Malignant Lymphomas |
Division of Molecular Histopathology, Department of Pathology, University of Cambridge, Cambridge, United Kingdom (YZ, HY, RH, M-QD); Nanfang Hospital, Southern Medical University, Guangzhou, China (YZ); Institute of Human Genetics, University Hospital Schleswig-Holstein Campus Kiel, Kiel, Germany (JIM-S, SG, RS); Molecular Cytogenetics, Institute of Cancer Research, Sutton, United Kingdom (Y-JL, RW, JS); Department of Histopathology, University College London, London, UK (PGI, AD)
Correspondence: Ming-Qing Du, Professor of Oncological Pathology, Division of Molecular Histopathology, Department of Pathology University of Cambridge, Box 231, Level 3 Lab Block, Addenbrookes Hospital Hills Road, Cambridge, CB2 2QQ United Kingdom. E-mail: mqd20{at}cam.ac.uk
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Design and Methods: We performed comparative genomic hybridisation using DNA samples extracted from microdissected tumour cells in 19 salivary gland MALT lymphomas. Recurrent chromosomal changes were further verified by interphase fluorescence in situ hybridization (FISH).
Results: Chromosomal gains were much more common than losses. Recurrent gains were found at 1p32-ter (42%), 9q33–34 (84%), 11q11–13 (42%), 17 (58%) and 18q21–22 (42%). Among these, the recurrent gains at 9q34, 11q11–13 and 18q21 were nearly the exclusive gain of the corresponding chromosome. Notably, chromosomal gains at 9q34, 11q13 and 18q21 were frequently concurrent, with 12/19 cases affecting at least two of the three loci. The genomic gains at these chromosomal regions were further confirmed by interphase FISH with probes targeting the TRAF2 and CARD9 (9q34), RELA and CCND1 (11q13), and MALT1 (18q21) loci.
Interpretation and Conclusions: Salivary gland MALT lymphomas show a conserved pattern of chromosomal gains, which appear to target genes positively modulating cell survival and proliferation.
Key words: salivary gland, MALT lymphoma, CGH.
Primary mucosa-associated lymphoid tissue (MALT) lymphoma of the salivary gland arises on a background of benign lymphoepithelial sialadenitis that is commonly associated with the autoimmune disorder Sjögrens syndrome.1 The salivary gland MALT lymphoma, as those in other mucosal sites, is usually indolent and responds favorably to treatment. Despite the fact that the majority of salivary gland MALT lymphomas tend to remain localized for a long period of time, even without treatment, a substantial proportion of cases disseminate, particularly to other salivary glands.2 In addition, salivary gland MALT lymphoma may transform into a diffuse large B-cell lymphoma.2
The molecular genetics underlying the development of salivary gland MALT lymphoma is largely unknown. The three chromosomal translocations specifically associated with MALT lymphoma have been examined. t(11;18) (q21;q21) generates a functional API2-MALT1 fusion product and rarely occurs in MALT lymphoma of the salivary gland despite it being frequently seen in those from the lung, stomach and ocular adnexa.3–5 t(1;14)(p22;q32) brings the entire BCL10 gene under the transcriptional control of the immunoglobulin gene enhancer and deregulates its expression.6,7 This translocation is also rarely seen in salivary gland cases.3,8 t(14;18)(q32;q21) deregulates MALT1 gene expression 9,10 and its occurrence in primary salivary gland MALT lymphoma remains a subjects of debate. The translocation was found in 5/42 (10%) cases in one study 8 and in 6/28 (21%) in another,4 but not seen in two more recent investigations that examined 59 and 15 cases.11,12 t(3;14) (p14;q32) is a newly identified chromosomal translocation in MALT lymphoma, which juxtaposes the FOXP1 gene to the IGH locus and deregulates its expression.13 The translocation has been frequently found in MALT lymphomas of the thyroid and ocular adnexa, but not in those of the salivary gland.13
As MALT lymphoma cells are difficult to grow in vitro, only a few cases of salivary gland MALT lymphoma have been studied by conventional cytogenetics.12,14,15 Nonetheless, studies by both conventional cytogenetic and interphase fluorescence in situ hybridization (FISH) indicate that both chromosomal gains, such as trisomies 3 and 18, and chromosomal losses may be frequently present in salivary gland MALT lymphoma.4,8,14,15 To further investigate such putative chromosomal changes in salivary gland MALT lymphoma, we studied 19 cases using comparative genomic hybridization (CGH), followed by investigations of the recurrent changes using interphase FISH.
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Microdissection and DNA extraction
Tumor cells (500–5000) were microdissected from freshly prepared hematoxylin and eosin (HE)-stained slides of formalin-fixed and paraffin-embedded tissues or fresh frozen lymphoma tissues in each case as described previously.16 The tumor cells microdissected from paraffin-embedded tissue sections were first treated in 20 µL of 1M sodium thiocyanate at 37°C for 12~16 hours to break the cross-links caused by formalin fixation. After washing three times with phosphate-buffered saline (PBS), the tumor cells were digested with proteinase K (2 mg/mL) in 30 mM Tris-HCl (pH 8.0) buffer containing 10 mM EDTA and 1% sodium dodecyl sulphate at 55°C for 2 days, followed by purification of DNA with the Wizard genomic DNA purification kit (Promega, Southampton, UK). Briefly, the cell digest was mixed with a 1/3 volume of protein precipitation solution and centrifuged. The resulting supernatant was transferred into a fresh tube and genomic DNA was precipitated with isopropanol, washed in 70% ethanol and air-dried. The DNA pellet was dissolved in 20 µL of 10 mM Tris-HCl (pH 8.0). DNA samples were also similarly extracted from whole sections of formalin-fixed paraffin-embedded tonsil tissues and were used as reference DNA in the CGH experiments described below.
DNA amplification and labeling
DNA samples were amplified by degenerate oligonucleotide primer (DOP) PCR using a method described previously.17 The tumor DNA was labeled with a PCR incorporation reaction using 5 µL of DOP PCR product as template in a total of 50 µL reaction mixture containing 2 U platinum Taq DNA polymerase (Invitrogen, Paisley, UK), 1xPCR buffer, 1.5m M MgCl2, 0.2 mM dATP, 0.2 mM dCTP, 0.2 mM dGTP, 0.1 mM dTTP, 0.02 mM SpectrumRed dUTP (Vysis, Surrey UK), and 1.2 µM DOP primer as described previously.17 The DNA extracted from whole sections of paraffin-embedded tonsils was similarly labeled with SpectrumGreen dUTP and was used as a reference. Five microliters of the labeling products were routinely analyzed on 1% agarose gels to check the quantity and size of the product. Those with satisfactory amplification and labeling were purified using QIAquick PCR purification kit (QIAGEN, West Sussex, UK) according to the manufacturers instructions. Equal amounts (45 µL) of the labeled test and reference DNA were mixed with 25 µL of human Cot I DNA (1 µg/µL, Invitrogen, Paisley, UK), precipitated with ethanol and dried in a vacuum.17 The DNA pellet was re-dissolved in 10 µL of hybridization buffer (70% formamide, 10% dextran sulfate and 2xSSC, pH 7.0).
CGH and digital image analysis
The normal metaphase spreads were denatured in 70% formamide and 2xSSC (pH 7.0) at 72°C for 2 min and dehydrated in an ethanol series. In the meantime, the mixture of the labeled test and reference DNA was denatured at 77°C for 5 min, then applied to the metaphase spreads and sealed with a coverslip. The hybridization was carried out at 37°C in a moist chamber for 2 days. After hybridization, the slides were washed in 0.4xSSC/0.3% IGEPAL (Sigma), pH7.0 at 72°C for 2 minutes, then in 2xSSC/0.1% IGEPAL at 42°C for 5 minutes twice, and finally in distilled water. Slides were mounted using anti-fade medium with DAPI (Vector Laboratories Inc., Burlingame, CA, USA).
Digital images were captured using a cooled CCD-camera (Photometrics, Arizona, USA) with Quips software (Version 3.1.2., Vysis, Richmond Surrey, UK) linked to a Zeiss Axioplan epifluoresence microscope (ZEISS, Jena, Germany). Between six and ten images of high quality metaphases in each case were analyzed using the same software package. The relative genomic gains and losses were determined by comparing the ratio of red (tumor DNA) and green (reference DNA) fluorescence intensity along all chromosomes and the thresholds used for recording chromosomal gains and losses were 1.20 and 0.80, respectively, in accordance with previous studies.17 The heterochromatic regions, p-arms of acrocentric chromosomes, and the entire X and Y chromosomes were excluded from analysis.
Interphase FISH
For further analysis of the most frequent chromosomal gains (9q34, 11q11–13 and 18q21) found by CGH analysis, we performed interphase FISH as detailed below.
Bioinformatic analysis identified several potential target genes in the commonly gained band 9q34.18 Among them, TRAF2 and CARD9 were selected as targets for the design of FISH probes in view of their interaction with BCL10 and their role in NF
B activation.19,20 BAC clones RP11–83N9/RP11–100C15 and RP11–251M1 flanking the CARD9 and NOTCH1 loci, and BAC clones RP11–83N9/RP11–100C15 together with BAC clone RP11–417A4 which is located telomeric of the TRAF2 locus, were selected as interphase FISH probes for investigation of chromosomal gain at 9q34.
Similarly, bioinformatic analysis of the genes mapping to 11q11–13 revealed a number of potential target genes. Among them, RELA and CCND1 were selected as targets for FISH probes in view of their respective roles in NF
B activation and cell cycle progression. For RELA, inter-phase FISH was performed using a probe as described previously,21 while for CCND1, interphase FISH was carried out using a commercial LSI Cyclin D1 SpectrumOrange/CEP 11 SpectrumGreen dual color probe (Vysis/Abbott Laboratories Ltd., Berkshire, UK).
For chromosomal gain at 18q21, MALT1 is likely the gene targeted6,7,9,10 and interphase FISH was carried out using commercial MALT1 dual color break apart rearrangement probes (Vysis/Abbott Laboratories Ltd, UK).
Bacterial culture, BAC DNA isolation and labeling, and probe preparation were performed as previously described.18,22 Locus-specific interphase FISH was performed on paraffin-embedded tissue sections essentially as described previously.3,18 The FISH slides were viewed and the hybridization signals for each probe were counted from 100 cells in each case.
All the above probes were investigated on formalin-fixed and paraffin-embedded tissue sections from eight to ten reactive tonsils to determine the threshold (mean±3 standard deviations) to diagnose chromosomal alterations in lymphoma cells.23
Statistical analysis
The statistical difference in the percentage of cells showing three or more copies of a gene locus by inter-phase FISH among different groups was investigated by the non-parametric Mann-Whitney U test.
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View this table: [in a new window] [Download PPT slide] |
Table 1. CGH and interphase FISH findings in salivary gland MALT lymphoma.
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Figure 1. Chromosomal gains and losses in salivary MALT lymphomas. Red lines indicate gains, while green lines indicate losses.
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Figure 2. Confirmation of chromosomal gain at 9q34, 11q13 and 18q21 by interphase FISH with probes flanking the CARD9/NOTCH1/TRAF2 and CARD9/NOTCH1, RELA and CCND1, and MALT1 loci, respectively. A case (no. 10) with CGH gain at 9q34 showing three co-localized green (BAC clones RP11–83N9/RP11–100C15) and red (RP11–417A4) signals (arrowhead), indicating three copies of the 9q34 region including CARD9, NOTCH1 and TRAF2. The same case displays three co-localized green (BAC clones RP11–83N9/RP11–100C15) and red (RP11–251M1) signals (arrowhead) for the probe flanking the CARD9 and NOTCH1 genes. A case (no. 3) with CGH gain at 11q11–13 shows three co-localized red and green signals in cells (arrowhead), indicating gain of an extracopy of the RELA gene. A case (no. 15) with CGH gain a 11q11–13 shows three red (CCND1) and two or three green signals (centromere probe) in cells (arrowhead), indicating gain of an extracopy of the CCND1 gene A case (no. 8) with CGH gain at 18q21 shows three co-localized green and red signals with MALT1 probe in cells (arrowhead), indicating gain of an extracopy of the MALT gene.
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In all cases examined by interphase FISH, there was no evidence suggesting gene amplification or chromosomal break at these loci.
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B pathway.24 The oncogenic products of these chromosomal translocations have been shown to constitutively activate NF
B, a transcriptional factor for a number of growth factors, cytokines and apoptosis inhibitors. Salivary gland MALT lymphoma, in common with the majority of MALT lymphomas including those from the lung and stomach, is typically negative for the above chromosomal translocations. The molecular genetics underlying the development of salivary gland MALT lymphoma is unclear. By screening chromosomal gains and losses using CGH, we showed that salivary gland MALT lymphomas are characterized by recurrent chromosomal gains at 9q34, 11q11–13 and 18q21. Although there was no evidence of gene amplification at these regions, the chromosomal gains were often concurrent.
For chromosomal gain at 18q21, the MALT1 gene has been proposed to be the target gene or one of the target genes in view of the findings that the MALT1 gene is targeted by chromosomal translocations in MALT lymphoma and is also amplified in cell lines from marginal zone B-cell lymphoma (SSK-41 and Karpas 1718).10 However, MALT1 gene amplification is rarely seen in primary lymphoma;10 rather, a gain of an extra copy of the gene is a common event in t(11;18)(q21;q21)-negative MALT lymphoma, including those of the salivary gland as demonstrated in this and several previous studies.4,8
For chromosomal gain at 9q34, TRAF2 and CARD9 were likely the genes targeted in view of their interaction with BCL10 and their role in NF
B activation.19,20 TRAF2 is involved in the activation of the NF
B pathway triggered by both innate and acquired surface immune receptor signalling. During the innate immune responses, TRAF2 transduces signal from the TNF receptor to the NF
B activation pathway.25 In the adaptive immune responses, TRAF2 may, like TRAF6, activate the IKK complex by polyubiquitination of NEMO (IKK
) in response to upstream signals from BCL10/MALT1.25,26 TRAF2 protein is abundantly expressed in various lymphoma cell lines and in Hodgkin/Reed-Sternberg cells of Hodgkin lymphoma, which are characterised by constitutive NK
B acivities.27,28 CARD9 is a key adaptor in Destin-1 (a major mammalian pattern recognition receptor) mediated NF
B activation and also involved in the activation of the kinases p38 and Jnk in non-TLR-mediated innate immune responses.29,30 In line with its role in inflammation and immune response, CARD9 is abundantly expressed in gastric MALT lymphoma.31
For chromosomal gain at 11q11–13, there are a number of potential target genes, of which RELA and CCND1 (cyclin D1) are likely relevant in the context of the current understanding of MALT lymphomagenesis. RELA is the p65 subunit of the NF
B family and typically forms a heterodimer with p50 or p52, which is the predominant NF
B species in many cell types.32 Like c-Rel, RELA is also targeted by gene amplification or chromosome translocation in hematologic malignancies, albeit at a much lower frequency.33 CCND1 is a crucial cyclin for cells to commit DNA synthesis and division, and is frequently targeted by chromosome translocation as well as gene amplification in lymphoid malignancies. There is compelling evidence suggesting a biological co-operation between NF
B and cell cycle regulation in normal and malignant cells. NF
B activation promotes cell cycle progression and suppresses terminal differentiation and these effects occur, at least partially, via NF
B-mediated CCND1 transcription activation.34
In summary, salivary gland MALT lymphomas show concurrent chromosomal gains at 9q34, 11q11–13 and 18q21, similar to those seen in t(11;18)(q21;q21) negative gastric MALT lymphoma.18 The gains at these chromosomal loci appear to target several genes, whose products positively modulate the NF
B pathway (TRAF2, CARD9, RELA, MALT1) or cell cycle (CCND1). The concurrent gain of extra-copies of these positive modulators could play a role in the pathogenesis of translocation negative MALT lymphomas.
YZ: collection of CGH data; HYE: collection of interphase FISH data; JIMS: design and testing FISH probes; SG: design and testing FISH probes; RH: bioinformatic analysis; YJL, RW, JS: CGH; RS: design of FISH probes and study design; PGI: pathology and case contribution; AD: pathology and case contribution; MQD: design of study, data analysis and manuscript writing.
The authors reported no potential conflicts of interest.
Funding: the laboratory of M-QD was supported by research grants from the Association for International Cancer Research and Leukaemia Research Fund, United Kingdom. Sieberts laboratory was supported by grants from the Deutsche Krebshilfe.
Received for publication April 20, 2006. Accepted for publication March 22, 2007.
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B. J Biol Chem 2000;275:41082-6.
B pathway. Nat Cell Biol 2005;7:758-65.[CrossRef][Web of Science][Medline]
B. Semin Immunol 2003;15:177-183.[CrossRef][Web of Science][Medline]
B and cell-cycle regulation: the cyclin connection. Cytokine Growth Factor Rev 2001;12:73-90.[CrossRef][Web of Science][Medline]This article has been cited by other articles:
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R. J. Bende, F. van Maldegem, and C. J.M. van Noesel Chronic inflammatory disease, lymphoid tissue neogenesis and extranodal marginal zone B-cell lymphomas Haematologica, August 1, 2009; 94(8): 1109 - 1123. [Abstract] [Full Text] [PDF] |
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