MALT1 and the API2-MALT1 fusion act between CD40 and IKK and confer NF-kappa B-dependent proliferative advantage and resistance against FAS-induced cell death in B cells

The most frequently recurring translocations in mucosa-associated lymphoid tissue (MALT) B-cell non-Hodgkin lymphoma, t(11;18)(q21;q21) and t(14;18)(q32; q21), lead to formation of an API2-MALT1 fusion or IgH-mediated MALT1 overexpression. Various approaches have implicated these proteins in nuclear factor kappaB (NF-kappa B) signaling, but this has not been shown experimentally in human B cells. Immunohistochemistry showed that MALT1 is predominantly expressed in normal and malignant germinal center B cells, corresponding to the differentiation stage of MALT lymphoma. We expressed MALT1 and apoptosis inhibitor-2 API2/MALT1 in human B-cell lymphoma BJAB cells and found both transgenes in membrane lipid rafts along with endogenous MALT1 and 2 binding partners involved in NF-kappa B signaling, B-cell lymphoma 10 (BCL10) and CARMA1 (caspase recruitment domain [CARD]-containing membrane-associated guanylate kinase [MAGUK] 1). API2-MALT1 and exogenous MALT1 increased constitutive NF-kappa B activity and enhanced I kappa B kinase (IKK) activation induced by CD40 stimulation. Both transgenes protected BJAB cells from FAS (CD95)-induced death, consistent with increases in NF-kappa B cytoprotective target gene expression, and increased their proliferation rate. Expression of a dominant-negative I kappa B alpha mutant showed that these survival and proliferative advantages are dependent on elevated constitutive NF-kappa B activity. Our findings support a model in which NF-kappa B signaling, once activated in a CD40-dependent immune response, is maintained and enhanced through deregulation of MALT1 or formation of an API2-MALT1 fusion.     

Nuclear Factor κB Activation and Antiapoptosis in Mucosa-Associated Lymphoid Tissue Lymphoma

Three distinct chromosomal translocations, t(11;18), t(1;14), and t(14;18), involving the API2-MALT1 fusion protein, BCL10, and MALT1 have been convincingly implicated in the pathogenesis of mucosa-associated lymphoid tissue (MALT) lymphomas. Recent genetic and biochemical studies have indicated that BCL10 and MALT1 form a physical and functional complex and are both essential for nuclear factor kappaB (NF-kappaB) activation by antigen receptor stimulation in lymphocytes. API2-MALT1 can bypass the BCL10/MALT1 pathway linking to NF-kappaB activation, thereby inducing antigen receptor-independent events of lymphocytes. BCL10/MALT1- and API2-MALT1-induced NF-kappaB activation can be assumed to be able to contribute to antiapoptosis, probably through NF-kappaB-mediated up-regulation of several apoptotic inhibitor genes. We also have provided direct evidence that API2-MALT1 can exert an antiapoptotic effect, in part through its direct interaction with apoptotic regulators. We therefore hypothesize that the antiapoptotic effect of API2-MALT1 may be mediated by the interaction with apoptotic regulators as well as by the up-regulation of apoptotic inhibitor genes. Finally, we hope that further studies will stimulate research leading to the development of therapeutic drugs that specifically inhibit the antigen receptor-stimulated NF-kappaB activation pathway. Such drugs should be useful for interfering with inappropriate proliferation of lymphocytes associated with inflammatory and neoplastic disorders, including MALT lymphomas.     

Update on MALT lymphomas

Gastric mucosa associated lymphoid tissue (MALT) lymphoma is a histologically distinct tumour derived from MALT acquired as a result of Helicobacter pylori infection. Eradication of H. pylori causes clinical regression of the lymphoma in 75% of cases. In seeking to identify those cases resistant to this therapy, and in the interests of further understanding the biology of MALT lymphoma, genetic alterations of MALT lymphomas have been investigated. Three translocations, t(11;18)(q21;q21), t(1;14)(p22;q32) and t(14;18)(q32;q21) are specifically associated with MALT lymphoma and the genes involved have been identified. T(11;18) results in a chimeric fusion between the API2 and MALT1 genes and is specifically associated with gastric MALT lymphomas that do not respond to eradication of H. pylori. T(1;14) and t(14;18) deregulate BCL10 and MALT1 expression, respectively. These three chromosomal translocations that involve different genes appear to share common oncogenic properties by targeting the same nuclear factor kappa B (NF kappa B) oncogenic pathway.     

BCL10 mutation does not represent an important pathogenic mechanism in gastric MALT-type lymphoma, and the presence of the API2-MLT fusion is associated with aberrant nuclear BCL10 expression

Two recurrent translocations have been associated with mucosa-associated lymphoid tissue (MALT)-type lymphoma, t(11;18)(q21;q21) and t(1;14)(p22;q32). The first, t(11;18)(q21;q21), results in the fusion protein API2-MLT (API2-MALT1). Through t(1;14)(p22;q32), the BCL10 gene is entirely transferred to the IgH gene, resulting in its overexpression. Wild-type BCL10 is implicated in apoptosis, and it has been suggested that mutated forms gain oncogenic activity. The occurrence of genomic BCL10 mutations in 35 gastric MALT-type lymphomas with or without t(11;18)(q21;q21) (10 and 25 cases, respectively) was investigated. DNA extracted from either whole tissue sections or microdissected clusters of tumor cells was used. Five polymerase chain reactions amplifying the coding exons were performed and were followed by direct sequencing of the products. Twenty differences with the published BCL10 sequence, all single nucleotide substitutions, were detected in 16 cases. Of these, 12 represented known polymorphisms, either at codon 8, 213, or 5. Of the remaining 8 substitutions, 2 were silent and 6 resulted in amino acid substitutions. Mutation analysis results were correlated with the BCL10 expression pattern. Aberrant nuclear BCL10 expression was detected in 14 cases. No association could be demonstrated between the latter and the presence of BCL10 mutations. In contrast, all 10 cases carrying t(11;18)(q21;q21) showed nuclear expression, whereas this staining pattern was absent in 21 of 25 cases without t(11;18)(q21;q21). These results demonstrate that BCL10 mutations are rare in gastric MALT-type lymphoma and are not related to the aberrant nuclear expression of BCL10. In contrast, they indicate that the presence of the API2-MLT fusion protein is associated with aberrant nuclear BCL10 expression.     

原发性胃淋巴瘤凋亡抑制蛋白2-黏膜相关淋巴瘤转位基因1融合基因检测的意义

目的 研究原发性胃淋巴瘤(PGL)内镜活检组织中凋亡抑制蛋白2-黏膜相关淋巴瘤转位基因1（API2-MALT1）融合基因检测的可行性,探讨该融合基因在PGL的表达及其在PGL诊断、治疗等方面的临床价值。方法对32例疑诊为PGL者进行超声内镜检查和黏膜活检,活检标本分别进行组织病理、免疫组织化学检查和用荧光定量RT-PCR测定API2-MALT1融合基因。总结、分析诊断明确的PGL中API2-MALT1融合基因的表达以及该融合基因与PGL诊断、分型和治疗等方面的关系。结果32例疑诊PGL者中14例经病理检查和免疫组织化学检查确诊为PGL,其中胃黏膜相关淋巴组织(MALT)淋巴瘤11例,胃弥漫性大B细胞淋巴瘤(DLBCL)3例。API2-MALT1融合基因检测阳性5例,均为胃MALT淋巴瘤,约占胃MALT淋巴瘤(5/11)的45％。3例DLBCL患者API2-MALT1融合基因检测均阴性。API2-MALT1融合基因阴性组病变浸润深度和淋巴结浸润状况较阳性组严重。5例API2-MALT1融合基因阳性者中幽门螺杆菌(Hp)阳性2例,9例阴性者中Hp阳性5例。API2-MALT1融合基因阳性组5例行抗Hp治疗皆无效,但化学治疗有效;阴性组中5例Hp阳性者完全缓解2例,4例Hp阴性者抗Hp治疗无效。结论 API2-MALT1融合基因是胃MALT淋巴瘤的常见遗传学异常。内镜定位活检标本通过荧光定量PCR法检测该融合基因在临床上是可行的,该融合基因的检测对PGL诊断、治疗和预后评估均有一定的价值。     

中国人黏膜相关淋巴组织结外边缘区淋巴瘤染色体易位的临床研究

目的 探讨中国人不同部位黏膜相关淋巴组织结外边缘区淋巴瘤(MALTL)中分子遗传学异常的发生情况.方法 应用间期荧光原位杂交(FISH)方法,检测217例不同部位MALTL的t(11;18)(q21;q21)/API2-MALT1、t(1;14)(p22;q32)/IGH-BCL10、t(14;18)(q32;q21)/IGH-MALT1和涉及BCL6基因的染色体易位.结果 染色体易位的总发生率为21%(46/217).全部病例共检测出4种主要染色体异常,其中第1种13%(29/217)为t(11;18)(q21;q21)/API2-MALT1,最常见的发生部位是肺47%(8/17)和小肠29%(4/14),其次为唾液腺1/6例、胃14%(12/84)和眼附属器6%(4/68).第2种1%(3/217)为t(1;14)(p22;q32)/IGH-BCL10,仪见于肺12%(2/17)和胃1%(1/84).第3种1%(2/217)为t(14;18)(q32;q21)/IGH-MALTI,仅见于肺6%(1/17)和眼附属器2%(1/68).第4种2%(4/217)为BCL6基因涉及的染色体易位,见于唾液腺1/6例和胃4%(3/84).4%(8/217)为涉及IGH基因但未知与其易位的伙伴基因的染色体易位.结论 以上4种染色体易位在中国人不同解剖部位的MALTL中的发生率有明显不同,与欧美国家所报道的染色体易位的发生率相比较,分布稍有差异.     

胃黏膜相关淋巴样组织淋巴瘤染色体易位t(11;18)与BCL10的表达

目的　检测胃黏膜相关淋巴样组织 (MALT)淋巴瘤的染色体易位t(11;18) (q2 1;q2 1)和BCL10蛋白表达的情况。方法　采用RT PCR检测胃MALT淋巴瘤和滤泡性胃炎 (FG)中API2 MLT融合及免疫组化检测BCL10蛋白、Ki 6 7表达情况 ,并结合临床病理进行分析。结果　 14例胃MALT淋巴瘤中有 3例 (2例低恶性 ,1例低～高恶性 )检测到API2 MLT融合 ,8例FG无此融合。BCL10在FG淋巴滤泡生发中心细胞胞质中弱表达 ,在胃MALT淋巴瘤中表达明显增强 ,且 4 2 .5 %的病例细胞核阳性。胃低～高恶性及弥漫大细胞淋巴瘤 (DLBCL)的Ki 6 7标记率显著强于低恶性MALT淋巴瘤 (P<0 .0 5 )。BCL10核表达与Ki 6 7阳性表达之间差异无显著性 (P >0 .0 5 ) ,但随Ki 6 7表达增强 ,BCL10核表达的概率增加。结论　API2 MLT融合和BCL10核表达可能与胃MALT淋巴瘤从低恶性向高恶性转化有关。RT PCR检测API2 MLT融合是检测t(11;18) (q2 1;q2 1)的一项重要工具     

Distinct comparative genomic hybridisation profiles in gastric mucosa-associated lymphoid tissue lymphomas with and without t(11;18)(q21;q21)

t(11;18)(q21;q21) occurs specifically in mucosa-associated lymphoid tissue (MALT) lymphoma and the translocation generates a functional API2-MALT1 fusion product that activates nuclear factor (NF)kappaB. t(11;18) positive lymphomas usually lack the chromosomal aberrations and microsatellite alterations frequently seen in the translocation-negative MALT lymphomas. To further understand their genetic differences, we investigated gastric MALT lymphomas with and without t(11;18) by comparative genomic hybridisation. In general, both chromosomal gains and losses were far more frequent in t(11;18)-negative (median = 3.4 imbalances) than t(11;18)-positive cases (median = 1.6 imbalances), with gains being more frequent than losses. Recurrent chromosomal gains involving whole or major parts of a chromosome were seen for chromosomes 3, 12, 18 and 22 (23%, 19%, 19% and 27% respectively). Discrete recurrent chromosomal gains were found at 9q34 (11/26 = 42%). Bioinformatic analysis of genes mapping to 9q34 revealed potential targets. Among them, TRAF2 and CARD9 are known interaction partners of BCL10, playing a role in NFkappaB activation. Interphase fluorescent in situ hybridisation confirmed genomic gain of the TRAF2, CARD9 and MALT1 loci in 5/6 and 2/2 cases showing chromosomal gains at 9q34 and 18q21 respectively. The results further highlight the genetic difference between MALT lymphomas with and without t(11;18). Moreover, our findings suggest that genomic gain of genes that modulate NFkappaB activation, such as MALT1, TRAF2 and CARD9, may play a role in the pathogenesis of the translocation-negative MALT lymphoma.     

MALT1 contains nuclear export signals and regulates cytoplasmic localization of BCL10

MALT1, BCL10 (B-cell lymphoma 10), and API2 (apoptosis inhibitor 2)-MALT1 are key molecules in mucosa-associated lymphoid tissue (MALT) lymphomagenesis. We previously reported that MALT1 and API2-MALT1 were localized only in cytoplasm, where we suggested that both molecules were likely to be active. In the study presented here, we further examined the localization-determining region by generating various mutants and were able to demonstrate that there were nuclear export signal (NES)-containing domains in the MALT1 C-terminal region. The use of leptomycin B, an NES-specific inhibitor, demonstrated that both MALT1 and API2-MALT1 were predominantly retained in the nuclei, indicating that these molecules were shuttling between nucleus and cytoplasm in an NES-dependent manner. It was also found that MALT1 was involved in the nuclear export of BCL10, which is originally localized in both nucleus and cytoplasm. These results correlate well with the nuclear BCL10 expression pattern in both t(1;14) and t(11;18) MALT lymphomas. The nucleocytoplasmic shuttling of MALT1 and BCL10 complex may indicate that these molecules are involved not only in the nuclear factor kappaB (NF-kappaB) pathway but also in other biologic functions in lymphocytes.