The API2/MALT1 fusion product may lead to germinal center B cell lymphomas by suppression of apoptosis

Hum Hered. 2001;51(1-2):1-7. doi: 10.1159/000022952.


Low-grade B cell lymphomas of mucosa-associated lymphoid tissue (MALT) represent a distinct clinicopathological entity that arises in a wide variety of extranodal sites. Genetically, MALT lymphomas are characterized by the t(11;18)(q21;q21). The genes involved in this translocation have been identified to be API2 on chromosome 11, which encodes an apoptotic inhibitor, and MALT1, a novel gene on chromosome 18. We identified the t(11;18)(q21;q21) by Southern blot analysis and reverse transcriptase PCR in 42% of a panel of extranodal MALT lymphomas. We also identified the breakpoints within the API2 and MALT1 genes in 7 patients, which revealed a consistent breakpoint after the third baculoviral inhibitor of apoptosis repeat domain within API2, and variable breakpoints in MALT1. We determined the API2/MALT1 fusion transcript in 2 cases by Northern blot analysis and also showed that MALT1 mRNA is constitutively expressed in a variety of human tissues. To understand the functional consequence of the translocation, we determined the pattern of expression of API2 and MALT1 through B lineage differentiation. API2 was expressed only in cell lines which correspond to mature B cells, whereas MALT1 mRNA was detectable in pre-B cells, mature B cells and plasma cells. These results suggest that fusion of MALT1 to API2 mediated by the t(11;18)(q21;q21) may result in an increased inhibition of germinal center B cell apoptosis and subsequent development of MALT lymphomas.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis*
  • B-Lymphocytes / metabolism
  • Blotting, Northern
  • Blotting, Southern
  • Caspases
  • Cell Differentiation
  • Gene Expression
  • Humans
  • Inhibitor of Apoptosis Proteins
  • Lymphoma, B-Cell, Marginal Zone / genetics*
  • Lymphoma, B-Cell, Marginal Zone / pathology
  • Mucosa-Associated Lymphoid Tissue Lymphoma Translocation 1 Protein
  • Neoplasm Proteins / genetics
  • Neoplasm Proteins / metabolism*
  • Oncogene Proteins, Fusion / genetics
  • Oncogene Proteins, Fusion / metabolism*
  • Proteins / genetics
  • Proteins / metabolism*
  • RNA / analysis
  • Sequence Analysis, RNA
  • Translocation, Genetic


  • Inhibitor of Apoptosis Proteins
  • Neoplasm Proteins
  • Oncogene Proteins, Fusion
  • Proteins
  • RNA
  • Caspases
  • MALT1 protein, human
  • Mucosa-Associated Lymphoid Tissue Lymphoma Translocation 1 Protein