BCL10 expression in normal and neoplastic lymphoid tissue. Nuclear localization in MALT lymphoma

BCL10 is an apoptotic regulatory molecule identified through its direct involvement in t(1;14)(p22;q32) of mucosa-associated lymphoid tissue (MALT) lymphoma. We examined BCL10 protein expression in various normal tissues and B-cell lymphomas by immunohistochemistry of formalin-fixed and paraffin-embedded tissues using mouse BCL10 monoclonal antibodies. BCL10 protein was expressed in lymphoid tissue but not in 21 various other tissues with the exception of breast. In normal B-cell follicles, the protein was expressed abundantly in the germinal center B cells, moderately in the marginal zone, but only weakly in the mantle zone B cells. Irrespective of their stage of B-cell maturation, BCL10 was predominantly expressed in the cytoplasm. In contrast, each of the four MALT lymphomas with t(1;14)(p22;q32) showed strong BCL10 expression in both the nucleus and cytoplasm. Twenty of 36 (55%) MALT lymphomas lacking the translocation exhibited BCL10 expression in both the nucleus and cytoplasm although at a much lower level, whereas the remaining 16 cases displayed only cytoplasmic BCL10. Unlike MALT lymphoma, both follicular and mantle cell lymphomas generally displayed BCL10 expression compatible to their normal cell counterparts. Our results show differential expression of BCL10 protein among various B-cell populations of the B-cell follicle, indicating its importance in B-cell maturation. The subcellular localization of BCL10 was frequently altered in MALT lymphoma in comparison with its normal cell counterparts, suggesting that ectopic BCL10 expression may be important in the development of this type of tumor.

Detection of t(11;18)(q21;q21) by interphase fluorescence in situ hybridization using API2 and MLT specific probes

The translocation of chromosome 11, long arm, region 2, band 1, to chromosome 18, long arm, region 2, band 1 (t(11;18)(q21;q21)) represents a recurrent chromosomal abnormality in extranodal marginal zone B-cell lymphoma (MZBCL) of mucosa-associated lymphoid tissue (MALT) type and leads to a fusion of the apoptosis inhibitor-2 (API2) gene on chromosome 11 and the MALT lymphoma-associated translocation (MLT) gene on chromosome 18. A 2-color fluorescence in situ hybridization (FISH) assay, which can be used for the detection of t(11;18) in interphase nuclei and metaphase chromosomes on fresh and archival tumor tissue, was developed. The P1 artificial chromosome (PAC) clone located immediately telomeric to the MLT gene and the PAC clone spanning the API2 gene were differentially labeled and used to visualize the derivative chromosome 11 resulting from t(11;18), as evident by the overlapping or juxtaposed red and green fluorescent signals. The assay was applied to interphase nuclei of 20 cases with nonmalignant conditions and 122 B-cell non-Hodgkin's lymphomas (NHLs). The latter group comprised 20 cases of nodal follicle center cell lymphoma and diffuse large B-cell NHL, 10 cases of gastric diffuse large B-cell lymphoma, 10 cases of hairy cell leukemia, and 82 cases of MZBCL (41 extranodal from various locations, 19 nodal, and 22 splenic MZBCL) including 35 cases with an abnormal karyotype, 2 of which revealed t(11;18). By interphase FISH, t(11;18) was detected in 8 gastrointestinal low-grade MALT-type lymphomas including the 2 cytogenetically t(11;18)(+) cases. In the 8 t(11;18)(+) cases, the FISH results were confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) using API2 and MLT specific primers. Our results indicate that t(11;18)(q21;q21) specifically characterizes a subgroup of low-grade MZBCL of the MALT-type and that the FISH assay described here is a highly specific and rapid test for the detection of this translocation.

MLL amplification in myeloid leukemias: A study of 14 cases with multiple copies of 11q23

We here report the clinical, cytogenetic, fluorescence in situ hybridization (FISH), and Southern blot data on 14 patients with a myeloid malignancy and structural aberration of chromosome band 11q23 associated with overrepresentation or amplification of the MLL gene. The number of copies of MLL varied from three (two cases) to a cluster consisting of multiple hybridization spots. Together with previous reports, available data indicate that amplification of 11q23/MLL is a recurrent genetic change in myeloid malignancy. It affects mainly elderly patients and is often associated with dysplastic bone marrow changes or with complex karyotypic aberrations, suggestive of genotoxic exposure. It is associated with a poor prognosis. In addition, FISH analysis of nine cases with additional 11q probes showed that the overrepresented chromosomal region is generally not restricted to MLL, and Southern blot analysis indicated that amplification does not involve a rearranged copy of this gene. The significance of MLL amplification and the mechanisms by which it could play a role in leukemogenesis and/or disease progression remain to be elucidated.

Analysis of the P53, RB/D13S25, and P16 tumor suppressor genes in marginal zone B-cell lymphoma: An interphase fluorescence in situ hybridization study

The genetic mechanisms underlying the genesis, disease progression, and high-grade transformation of marginal zone B-cell lymphoma (MZBCL) are poorly understood. We analyzed 33 cases of histologically and immunophenotypically well-characterized MZBCL (12 extranodal, 11 nodal, and 10 splenic MZBCL; 27 at primary diagnosis and six during the course of disease) by dual-color interphase fluorescence in situ hybridization (FISH) for deletions of tumor suppressor genes. We investigated loci known to play a role in the genesis or disease progression of other subtypes of lymphoid malignancies, namely the P53 gene (17p13), the retinoblastoma gene (RB, 13q14), the D13S25 locus (13q14), and the P16(INK4A) gene (9p21). Heterozygous deletions of P53 were detected in three out of the 33 cases, including two splenic and one extranodal MZBCL. One of these patients was analyzed at primary diagnosis and two during the course of disease. Heterozygous deletions of the RB gene (nodal MZBCL) and D13S25 (splenic MZBCL) were found in one case each. P16 deletions were not detected in any of our cases. We conclude that deletions of the analyzed tumor suppressor genes are relatively rare in MZBCL, which contrasts with the findings in some other subtypes of NHL.

Hepatosplenic alphabeta T-cell lymphoma: an unusual case with clinical, histologic, and cytogenetic features of gammadelta hepatosplenic T-cell lymphoma

Hepatosplenic gammadelta T-cell lymphoma is a recently identified entity in which lymphoma cells bearing the gammadelta T-cell receptor (TCR) infiltrate the sinusoids of the liver and the sinuses of the splenic red pulp and bone marrow, without lymph node involvement. It is also characterized by a recurrent cytogenetic finding, isochromosome 7q (i7q10). The authors report a case of hepatosplenic lymphoma of alphabeta T-cell phenotype that shares the same clinical, histologic, and cytogenetic characteristics of the previously described hepatosplenic gammadelta T-cell lymphoma. Fluorescent in situ hybridization performed with chromosome 7 probes showed the typical pattern of isochromosome 7q. Genomic analysis of the TCR gamma locus failed to detect a clonal rearrangement. This unique case of hepatosplenic lymphoma of alphabeta T-cell phenotype supports the possibility that lymphoid populations of different alphabeta or gammadelta phenotype that share similar homing and presumably functional properties could give rise to lymphomas displaying similar clinical and pathologic findings.

Genetic abnormalities in marginal zone B-cell lymphoma

Marginal zone B-cell lymphoma (MZBCL) including extranodal mucosa-associated lymphoid tissue (MALT)-type lymphoma, nodal, and splenic MZBCL represents a distinct subtype of B-non-Hodgkin's lymphoma. Recently, important progress in the elucidation of the genetic mechanisms underlying the pathogenesis and disease progression of these lymphomas has been made. The API2 gene, an inhibitor of apoptosis, and the novel MLT gene have been found to be altered by the t(11;18)(q21;21), which represents the most frequent structural chromosomal abnormality in extranodal low-grade MALT lymphoma. Another gene involved in the regulation of apoptosis, the BCL10 gene, has been cloned from a MALT lymphoma cytogenetically characterized by the t(1;14)(p22;q32). Along the same lines, inactivating mutations of the proapoptotic FAS gene have been detected in a relatively high proportion of extranodal MZBCLs. Considering these data and the fact that at least some MALT lymphomas show low levels of apoptosis and seem to escape from FAS-mediated apoptosis one may speculate that abrogation of apoptosis constitutes a central pathogenetic mechanism in the development of these lymphomas. The pathogenetic role of trisomy 3, the most frequent numerical chromosomal change of MZBCL, is not known. The minimal overrepresented region has been delineated to 3q21-23 and 3q25-29 using comparative genomic hybridization. The BCL6 proto-oncogene, located on 3q27, which is rearranged in some MZBCL and a high proportion of large cell B-cell lymphomas with extranodal localization, represents one of the candidate genes residing in these critical regions.

Inv(2)(p23q35) in anaplastic large-cell lymphoma induces constitutive anaplastic lymphoma kinase (ALK) tyrosine kinase activation by fusion to ATIC, an enzyme involved in purine nucleotide biosynthesis

The non-Hodgkin lymphoma (NHL) subtype anaplastic large-cell lymphoma (ALCL) is frequently associated with a t(2;5)(p23;q35) that results in the fusion of the ubiquitously expressed nucleophosmin (NPM) gene at 5q35 to the anaplastic lymphoma kinase (ALK) gene at 2p23, which is not normally expressed in hematopoietic tissues. Approximately 20% of ALCLs that express ALK do not contain the t(2;5), suggesting that other genetic abnormalities can result in aberrant ALK expression. Here we report the molecular characterization of an alternative genetic means of ALK activation, the inv(2)(p23q35). This recurrent abnormality produces a fusion of the amino-terminus of 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/IMP cyclohydrolase (ATIC), a bifunctional homodimeric enzyme that catalyzes the penultimate and final steps of de novo purine nucleotide biosynthesis, with the intracellular portion of the ALK receptor tyrosine kinase. RT-PCR analysis of 5 ALCL tumors that contained the inv(2) revealed identical ATIC-ALK fusion cDNA junctions in all of the cases. Transient expression studies show that the ATIC-ALK fusion transcript directs the synthesis of an approximately 87-kd chimeric protein that is localized to the cytoplasm, in contrast to NPM-ALK, which typically exhibits a cytoplasmic and nuclear subcellular distribution. ATIC-ALK was constitutively tyrosine phosphorylated and could convert the IL-3-dependent murine hematopoietic cell line BaF3 to cytokine-independent growth. Our studies demonstrate an alternative mechanism for ALK involvement in the genesis of NHL and suggest that ATIC-ALK activation results from ATIC-mediated homodimerization. In addition, expected decreases in ATIC enzymatic function in ATIC-ALK-containing lymphomas may render these tumors more sensitive to antifolate drugs such as methotrexate. (Blood. 2000;95:2144-2149)

Genetic abnormalities in marginal zone B-cell lymphoma

Marginal zone B-cell lymphoma (MZBCL) including extranodal mucosa-associated lymphoid tissue (MALT)-type lymphoma, nodal, and splenic MZBCL represents a distinct subtype of B-non-Hodgkin's lymphoma. Recently, important progress in the elucidation of the genetic mechanisms underlying the pathogenesis and disease progression of these lymphomas has been made. The API2 gene, an inhibitor of apoptosis, and the novel MLT gene have been found to be altered by the t(11;18)(q21;21), which represents the most frequent structural chromosomal abnormality in extranodal low-grade MALT lymphoma. Another gene involved in the regulation of apoptosis, the BCL10 gene, has been cloned from a MALT lymphoma cytogenetically characterized by the t(1;14)(p22;q32). Along the same lines, inactivating mutations of the proapoptotic FAS gene have been detected in a relatively high proportion of extranodal MZBCLs. Considering these data and the fact that at least some MALT lymphomas show low levels of apoptosis and seem to escape from FAS-mediated apoptosis one may speculate that abrogation of apoptosis constitutes a central pathogenetic mechanism in the development of these lymphomas. The pathogenetic role of trisomy 3, the most frequent numerical chromosomal change of MZBCL, is not known. The minimal overrepresented region has been delineated to 3q21-23 and 3q25-29 using comparative genomic hybridization. The BCL6 proto-oncogene, located on 3q27, which is rearranged in some MZBCL and a high proportion of large cell B-cell lymphomas with extranodal localization, represents one of the candidate genes residing in these critical regions.

Fusion of a novel gene, BTL, to ETV6 in acute myeloid leukemias with a t(4;12)(q11-q12;p13)

The ETV6 gene (also known as TEL) is the main target of chromosomal translocations affecting chromosome band 12p13. The rearrangements fuse ETV6 to a wide variety of partner genes in both myeloid and lymphoid malignancies. We report here 4 new cases of acute myeloid leukemia (AML) with very immature myeloblasts (French-American-British [FAB]-M0) and with a t(4;12)(q11-q12;p13). In all cases, ETV6 was found recombined to a new gene, homologous to the mouse Brx gene. The gene was named BTL (Brx-like Translocated in Leukemia). Reverse transcriptase-polymerase chain reaction (RT-PCR) experiments indicate that the expression of the BTL-ETV6 transcript, but not of the reciprocal ETV6-BTL transcript, is a common finding in these leukemias. In contrast to the majority of other ETV6 fusions, both the complete helix-loop-helix (HLH) and ETS DNA binding domains of ETV6 are present in the predicted BTL-ETV6 fusion protein, and the chimeric gene is transcribed from the BTL promoter.

Secondary chromosome changes in mantle cell lymphoma

BACKGROUND AND OBJECTIVE

Mantle cell lymphomas (MCLs) comprise a rare but distinct clinicopathological entity usually associated with t(11;14). This translocation is regarded as a primary event, but it has been suggested that other as yet unidentified genetic alterations are required for development and progression of MCL.

DESIGN AND METHODS

In order to identify recurrent secondary changes that might point towards specific chromosomal regions contributing to the pathogenesis of MCL we studied 43 MCL cases in which clonal chromosomal abnormalities have been found during cytogenetic analysis.

RESULTS

In this series 83% of cases were characterized by t(11;14) and in the majority of them the t(11;14) was associated with multiple other chromosomal aberrations. Recurrent secondary changes were found in which imbalances of genetic material prevailed, losses being more common than gains. The former involved thirteen chromosomes, especially 13, 6q, 9q, 11q, 8/8p, 10/10p, and 14, whereas recurrent gains affected 3/3q. Non-randomly occurring breakpoints were relatively infrequent. The identified anomalies were also involved in aberrations observed in the group of MCL not associated with t(11;14). Some of them are shared with other B-cell proliferations.

INTERPRETATION AND CONCLUSIONS

The data presented here indicate that MCL is characterized by consistently occurring secondary chromosome changes. Their significance for the development and/or progression of MCL needs to be elucidated and confirmed by further investigations.

The apoptosis inhibitor gene API2 and a novel 18q gene, MLT, are recurrently rearranged in the t(11;18)(q21;q21) associated with mucosa-associated lymphoid tissue lymphomas

Marginal zone cell lymphomas of the mucosa-associated lymphoid tissue (MALT) are the most common subtype of lymphoma arising at extranodal sites. The t(11;18)(q21;q21) appears to be the key genetic lesion and is found in approximately 50% of cytogenetically abnormal low-grade MALT lymphomas. We show that the API2 gene, encoding an inhibitor of apoptosis also known as c-IAP2, HIAP1, and MIHC, and a novel gene on 18q21 characterized by several Ig-like C2-type domains, named MLT, are recurrently rearranged in the t(11;18). In both MALT lymphomas analyzed, the breakpoint in API2 occurred in the intron separating the exons coding respectively for the baculovirus IAP repeat domains and the caspase recruitment domain. The breakpoints within MLT differed but the open reading frame was conserved in both cases. In one case, the translocation was accompanied by a cryptic deletion involving the 3' part of API2. As a result, the reciprocal transcript was not present, strongly suggesting that the API2-MLT fusion is involved in the oncogenesis of MALT lymphoma.

Molecular cytogenetics localizes two new breakpoints on 11q23.3 and 21q11.2 in myelodysplastic syndrome with t(11;21) translocation

Translocation t(11;21)(q24;q11.2) is a rare but recurrent chromosomal abnormality associated with myelodysplastic syndrome (MDS) that until now has not been characterized at the molecular level. We report here results of a molecular cytogenetic analysis of this translocation in a patient with refractory anemia. Using FISH with a panel of 11q and 21q cosmid/YAC probes, we localized the chromosome 11 breakpoint at q23.3 in a region flanked by CP-921G9 and CP-939H3 YACs, distal to the HRX/MLL locus frequently involved in acute leukemias. The chromosome 21 breakpoint was mapped in a 800-kb fragment inserted into the CP-145E3 YAC at 21q11.2, proximal to the AML1 gene. It is noteworthy that in all four cases with a t(11;21) reported until now, a second der(11)t(11;21) and loss of normal chromosome 11 could be observed either at diagnosis or during the course of the disease. Since in our case heteromorphism was detected by FISH on the centromeric region of the two der(11), the second der(11) chromosome could be the result of a mitotic recombination that had occurred on the long arm of chromosome 11, rather than of duplication of the original der(11). Constancy of secondary karyotypic changes resulting in an extra copy of the putative chimeric gene at der(11), loss of 11 qter sequences, and partial trisomy 21 suggest that neoplastic progression of MDS cases with a t(11;21) may be driven by the same mechanism(s).

A physical, transcript, and deletion map of chromosome region 12p12.3 flanked by ETV6 and CDKN1B: hypermethylation of the LRP6 CpG island in two leukemia patients with hemizygous del(12p)

FISH analyses and loss of heterozygosity studies have delineated a commonly deleted region in hematological malignancies flanked by ETV6 and CDKN1B on chromosome 12p12.3. The same chromosomal region is also a target for deletions in certain solid tumors. As an initial step toward the cloning of a potential tumor suppressor gene at 12p12.3, we mapped the ETV6-CDKN1B region physically using bacterial artificial chromosome (BAC) and P1-derived clone (PAC) contigs. The 1.2-Mb high-resolution, contiguous map extends from D12S1095 to D12S929 and consists of 19 PACs and 20 BACs. Pulsed-field gel electrophoresis experiments confirmed the integrity of the clone-based map and identified six CpG islands in the region. A transcript map was generated by performing hybridization selection experiments with the genomic clones, by evaluating known 12p ESTs for their presence in the contig, and by sequence analysis of CpG islands in the region. Altogether evidence was gathered for the presence of the recently published LRP6 gene and at least seven other new genes in this chromosomal region. The CLAPS3 gene, mapped between D12S391 and D12S358, was reassigned to chromosome 5 since genomic sequencing demonstrated the chromosome 12p sequence to be a pseudogene. Polymorphic CA repeats were identified approximately every 100 kb, which will support future analysis of loss of heterozygosity in tumors. Fluorescence in situ hybridization analysis of leukemia patients with del(12p) further refined the commonly deleted segment to 600 kb between ETV6 and D12S358, which apparently excludes CDKN1B. Methylation changes of the CpG islands in the ETV6-CDKN1B interval were assessed by Southern analysis for leukemia patients with hemizygous 12p deletions. A "de novo" methylation was detected only at the LRP6 CpG island in 2 of 22 leukemia patients tested and was confirmed by methylation-sensitive PCR and sequencing. The genomic structure of LRP6 was elucidated to allow screening for inactivating mutations, but only intragenic polymorphisms were identified. Hypermethylation of CpG islands associated with gene promoters is reported as a common mechanism for gene silencing and tumor suppressor inactivation. Therefore the consequences of the LRP6 CpG island methylation and its role in the observed phenotype need further investigation.

Bcl10 is involved in t(1;14)(p22;q32) of MALT B cell lymphoma and mutated in multiple tumor types

MALT B cell lymphomas with t(1;14)(p22;q32) showed a recurrent breakpoint upstream of the promoter of a novel gene, Bcl10. Bcl10 is a cellular homolog of the equine herpesvirus-2 E10 gene: both contain an amino-terminal caspase recruitment domain (CARD) homologous to that found in several apoptotic molecules. Bcl10 and E10 activated NF-kappaB but caused apoptosis of 293 cells. Bcl10 expressed in a MALT lymphoma exhibited a frameshift mutation resulting in truncation distal to the CARD. Truncated Bcl10 activated NF-kappaB but did not induce apoptosis. Wild-type Bcl10 suppressed transformation, whereas mutant forms had lost this activity and displayed gain-of-function transforming activity. Similar mutations were detected in other tumor types, indicating that Bcl10 may be commonly involved in the pathogenesis of human malignancy.

Involvement of MLL gene in a t(10;11)(q22;q23) and a t(8;11)(q24;q23) identified by fluorescence in situ hybridization

We describe two cases of acute myeloblastic leukemia, classified as M4 and M5 in the French-American-British nomenclature, with an 11q23 rearrangement at karyotypic analysis. The involvement of the MLL gene with two new partner loci on chromosome 10q22 and 8q24, respectively, was demonstrated by fluorescence in situ hybridization using a YAC clone B22B2L.

The cryptic inv(2)(p23q35) defines a new molecular genetic subtype of ALK-positive anaplastic large-cell lymphoma

Recently, a distinctive entity characterized by expression of the anaplastic lymphoma kinase (ALK) protein [most frequently due to the t(2;5)(p23;q35)-associated NPM-ALK fusion] has emerged within the heterogenous group of non-Hodgkin's lymphomas (NHL) classified as anaplastic large-cell lymphoma (ALCL). Sporadic variant 2p23/ALK abnormalities identified in ALK-positive ALCL indicate that genes other than NPM may also be involved in the deregulation of ALK and lymphomagenesis. We report here three cases with an inv(2)(p23q35) detected by fluorescence in situ hybridization (FISH) in young male patients with ALK-positive ALCL. In contrast to ALCL cases with the classical t(2;5)(p23;q35) that usually show both cytoplasmic and nuclear or predominantly nuclear alone localization of the NPM-ALK chimeric product, in all three cases with an inv(2)(p23q35) the ALK protein accumulated in the cytoplasm only, supporting the previous assumption that the oncogenic potential of ALK may not be dependent on its nuclear localization. As the first step to identify the ALK partner gene involved in the inv(2)(p23q35), we performed extensive FISH studies and demonstrated that the 2q35 breakpoint occurred within the 1,750-kb region contained within the 914E7 YAC. Moreover, a striking association of the inv(2)(p23q35) with a secondary chromosomal change, viz, ider(2)(q10)inv(2)(p23q35), carrying two additional copies of the putative ALK-related fusion gene, was found in all three patients, suggesting that, in contrast to the standard t(2;5)/NPM-ALK fusion, multiple copies of the putative 2q35-ALK chimeric gene may be required for efficient tumor development. In summary, we demonstrate that the inv(2)(p23q35), a variant of the t(2;5)(p23;q35), is a recurrent chromosomal abnormality in ALK-positive ALCL, the further characterization of which should provide new insight into the pathogenesis of these lymphomas.

Rearrangement between the MYH11 gene at 16p13 and D12S158 at 12p13 in a case of acute myeloid leukemia M1 (AML-M1)

A case of acute myeloid leukemia (AML) M1 with bone marrow eosinophilia was characterized by cytogenetics and fluorescence in situ hybridization (FISH). A complex karyotype including a der(12)t(12;17)(p12-13;q11) and a der(16)t(16;20)(p13;p11) was found at diagnosis. FISH studies with probes for chromosome 16 and for the short arm of chromosome 12 showed even more complex rearrangements. Analysis with a panel of probes for 12p showed that D12S158 spanned the breakpoint on the der(12). Unexpectedly, FISH signals were found on the der(12) and on the der(6) at band p13, the site of juxtaposition between the short arm of chromosome 16 and chromosome 20. Moreover, both YAC 854E2, containing the MYH11 gene, and cosmid ZIT133, encompassing the MYH11 breakpoint in inv(16) and t(16;16) of AML-M4 with eosinophilia, demonstrated fluorescent signals on the normal 16, on the der(16), and on the der(12). These data clearly support a reciprocal exchange between D12S158 at 12p13.3 and the MYH11 gene at 16p13. In addition, experiments with two PAC clones for the CBFB gene at 16q22 excluded the presence of a masked inv(16). An interstitial deletion, independent from the translocation and flanked by VWF and KRAS2, was also detected on the der(12).

Molecular cloning of translocation t(1;14)(q21;q32) defines a novel gene (BCL9) at chromosome 1q21

Abnormalities of chromosome 1q21 are common in B-cell malignancies and have been associated with a poor response to therapy. The nature of the involved gene(s) on chromosome 1q21 remains unknown. A cell line (CEMO-1) has recently been established from a patient with precursor-B-cell acute lymphoblastic leukemia (ALL), which exhibited a t(1;14)(q21;q32). To identify the gene involved in this translocation, we have cloned both rearranged IGHJ alleles using long-distance inverse polymerase chain reaction (LDI-PCR). Two IGHJ fragments were amplified from CEMO-1 DNA and sequenced. One allele showed novel sequences upstream of JH5 with no homology to either IGH or any other sequences on the databases. Using a single-copy Xho I fragment immediately 5' of JH5, PAC clones were isolated and mapped to chromosome 1q21 on normal metaphases by fluorescence in situ hybridization (FISH), confirming that this allele represented the t(1;14)(q21;q32) breakpoint. Sequence analysis of the 1q21 Xho I fragment showed identity with an expressed sequence tag (EST), and this probe was therefore used to probe Northern blots. Two transcripts of 6.3 kb and 4.2 kb expressed at low level in mRNA from all tissues were detected: a third transcript of 1.6 kb was expressed only in thymus, spleen, and small intestine. Full-length BCL9 cDNA clones were obtained from a normal human fetal brain cDNA library supplemented by 5' and 3' RACE. Sequence analysis predicted a protein of 1394 amino acids containing 18% proline, 11% glycine, 11% serine, and 6% methionine, but no recognizable protein motifs or significant homologies to any other known proteins. The CEMO-1 1q21 breakpoint fell within the 3' UTR of the BCL9 gene. Low-level expression of BCL9 was detected in Epstein-Barr virus-transformed normal B cells by Northern blot; in contrast, abundant BCL9 expression was observed in CEMO-1, indicating that deregulated expression of this gene was one pathological consequence of the translocation. Screening of a panel of 39 B-cell malignancies with 1q abnormalities by Southern blot showed one additional case with a breakpoint in the 3' UTR of BCL9, indicating that this was a recurrent breakpoint. FISH analysis using an 850-kb YAC spanning BCL9 identified a further case with t(1;22)(q21;q11) causing juxtaposition of BCL9 to the IGlambda locus. Other breakpoints were heterogeneous, falling both centromeric (10 cases) and telomeric (10 cases) of the BCL9 gene. These data suggest that BCL9 may be the target of translocation in some B-cell malignancies with abnormalities of 1q21 and that deregulated BCL9 expression may be important in their pathogenesis.

Fluorescence in situ hybridization characterization of new translocations involving TEL (ETV6) in a wide spectrum of hematologic malignancies

The ETV6 (also known as TEL) gene on chromosome 12p13 is the target of a number of translocations associated with various hematologic malignancies. The contribution of ETV6 to leukemogenesis occurs through different mechanisms that involve either its helix-loop-helix dimerization domain or its E26 transformation-specific (ETS) DNA-binding domain. Using fluorescence in situ hybridization we characterized seven new ETV6 rearrangements in chronic myeloid leukemia, acute myeloid leukemia, acute lymphoblastic leukemia, and non-Hodgkin's lymphoma. These aberrations, not always discernible at the cytogenetic level, include a t(5;12)(q31;p13), t(6;12;17)(p21;p13;q25), t(7;12)(p15;p13), t(7;12)(p12;p13), t(7;12)(q36;p13), t(12;13)(p13;q12), and a not completely defined t(12;?)(p13;?). Loss or disruption of the second ETV6 allele by a del(12)(p12p13) or by an intragenic ETV6 deletion was detected in two cases. In six cases the 12p13 breakpoint occurred in the 5' end of ETV6, upstream to exons encoding the HLH domain, whereas the remaining case had a breakpoint between the exons coding for the HLH domain and the exons coding for the ETS domain of ETV6. These observations provide further evidence for the multiple contributions of ETV6 in the pathogenesis of a wide range of hematologic malignancies.

Molecular delineation of 13q deletion boundaries in 20 patients with myeloid malignancies

Fluorescent in situ hybridization (FISH) analysis with a panel of DNA probes for 13q13.1-q14.3 was performed on 20 cases of myeloid malignancies, of which 17 showed a del(13)(q) and three had translocations affecting 13q. By chromosome morphology, deletions consistently involved bands q14 and q21. In addition to confirming the chromosome data, FISH allowed us to delineate a commonly deleted region that was flanked by YAC 833A2 and YAC 854D4. Three cases with 13q translocations unexpectedly showed accompanying cryptic microdeletions of 13q, and in one case the commonly deleted region could be narrowed to a genomic segment, which includes YAC 937C7, RB1, and YAC 745E3. Homozygous deletions were not detected. This region overlaps with the smallest deleted region of 13q14 in chronic lymphocytic leukemia.

Lymph node histology in typical and atypical chronic lymphocytic leukemia

According to the French-American-British (FAB) proposal on the classification of chronic lymphoid leukemia (CLL), the disorder can be subdivided into typical and atypical CLL. We recently demonstrated the prognostic significance of this subgrouping and based on these results we suggested that typical and atypical CLL represent two closely related, but different entities. These results prompted us to investigate 42 patients diagnosed with CLL based on the results of lymph node biopsy in order to identify the histologic counterpart of the CLL variants. A first group of 14 cases showed a monomorphic proliferation of small round lymphocytes associated with the occurrence of small pseudofollicles. All these cases were diagnosed as typical CLL on peripheral blood (13 cases) or bone marrow smear (1 case). The remaining 28 cases showed aberrant histologic features characterized by the presence of large numbers of paraimmunoblasts and prolymphocytes, forming very large pseudofollicles, and/or by nuclear irregularities of the neoplastic cells. Based on peripheral blood smears (22 cases) or bone marrow smears (six cases), two cases showed no peripheral blood involvement, 21 cases were diagnosed as atypical CLL, and five as typical CLL. From these data we can conclude that a histologic counterpart of the CLL variants recognized in the FAB proposal does exist; moreover, our data may explain reports on lymph node involvement by CLL composed of small cleaved cells and clarify the occurrence of pseudofollicles in cases described as mantle cell lymphomas.

Fusion of TEL, the ETS-variant gene 6 (ETV6), to the receptor-associated kinase JAK2 as a result of t(9;12) in a lymphoid and t(9;15;12) in a myeloid leukemia

Translocations in hematologic disease of myeloid or lymphoid origin with breakpoints at chromosome band 12p13 frequently result in rearrangements of the Ets variant gene 6 (ETV6). As a consequence either the ETS DNA-binding domain or the Helix-Loop-Helix (HLH) oligomerization domain of ETV6 is fused to different partner genes. We show here that a t(9;12)(p24;p13) in a case of early pre-B acute lymphoid leukemia and a t(9;15;12)(p24;q15;p13) in atypical chronic myelogenous leukemia in transformation involve the ETV6 gene at 12p13 and the JAK2 gene at 9p24. In each case different fusion mRNAs were found, with only one resulting in an open reading frame for a chimeric protein consisting of the HLH oligomerization domain of ETV6 and the protein tyrosine kinase (PTK) domain of JAK2. The cloning of the complete human JAK2 coding and genomic sequences and of the genomic junction fragments of the translocations allowed a characterization of the different splice events leading to the various mRNAs. JAK2 plays a central role in non-protein tyrosine kinase receptor signaling pathways, which could explain its involvement in malignancies of different hematologic lineages. Besides hop in Drosophila no member of the JAK family has yet been implicated in tumorigenesis.

Philadelphia-like translocation t(9;22)(q34;q11) found in a follicular lymphoma involving not BCR and ABL but IGL-mediated rearrangement of an unknown gene on 9q34

In a case of follicular center cell lymphoma (FCCL) without evidence of histologic progression towards a high-grade lymphoma, t(9;22)(q34;q11) was found simultaneously with a t(14;18)(q32;q21) and a t(8;14)(q24;q32). Molecular studies of this case showed BCL2 and MYC rearrangements in addition to the rearrangements of immunoglobulin heavy (IGH) and lambda (IGL) loci. Investigation of the t(9;22) using Southern blot and RT-PCR analysis failed to detect M-bcr or m-bcr rearrangements of BCR. Two-color fluorescence in situ hybridization (FISH) with ABL and BCR probes revealed presence of a "fusion" signal, but its atypical localization [der(9)] and gene order [cen-ABL-BCR-tel] indicated that this translocation differed from the t(9;22) in chronic myeloid leukemia and did not involve either ABL or BCR. In addition, further FISH analysis using 9q34- and 22q11-specific probes localized the breakpoint on chromosome 9 distal to the NOTCH1 gene and the breakpoint on 22q11 in the IGL gene cluster. These results indicate an IGL-mediated rearrangement of an unknown gene at 9q34 that together with BCL2 and MYC might be involved in the lymphomagenesis of the present case of FCCL and perhaps in other cases of non-Hodgkin lymphoma in which t(9;22) is sporadically occurring.