Stability and subcellular localization of API2-MALT1 chimeric protein involved in t(11;18) (q21;q21) MALT lymphoma

Oncogene. 2003 Nov 6;22(50):8085-92. doi: 10.1038/sj.onc.1207002.


t(11; 18) (q21; q21) is a chromosomal aberration specific to low-grade mucosa-associated lymphoid tissue (MALT) lymphoma, and generates the chimeric product apoptosis inhibitor 2 (API2)-MALT1, which has been suggested to play an important role in MALT lymphomagenesis. However, little is known about the characteristics of API2, MALT1, and API2-MALT1 proteins. We therefore investigated the subcellular localization and stability of these products. API2 was localized in the nucleus and the cytoplasm, and MALT1 and API2-MALT1 in the cytoplasm only. Western blot analysis showed that the products of API2 and MALT1 were unstable, while the API2-MALT1 product was stable. The API2 deletion mutants at the end of the C-terminal and the MALT1 deletion mutants at the end of the N-terminal were stable compared with the full-length products. These results indicate that the domains responsible for protein instability are located in the end of the C-terminal of API2 and in that of the N-terminal of MALT1, and also that API2-MALT1 became stable because it lacks these domains. It has been suggested that NF-kappaB activation plays an important role in the tumorigenesis of MALT lymphoma. Our findings further suggest that the stabilized expression of API2-MALT1 products may continuously stimulate the NF-kappaB activating pathway, thus leading to MALT lymphomagenesis.

MeSH terms

  • Animals
  • Apoptosis / genetics
  • Apoptosis / physiology
  • Blotting, Western
  • Caspases
  • Chromosomes, Human, Pair 11*
  • Chromosomes, Human, Pair 18*
  • Fluorescent Antibody Technique
  • Genomic Instability*
  • Humans
  • Inhibitor of Apoptosis Proteins
  • Lymphoma, B-Cell, Marginal Zone / genetics*
  • Lymphoma, B-Cell, Marginal Zone / metabolism
  • Microscopy, Fluorescence
  • 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
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Translocation, Genetic*


  • API2-MALT1 fusion protein, human
  • Inhibitor of Apoptosis Proteins
  • Neoplasm Proteins
  • Oncogene Proteins, Fusion
  • Proteins
  • Recombinant Fusion Proteins
  • Caspases
  • MALT1 protein, human
  • Mucosa-Associated Lymphoid Tissue Lymphoma Translocation 1 Protein