease domains of yeast Dis3 elicit genome instability phenotypes; however, these DIS3 mutations do not increase DNA damage or RNA processing defects that lead to the accumulation of polyadenylated RNA in the nucleus. These data suggest that specific DIS3 activities support mitotic fidelity in yeast.

The RNA Exosome and Human Disease

The evolutionarily conserved RNA exosome is a multisubunit ribonuclease complex that processes and/or degrades numerous RNAs. Recently, mutations in genes encoding both structural and catalytic subunits of the RNA exosome have been linked to human disease. Mutations in the structural exosome gene EXOSC2 cause a distinct syndrome that includes retinitis pigmentosa, hearing loss, and mild intellectual disability. In contrast, mutations in the structural exosome genes EXOSC3 and EXOSC8 cause pontocerebellar hypoplasia type 1b (PCH1b) and type 1c (PCH1c), respectively, which are related autosomal recessive, neurodegenerative diseases. In addition, mutations in the structural exosome gene EXOSC9 cause a PCH-like disease with cerebellar atrophy and spinal motor neuronopathy. Finally, mutations in the catalytic exosome gene DIS3 have been linked to multiple myeloma, a neoplasm of plasma B cells. How mutations in these RNA exosome genes lead to distinct, tissue-specific diseases is not currently well understood. In this chapter, we examine the role of the RNA exosome complex in human disease and discuss the mechanisms by which mutations in different exosome subunit genes could impair RNA exosome function and give rise to diverse diseases.

Transformation of mature mouse B cells into malignant plasma cells in vitro via introduction of defined genetic elements

An experimental system where defined alterations in gene function or gene expression levels in primary B cells would result in the development of transformed plasma cells in vitro would be useful in order to facilitate studies of the underlying molecular mechanisms of plasma cell malignancies. Here, such a system is described in which primary murine B cells rapidly become transformed into surface CD138⁺ , IgM^-/low , CD19^- IgM-secreting plasma cells as a result of expression of the transcription factors IRF4 and MYC together with simultaneous expression of BMI1, mutated p53 or silencing of p19^Arf , and suppression of intrinsic apoptosis through expression of BCLXL. Analysis of gene expression patterns revealed that this combination of transforming genes resulted in expression of a number of genes previously associated with terminally differentiated B cells (plasma cells) and myeloma cells, whereas many genes associated with mature B cells and B-cell lymphomas were not expressed. Upon transplantation, the transformed cells preferentially localized to the bone marrow, presenting features of a plasma cell malignancy of the IgM isotype. The present findings may also be applicable in the development of novel methods for production of monoclonal antibodies.