Hyperphosphorylated paratarg-7: a new molecularly defined risk factor for monoclonal gammopathy of undetermined significance of the IgM type and Waldenstrom macroglobulinemia

Autoimmune Diseases and Plasma Cells Dyscrasias: Pathogenetic, Molecular and Prognostic Correlations

Multiple myeloma and monoclonal gammopathy of undetermined significance are plasma cell dyscrasias characterized by monoclonal proliferation of pathological plasma cells with uncontrolled production of immunoglobulins. Autoimmune pathologies are conditions in which T and B lymphocytes develop a tendency to activate towards self-antigens in the absence of exogenous triggers. The aim of our review is to show the possible correlations between the two pathological aspects. Molecular studies have shown how different cytokines that either cause inflammation or control the immune system play a part in the growth of immunotolerance conditions that make it easier for the development of neoplastic malignancies. Uncontrolled immune activation resulting in chronic inflammation is also known to be at the basis of the evolution toward neoplastic pathologies, as well as multiple myeloma. Another point is the impact that myeloma-specific therapies have on the course of concomitant autoimmune diseases. Indeed, cases have been observed of patients suffering from multiple myeloma treated with daratumumab and bortezomib who also benefited from their autoimmune condition or patients under treatment with immunomodulators in which there has been an arising or worsening of autoimmunity conditions. The role of bone marrow transplantation in the course of concomitant autoimmune diseases remains under analysis.

The epidemiology of Waldenström macroglobulinemia

Waldenström macroglobulinemia (WM) is a rare subtype of non-Hodgkin lymphoma characterized by the presence of lymphoplasmacytic lymphoma (LPL) in the bone marrow accompanied by a monoclonal immunoglobulin type M (IgM) in the serum. WM was first described only 80 years ago and became reportable in the US as a malignancy in 1988. Very little systematic research was conducted prior to 2000 to characterize incidence, clinical characteristics, risk factors or diagnostic and prognostic criteria, and there were essentially no WM-specific clinical interventional trials. Since the inaugural meeting of the International Workshop in Waldenström's Macroglobulinemia (IWWM) in 2000, WM has become the focus of a steadily increasing and productive body of research, engaging a growing number of investigators throughout the world. This introductory overview provides summary of the current understanding of the epidemiology of WM/LPL as a backdrop for a series of consensus panel recommendations arising from research presented at the 11th IWWM.

B‐cell receptors of EBV‐negative Burkitt lymphoma bind modified isoforms of autoantigens

Burkitt lymphoma (BL) represents the most aggressive B‐cell‐lymphoma. Beside the hallmark of IG‐MYC‐translocation, surface B‐cell receptor (BCR) is expressed, and mutations in the BCR pathway are frequent. Coincidental infections in endemic BL, and specific extra‐nodal sites suggest antigenic triggers. To explore this hypothesis, BCRs of BL cell lines and cases were screened for reactivities against a panel of bacterial lysates, lysates of Plasmodium falciparum, a custom‐made virome array and against self‐antigens, including post‐translationally modified antigens.

An atypically modified, SUMOylated isoform of Bystin, that is, SUMO1‐BYSL was identified as the antigen of the BCR of cell line CA46. SUMO1‐BYSL was exclusively expressed in CA46 cells with K139 as site of the SUMOylation. Secondly, an atypically acetylated isoform of HSP40 was identified as the antigen of the BCR of cell line BL41. K104 and K179 were the sites of immunogenic acetylation, and the acetylated HSP40 isoform was solely present in BL41 cells. Functionally, addition of SUMO1‐BYSL and acetylated HSP40 induced BCR pathway activation in CA46 and BL41 cells, respectively. Accordingly, SUMO1‐BYSL‐ETA’ immunotoxin, produced by a two‐step intein‐based conjugation, led to the specific killing of CA46 cells. Autoantibodies directed against SUMO1‐BYSL were found in 3 of 14 (21.4%), and autoantibodies against acetylated HSP40 in 1/14(7.1%) patients with sporadic Burkitt‐lymphoma. No reactivities against antigens of the infectious agent spectrum could be observed.

These results indicate a pathogenic role of autoreactivity evoked by immunogenic post‐translational modifications in a subgroup of sporadic BL including two EBV‐negative BL cell lines.

Identification of the atypically modified autoantigen Ars2 as the target of B-cell receptors from activated B-cell-type diffuse large B-cell lymphoma

It has been suggested that stimulation of B-cell receptors (BCR) by specific antigens plays a pathogenic role in diffuse large B-cell lymphoma (DLBCL). Here, it was the aim to screen for specific reactivities of DLBCL-BCR in the spectrum of autoantigens and antigens of infectious origin. Arsenite resistance protein 2 (Ars2) was identified as the BCR target of three of five activated B-cell type DLBCL cell lines and two of 11 primary DLBCL cases. Compared to controls, Ars2 was hypophosphorylated exclusively in cases and cell lines with Ars2-specific BCR. In a validation cohort, hypophosphorylated Ars2 was found in eight of 31 activated B-cell type DLBCL, but in only one of 20 germinal center B-cell like type DLBCL. Incubation with Ars2 induced BCR-pathway activation and increased proliferation, while an Ars2/ETA’ toxin conjugate induced killing of cell lines with Ars2-reactive BCR. Ars2 appears to play a role in a subgroup of activated B-cell-type DLBCL. Moreover, transformed DLBCL lines with Ars2-reactive BCR still showed growth advantage after incubation with Ars2. These results provide knowledge about the pathogenic role of a specific antigen stimulating the BCR pathway in DLCBL.

Monoclonal immunoglobulins promote bone loss in multiple myeloma

Most patients with multiple myeloma develop a severe osteolytic bone disease. The myeloma cells secrete immunoglobulins, and the presence of monoclonal immunoglobulins in the patient's sera is an important diagnostic criterion. Here, we show that immunoglobulins isolated from myeloma patients with bone disease promote osteoclast differentiation when added to human preosteoclasts in vitro, whereas immunoglobulins from patients without bone disease do not. This effect was primarily mediated by immune complexes or aggregates. The function and aggregation behavior of immunoglobulins are partly determined by differential glycosylation of the immunoglobulin-Fc part. Glycosylation analyses revealed that patients with bone disease had significantly less galactose on immunoglobulin G (IgG) compared with patients without bone disease and also less sialic acid on IgG compared with healthy persons. Importantly, we also observed a significant reduction of IgG sialylation in serum of patients upon onset of bone disease. In the 5TGM1 mouse myeloma model, we found decreased numbers of lesions and decreased CTX-1 levels, a marker for osteoclast activity, in mice treated with a sialic acid precursor, N-acetylmannosamine (ManNAc). ManNAc treatment increased IgG-Fc sialylation in the mice. Our data support that deglycosylated immunoglobulins promote bone loss in multiple myeloma and that altering IgG glycosylation may be a therapeutic strategy to reduce bone loss.

Role of Specific B-Cell Receptor Antigens in Lymphomagenesis

The B-cell receptor (BCR) signaling pathway is a crucial pathway of B cells, both for their survival and for antigen-mediated activation, proliferation and differentiation. Its activation is also critical for the genesis of many lymphoma types. BCR-mediated lymphoma proliferation may be caused by activating BCR-pathway mutations and/or by active or tonic stimulation of the BCR. BCRs of lymphomas have frequently been described as polyreactive. In this review, the role of specific target antigens of the BCRs of lymphomas is highlighted. These antigens have been found to be restricted to specific lymphoma entities. The antigens can be of infectious origin, such as H. pylori in gastric MALT lymphoma or RpoC of M. catarrhalis in nodular lymphocyte predominant Hodgkin lymphoma, or they are autoantigens. Examples of such autoantigens are the BCR itself in chronic lymphocytic leukemia, LRPAP1 in mantle cell lymphoma, hyper-N-glycosylated SAMD14/neurabin-I in primary central nervous system lymphoma, hypo-phosphorylated ARS2 in diffuse large B-cell lymphoma, and hyper-phosphorylated SLP2, sumoylated HSP90 or saposin C in plasma cell dyscrasia. Notably, atypical posttranslational modifications are often responsible for the immunogenicity of many autoantigens. Possible therapeutic approaches evolving from these specific antigens are discussed.

Polyclonal serum free light chain elevation is associated with increased risk of monoclonal gammopathies

Monoclonal gammopathies (MG) constitute a spectrum of disorders starting from a monoclonal gammopathy of undetermined significance (MGUS) to active disease requiring therapy such as multiple myeloma. MG are characterized by proliferation of clonal plasma cells (PC) secreting a monoclonal protein either as intact immunoglobulin or free kappa or lambda free light chains (FLC). We hypothesized that a polyclonal elevation of serum FLC may indicate an inflammatory state that precedes development of MG. We studied 15,630 individuals from Olmsted county, who did not have MGUS based on baseline screening studies. At a median follow-up of 18.1 years, 264 patients had developed a clonal PC disorder; 252 with MGUS, 1 with SMM, 8 with MM, and 3 with amyloidosis, translating to an annual incidence of development of a MG of 0.1%. We examined the baseline polyclonal ΣFLC (kappa + lambda FLC) from the initial screening and grouped them into deciles. The highest decile group had a 2.6-fold (95% CI; 1.8, 3.7) increase in the risk of developing a MG, P < 0.001. We demonstrate for the first time, the increased risk of developing MG in patients with elevated serum FLC, suggesting that an underlying inflammatory state may play an etiologic role.

Hyper-N-glycosylated SAMD14 and neurabin-I as driver autoantigens of primary central nervous system lymphoma

To address the role of chronic antigenic stimulation in primary central nervous system lymphoma (PCNSL), we searched for autoantigens and identified sterile α-motif domain containing protein 14 (SAMD14) and neural tissue-specific F-actin binding protein I (neurabin-I) as autoantigenic targets of the B-cell receptors (BCRs) from 8/12 PCNSLs. In the respective cases, SAMD14 and neurabin-I were atypically hyper-N-glycosylated (SAMD14 at ASN339 and neurabin-I at ASN1277), explaining their autoimmunogenicity. SAMD14 and neurabin-I induced BCR pathway activation and proliferation of aggressive lymphoma cell lines transfected with SAMD14- and neurabin-I-reactive BCRs. Moreover, the BCR binding epitope of neurabin-I conjugated to truncated Pseudomonas exotoxin-killed lymphoma cells expressing the respective BCRs. These results support the role of chronic antigenic stimulation by posttranslationally modified central nervous system (CNS) driver autoantigens in the pathogenesis of PCNSL, serve as an explanation for their CNS tropism, and provide the basis for a novel specific treatment approach.

Serum immunoreactivity of cancer/testis antigen OY-TES-1 and its tissues expression in glioma

OY-TES-1 is a member of the cancer/testis antigen family that is expressed in healthy testis tissue and certain types of cancerous tissue. The present study aimed to analyze the expression pattern of OY-TES-1 and serum anti-OY-TES-1 antibody concentration in patients with glioma. OY-TES-1 mRNA was detected in 28/36 (78%) of glioma cases using conventional reverse transcription polymerase chain reaction (RT-PCR) analysis. RT-quantitative-PCR revealed that OY-TES-1 was expressed at a higher level in glioma tissues compared with normal adult tissues (with the exception of testis tissue). Anti-OY-TES-1 antibodies were present in the serum of 5/36 (14%) of patients with glioma, but absent in all the serum samples from 107 healthy donors. Immunohistochemical analysis demonstrated that OY-TES-1 protein was expressed in all glioma tissues from patients with anti-OY-TES-1 antibody seropositivity. These results suggest that OY-TES-1 is a novel candidate for glioma immunotherapy.

Waldenstrom Macroglobulinemia: Genomic Aberrations and Treatment

Waldenström macroglobulinemia (WM) is a rare, indolent, and monoclonal immunoglobulin M-associated lymphoplasmacytic disorder with unique clinicopathologic characteristics. Over the past decade, remarkable progress has occurred on both the diagnostic and therapeutic fronts in WM. A deeper understanding of the disease biology emanates from the seminal discoveries of myeloid differentiation primary response 88 (MYD88) L265P somatic mutation in the vast majority of cases and C-X-C chemokine receptor, type 4, mutations in about a third of patients. Although WM remains an incurable malignancy, and the indications to initiate treatment are largely unchanged, the therapeutic armamentarium continues to expand. Acknowledging the paucity of high-level evidence from large randomized controlled trials, herein, we evaluate the genomic aberrations and provide a strategic framework for the management in the frontline as well as the relapsed/refractory settings of symptomatic WM.

The molecular basis for development of proinflammatory autoantibodies to progranulin

Recently we identified in a wide spectrum of autoimmune diseases frequently occurring proinflammatory autoantibodies directed against progranulin, a direct inhibitor of TNFR1 & 2 and of DR3. In the present study we investigated the mechanisms for the breakdown of self-tolerance against progranulin. Isoelectric focusing identified a second, differentially electrically charged progranulin isoform exclusively present in progranulin-antibody-positive patients. Alkaline phosphatase treatment revealed this additional progranulin isoform to be hyperphosphorylated. Subsequently Ser81, which is located within the epitope region of progranulin-antibodies, was identified as hyperphosphorylated serine residue by site directed mutagenesis of candidate phosphorylation sites. Hyperphosphorylated progranulin was detected exclusively in progranulin-antibody-positive patients during the courses of their diseases. The occurrence of hyperphosphorylated progranulin preceded seroconversions of progranulin-antibodies, indicating adaptive immune response. Utilizing panels of kinase and phosphatase inhibitors, PKCβ1 was identified as the relevant kinase and PP1 as the relevant phosphatase for phosphorylation and dephosphorylation of Ser81. In contrast to normal progranulin, hyperphosphorylated progranulin interacted exclusively with inactivated (pThr320) PP1, suggesting inactivated PP1 to cause the detectable occurrence of phosphorylated Ser81 PGRN. Investigation of possible functional alterations of PGRN due to Ser81 phosphorylation revealed, that hyperphosphorylation prevents the interaction and thus direct inhibition of TNFR1, TNFR2 and DR3, representing an additional direct proinflammatory effect. Finally phosphorylation of Ser81 PGRN alters the conversion pattern of PGRN. In conclusion, inactivated PP1 induces hyperphosphorylation of progranulin in a wide spectrum of autoimmune diseases. This hyperphosphorylation prevents direct inhibition of TNFR1, TNFR2 and DR3 by PGRN, alters the conversion of PGRN, and is strongly associated with the occurrence of neutralizing, proinflammatory PGRN-antibodies, indicating immunogenicity of this alternative secondary modification.

CD4⁺ T cells in chronic autoantigenic stimulation in MGUS, multiple myeloma and Waldenström's macroglobulinemia

Hyperphosphorylated paratarg-7 (pP-7) carrier state is the strongest and most frequent molecular risk factor for MGUS, multiple myeloma (MM) and Waldenström's macroglobulinemia (WM), inherited autosomal-dominantly and, depending on the ethnic background, found in up to one third of patients with MGUS/MM. Since P-7 is the antigenic target of paraproteins that do not distinguish between wtP-7 and pP-7, we investigated CD4(+) T-cell responses in pP-7(+) patients and controls. Peptides spanning amino acids 1-35 or 4-31 containing phosphorylated or nonphosphorylated serine17 were used for stimulation. CD4(+) cells from 9/14 patients (65%) showed a pP-7 specific HLA-DR restricted response. These results demonstrate that pP-7 specific CD4(+) cells can mediate help for pP-7 specific chronic antigenic stimulation of P-7 specific B cells, which might ultimately result in the clonal evolution of a B cell into MGUS/MM/WM producing a P-7 specific paraprotein. Prerequisites for pP-7 specific stimulation of CD4(+) cells appear to be both a pP-7 carrier state and an HLA-DR subtype able to present and recognize pP-7. Our results serve as an explanation for the exclusive autoimmunogenicity of the hyperphosphorylated variant of P-7 and for the different hazard ratios of pP-7 carriers from different ethnic origins to develop MGUS/MM/WM.

Sumoylated HSP90 is a dominantly inherited plasma cell dyscrasias risk factor

Posttranslationally modified proteins serve as autoimmunogenic targets in a wide spectrum of autoimmune diseases. Here, we identified a posttranslationally modified paraprotein target (paratargs) in monoclonal gammopathies of undetermined significance (MGUS), multiple myelomas (MM), and Waldenstrom's macroglobulinemias (WM) using protein macroarrays that were sumoylated and screened for reactivity with paraproteins from MGUS, MM, and WM patients. We found that paraproteins from a proportion of European, African-American, and Japanese patients specifically reacted with the sumoylated heat-shock protein 90 β isoform-α (HSP90-SUMO1, where SUMO indicates small ubiquitin-like modifier), while no reactivity with HSP90-SUMO1 was detected in over 800 controls. HSP90-SUMO1 was present in blood cells from all patients with HSP90-SUMO1-binding paraproteins. We determined that the HSP90-SUMO1 carrier state is autosomal-dominantly inherited and caused by the inability of SUMO peptidase sentrin/SUMO-specific protease 2 (SENP2) to desumoylate HSP90-SUMO1. HSP90-SUMO1 was detected in a small percentage of healthy individuals from all backgrounds; however, only MGUS, MM, and WM patients who were HSP90-SUMO1 carriers produced HSP90-SUMO1-specific paraproteins, suggesting that sumoylated HSP90 promotes pathogenesis of these diseases through chronic antigenic stimulation. This study demonstrates that harboring HSP90-SUMO1 identifies healthy individuals at risk for plasma cell dyscrasias and that dominant inheritance of posttranslationally modified autoantigenic paratargs is one of the strongest molecular defined risk factors for MGUS, MM, and WM.

Inactivation of protein-phosphatase 2A causing hyperphosphorylation of autoantigenic paraprotein targets in MGUS/MM is due to an exchange of its regulatory subunits

Hyperphosphorylated paratarg-7 (pP-7) carrier state is the strongest molecularly defined risk factor for monoclonal gammopathy of undetermined significance (MGUS), multiple myeloma (MM) and Waldenstrom's macroglobulinemia (WM). pP-7 is inherited as autosomal-dominant trait and depending on the ethnic background is found in over one-third of MGUS/MM patients. P-7, which is the antigenic paraprotein target in these patients, is hyperphosphorylated at serine17. P-7 hyperphosphorylation can be induced in wild-type P-7 (wtP-7) carriers by PKCζ and reverted by protein-phosphatase 2A (PP2A). Here we show that dephosphorylation of pP-7 is defective in pP-7 carriers due to inactivation of the PP2A by substitution of the regulatory B55δ subunit with B56γ3. In lymphoblastoid cell lines from pP-7 carriers, transfection of recombinant B55δ or treatment with ceramide led to a partial reconstitution of PP2A activity and dephosphorylation of pP-7 to wtP7. Similar results were observed with other previously reported autoantigenic paraproteins targets. In conclusion, the mechanisms responsible for the defective dephosphorylation and maintaining the hyperphosphorylated state of P-7 and other autoantigenic paraprotein targets have been elucidated, facilitating the identification of the genetic basis underlying this phenomenon which is obviously common in the pathogenesis of MGUS/MM/WM and not restricted to pP-7 cases.

Genetic factors and pathogenesis of Waldenström's macroglobulinemia

Waldenström's macroglobulinemia (WM) is an indolent but incurable B-cell malignancy. Over the last decade, advances in the molecular field brought about by the use of high-throughput genomic analyses-including array-based comparative genomic hybridization and massively parallel genome sequencing-have considerably improved our understanding of the genetic basis of WM. Its pathogenesis, however, remains fragmented. Important steps have been made in elucidating the underlying aberrations and deregulated mechanisms of the disease, and thereby providing invaluable information for identifying biomarkers for disease diagnosis, risk stratification, and therapeutic approaches. We review the genetic basis of the disease.

Over one-third of African-American MGUS and multiple myeloma patients are carriers of hyperphosphorylated paratarg-7, an autosomal dominantly inherited risk factor for MGUS/MM

As hyperphosphorylated paratarg-7 (pP-7) carrier state was shown to be the first molecularly defined autosomal dominantly inherited risk factor for monoclonal gammopathy of unknown significance (MGUS) and multiple myeloma (MM) in a European population, the prevalence of pP-7 carrier state among African-Americans who have a significantly higher incidence of MGUS/MM is of interest. We therefore determined pP-7 carrier state and paraproteins with specificity for P-7 in African-American, European and Japanese patients with MGUS/MM and healthy controls. By isoelectric focusing and ELISA, a paratarg-7-specific paraprotein and the associated pP-7 carrier state was observed in 30/81 (37.0%) African-American, 42/252 (16.7%) European and 7/176 (4.0%) Japanese MGUS/MM patients (p < 0.001). A pP-7 carrier state was found in 11/100 (11.0%) African-American, 8/550 (1.5%) European and 1/278 (0.4%) Japanese healthy controls (p < 0.001), resulting in an odds ratio for MGUS/MM of 4.8 (p < 0.001) among African-American, 13.6 among European (p < 0.001) and 11.5 (p = 0.023) among Japanese carriers of pP-7. We conclude that pP-7 carriers are most prevalent among African-Americans, but a pP-7 carrier state is the strongest molecularly defined single risk factor for MGUS/MM known to date in all three ethnic groups. The high prevalence of pP-7 carriers among African-American patients emphasizes a predominant role of this genetic factor in the pathogenesis of these diseases. The large number of pP7 African-American patients and controls should facilitate the identification of the SNP or mutation underlying the pP-7 carrier state.

Inherited predisposition to multiple myeloma

Multiple myeloma (MM) is the second most common hematologic malignancy in the United States, after non-Hodgkin lymphoma. Family pedigree analyses of high-risk families, case-control studies and racial disparities in disease incidence all point to a potential inherited predisposition to MM. Genome-wide association studies (GWASs) have identified susceptibility loci in a number of cancers and such studies are currently underway in MM. To date, GWASs in MM have identified several potential regions of interest for further study on chromosomes 3p22, 7p15.3, 8q24 and 2p23.3. In addition, several targets of paraproteins (so called 'paratargs') in MM have been identified. Hyperphosphorylation of the paratarg protein, which is inherited in an autosomal dominant manner, appears a common mechanism underlying the antigenicity of these proteins. One particular protein, hyperphosphorylated paratarg-7 (pP-7) is a common target in persons with myeloma and has also been identified in affected members of several high-risk MM families. It appears that the frequency of pP-7 as an antigenic target may be particularly high in African American patients with MM, which could be part of the explanation for observed racial disparities in the incidence of MM. In this review we focus on available data in the area of inherited predisposition to MM, and highlight future research directions.

Candidate genes of Waldenström's macroglobulinemia: current evidence and research

Waldenström's macroglobulinemia (WM) is a relatively uncommon, indolent malignancy of immunoglobulin M-producing B cells. The World Health Organization classifies it as a lymphoplasmacytic lymphoma and patients typically present with anemia, hepatosplenomegaly and diffuse lymphadenopathies. Historically, the genetic characterization of the disease has been hampered by the relatively low proliferative rate of WM cells, thus making karyotyping challenging. The use of novel technologies such as fluorescence in situ hybridization, gene array, and whole genome sequencing has contributed greatly to establishing candidate genes in the pathophysiology of WM and to identifying potential treatment targets, such as L265P MYD88. The discovery of microRNAs and the recognition of epigenetics as a major modulatory mechanism of oncogene expression and/or oncosuppressor silencing have aided in further understanding the pathogenesis of WM. Once thought to closely resemble multiple myeloma, a cancer of terminally differentiated, immunoglobulin-secreting plasma cells, WM appears to genetically cluster with other indolent B-cell lymphomas such as chronic lymphocytic leukemia/small cell lymphoma. The relative high incidence of familial cases of WM and other B-cell malignancies has been helpful in identifying high-risk gene candidates. In this review, we focus on the established genes involved in the pathogenesis of WM, with special emphasis on the key role of derangement of the nuclear factor kappa B signaling pathway and epigenetic mechanisms.

Molecular pathogenesis of Waldenstrom's macroglobulinemia

Waldenström's macroglobulinemia is an indolent, lymphoproliferative disease, characterized by a heterogeneous lymphoplasmacytic bone marrow infiltrate and high immunoglobulin M production. While technological advances over the past several decades have dramatically improved the possibilities of studying the molecular basis of Waldenström's macroglobulinemia, the pathogenesis of the disease remains fragmented. Undoubtedly, research has been successful in uncovering underlying aberrations and deregulated mechanisms in this disease, providing useful information for identifying biomarkers for disease diagnosis, risk stratification and therapeutic intervention, but there is still a long way to go before the pathogenesis of Waldenström's macroglobulinemia is fully revealed. In addition, the low number of in vitro or in vivo models significantly challenges extensive analysis. In this manuscript, we review the molecular basis of this disease.

Familial monoclonal gammopathy of undetermined significance and multiple myeloma: epidemiology, risk factors, and biological characteristics

Monoclonal gammopathy of undetermined significance (MGUS), a precursor to multiple myeloma (MM), is one of the most common premalignant conditions in the general population. The cause of MGUS is largely unknown. Recent studies show that there is an increased prevalence of MGUS in blood relatives of persons with lymphoproliferative and plasma cell proliferative disorders, suggesting presence of shared underlying genetic influences. In the past few years, additional studies have examined risk factors and biologic characteristics that may contribute to the increased prevalence of MGUS among relatives of probands with MGUS, MM, and other blood malignancies. This article reviews the known epidemiology and risk factors for familial MGUS and myeloma, the risk of lymphoproliferative disorders and other malignancies among blood-relatives of patients with MGUS and MM, and discusses future directions for research.

Hyperphosphorylation of autoantigenic targets of paraproteins is due to inactivation of PP2A

Paratarg-7, a frequent autoantigenic target, and all other autoantigenic targets of human paraproteins molecularly defined to date are hyperphosphorylated in the respective patients compared with healthy controls, suggesting that hyperphosphorylation of autoantigenic paraprotein targets is a general mechanism underlying the pathogenesis of these paraproteins. We now show that hyperphosphorylation of paratarg-7 occurs because of an additional phosphorylation of Ser17, which is located within the paraprotein-binding epitope. Coimmunoprecipitation identified phosphokinase C ζ (PKCζ) as the kinase responsible for the phosphorylation of most, and phosphatase 2A (PP2A) as the phosphatase responsible for the dephosphorylation of all hyperphosphorylated autoantigenic targets of paraproteins. Single-nucleotide polymorphisms (SNPs) or mutations of PKCζ and PP2A were excluded. However, PP2A was inactivated by phosphorylation of its catalytic subunit at Y307. Stimulation of T cells from healthy carriers of wild-type paratarg-7 induced a partial and transient hyperphosphorylation between days 4 and 18, which was maintained by incubation with inhibitors of PP2A, again indicating that an inactivation of PP2A is responsible for the hyperphosphorylation of autoantigenic paraprotein targets. We conclude that the genetic defect underlying the dominantly inherited hyperphosphorylation of autoantigenic paraprotein targets is not in the PP2A itself, but in genes or proteins controlling PP2A activity by phosphorylation of its catalytic subunit.

Paraproteins of familial MGUS/multiple myeloma target family-typical antigens: hyperphosphorylation of autoantigens is a consistent finding in familial and sporadic MGUS/MM

Paratarg-7 (P-7) is a frequent paraprotein target in monoclonal gammopathy of undetermined significance (MGUS), multiple myeloma (MM), and Waldenström macroglobulinemia. Patients with P-7-specific paraproteins carry a hyperphosphorylated paratarg-7 (pP-7). Because pP-7 carrier state is dominantly inherited, we determined the paraprotein targets in 4 families with familial MGUS/MM. No antigenic target was identified for the paraproteins from 2 members of one family. Paraproteins from affected members of 2 other families targeted P-7, and paraproteins from 4 affected members of a fourth family targeted P-8, which is encoded by the ATG13 gene. P-8 was hyperphosphorylated in the affected family members (pP-8) and pP-8 carrier state is inherited in a dominant fashion. Six additional autoantigenic nonfamilial paraprotein targets were also hyperphosphorylated in the respective patients compared with normal controls. We conclude that paraproteins of affected members with familial MGUS/MM share family-typical hyperphosphorylated antigens and hyperphosphorylation of paraprotein targets might be a general mechanism underlying the pathogenesis of MGUS/MM.