Recurrent alterations of the WW domain containing oxidoreductase gene spanning the common fragile site FRA16D in multiple myeloma and monoclonal gammopathy of undetermined significance

Wwox Deletion in Mouse B Cells Leads to Genomic Instability, Neoplastic Transformation, and Monoclonal Gammopathies

WWOX (WW domain containing oxidoreductase) expression loss is common in various cancers and characteristic of poor prognosis. Deletions, translocations, and loss of expression affecting the WWOX gene are a common feature of various B cell neoplasms such as certain B cell lymphomas and multiple myeloma. However, the role of this common abnormality in B cell tumor initiation and/or progression has not been defined. In this study, we conditionally deleted Wwox early in B cell development by means of breeding Cd19-Cre transgenic mice crossed to Wwox floxed mice (Cd19 Wwox KO). We observed a significant reduced survival in Cd19 Wwox KO mice and the development of B cell neoplasms including B cell lymphomas, plasma cell neoplasias characterized by increased numbers of CD138+ populations as well as monoclonal gammopathies detected by serum protein electrophoresis. To investigate whether Wwox loss could play a role in genomic instability, we analyzed DNA repair functions during immunoglobulin class switch joining between DNA segments in antibody genes. While class switch recombination (CSR) was only slightly impaired, Wwox deficiency resulted in a dramatic shift of double strand break (DSB) repair from normal classical-NHEJ toward the microhomology-mediated alternative-NHEJ pathway, a pathway associated with chromosome translocations and genome instability. Consistent with this, Wwox deficiency resulted in a marked increase of spontaneous translocations during CSR. This work defines for the first time a role for Wwox for maintaining B cell genome stability during a process that can promote neoplastic transformation and monoclonal gammopathies.

Germline Risk Contribution to Genomic Instability in Multiple Myeloma

Genomic instability, a well-established hallmark of human cancer, is also a driving force in the natural history of multiple myeloma (MM) - a difficult to treat and in most cases fatal neoplasm of immunoglobulin producing plasma cells that reside in the hematopoietic bone marrow. Long recognized manifestations of genomic instability in myeloma at the cytogenetic level include abnormal chromosome numbers (aneuploidy) caused by trisomy of odd-numbered chromosomes; recurrent oncogene-activating chromosomal translocations that involve immunoglobulin loci; and large-scale amplifications, inversions, and insertions/deletions (indels) of genetic material. Catastrophic genetic rearrangements that either shatter and illegitimately reassemble a single chromosome (chromotripsis) or lead to disordered segmental rearrangements of multiple chromosomes (chromoplexy) also occur. Genomic instability at the nucleotide level results in base substitution mutations and small indels that affect both the coding and non-coding genome. Sometimes this generates a distinctive signature of somatic mutations that can be attributed to defects in DNA repair pathways, the DNA damage response (DDR) or aberrant activity of mutator genes including members of the APOBEC family. In addition to myeloma development and progression, genomic instability promotes acquisition of drug resistance in patients with myeloma. Here we review recent findings on the genetic predisposition to myeloma, including newly identified candidate genes suggesting linkage of germline risk and compromised genomic stability control. The role of ethnic and familial risk factors for myeloma is highlighted. We address current research gaps that concern the lack of studies on the mechanism by which germline risk alleles promote genomic instability in myeloma, including the open question whether genetic modifiers of myeloma development act in tumor cells, the tumor microenvironment (TME), or in both. We conclude with a brief proposition for future research directions, which concentrate on the biological function of myeloma risk and genetic instability alleles, the potential links between the germline genome and somatic changes in myeloma, and the need to elucidate genetic modifiers in the TME.

Modeling WWOX Loss of Function in vivo: What Have We Learned?

The WW domain–containing oxidoreductase (WWOX) gene encompasses a common fragile sites (CFS) known as FRA16D, and is implicated in cancer. WWOX encodes a 46kDa adaptor protein, which contains two N-terminal WW–domains and a catalytic domain at its C–terminus homologous to short–chain dehydrogenase/reductase (SDR) family proteins. A high sequence conservation of WWOX orthologues from insects to rodents and ultimately humans suggest its significant role in physiology and homeostasis. Indeed, data obtained from several animal models including flies, fish, and rodents demonstrate WWOX in vivo requirement and that its deregulation results in severe pathological consequences including growth retardation, post–natal lethality, neuropathy, metabolic disorders, and tumorigenesis. Altogether, these findings set WWOX as an essential protein that is necessary to maintain normal cellular/physiological homeostasis. Here, we review and discuss lessons and outcomes learned from modeling loss of WWOX expression in vivo.

[Association of miRNA-196b-5p and miRNA-99a-5p with autophagy and apoptosis in multiple myeloma cells]

Objective: To investigate the relationship between miRNA-196b-5p and miRNA-99a-5p expression and autophagy and apoptosis in multiple myeloma cells. Methods: Human myeloma cell line U266 and normal CD138+ plasma cells were selected as the research objects. The subjects were divided into 45 cases of multiple myeloma patients and 40 healthy controls. The expression of miRNA-196b-5p and miRNA-99a-5p was measured by real-time quantitative PCR, and Western blot was used to determine the expression of autophagy related protein LC3-Ⅱ, LC3-Ⅰ, P62, Beclin-1 expression, apoptosis related protein CL caspase3, CL caspase7, Bcl-2, Bax, and TGF-β/Smad pathway associated proteins TGF-β1, Smad2/3, p-Smad3 and Smad7. The cell apoptosis rate was determined by flow cytometry. The correlation between miRNA expression level and clinical characteristics of multiple myeloma patients was analyzed. Results: Compared with normal plasma cells, the expression of miRNA-196b-5p in myeloma cells increased significantly (0.43±0.15 vs 2.44±0.63 or 2.02±0.85, all P<0.001), the expression of miRNA-99a-5p was significantly decreased (1.87±0.61 vs 0.62±0.15 or 0.80±0.33, P<0.001), LC3-Ⅱ/LC3-Ⅰ increased significantly (P<0.05), Beclin-1 expression increased significantly (P<0.05), P62 expression decreased significantly (P<0.05). The expression of Bax, CL caspase3 and CL caspase7 decreased significantly (P<0.05), and the expression of Bcl-2 increased significantly (P<0.05) and apoptosis rate significantly decreased (P<0.05). After transfected with miRNA-196b-5p mimic or miRNA-99a-5p inhibitor, the LC3-Ⅱ/LC3-Ⅰ of CD138+ plasma cells increased significantly (P<0.05), the expression of Beclin-1 increased significantly (P<0.05), P62 expression decreased significantly (P<0.05), and the apoptosis rate significantly decreased (P<0.05). However, after autophagy inhibitor of 3-MA was administered, the apoptotic rate of the above reaction system did not change significantly (P>0.05). The expression of miRNA-196b-5p and miRNA-99a-5p was significantly correlated with DS and ISS stage in multiple myeloma patients (P<0.05). Conclusion: miRNA-196b-5p and miRNA-99a-5p are closely related to the clinical characteristics of patients with multiple myeloma. The overexpression of miRNA-196b-5p and down regulation of miRNA-99a-5p could inhibit the apoptosis of myeloma cells by up regulation of autophagy, and the mechanism is related to the activation of the TGF-β/Smad signaling pathway.