At least two distinct recurrent chromosomal translocations have been implicated in the pathogenesis of MALT lymphoma. The first, t(1;14), results in the transfer of the entire Bcl10 gene to chromosome 14 wherein Bcl10 expression is inappropriately stimulated by the neighboring Ig enhancer. The second, t(11;18), results in the synthesis of a novel fusion protein, API2-MALT1. Until now, no common mechanism of action has been proposed to explain how the products of these seemingly unrelated translocations may contribute to the same malignant process. We show here that Bcl10 and MALT1 form a strong and specific complex within the cell, and that these proteins synergize in the activation of NF-B. The data support a mechanism of action whereby Bcl10 mediates the oligomerization and activation of the MALT1 caspase-like domain. This subsequently activates the IKK complex through an unknown mechanism, setting in motion a cascade of events leading to NF-B induction. Furthermore, the API2-MALT1 fusion protein also strongly activates NF-B and shows dependence upon the same downstream signaling factors. We propose a model whereby both the Bcl10⅐MALT1 complex and the API2-MALT1 fusion protein activate a common downstream signaling pathway that originates with the oligomerization-dependent activation of the MALT1 caspase-like domain.

Recent progress in molecular analysis of low-grade B cell lymphoma has revealed that API2 at 11q21 and a novel gene, MALT1 at 18q21, are involved in t(11;18)(q21;q21), a characteristic chromosome aberration for mucosa-associated lymphoid tissue (MALT) type lymphoma. We describe here the establishment of a reverse transcription-polymerase chain reaction (RT-PCR) assay that we used to analyze 22 cases of MALT lymphoma. All five cases that were shown to possess t(11;18)(q21;q21) showed the specific amplification of API2-MALT1 chimeric transcripts. Of the remaining 17 cases for which cytogenetic data were not available, three cases demonstrated the presence of fusion transcripts, indicating that a significant percentage of MALT lymphoma cases of the present series appeared to possess t(11;18). A single fragment was observed in each of these cases, but the size varied from case to case. Sequencing analysis revealed that there are two breakpoints in API2 and three in MALT1, and that all of the fusion transcripts are in-frame. On the basis of these results, four kinds of chimeric proteins can be predicted for the present series. Thus, the RT-PCR assay used here should serve as an effective molecular tool for understanding molecular pathogenesis and the clinical significance of API2-MALT1 for MALT lymphomas.

Invasive fungal infection (IFI) causes morbidity and mortality among patients with hematological malignancies who receive cytotoxic chemotherapy or hematopoietic stem cell transplantation (HSCT). We evaluated the incidence and treatment outcomes of proven and probable IFI in 22 institutions between 2006 and 2008 following the recent European Organization for Research and Treatment of Cancer/Mycosis Study Group (EORTC/MSG) consensus criteria. We analyzed 2,821 patients with hematological malignancies, including 597 who had undergone HSCT; these included patients with acute leukemia (n = 697), myelodysplastic syndrome (n = 284), lymphoma (n = 1465), or multiple myeloma (n = 375). IFIs were diagnosed in 38 (1.3%) patients (18 proven and 20 probable), including 20 patients who underwent HSCT and 18 who received chemotherapy alone; these included patients with aspergillosis (n = 23), candidiasis (n = 6), mucormycosis (n = 6), trichosporonosis (n = 2), and geotrichosis (n = 1). The incidence of IFI was 5.4 % in allogeneic HSCT patients, 0.4 % in autologous HSCT patients, and 0.8 % in patients receiving chemotherapy alone. Eighteen patients with aspergillosis were diagnosed with probable pulmonary IFI as determined by computed tomography scan and positive galactomannan assay. Overall, antifungal targeted therapies resulted in successful outcomes in 60.0 % of patients. IFI-attributable mortality rate was higher in HSCT patients than in those receiving chemotherapy alone, but the difference was not statistically significant.

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