Helicobacter pylori-negative gastric mucosa-associated lymphoid tissue lymphomas: A review

Since Isaacson and Wright first reported on the extra-nodal marginal zone B-cell lymphoma of the stomach in 1983, following studies have clarified many aspects of this disease. We now know that the stomach is the most affected organ by this disease, and approximately 90% of gastric mucosa-associated lymphoid tissue (MALT) lymphomas are related to Helicobacter pylori (H. pylori) infection. This implies that approximately 10% of gastric MALT lymphomas occur independent of H. pylori infection. The pathogenesis of these H. pylori-negative gastric MALT lymphomas remains unclear. To date, there have been several speculations. One possibility is that genetic alterations result in nuclear factor-kappa B (NF-κB) activation. Among these alterations, t(11;18)(q21;q21) is more frequently observed in H. pylori-negative gastric MALT lymphomas, and such translocation results in the synthesis of fusion protein API2-MALT1, which causes canonical and noncanonical NF-κB activation. Another possibility is infection with bacteria other than H. pylori. This could explain why H. pylori eradication therapy can cure some proportions of H. pylori-negative gastric MALT lymphoma patients, although the bacteria responsible for MALT lymphomagenesis are yet to be defined. Recent advances in endoscopy suggest magnifying endoscopy with narrow band imaging as a useful tool for both detecting gastric MALT lymphoma lesions and judging the response to treatment. A certain proportion of H. pylori-negative gastric MALT lymphoma patients respond to eradication therapy; hence, H. pylori eradication therapy could be considered as a first-line treatment for gastric MALT lymphomas regardless of their H. pylori infection status.

Involvement of non-Helicobacter pylori helicobacter infections in Helicobacter pylori-negative gastric MALT lymphoma pathogenesis and efficacy of eradication therapy

BACKGROUND

Eradication therapy is known to be effective against Helicobacter pylori-positive gastric MALT lymphoma but predicting the efficacy of eradication therapy against Helicobacter pylori-negative gastric MALT lymphoma is difficult. Recent reports have shown that non-Helicobacter pylori helicobacter infections induce gastric MALT lymphoma, and we aimed to clarify whether non-Helicobacter pylori helicobacter infections are associated with the efficacy of eradication therapy.

METHODS

We analyzed eradication therapy as a first-line treatment for 182 cases of gastric MALT lymphoma, classified according to Helicobacter pylori infection and API2-MALT1 mutation status. We also evaluated the non-Helicobacter pylori helicobacter infection status in 29 Helicobacter pylori-negative cases via PCR with DNA extracted from paraffin-embedded biopsy tissues. Finally, we analyzed the relationship between non-Helicobacter pylori helicobacter infection status and eradication therapy outcome.

RESULTS

The API2-MALT1 mutation was observed in 13/182 patients (7.1%), none of whom were cured by eradication therapy. Helicobacter pylori-negative cases had a significantly higher non-Helicobacter pylori helicobacter infection rate than Helicobacter pylori-positive cases (16/29, 55% vs. 3/29, 10%; P < 0.05). Among the Helicobacter pylori-negative cases, non-Helicobacter pylori helicobacter-positive cases had a significantly higher complete response rate than non-Helicobacter pylori helicobacter-negative cases (12/16, 75% vs. 3/13, 23%; P < 0.05).

CONCLUSION

Helicobacter pylori-negative and API2-MALT1-negative gastric MALT lymphoma cases exhibited a high rate of non-Helicobacter pylori helicobacter infections, which may have contributed to the success of eradication therapy. Therefore, we recommend eradication therapy as a first-line treatment for non-Helicobacter pylori helicobacter-positive gastric MALT lymphoma.

Establishment and characterization of a MALT lymphoma cell line carrying an API2-MALT1 translocation

MALT lymphomas with API2(BIRC3)-MALT1 translocation usually have an indolent clinical course and rarely transform into aggressive lymphoma, and there have been no lymphoma cell lines carrying API2-MALT1 translocation reported to date. We established a novel lymphoma cell line named BMA19, carrying the API2-MALT1 translocation from a patient with histologic transformation of intestinal MALT lymphoma. The cells were suggested to carry API2-MALT1 and MYC-IGH translocations by chromosomal analysis, and these translocations were confirmed by polymerase chain reaction analysis. The expression of MYC was shown to be enhanced as a result of the MYC-IGH translocation, and it is considered to have played a role in the histologic transformation of MALT lymphoma. Whole exome sequencing of BMA19 identified several nucleotide variations in genes reported to be mutated in previous studies of marginal zone lymphomas. The MALT1 inhibitor MI-2 specifically decreased cell growth, and the BMA19 cell line was suggested to be still dependent on the API2-MALT1 signal. Subtractive microarray analysis showed that one of the earliest events resulting from MALT1 inhibition is increased susceptibility to endoplasmic reticulum stress-induced apoptosis. The BMA19 cell line is considered to conserve the biological properties of MALT lymphoma and is expected to be a valuable tool for research into the pathogenesis of MALT lymphoma with an API2-MALT1 translocation.

A case of API2-MALT1-positive gastric MALT lymphoma with concomitant diffuse large B-cell lymphoma

API2-MALT1 translocation-positive gastric marginal zone lymphomas of mucosa-associated lymphoid tissue (MALT) lymphoma is thought to transform to diffuse large B-cell lymphoma (DLBCL) rarely. A 69-year-old man presented with epigastralgia. Esophagogastroduodenoscopy showed multiple ulcerations in the stomach. Endoscopic biopsies revealed MALT lymphoma, with Helicobacter pylori infection. The patient underwent eradication therapy with no improvement, and was thereafter followed without additional therapy at his request. Twelve years after initial diagnosis, follow-up computed tomography (CT) showed multiple nodules in bilateral lungs, and a needle biopsy revealed MALT lymphoma, the same as in the stomach and API2-MALT1 translocation was found. Because he again refused additional therapy, follow-up was continued. 15 years after initial diagnosis, CT showed lymphadenopathy at the splenic hilum. At first we suspected disease progression of gastric MALT lymphoma, however a needle biopsy revealed DLBCL without API2-MALT1. Thus, the tumor at the splenic hilum was finally diagnosed as a de novo DLBCL as a second malignancy. Although treatment with rituximab given his age and his wishes was attempted, he died of DLBCL 15 years after the initial diagnosis. We experienced an API2-MALT1-positive gastric MALT lymphoma with concomitant DLBCL, not transformed to DLBCL over a 15-year clinical course.

MALT1 substrate cleavage: what is it good for?

CARD-BCL10-MALT1 (CBM) signalosomes connect distal signaling of innate and adaptive immune receptors to proximal signaling pathways and immune activation. Four CARD scaffold proteins (CARD9, 10, 11, 14) can form seeds that nucleate the assembly of BCL10-MALT1 filaments in a cell- and stimulus-specific manner. MALT1 (also known as PCASP1) serves a dual function within the assembled CBM complexes. By recruiting TRAF6, MALT1 acts as a molecular scaffold that initiates IκB kinase (IKK)/NF-κB and c-Jun N-terminal kinase (JNK)/AP-1 signaling. In parallel, proximity-induced dimerization of the paracaspase domain activates the MALT1 protease which exerts its function by cleaving a set of specific substrates. While complete MALT1 ablation leads to immune deficiency, selective destruction of either scaffolding or protease function provokes autoimmune inflammation. Thus, balanced MALT1-TRAF6 recruitment and MALT1 substrate cleavage are critical to maintain immune homeostasis and to promote optimal immune activation. Further, MALT1 protease activity drives the survival of aggressive lymphomas and other non-hematologic solid cancers. However, little is known about the relevance of the cleavage of individual substrates for the pathophysiological functions of MALT1. Unbiased serendipity, screening and computational predictions have identified and validated ~20 substrates, indicating that MALT1 targets a quite distinct set of proteins. Known substrates are involved in CBM auto-regulation (MALT1, BCL10 and CARD10), regulation of signaling and adhesion (A20, CYLD, HOIL-1 and Tensin-3), or transcription (RelB) and mRNA stability/translation (Regnase-1, Roquin-1/2 and N4BP1), indicating that MALT1 often targets multiple proteins involved in similar cellular processes. Here, we will summarize what is known about the fate and functions of individual MALT1 substrates and how their cleavage contributes to the biological functions of the MALT1 protease. We will outline what is needed to better connect critical pathophysiological roles of the MALT1 protease with the cleavage of distinct substrates.