Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
2000-05-26
2004-02-10
Guzo, David (Department: 1636)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S023100, C536S024300
Reexamination Certificate
active
06689875
ABSTRACT:
TECHNICAL FIELD
The invention relates to the fields of medicine and diagnostics. More in particular, the invention relates to medicine and the diagnosis of tumours.
BACKGROUND
Recurrent translocations acquired in a process of transformation are well recognised in nodal B-cell lymphomas. These translocations characterise distinct subtypes of disease and involve genes controlling cell proliferation and apoptosis. BCL2, which suppresses apoptosis, was cloned from the t(14;18)(q21;q32) found in most cases of follicular B-cell lymphoma, whereas translocations involving the BCL1/CyclinD1 gene on chromosome 11q13 are seen in nearly all cases of mantle cell lymphoma.
1
By contrast, the genetic mechanisms underlying the genesis and disease progression of extranodal marginal zone B-cell lymphomas of the mucosa-associated lymphoid tissue (MALT) type, a recently recognised distinct subtype of B-cell Non-Hodgkin's Lymphoma's (NHL), are not known.
2
MALT lymphomas account for five to ten percent of all NHLs and the vast majority of lymphomas arising at extranodal sites. They originate in a setting of chronic inflammation triggered by chronic infection or autoimmune disorders, such as
Helicobacter pylori
gastritis, Sjögren's syndrome, and Hashimoto's thyreoiditis.
3
In vitro experiments have shown that
H. pylori
specific T-cells provide contact dependent help for the growth of the malignant B-cells of gastric MALT.
4
The etiological link between low-grade gastric MALT lymphomas and
H. pylori
infection has also been demonstrated by the regression of some cases with antibiotic therapy.
5,6
The preferential use of immunoglobulin variable region genes (V
H
) associated with autoimmune disorders indicate that some MALT lymphomas may arise from autoreactive B-cells.
7,8
Since biopsies of these lymphomas are relatively rarely subjected to cytogenetic analysis and their in vitro proliferation is often poor, abnormal karyotypic data have been published for only 46 low-grade MALT lymphomas
9-17
, 5 extranodal small lymphocytic lymphomas of probable marginal zone origin
18-20
, and 23 high-grade gastric MALT lymphomas
14,15
. Recurrent abnormalities in these cases include trisomies of chromosomes 3, 7, 12, and 18
11,17,21
, the t(1;14)(p22;q32) which has been described in two cases 17 and the t(11;18)(q21;q21). The t(11;18)(q21;q21) has been detected in 15 out of the 51 low-grade lymphomas arising from various extranodal sites
9,12,14,18-20
but in none of the high-grade MALT lymphomas or any other subtype of NHL. In the largest cytogenetic series, this translocation has been found in 7 out of 13 cases of low-grade MALT lymphomas with an abnormal karyotype.
14
These data clearly indicate that the t(11;18) represents the most frequent structural abnormality in low-grade MALT lymphomas and seems to specifically characterise this disease entity. An attempt to delineate the breakpoint at 18q21.1 has been described by Akagi et al. (Genes, Chromosomes and Cancer, 24 (1999): 315-321). A detailed characterization, however, is urgently needed.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a detailed molecular genetic characterisation of the 11q21 and 18q21 breakpoint regions in MALT lymphomas characterised by the t(11;18)(q21;q21). The invention further identifies that the API2 gene also known as c-IAP2
22
, HIAP1
23
and MIHC
24
, an inhibitor of apoptosis, and a novel gene on 18q21, named MLT, are rearranged in this translocation. The invention also identifies that truncation of the API2 gene distal to its three BIR domains and fusion of this truncated gene with the carboxy-terminal region of MLT may lead to increased inhibition of apoptosis and thereby confer a survival benefit to MALT type B-cell lymphomas. In other words, the present invention discloses that, surprisingly, truncation of the API2 gene and fusion to the new MLT gene is crucial for the development of MALT type B-cell lymphomas.
In one aspect, the invention teaches that the t(11;18)(q21;q21) associated with extranodal marginal zone B-cell lymphomas of the MALT type results in the expression of a chimeric transcript fusing 5′-API2 on chromosome 11 to 3′-MLT on chromosome 18. The occurrence of the t(11;18) translocation in not less than 17 out of 51 published cases of low-grade MALT lymphomas
9,12,14,18-20
including the two cases described herein, along with its presence as the sole cytogenetic abnormality in 16 out of the 17 reported cases indicates that the t(11;18) represents one of the main recurrent, disease-specific translocations in NHL.
Several observations point to the API2-MLT fusion as the oncogenic lesion underlying the t(11;18). The chimeric cDNA was cloned from two independent tumours. In one case, the genomic breakpoints were also cloned and the structure of both genes and the localisation of the breakpoints is in agreement with the expression of the fusion transcript. The cryptic deletion of the 3′ part of API-2 in case 1 precludes the expression of a reciprocal MLT-API2 transcript in this case. As a result of the deletion, the 5′-end of the MLT gene is fused to the 5′-end of the MMP20 gene on the der(18). As both genes are present on opposite strands of the DNA no MLT-MMP20 transcript is expressed. Furthermore, FISH experiments with PACs for respectively MLT, API2 and MMP20 clearly suggest that in case 2 a balanced translocation occurred not involving a break in the MMP20 gene further arguing against any significance of the MLT-MMP20 fusion.
API2 belongs to the family of inhibitor of apoptosis proteins (“IAP”), which play an evolutionary conserved role in regulating programmed cell death in diverse species (International Patent Application WO 97/06182 to Rothe and Goeddel). The IAP genes were first identified in baculoviruses in which they demonstrated an ability to suppress the host cell apoptotic response to viral infection.
33
Subsequently, five human IAP relatives have been described: NIAP, API1 (also known as cIAP1, HIAP2, MIHB), API2 (cIAP2, HIAP1, MIHC), XMAP-hILP and survivin.
22-24,34-37
The common structural features of all IAP family members is a motif termed baculovirus IAP repeat (“BIR”) occurring in one to three copies, a caspase recruitment domain or CARD
30
located between the BIR domain(s) and a carboxy-terminal zinc binding RING finger domain
3
that is present in all IAPs with the exception of NIAP and survivin. The human API1 and API2 proteins were originally identified as proteins that are recruited to the cytosolic domain of the tumour necrosis factor (TNF) receptor II via their association with the TNF-associated factor (TRAF) proteins, TRAF-1 and TRAF-2
22
and have been subsequently shown to suppress different apoptotic pathways by inhibiting distinct caspases, such as caspase-3, caspase-7, and pro-caspase-9.
35-38
The function of the novel MLT gene (also known as “MALT1”) located on chromosome 18q21 is not yet known. Its closest homologue is a hypothetical
C. elegans
gene. The carboxy-terminal part of this gene is characterised by the presence two Ig-like C2-type domains and a domain similar to the murine Ig gamma chain VDJ4 sequence (Accession no. M13070). The C2 domains are only present in the longer fusion cDNA of case 2 and thus probably have no functional significance in the tumour.
The molecular mechanism of action of the API2-MLT fusion remains to be elucidated. Without being limited by theory, it is hypothesised that the fusion protein resulting from the t(11;18) may lead to increased inhibition of apoptosis and thereby confer a survival advantage to MALT lymphomas and allow antigen-independent proliferation. Indeed, MALT lymphomas have been shown to display low levels of apoptosis
39
, to escape from FAS-mediated apoptosis
40
and about 20% of low-grade MALT lymphomas do not respond to
H. pylori
eradication therapy.
6
The truncation of API2 after the BIR domains could release their anti-apototic effects from regulation by the CARD and RING domains. Recent studies have shown that the BIR domain-co
Baens Mathijs
Dierlamm Judith
Marijnen Peter
Guzo David
Nguyen Quang
TraskBritt
Vlaams Interuniversitair Instituut voor Biotechnologie vzw
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