Waved aCGH: to smooth or not to smooth.

Array-based comparative genomic hybridization (aCGH) is a powerful tool to detect genomic imbalances in the human genome. The analysis of aCGH data sets has revealed the existence of a widespread technical artifact termed as 'waves', characterized by an undulating data profile along the chromosome. Here, we describe the development of a novel noise-reduction algorithm, waves aCGH correction algorithm (WACA), based on GC content and fragment size correction. WACA efficiently removes the wave artifact, thereby greatly improving the accuracy of aCGH data analysis. We describe the application of WACA to both real and simulated aCGH data sets, and demonstrate that our algorithm, by systematically correcting for all known sources of bias, is a significant improvement on existing aCGH noise reduction algorithms. WACA and associated files are freely available as Supplementary Data.

MEF2C haploinsufficiency caused by either microdeletion of the 5q14.3 region or mutation is responsible for severe mental retardation with stereotypic movements, epilepsy and/or cerebral malformations.

BACKGROUND: Over the last few years, array-comparative genomic hybridisation (CGH) has considerably improved our ability to detect cryptic unbalanced rearrangements in patients with syndromic mental retardation. METHOD: Molecular karyotyping of six patients with syndromic mental retardation was carried out using whole-genome oligonucleotide array-CGH. RESULTS: 5q14.3 microdeletions ranging from 216 kb to 8.8 Mb were detected in five unrelated patients with the following phenotypic similarities: severe mental retardation with absent speech, hypotonia and stereotypic movements. Facial dysmorphic features, epilepsy and/or cerebral malformations were also present in most of these patients. The minimal common deleted region of these 5q14 microdeletions encompassed only MEF2C, the gene for a protein known to act in brain as a neurogenesis effector, which regulates excitatory synapse number. In a patient with a similar phenotype, an MEF2C nonsense mutation was subsequently identified. CONCLUSION: Taken together, these results strongly suggest that haploinsufficiency of MEF2C is responsible for severe mental retardation with stereotypic movements, seizures and/or cerebral malformations.

Recurrent genomic aberrations combined with deletions of various tumour suppressor genes may deregulate the G1/S transition in CD4+CD56+ haematodermic neoplasms and contribute to the aggressiveness of the disease.

CD4+CD56+ haematodermic neoplasms (HDN) constitute a rare disease characterized by aggressive clinical behaviour and a poor prognosis. Tumour cells from HDN are leukaemic counterparts of plasmacytoid dendritic cells (pDCs). Despite increased knowledge of the ontogenetic origin of these tumours, the genetic causes and oncogenic signalling events involved in malignant transformation are still unknown. To delineate novel candidate regions and disease-related genes, we studied nine typical CD4+CD56+ HDN cases using genome-wide high-resolution array comparative genomic hybridization (CGH). Genomic imbalances, which were predominantly losses, were frequently detected. Gross genomic losses or gains involving an entire chromosome were observed in eight cases. The most frequent imbalances were deletions of chromosome 9, chromosome 13 and partial losses affecting 17p or 12p. Combinations of deletions of tumour suppressor genes (TSG), namely RB1, CDKN1B (p27), CDKN2A, (p16(ink4a), p14(arf)) or TP53 (p53), were observed in all cases. These results indicate that deletion events altering G1/S regulation are crucial for HDN oncogenesis. Furthermore, in addition to frequent sporadic gene losses, in one case we observed a 8q24 interstitial deletion that brought MYC closer to miR-30b/miR-30d, which may be related to their deregulation. Taken together, these results indicate that in addition to frequent G1/S checkpoint alterations, various genetic events could contribute to the chemoresistance of the tumour.

Autocrine induction of invasion and metastasis by tumor-associated trypsin inhibitor in human colon cancer cells.

From the conditioned medium of the human colon carcinoma cells, HT-29 5M21 (CM-5M21), expressing a spontaneous invasive phenotype, tumor-associated trypsin inhibitor (TATI) was identified and characterized by proteomics, cDNA microarray approaches and functional analyses. Both CM-5M21 and recombinant TATI, but not the K18Y-TATI mutant at the protease inhibitor site, trigger collagen type I invasion by several human adenoma and carcinoma cells of the colon and breast, through phosphoinositide-3-kinase, protein kinase C and Rho-GTPases/Rho kinase-dependent pathways. Conversely, the proinvasive action of TATI in parental HT29 cells was alleviated by the TATI antibody PSKAN2 and the K18Y-TATI mutant. Stable expression of K18Y-TATI in HT-29 5M21 cells downregulated tumor growth, angiogenesis and the expression of several metastasis-related genes, including CSPG4 (13.8-fold), BMP-7 (9.7-fold), the BMP antagonist CHORDIN (5.2-fold), IGFBP-2 and IGF2 (9.6- and 4.6-fold). Accordingly, ectopic expression of KY-TATI inhibited the development of lung metastases from HT-29 5M21 tumor xenografts in immunodeficient mice. These findings identify TATI as an autocrine transforming factor potentially involved in early and late events of colon cancer progression, including local invasion of the primary tumor and its metastatic spread. Targeting TATI, its molecular partners and effectors may bring novel therapeutic applications for high-grade human solid tumors in the digestive and urogenital systems.

Genotype phenotype correlation of 30 patients with Smith-Magenis syndrome (SMS) using comparative genome hybridisation array: cleft palate in SMS is associated with larger deletions.

BACKGROUND: Smith-Magenis syndrome (SMS) is rare (prevalence 1 in 25 000) and is associated with psychomotor delay, a particular behavioural pattern and congenital anomalies. SMS is often due to a chromosomal deletion of <4 Mb at the 17p11.2 locus, leading to haploinsufficiency of numerous genes. Mutations of one of these gemes, RAI1, seems to be responsible for the main features found with heterozygous 17p11.2 deletions. METHODS: We studied DNA from 30 patients with SMS using a 300 bp amplimers comparative genome hybridisation array encompassing 75 loci from a 22 Mb section from the short arm of chromosome 17. RESULTS: Three patients had large deletions (10%). Genotype-phenotype correlation showed that two of them had cleft palate, which was not found in any of the other patients with SMS (p<0.007, Fisher's exact test). The smallest extra-deleted region associated with cleft palate in SMS is 1.4 Mb, contains <16 genes and is located at 17p11.2-17p12. Gene expression array data showed that the ubiquitin B precursor (UBB) is significantly expressed in the first branchial arch in the fourth and fifth weeks of human development. CONCLUSION: These data support UBB as a good candidate gene for isolated cleft palate.

Peptides that mimic Candida albicans-derived beta-1,2-linked mannosides.

Beta-1,2-linked mannosides from Candida albicans phosphopeptidomannan (PPM) bind to macrophages through a receptor independent from the macrophage alpha-linked mannose receptor and stimulate these cells to secrete immune mediators. Anti-beta-1,2-linked mannoside but not anti-alpha-linked mannoside antibodies produced after immunization with neoglycoproteins protect animals from disseminated candidiasis. In this study, peptides that mimic beta-1,2-linked mannosides were isolated using phage display methodology. A phage library expressing random peptides was panned with an anti-beta-1,2-linked mannoside monoclonal antibody (mAb). After three rounds of biopanning, the isolated phages were able to inhibit recognition of C. albicans by the mAb. Sixty percent of the phages had an identical DNA insert corresponding to the peptide sequence FHENWPS that was recognized specifically by the mAb. Injection of KLH-coupled peptide into mice generated high titers of polyclonal antibodies against C. albicans yeast cell walls. The anti-FHENWPS antibodies bound to C. albicans PPM and were inhibited by soluble beta-1,2-mannotetraose. Together, these data provide evidence for mimotopic activity of the peptide selected by biopanning with the anti-beta-1,2-oligomannoside mAb.

High incidence of biallelic point mutations in the Runt domain of the AML1/PEBP2 alpha B gene in Mo acute myeloid leukemia and in myeloid malignancies with acquired trisomy 21.

The AML1 gene, situated in 21q22, is often rearranged in acute leukemias through t(8;21) translocation, t(12;21) translocation, or less often t(3;21) translocation. Recently, point mutations in the Runt domain of the AML1 gene have also been reported in leukemia patients. Observations for mutations of the Runt domain of the AML1 gene in bone marrow cells were made in 300 patients, including 131 with acute myeloid leukemia (AML), 94 with myelodysplastic syndrome (MDS), 28 with blast crisis chronic myeloid leukemia (CML), 3 with atypical CML, 41 with acute lymphoblastic leukemia (ALL), and 3 with essential thrombocythemia (ET). Forty-one of the patients had chromosome 21 abnormalities, including t(8;21) in 6 of the patients with AML, t(12;21) in 8 patients with ALL, acquired trisomy 21 in 17 patients, tetrasomy 21 in 7 patients, and constitutional trisomy 21 (Down syndrome) in 3 patients. A point mutation was found in 14 cases (4.7%), including 9 (22%) of the 41 patients with AML of the Mo type (MoAML) (none of them had detectable chromosome 21 rearrangement) and 5 (38%) of the 13 myeloid malignancies with acquired trisomy 21 (1 M1AML, 2 M2AML, 1 ET, and 1 atypical CML). In at least 8 of 9 mutated cases of MoAML, both AML alleles were mutated: 3 patients had different stop codon mutations of the 2 AML1 alleles, and 5 patients had the same missense or stop codon mutation in both AML1 alleles, which resulted in at least 3 of the patients having duplication of the mutated allele and deletion of the normal residual allele, as shown by FISH analysis and by comparing microsatellite analyses of several chromosome 21 markers on diagnosis and remission samples. In the remaining mutated cases, with acquired trisomy 21, a missense mutation of AML1, which involved 2 of the 3 copies of the AML1 gene, was found. Four of the 7 mutated cases could be reanalyzed in complete remission, and no AML1 mutation was found, showing that mutations were acquired in the leukemic clone. In conclusion, these findings confirm the possibility of mutations of the Runt domain of the AML1 gene in leukemias, mainly in MoAML and in myeloid malignancies with acquired trisomy 21. AML1 mutations, in MoAML, involved both alleles and probably lead to nonfunctional AML1 protein. As AML1 protein regulates the expression of the myeloperoxidase gene, the relationship between AML1 mutations and Mo phenotype in AML will have to be further explored. (Blood. 2000;96:2862-2869)

Therostasin, a novel clotting factor Xa inhibitor from the rhynchobdellid leech, Theromyzon tessulatum.

Therostasin is a potent naturally occurring tight-binding inhibitor of mammalian Factor Xa (K(i), 34 pm), isolated from the rhynchobdellid leech Theromyzon tessulatum. Therostasin is a cysteine-rich protein (8991 Da) consisting of 82 amino acid residues with 16 cysteine residues. Its amino acid sequence has been determined by a combination of techniques, including Edman degradation, enzymatic cleavage, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) on the native and s-beta-pyridylethylated compound. Sequence analysis reveals that it shares no significant homology with other Factor Xa inhibitors except for the putative reactive site. Moreover, it contains a signature pattern for proteins of the endothelin family, potent vasoconstrictors isolated in mammal and snake venom. Therostasin cDNA (825 bp) codes for a polypeptide of 82 amino acid residues preceded by 19 residues, representing a signal peptide sequence. As for the other known inhibitors of Factor Xa, therostasin is expressed and stored in the cells of the leech salivary glands.

Nonrandom 4p13 rearrangements of the RhoH/TTF gene, encoding a GTP-binding protein, in non-Hodgkin's lymphoma and multiple myeloma.

We recently isolated the RhoH/TTF gene by its fusion to the LAZ3/BCL6 gene, in a non-Hodgkin's lymphoma (NHL) cell line, which bore a t(3;4)(q27;p11-13) translocation. This gene encodes a novel Rho GTP-binding protein and is specifically expressed in hematopoietic tissues. We made its precise mapping at band 4p13, and described its partial genomic structure. Using fluorescence in situ hybridization and molecular analyses, we report here on the rearrangement of the RhoH/TTF gene, at band 4p13, in four cases of NHL with t(3;4)(q27;p13) translocation and its fusion to the LAZ3/BCL6 gene at band 3q27, in three of these cases. RT-PCR analysis of two cases allowed the detection of variable fusion transcripts emerging from the rearranged alleles, and in one case, a deregulated expression of both RhoH/TTF and LAZ3/BCL6 genes, by promoter substitution, was observed. We also show here another rearrangement of the RhoH/TTF gene in a patient with multiple myeloma and t(4;14)(p13;q32) translocation, with breakage within the IGH gene. It is the first report which describes the recurrent chromosomal alteration of a GTP-binding protein encoding gene, in patients with hematopoietic malignancies.

FISH analysis with a YAC probe improves detection of LAZ3/BCL6 rearrangement in non-Hodgkin's lymphoma.

INTRODUCTION: Chromosomal translocations involving the chromosome 3q27 region are common in B-cell non-Hodgkin's lymphoma (NHL), mainly diffuse large cell lymphoma (DLCL) and less often in follicular lymphoma. Most of these rearrangements involve the same major translocation cluster (MTC) on the 3q27 region, disrupting the LAZ3/BCL6 gene. Some of those translocations are difficult to detect by cytogenetic analysis and/or Southern-blot analysis. In the present report we used a FISH assay to improve the detection of LAZ3/BCL6 rearrangements. METHODS: We isolated a YAC clone (803g3), containing the BCL6 gene, in order to analyze by FISH 19 cases of B-cell non-Hodgkin's lymphoma with cytogenetically detectable 3q27 rearrangement, including reciprocal translocation in 11 cases, deletion in two cases, and addition of undefined chromosomal material on 3q27 in six cases. RESULTS: In the 11 cases with reciprocal translocation, FISH results confirmed cytogenetic data and showed disruption of the LAZ3 region: four t(3;4)(q27;p13), two t(3;11)(q27;q23.1), four t(3;14)(q27;q32) and one t(2;3)(p12;q27). In two of the cases, reciprocal t(3;14) was associated with other cytogenetically detectable abnormalities of 3q27, but FISH showed that they did not affect the LAZ3 gene region. FISH demonstrated a reciprocal translocation with LAZ3 gene rearrangement in two of the six patients with add 3q27: one t(3;11) and one t(3;14). In the two patients with del(3q27), one had two 3q27 FISH signals and one had only one 3q27 FISH signal, but no LAZ3 gene rearrangement was observed. CONCLUSION: We have identified a YAC containing the LAZ3/BCL6 gene. This YAC probe could be useful in clinical practice to demonstrate LAZ3 rearrangements by FISH analysis on tumor samples in NHL.

Overexpressed BCL6 (LAZ3) oncoprotein triggers apoptosis, delays S phase progression and associates with replication foci.

One of the most frequent genetic abnormalities associated with non Hodgkin lymphoma is the structural alteration of the 5' non coding/regulatory region of the BCL6 (LAZ3) protooncogene. BCL6 encodes a POZ/Zn finger protein, a structure similar to that of many Drosophila developmental regulators and to another protein involved in a human hematopoietic malignancy, PLZF. BCL6 is a sequence specific transcriptional repressor controlling germinal center formation and T cell dependent immune response. Although the expression of BCL6 negatively correlates with cellular proliferation in different cell types, the influence of BCL6 on cell growth and survival is currently unknown so that the way its deregulation may contribute to cancer remains elusive. To directly address this issue, we used a tetracycline-regulated system in human U2OS osteosarcoma cells and thus found that BCL6 mediates growth suppression associated with impaired S phase progression and apoptosis. Interestingly, overexpressed BCL6 can colocalize with sites of ongoing DNA synthesis, suggesting that it may directly interfere with S phase initiation and/or progression. In contrast, the isolated Zn finger region of BCL6, which binds BCL6 target sequence but lacks transcriptional repression activity, slows, but does not suppress, U2OS cell growth, is less efficient at delaying S phase progression, and does not trigger apoptosis. Thus, for a large part, the effects of BCL6 overexpression on cell growth and survival depend on its ability to engage protein/protein interactions with itself and/or its transcriptional corepressors. That BCL6 restricts cell growth suggests that its deregulation upon structural alterations may alleviate negative controls on the cell cycle and cell survival.

Nonrandom fusion of L-plastin(LCP1) and LAZ3(BCL6) genes by t(3;13)(q27;q14) chromosome translocation in two cases of B-cell non-Hodgkin lymphoma.

The LAZ3(BCL6) gene on chromosome band 3q27 is nonrandomly disrupted in B-cell non-Hodgkin lymphoma (B-NHL) by chromosomal translocations clustered within a 3.3-kb MTC (major translocation cluster) located between the two first noncoding exons. These translocations generally result in the expression of a chimeric mRNA transcript between the LAZ3 gene and sequences derived from the partner chromosome. Using RACE RT-PCR, we previously demonstrated fusion of LAZ3 with the RhoH/TTF gene, a hemopoietic cell-specific small GTPase involved in cytoskeleton organization, and with the BOB1/OBF1 gene, a B-cell-specific coactivator of octamer-binding transcription factors, following translocations t(3;4)(q27;p13) and t(3;11)(q27;q23), respectively. Here we report the identification of the L-Plastin(LCP1) gene as a novel LAZ3 partner in chimeric transcripts resulting from a t(3;13)(q27;q14) translocation, in two cases of B-cell lymphoma. As a consequence of the translocation, the 5' regulatory region of each gene was exchanged, creating both LCP1-LAZ3 and reciprocal LAZ3-LCP1 fusion transcripts in one case, and only a LCP1-LAZ3 fusion transcript in the other. The 13q14 chromosome region is frequently disrupted in various proliferative disorders, and the LCP1 gene defines a new breakpoint site in this region. This gene encodes an actin-binding protein and is the second LAZ3 partner gene, with the RhoH/TTF gene, involved in actin cytoskeleton organization. Genes Chromosomes Cancer 26:97-105, 1999.

A novel 9-base pair duplication in RET exon 8 in familial medullary thyroid carcinoma.

Familial medullary thyroid carcinoma (FMTC) and multiple endocrine neoplasia type 2A syndromes are dominantly inherited diseases caused by activating germline mutations of the RET protooncogene. The majority of these patients carry a germline point mutation affecting one of five cysteine residues encoded by exon 10 (codon 609, 611, 618, or 620) or 11 (codon 634). In a few FMTC families, point mutations involving noncysteine codons in exon 13 (codons 768, 790, and 791), 14 (codon 804), or 15 (codon 891) have been reported. Hirschsprung's disease is a nonneoplastic disorder associated with RET mutations leading to a loss of function effect. Mutations are identified in 50% of the familial cases and are scattered along the gene. We now report the study of a FMTC family with four affected members and a history of fatal neonatal intestinal obstruction in the sister of the proband. Genetic analysis demonstrated the absence of an usual FMTC mutation and the presence of a germline 9-bp duplication in RET exon 8 in the heterozygous state in all patients with MTC. This new mutation creates an additional cysteine residue in the extracellular cysteine-rich domain of RET. Further studies are warranted to confirm whether this new mutation is causing MTC only or could be associated with Hirschsprung's disease.

The LAZ3(BCL-6) oncoprotein recruits a SMRT/mSIN3A/histone deacetylase containing complex to mediate transcriptional repression.

Recent works demonstrated that some transcriptional repressors recruit histone deacetylases (HDACs) either through direct interaction, or as a member of a multisubunit repressing complex containing other components referred to as corepressors. For instance, the bHLH-Zip transcriptional repressors MAD/MXI recruit HDACs together with the mSIN3 corepressors, whereas unliganded nuclear receptors contact another corepressor, SMRT (or its relative N-CoR), which, in turn, associates with both mSIN3 and HDACs to form the repressor complex. Recently, we reported that SMRT also directly associates with LAZ3(BCL-6), a POZ/Zn finger transcriptional repressor involvedin the pathogenesis of non-Hodgkin lymphomas. However, whether LAZ3 recruits the HDACs-containing repression complex is currently unknown. We report here that LAZ3 associates with corepressor mSIN3A both in vivo and in vitro , and found that a central region, which harbours autonomous repression activity, is mainly responsible for this interaction. Conversely, the N-terminal half of mSIN3A is both necessary and sufficient to bind LAZ3. Moreover, we show that LAZ3 also interacts with an HDAC (HDAC-1) through its POZ domain in vitro while the immunoprecipitation of LAZ3 results in the coretention of an endogenous HDAC activity in vivo . Finally, inhibitors of HDACs significantly reduce the LAZ3-mediated repression. Taken together, we conclude that LAZ3 recruits a repressing complex containing SMRT, mSIN3A and a HDAC, and that its full repressing potential on transcription requires HDACs activity. Our results identify HDACs as molecular targets of LAZ3 oncogene and further strengthen the connection between aberrant chromatin acetylation and human cancers.

Translocation (3;13)(q27;q14): a nonrandom and probably secondary structural change in non-Hodgkin lymphomas.

Three cases of (3;13)(q27;q14) translocation observed in different histological types of non-Hodgkin lymphomas (NHLs) are reported here. This new recurring translocation in NHL was secondary in at least two of the patients because it was associated with another specific change [i.e., t(8;14) (q24;q32) in Burkitt lymphoma and t(14;18)(q32;q21) in typical follicular lymphoma]. In two of the cases for which molecular analysis was performed, a rearrangement of the LAZ-3/BCK-6 gene was found.

Increased expression of the LAZ3 (BCL6) proto-oncogene accompanies murine skeletal myogenesis.

The structural alterations of the LAZ3 (BCL6) gene are one of the most frequent events found in non-Hodgkin lymphoma. LAZ3 encodes a transcriptional repressor with a POZ/zinc finger structure similar to several Drosophila development regulators and to the human promyelocytic leukemia-associated PLZF gene. Consistent with the origin of LAZ3-associated malignancies, LAZ3 is expressed in mature B-cells and required for germinal center formation. However, its ubiquitous expression, with predominant levels in skeletal muscle, suggests that it may act outside the lymphoid system. To study how LAZ3 could be involved in skeletal muscle differentiation, we examined its expression in the C2 muscle cells. We report here that LAZ3 is upregulated at both mRNA and protein levels during the differentiation of proliferating C2 myoblasts into post-mitotic myotubes. This rise in LAZ3 expression is both precocious and sustained, and is not reversed when myotubes are re-exposed to mitogen-rich medium, suggesting that irreversible evens occurring upon myogenic terminal differentiation contribute to lock LAZ3 upregulation. In addition, using two different models, we found that a "simple" growth-arrest upon serum starvation is not sufficient to induce LAZ3 upregulation which rather appears as a feature of myogenic commitment and/or differentiation. Finally, BrdU incorporation assays in C2 cells entering the differentiation pathway indicate that "high" LAZ3 expression strongly correlates with their exit from the cell cycle. Taken as a whole, these findings suggest that LAZ3 could play a role in muscle differentiation. Together with some results reported in other cell types, we propose that LAZ3 may contribute to events common to various differentiation processes, possibly the induction and stabilization of the withdrawal from the cell cycle.

Corepressor SMRT binds the BTB/POZ repressing domain of the LAZ3/BCL6 oncoprotein.

The LAZ3/BCL6 (lymphoma-associated zinc finger 3/B cell lymphomas 6) gene frequently is altered in non-Hodgkin lymphomas. It encodes a sequence-specific DNA binding transcriptional repressor that contains a conserved N-terminal domain, termed BTB/POZ (bric-à-brac tramtrack broad complex/pox viruses and zinc fingers). Using a yeast two-hybrid screen, we show here that the LAZ3/BCL6 BTB/POZ domain interacts with the SMRT (silencing mediator of retinoid and thyroid receptor) protein. SMRT originally was identified as a corepressor of unliganded retinoic acid and thyroid receptors and forms a repressive complex with a mammalian homolog of the yeast transcriptional repressor SIN3 and the HDAC-1 histone deacetylase. Protein binding assays demonstrate that the LAZ3/BCL6 BTB/POZ domain directly interacts with SMRT in vitro. Furthermore, DNA-bound LAZ3/BCL6 recruits SMRT in vivo, and both overexpressed proteins completely colocalize in nuclear dots. Finally, overexpression of SMRT enhances the LAZ3/BCL6-mediated repression. These results define SMRT as a corepressor of LAZ3/BCL6 and suggest that LAZ3/BCL6 and nuclear hormone receptors repress transcription through shared mechanisms involving SMRT recruitment and histone deacetylation.

Genomic structure and assignment of the RhoH/TTF small GTPase gene (ARHH) to 4p13 by in situ hybridization.

The RhoH/TTF (ARHH) gene encodes a new member of the Ras superfamily of small GTPases. The gene was identified by fusion to the BCL6/LAZ3 oncogene in an initially described t(3;4)(q27;p11) translocation in a non-Hodgkin's lymphoma cell line. The predicted amino acid sequence of the RhoH/TTF gene product includes Rho-like GTPase structural motifs. The RhoH/TTF gene is restrictively expressed in hematopoietic cells and tissues. Mutations in the human RAS genes have been shown previously to be tumorigenic; in the search for a potential implication of the RhoH/TTF gene in hemopoietic malignancies, we established its genomic structure. The RhoH/TTF gene spans 35 kb and contains two exons, with the second bearing the entire amino-acid-coding region. Chromosomal mapping, by FISH experiments, places the RhoH/TTF gene on the short arm of chromosome 4, band p13.

Small deletions occur in highly conserved regions of the LAZ3/BCL6 major translocation cluster in one case of non-Hodgkin's lymphoma without 3q27 translocation.

The LAZ3/BCL6 gene encoding a Zinc-finger nuclear protein is altered in Non-Hodgkin's Lymphomas (NHLs) by translocations, mutations and/or deletions clustered in its 5' non coding region, in a 3.3 Kbp EcoRI fragment which thus defines the Major Translocation Cluster (MTC). In the present study, we describe at the molecular level the deletions found in the MTC of two (NHL) cases using, (i) DNA obtained from a patient (GUI) with a monosomy 3 and three microdeletions of 101, 22, 25 bp in its unique untranslocated 3q27 allele; (ii) a cell line derived from a patient (VAL) carrying a t(3;4) (q27;p11) translocation and a 2.4 Kbp deletion in the untranslocated allele. As the MTC is recurrently subject to alterations, we have cloned and sequenced the murine equivalent of the human MTC and promoter region in an attempt to identify sequences well conserved in mammals that may be thus important for the LAZ3/BCL6 gene regulation. We show that the human and mouse 5' upstream regions of the LAZ3/BCL6 gene although mainly intronic share a particularly high homology of 79% on the overall sequence. Strikingly, the small sequences which are deleted in patient (GUI) are highly conserved (81%, 100% and 92% respectively). Furthermore, they may play a role in the pathogenesis since proteins prepared from B cell lines and HeLa nuclear extracts bind to these sequences in gel retardation assays. Although a large part of this region is intronic, the high conservation of its sequence and the frequency of alterations in NHLs suggest that they are likely to be significant for the regulation of the LAZ3/BCL6 gene.

Heterogeneity of breakpoints at the transcriptional co-activator gene, BOB-1, in lymphoproliferative disease.

Chromosome 11q23 is frequently a site of chromosomal translocation in both acute leukemias and chronic lymphoproliferative disorders. In the former, an 8 kb region within the MLL gene is consistently involved, whereas in the latter breakpoints appear to be heterogeneous. In a B cell acute leukemia cell line with t(14;18)(q32.3;q21.3) we have previously demonstrated a reciprocal translocation between the LAZ3/BCL6 gene at 3q27 and the B cell specific transcriptional coactivator gene BOB-1 at 11q23.1, implicating BOB-1 as a potential proto-oncogene. To confirm the chromosomal localization of BOB-1 we have mapped it by FISH to 11q23.1. It lay immediately telomeric of the ATM gene. We have also investigated the frequency of BOB-1 rearrangements in a panel of 32 cell lines and 71 patient samples. In one case of T cell prolymphocytic leukemia-a disease where 11q23 abnormalities are observed-a chromosomal rearrangement was identified 3.3-0.9 kb centromeric of the 3' end of the gene. Thus, there is a heterogeneity of breakpoints associated with BOB-1 while the frequency of the gene's involvement in lymphoproliferative diseases is low.