Extranodal Marginal Zone B-Cell Lymphoma Of Mucosa-Associated Lymphoid Tissue: A Comparing Study Of Clonal Links, Gene Expression Profiles And Expression Of FOXP1 Gene Of Non-Transformed And Transformed Neoplastic Components

Background and Objective: The pathogenesis and progression of MALT lymphoma is a continuous and multistage process. It is not rare that some components of small centrocyte-like cells of a MALT lymphoma could transform into a diffuse large B-cell lymphoma in the process of neoplastic progression. In the present study, the clonal diversity of IgH gene, gene expression profiles, and expression of FOXP1 gene between non-transformed small cells and transformed larger cells were analyzed in order to identify clonal correlations, scan the candidate genes related the transformation, and estimate the FOXP1 gene expression between MALT lymphoma and its transformed components.Materials and Methods: Laser microdissection technique was used to separated and picked up the non-transformed and transformed components from 6 pairs of MALT lymphoma with larger cell transformation, respectively. Then, PCR and sequencing techniques were used to detect the IgH gene rearrangement and to analyze the clonal diversity. The total RNA from one case of Hashimoto thyroiditis, one case of thyroid MALT lymphoma, and one case of thyroid MALT lymphoma with transformation was retrotranscribed into cDNA and hybrided with Human Genome U133A Plus 2.0 gene microarray chips which contains 38,500 genes in order to detect their gene expression profiles. The special attention was focused on the genes expressed differently between MALT lynphoma and MATL lynphoma with transformation. The expression of FOXP1 gene in MALT lymphoma and its transformed components was measured at mRNA and protein levels by real-time PCR(101 cases), immunohistochemistry(115 cases), and Western blot hybridization methods(6 cases). The relationships between FOXP1 expression and clinocopathological features and prognosis were also analyzed.Results: Clonal IgH gene rearrangement was detected in all 6 pairs of MALT lymphoma and its transformed components. Sequencing results showed that there were identical rearranged D and J segments between the non-transformed and transformed components in each of 6 pairs, although there was one different nucleotide in the rearranged N and D segments respectively in each of 2 pairs.The genome-wide expression profiling showed as follows:(1) Comparing with Hashimoto thyroiditis, there were an at least 2-fold increased expression of 1123 genes, and an at least 2-fold decreased expression of 1153 genes in thyroid MALT lymphoma. There were an at least 2-fold increased expression of 1488 genes and an at least 2-fold decreased expression of 1609 genes between thyroid transformed and non-transformed MALT lymphoma.(2) The important up-regulated genes in thyroid MALT lymphoma and transformed component included the following groups: FOXP1, bcl-6, and MALT-1 genes; genes related DNA duplication and mRNA synthesis.(3) The down-regulated genes were genes of TGF-βsignaling pathway in transformed MALT lymphoma.(4) Up or down-regulation were found in different members of genes related some pathways, which included genes involved in metabolism of glucose, fatty acid, amino acid and nucleotide, genes related to apoptosis and cell cycle, genes of calcium regulation in cardiac cells, ribosome protein, integrin mediated cell adhesion and translation factors in thyroid MALT lymphoma and its transformed component.Different expression levels of FOXP1 mRNA(101 cases) and protein(115 cases) were found between non-transformed and transformed MALT lymphoma with statistic difference, and Western blot reconfirmed a higher expression of FOXP1 protein in transformed MALT lymphoma(2 cases) than that in non-transformed ones(4cases). The FOXP1 positive group(nuclear expression rate≥30%) appeared a higher percentage with large cell transformation and a higher Ki-67 index than FOXP1 negative group(nuclear expression rate<30%). There were no differences in age, gender, site, expression of API2-MALT1 fusion gene, bcl-10 protein, and survival between the FOXP1 positive and negative group.Conclusions: Our results suggest that:(1) there are monoclonal proliferations of B-cells in MALT lymphoma and its transformed components, and the neoplastic B-cell clone of transformed large cells develops from non-transformed small neoplastic cells, although there is an intraclonal diversity between them;(2) there are different gene expression profiles among Hashimoto thyroiditis, thyroid MALT lymphoma, and thyroid MALT lymphoma with larger cell transformation;(3) FOXP1 gene expression could be a new indicator that implies the large cell transformation of MALT lymphoma.