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.     

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。     

Clinical impact of genetic aberrations in gastric MALT lymphoma: a comprehensive analysis using interphase fluorescence in situ hybridisation

BACKGROUND AND AIMS: There is a need for genetic biomarkers to guide prognosis and management of gastric mucosa-associated lymphoid tissue (MALT) lymphomas. We assessed the incidence and clinical significance of the MALT lymphoma-associated genetic abnormalities t(11;18)/API2-MALT1, t(1;14)/BCL10-IGH, t(14;18)/IGH-MALT1, t(3;14)/FOXP1-IGH, and extra copies of MALT1 and FOXP1 in gastric MALT lymphomas from Japan. METHODS: The presence of translocations and copy number changes involving MALT1, IGH and FOXP1 were assessed in 90 cases of gastric MALT lymphoma using interphase fluorescence in situ hybridisation (FISH). In cases carrying a MALT1 translocation, FISH for API2-MALT1 was performed, whereas in those carrying an IGH translocation, FISH was performed for BCL10, BCL6, BCL2, c-MYC and/or CCND1. RESULTS: t(11;18)/API2-MALT1 was detected in 18 of 87 (21%) cases and was significantly associated with Helicobacter pylori-negativity, resistance to H pylori eradication and Bcl10 nuclear expression. Four of 68 (6%) cases carried a translocation involving IGH and FOXP1 (n = 1), BCL2 (n = 1) or an unknown partner (n = 2). Neither t(1;14)/BCL10-IGH nor t(14;18)/IGH-MALT1 was detected. Extra copies of MALT1 and FOXP1 were detected in 18 of 71 (25%) cases and 10 of 59 (17%) cases, respectively. The presence of extra copies of MALT1 was significantly associated with progression or relapse of lymphoma, and was an independent adverse prognostic factor for event-free survival as determined by multivariate analysis. CONCLUSIONS: t(11;18)/API2-MALT1 is frequent, whereas IGH-involved translocations are rare in gastric MALT lymphoma in Japan. The presence of extra copies of MALT1, often suggestive of partial or complete trisomy 18, is a frequent genetic aberration in gastric MALT lymphoma, which appears to predict adverse clinical behaviour.     

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.     

High frequency of t(11;18) in gastric mucosa-associated lymphoid tissue lymphomas in Taiwan,including one patient with high-grade transformation

t(11;18)(q21;q21), the most frequent chromosomal aberration of mucosa-associated lymphoid tissue (MALT) lymphoma, occurs in 30% of gastric patients.Although the translocation is often associated with an 'aggressive' course, it has not been described in transformed MALT lymphomas. We screened 15 gastric MALT lymphomas [three with concurrent or subsequent high-grade transformation and 11 diffuse large B-cell lymphomas (DLBCLs)] in Chinese patients for t(11;18). t(11;18) was found in 9/15 (60%) MALT lymphomas, but not in any DLBCLs. One patient, with subsequent high-grade transformation, showed the translocation in low- and high-grade lesions. t(11;18) was frequent in Chinese gastric MALT lymphomas and unusually one transformed lymphoma carried the translocation.     

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.     

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.     

A case of H. pylori and API2-MALT1 gene-negative gastric mucosa-associated lymphoid tissue lymphoma with a carcinoma-like signet-ring cell lymphoepithelial lesion]

A 60-year-old woman presented in February 2003 with an ulcer on the lesser curvature of the anglus. The endoscopic biopsy specimens showed epithelial signet-ring cell associated with lymphoid infiltration, suggesting a diagnosis of gastric cancer. Histopathological examination confirmed the diagnosis of low-grade B-cell lymphoma of MALT with epithelial signet-ring cell lymphoepithelial lesion, which was negative for H. pylori and t (11;18) (q21;q21) translocation (API2-MALT1 gene). This case was treated with H. pylori eradication and additional radiation therapy, and the tumor was disappeared.