The status of CDKN2A alpha (p16INK4A) and beta (p14ARF) transcripts in thyroid tumour progression

CDKN2A locus on chromosome 9p21 encodes two tumour suppressor proteins pl6^INK4A, which is a regulator of the retinoblastoma (RB) protein, and p14^ARF, which is involved in the ARF–Mdm2–p53 pathway. The aim of this study was to determine if CDKN2A gene products are implicated in differentiated thyroid carcinogenesis and progression. We used real-time quantitative RT–PCR and immunohistochemistry to assess both transcripts and proteins levels in 60 tumours specimens. Overexpression of p14^ARF and pl6^INK4A was observed in follicular adenomas, follicular carcinomas and papillary carcinomas, while downregulation was found in oncocytic adenomas compared to nontumoral paired thyroid tissues. These deregulations were statistically significant for pl6^INK4a (P=0.006) in follicular adenomas and close to statistical significance for p14^ARF in follicular adenomas (P=0.06) and in papillary carcinomas (P=0.05). In all histological types, except papillary carcinomas, we observed a statistically significant relationship between p14^ARF and E2F1 (r=0.64 to 1, P<0.05). Our data are consistent with involvement of CDKN2A transcript upregulation in thyroid follicular tumorigenesis as an early event. However, these deregulations do not appear to be correlated to the clinical outcome and they could not be used as potential prognostic markers.

Expression of TAp73 and DeltaNp73 isoform transcripts in thyroid tumours

AIM

This study was aimed to determine p73 status in thyroid tumours.

METHODS

Differential expression of the TAp73, DeltaTAp73 transcripts was measured in a panel of 60 thyroid malignancies by quantitative RT-PCR.

RESULTS

By comparison to normal thyroid tissue surrounding the tumours, we observed significant downregulation of TP73 transcripts in adenomas and in differentiated carcinomas. Correlations were found in normal tissue specimens between the expression of TAp73 and DeltaNp73 transcripts and that of p53, p14ARF p16INK4a, but these correlations were lost in carcinomas (PTC or FTC).

CONCLUSIONS

We have found significant variations of TAp73, DeltaNp73, p53, p14ARF p16INK4a, expressions and correlations between the expressions of those different genes in thyroid cancer.

Correlation of clinical features and methylation status of MGMT gene promoter in glioblastomas

In an effort to extend the potential relationship between the methylation status of MGMT promoter and response to CENU therapy, we examined the methylation status of MGMT promoter in 44 patients with glioblastomas. Tumor specimens were obtained during surgery before adjuvant treatment, frozen and stored at -80 degrees C until for DNA extraction process. DNA methylation patterns in the CpG island of the MGMT gene were determined in every tumor by methylation specific PCR (MSP). These results were then related to overall survival and response to alkylating agents using statistical analysis. Methylation of the MGMT promoter was detected in 68% of tumors, and 96.7% of methylated tumors exhibited also an unmethylated status. There was no relationship between the methylation status of the MGMT promoter and overall survival and response to alkylating agents. Our observations do not lead us to consider promoter methylation of MGMT gene as a prognostic factor of responsiveness to alkylating agents in glioblastomas.

Topoisomerase II alpha and telomerase expression in papillary thyroid carcinomas

BACKGROUND

Altered topoisomerase II alpha (Topo II alpha) expression and telomerase activity (TA) reflect tumour cell growth and malignant transformation.

METHODS

We examined TA by using a TRAP assay and expression of Topo II alpha by immunohistochemical analysis in a series of 27 cases of papillary thyroid carcinoma (PTC).

RESULTS

Topo II alpha labelling index (LI) ranged from 0.1 to 4.2% and was significantly associated with patient age (r=-0.42, p=0.003), with higher levels of Topo II alpha in patients under 40 years. There was no relationship between Topo II alpha LI, AGES score or other clinical outcome. TA was detected in 14 PTC, with relative levels ranging from 1.2 to 102 units. A significant positive correlation between the multiplicity of tumoral foci and the TA levels (p<10(-2)) was noted.

CONCLUSION

We concluded that Topo II alpha cannot be used as a marker of tumour aggressiveness. Furthermore, enhanced Topo II alpha expression in PTCs from patients less than 40 years old suggests that this age group might benefit from Topo II inhibitor chemotherapy.

[Clearing up the p16INK4a-p14/p19ARF imbroglio?]

Since its discovery, the CDKN2/MTS1 locus has been considered as an important site for the understanding of cell cycle deregulations that are involved in cancer cell generation. A comprehensive approach of the respective roles played by the two p16INK4a and p14/p19ARF (ARF) proteins encoded by this locus was not yet achieved because of the structural intrication of their genes. Inactivation of the only p16INK4a gene in mouse allowed to get better insight into this puzzle. In vivo results presented by de Pinho's group showed that inactivation of both p16INK4a alleles generated a panel of various types of tumors from the 28th week following birth. Bern's group dit not confirm this result but showed that the presence of only one ARF functional copy increases sensitivity of p16-/- mice to tumor occurrence indicating that insufficient dosage of ARF protein may facilitate tumorigenesis. It seems now established that, at least in mouse, ARF controls senescence in vitro, immortalisation and transformation by oncogenic ras. p16INK4a inactivation appears to be crucial for the induction of carcinogens-induced tumors.

Human LPP gene is fused to MLL in a secondary acute leukemia with a t(3;11) (q28;q23)

The mixed lineage leukemia, MLL, gene is frequently rearranged in patients with secondary leukemia following treatment with DNA topoisomerase II inhibitors. By FISH and Southern blot analyses we identified a rearrangement in the MLL gene due to a novel t(3;11)(q28;q23) chromosomal translocation in a patient who developed AML-M5 3 years after treatment for a follicular lymphoma. Through inverse PCR, the LPP (lipoma preferred partner) gene on 3q28 was identified as the MLL fusion partner. LPP contains substantial identity to the focal adhesion protein, zyxin, and is frequently fused to HMGIC in lipomas. The breakpoint occurred in intron 8 of MLL and LPP. Two in-frame MLL-LPP transcripts, which fuse MLL exon 8 to LPP exon 9, were detected by RT-PCR, although the smaller of these contained a deletion of 120 bp from the MLL sequence. The predicted MLL-LPP fusion protein includes the A/T hook motifs and methyltransferase domain of MLL joined to the two last LIM domains of LPP. A reciprocal LPP-MLL transcript, predicted to include the proline-rich and leucine zipper motifs, and the first LIM domain of LPP were also detected by RT-PCR. In summary, LPP is a newly identified MLL fusion partner in secondary leukemia resulting from topoisomerase inhibitors. The MLL-LPP and LPP-MLL predicted proteins contain many of the features present in other MLL rearrangements.

Human ARF binds E2F1 and inhibits its transcriptional activity

The INK4a/ARF locus which is frequently inactivated in human tumours encodes two different tumour suppressive proteins, p16(INK4a) and ARF. p16(INK4a) is a major component of the RB pathway. ARF is part of an ARF-mdm2-p53 network that exerts a negative control on hyperproliferative signals emanating from oncogenic stimuli. Among these is the transcription factor E2F1, a final effector of the RB pathway, that induces ARF expression. Recent data suggest that ARF function is not restricted to the p53 pathway. However, ARF target(s) implicated in this p53-independent function remains to be identified. We show that ARF is able to inhibit the proliferation of human cell lines independently of their p53 status. In this context, we demonstrate that ARF interacts physically with E2F1 and inhibits its transcriptional activity. Moreover, we show that mdm2 is required for the modulation of E2F1 activity by ARF. Beside the well-known p53 and mdm2 partners, these results identify E2F1 as a new ARF target. Thus, ARF can be viewed as a dual-acting tumour suppressor protein in both the p53 and RB pathways, further emphasizing its role in tumour surveillance.

Human ARF protein interacts with topoisomerase I and stimulates its activity

The ARF gene (p19(ARF) in mouse and p14(ARF) in man) has become a central actor of the cell cycle regulation process as it participates to the ARF-MDM2-p53 pathway and the Rb-E2F-1 pathway. By use of immunoprecipitation and Western blotting (IP/WB), we now show that ARF physically associates with topoisomerase I (Topo I). ARF-Topo I immune complexes were detected in SF9 insect cells infected with recombinant baculoviruses encoding the two genes as well as in 293 cells that express endogenously these proteins. Preparations of a GST-ARF recombinant protein stimulated the DNA relaxation activity of Topo I but, in contrast, had no effect on the decatenation activity of Topo II. The Topo I stimulation was also detected in cell extracts of SF9 cells expressing both proteins. A confocal microscopy study indicated that part of ARF and Topo I colocalized in the granular component structure of the nucleolus. As a whole, our data indicate that Topo I is a new partner of ARF and suggest that ARF is involved in cell reactions that require Topo I.

Different combinations of genetic/epigenetic alterations inactivate the p53 and pRb pathways in invasive human bladder cancers

Inactivation of both the pRb (pRb-cyclin D1/cyclin-dependent kinase 4/6-p16) and p53 (p53-p21(WAF1)-p14(ARF)) pathways is thought to be essential for immortalization in vitro and malignant transformation in vivo. We identified different combinations of pRb and p53 pathway alterations in 12 invasive transitional cell carcinomas (TCCs) and addressed the functional significance of the different combinations observed. Results showed four combinations of alterations including -pRb/-p53 (ie., pRb inactivated in the pRb pathway and p53 inactivated in the p53 pathway; four TCCs), -p16/-p53 (four TCCs), -p16/-p21(WAF1) (one TCC), and -p16/ -p14(ARF) (two TCCs). These groups include two new combinations (ie., -p16/-p53 and -p16/-p21(WAF1)) not reported previously for TCCs. An alteration in the key components of the p53 pathway was not detected in one invasive TCC that had inactivated p16. Note that all four TCCs with inactivated pRb had mutant p53; thus, the combinations of -pRb/ -p21(WAF1) and -pRb/-p14(ARF) were not observed. Only two of eight TCCs with altered p16 had concomitant p14(ARF) loss, demonstrating that simultaneous inactivation of these two 9p21INK4a tumor suppressor genes is not obligatory. To determine the biological phenotypes of TCCs with different combinations of pRb and p53 pathway alterations, their downstream responses to gamma radiation were studied in vitro. As expected, none of eight TCCs with mutant p53 responded to gamma radiation by elevation of p53, p21(WAF1), or mdm2 or by cell cycle arrest. Only two of four TCCs with wild-type p53 and wild-type pRb (the combination of -p16/-p14(ARF)) showed normal downstream responses to gamma radiation and underwent cell cycle arrest. Two TCCs with wild-type pRb and wild-type p53 (the combination of -pl6/-p21(WAF1) and one TCC with -p16) failed to show cell cycle arrest in response to radiation. This was attributed to the absence of p21(WAF1) in one TCC. In summary, these data support a model of invasive bladder cancer pathogenesis in which both the pRb and p53 pathways are usually inactivated and the biology of the tumor is impacted by the mechanism of their inactivations.

[The ARF-p53 pathway: a line of defence against oncogenic signals]

The MTS1 (Multiple Tumor Suppressor 1) locus is a very original one as its organization results in the expression of two alternative transcripts that encode two structurally and functionally different proteins: INK4a and ARF (also designated p19ARF in mouse and p14ARF in man). Recent findings indicate that the latter is a major component of a regulatory pathway of oncogenic signals culminating in p53 activation by stabilisation of the protein. While the importance of this pathway has been overtly established in animal experimental oncology, it still has to be further documented in human oncology in order for this gene to acquire its full biological significance.

The human p19ARF protein encoded by the beta transcript of the p16INK4a gene is frequently lost in small cell lung cancer

The p16IN4/CDKN2/MTS1 gene encodes two structurally different proteins: a cyclin-dependent kinase inhibitor called p16INK4a, which regulates retinoblastoma protein-dependent G1 arrest, and a cell cycle inhibitor designated p19ARF, which arrests cell growth in G1-S and also in G2-M. Whereas inactivation of p16INK4a has been described as a frequent event in lung cancer, the current function of p19ARF is still poorly understood. We have examined the expression of the human p19ARF (hp19ARF) protein in a large series of lung cancers using immunohistochemistry and showed that the protein was more frequently lost in high-grade neuroendocrine (NE) lung tumors (large cell NE carcinoma and small cell lung carcinoma; 51 of 78, 65%) than it was in non-small cell lung cancer (25 of 101, 25%). No deleterious mutation was found in exons 1beta and 2 of hp19ARF in those NE tumors with negative immunoreactivity, and a beta transcript was detected in the majority of them. Concomitant absence of hp19ARF and retinoblastoma proteins was frequently detected in high-grade NE lung tumors, whereas no relationship could be found between the status of hp19ARF and p53 proteins in those tumors. These results are consistent with an alternative growth suppressor function for hp19ARF in NE lung cancer that is distinct from that of p16INK4a. Moreover, the frequent uncoupling between the beta transcript and the hp19ARF protein suggests a novel mechanism of inactivation at the translational level.

[When p19ARF finds a partner or new "dangerous liaisons"]

In man, the MTS1 (multiple tumor suppressor 1) locus has been located on chromosome band 9p21 and encodes two unrelated genes, p16INK4a and p19ARF that both act, through different mechanisms, as cell proliferation inhibitors. The inhibitory mechanism of p19ARF has begun to be elucidated by the finding that the protein has the ability to bind the mdm2 oncoprotein. mdm2 is implicated in the degradation of p53 and its functional inactivation. While this result provides an opportunity for understanding the tumor suppression role of p19ARF, it allows to define a new cell cycle regulatory pathway, the p19ARF-p53 pathway. In this respect, MTS1 is unique in its ability to control two crucial pathways that regulate the cell cycle. For this reason, it will be crucial to investigate the status of p19ARF in a variety human tumors.

Contribution of the dual coding capacity of the p16INK4a/MTS1/CDKN2 locus to human malignancies

During the three last years, the so-called p16 locus on human chromosome band 9p21 has been increasingly implicated in different cancers by a variety of alterations abolishing both copies of the p16INK4a/MTS1/CDKN2 gene and the adjacent p15INK4b gene, two members of a family of specific inhibitors of the cyclin D 1-3-CDK4/6 complexes that control cell cycle progression of the G1 to S phase. While these properties are characteristic of tumor suppressor genes, abundant experimental data have clearly identified a link between the loss of function of p16INK4a and tumorigenic processes. The role of p15INK4b alterations in the onset of natural and experimental tumors is less obvious. New light may be shed on the role of the p16 locus in tumor development by the recent finding that an alternative transcript from the p16INK4a gene encodes p19ARF, a negative regulator of cell cycle progression which is unrelated to p16 and p15 and does not act by binding any CDK. Hence, this protein appears to be an element of a novel negative cell cycle control mechanism, whose impairing might be involved in tumorigenesis.

[Alternative protein p19ARF: a genuine tumor suppressor gene]

The p16INK4a gene located in the MTS1 (multiple tumor suppressor 1) locus encodes two proteins, p16INK4a and p19ARF, which are structurally unrelated but functionally similar as both inhibit cell cycle progression. In this review, we report and comment new data obtained from mice knockouted for p19ARF without interfering with the expression of p16INK4a. This results in the rapid occurrence of a spectrum of tumors. These data establish that p19ARF is a genuine tumor suppressor protein and raise the questions of the relationship between the two proteins and their respective importance in malignancies.

The human protein p19ARF is not detected in hemopoietic human cell lines that abundantly express the alternative beta transcript of the p16INK4a/MTS1 gene

The p16/MTS1/CDKN2 gene on human chromosome band 9p21 encodes two unrelated proteins: p16INK4a, a specific inhibitor of the cyclin D-dependent kinases CKD4 and CDK6, and the structurally unrelated p19ARF protein that arrests cell growth in G1/S and also in G2/M. By use of polyclonal antibodies, the human p19ARF (hp19ARF) protein has been identified in the nucleus of various cells including normal cultured fibroblasts. The level of this protein did not fluctuate throughout the cell cycle and was more elevated in fibroblasts with limited or arrested growth, suggesting that p19ARF accumulated in presenescent or senescent cells. Interestingly, hp19ARF was not detected in several hemopoietic tumor cell lines (mainly of B-type lymphoid origin) that expressed abundant amounts of the p16beta transcript. This finding indicates that in certain tumors, the expression of hp19ARF RNA and protein may be uncoupled. Furthermore, it suggests that disruption of a translational mechanism may be involved in the inactivation of hp19ARF.

FISH analysis of translocations involving the short arm of chromosome 9 in lymphoid malignancies

Deletion of the short arm of chromosome 9 (9p), resulting in the loss of the p16INK4a/MTS1 gene, now called CDKN2, has been found to occur frequently in acute lymphoblastic leukemia, even in the absence of a microscopically visible deletion. In this study, we have used YAC probes encompassing the CDKN2 locus to analyze by fluorescence in situ hybridization patients with leukemia and lymphoma and translocations involving 9p in order to establish the CDKN2 status in relation to the karyotype. We found that, in leukemic cells exhibiting loss of heterozygosity at the CDKN2 locus, the deleted allele was from the cytogenetically normal chromosome 9, whereas the other allele was located on a rearranged chromosome. This finding suggests that CDKN2 gene loss is nonrandomly associated with 9p translocation in lymphoid proliferations. Genes Chromosom.

[Tribulations of the p16/MTS1/CDKN2 tumor gene suppressor: a continuing saga]

Since its recent discovery on chromosome 9p21 band, the p16INK4a/MTS1/CDKN2 gene has been reported as one of the most frequently impaired tumor suppressor genes (ranking second after p53) in a variety of malignancies, including acute lymphoblastic leukemias. In fact, the situation is likely to be more complex than expected: the gene has a very unusual status in that sense that it encodes two structurally unrelated but functionally similar proteins, p16INK4a and p19ARF. In this minireview, the present status of the gene is examined.

The I protein of the heterogeneous nuclear ribonucleoprotein complex is a novel dog nuclear autoantigen

In eukaryotic cells, heterogeneous nuclear RNA is associated with a set of abundant nuclear proteins to form complex ribonucleoprotein structures (hnRNP). Autoantibodies to hnRNP G protein have been previously reported in German shepherd dogs with lupus-like syndrome. In the present study, we describe the characterization of a novel antigen recognized by a serum from a schnauzer dog with a non-erosive polyarthritis. The autoantibodies give, by indirect immunofluorescence, a nuclear pattern with staining close to one of the nucleoli. Immunoblotting and immunoprecipitation data reveal that the autoantigens are in fact two closely related basic proteins (average pI 8.7) with apparent molecular weights of 56 kDa (p56) and 59 kDa (p59). The results of immunoprecipitation with anti-hnRNP antibodies and DNA affinity column chromatography strongly suggest that these autoantigens correspond to hnRNP I proteins. This point was confirmed by cloning and sequencing a cDNA clone encoding the complete sequence of the antigens. In addition, we found that anti-hnRNP I antibodies preferentially stain certain loops of the Pleurodeles waltl lampbruch chromosomes. These data, added to previous ones on anti-p43/hnRNP G protein in German shepherd dogs with lupus-like syndrome, confirm the interest of this category of antibodies to hnRNP proteins in autoimmune disorders.

Dual localization of the human gene encoding hnRNP I/PTB protein to chromosomes 19p13.3 and 14q23

A cDNA probe representative of the human hnRNP I/PTB gene was used to perform fluorescence in situ hybridization (FISH) on metaphases of human chromosomes. A new localization was found on band 19p13.3 in addition to the previously reported localization to band 14q23. Identical results were obtained when FISH analysis was repeated with probes covering different parts of the hnRNP I cDNA clone. This supported the notion that most, if not all, of the sequences of the different parts of this clone are present on both chromosomes. Moreover, Southern blot analysis of DNAs from interspecies somatic hybrids containing chromosomes 19 and 14 revealed that the whole hnRNP I cDNA probe generated very similar patterns in each hybrid DNA. These data suggest that two closely related copies of the hnRNP I gene exist in the human genome.

Inactivation of the P16INK4/MTS1 gene by a chromosome translocation t(9;14)(p21-22;q11) in an acute lymphoblastic leukemia of B-cell type

We have reported previously a preliminary study of a t(9;14)(p21-22; q11) in B-cell acute lymphoblastic leukemia. This translocation had rearranged the TCRA/D locus on chromosome band 14q11 and the locus encoding the tumor suppressor gene P16INK4/MTS1 (P16) on band 9p21 (D. Duro et al., Oncogene, 11: 21-29, 1995). In the present report, the breakpoints were precisely localized on each chromosome partner. On the 14q- derivative, the sequence derived from chromosome 9 was interrupted at 1.0 kb upstream of the first exon of P16, close to a consensus recombination heptamer, CACTGTG. In addition, the chromosome 14 breakpoint was localized at the end of the TCRD2 (delta 2) segment, and 22 residues with unknown origin were present at the translocation junction. On the 9p+ derivative, chromosome 9 sequences were in continuity with those displaced onto chromosome 14, and the 14q11 breakpoint was located within TCRJA29 segment. These features are consistent with aberrant activity of the TCR gene recombinase complex. Although all three coding exons of P16 were displaced onto the chromosome 14q-derivative, no P16 transcript was detected in the leukemic cells. Because the region spanning the P16 exon 1 was not inactivated by methylation and because the other P16 allele was deleted, the implication is that the chromosome breakpoint was likely to disrupt regulatory elements involved in the normal expression of the gene. As a whole, then, our results show that translocations affecting band 9p21 can participate to the inactivation of P16, thus justifying a systematic survey of translocations of the 9p21 band in acute lymphoblastic leukemia.

Presence of three recurrent chromosomal reaarrangements, t(2;3)(p12;q37), del(8)(q24), and t(14;18), in an acute lymphoblastic leukemia

A complex chromosomal abnormality associating three recurrent rearrangements, t(2;3)((p12;q37), del (8)(q24) and t(14;18)(q32;q21), was detected in a patient with acute lymphoblastic leukemia of the Burkitt type. Southern blot studies showed rearrangements of the MYC, BCL2, and JH genes, thus confirming the cytogenetic data. However, no rearrangement of the LAZ3/BCL6 gene, normally localized on band 3q27, could be detected. The simultaneous presence of three recurrent rearrangements specific for lymphoid malignancies addresses the question of their timing in the malignant process and the prognostic significance of the association of such anomalies.

A new type of p16INK4/MTS1 gene transcript expressed in B-cell malignancies

Chromosome band 9p21-22 is frequently altered by nonrandom abnormalities, mainly deletions, in hemopoietic malignancies of the lymphoid lineage. We have analysed a translocation t(9;14)(p21-p22;q11) in a B-cell type acute lymphoblastic leukemia. Location of the 14q11 breakpoint within the TCR-alpha/delta locus allowed the isolation of a fusion transcript composed of a 3' segment containing part of the constant region of the TCR-alpha gene and a 5' segment from chromosome 9, designated 0.18. This 0.18 segment was also part of cDNAs isolated from two tumoral B-cell lines (RPMI-8226, Raji). In both cases, 0.18 was juxtaposed 5' to a sequence corresponding to exons 2 and 3 of the p16INK4/MTS1 gene which is located on band 9p21-22. Unexpectedly, none of the two ATG codons found in 0.18 was in phase with that of the exons 2 and 3 of p16INK4/MTS1. Furthermore, in vitro translation product of a RPMI-8226 cDNA clone generated a product that was not immunoprecipitated by antibodies specific of the C-terminal end of the p16INK4/MTS1 protein. Evidence for similar transcripts in non tumoral lymphoid B cells (unstimulated peripheral blood lymphocytes (PBL) and lymphoblastoid cell lines) were obtained by using amplimers representative of the 0.18 segment and the p16INK4/MTS1 exon 2. Altogether, these data are consistent with the existence of a new type of p16INK4/MTS1 transcript whose significance is discussed.

Distinct MLL gene rearrangements associated with successive acute monocytic and lymphoblastic leukemias in the same patient

A patient with acute monocytic leukemia (AMoL) and t(6;11)(q27;q23) developed acute lymphoblastic leukemia (ALL) and t(4;11)(q21;23), 10 months after complete remission of the AMoL. The MLL gene, normally located at band 11q23, appeared differently rearranged in the cells of these two leukemias, showing a different origin for the two malignant clones. The responsibility of etoposide, used in treatment of the AML, in the occurrence of the ALL is probable in this patient.

Alterations of the putative tumor suppressor gene p16/MTS1 in human hematological malignancies

The chromosome band 9p21-22 is frequently rearranged or deleted in a variety of tumors including hematological malignancies. This supports the notion of a tumor suppressor gene in this chromosome region. Indeed, the p16/MTS1 gene encoding a cyclin-dependent kinase (CDK) inhibitor has been shown to be frequently deleted and/or inactivated by nonsense mutations in a number of tumors. We have examined 98 DNA samples from blood, bone marrow cells and lymph node biopsies of patients with leukemia (ALL and AML) or lymphoma (follicular lymphoma and T-cell lymphoma), using Southern blot hybridization and a p16/MTS1-specific probe. Molecular abnormalities, mainly homozygous deletions, were found principally in ALL (8 out of 22 patients), much less frequently in AML (2/32) and lymphoma (2/32). While these data argue in favor of a large involvement of p16/MTS1 in ALL, AML and lymphomas appear to be less frequently implicated.

GATA-and SP1-binding sites are required for the full activity of the tissue-specific promoter of the tal-1 gene

The tal-1 gene, which is frequently activated in human T cell acute leukemias (T-ALLs), codes for a protein of the basic helix-loop-helix family (b-HLH) and potentially a transcription factor. In human and murine hematopoiesis tal-1 is expressed during the differentiation of the erythroid, megakaryocytic and mastocytic cell lineages. The expression of tal-1 appears to be comodulated with that of the transcription factor GATA-1 gene, suggesting that the GATA-1 protein may regulate the tal-1 gene activity in these hematopoietic lineages. To get further insights into the molecular mechanisms that control tal-1 expression, we have isolated 5' sequences of the murine gene and compared them to their human counterparts. The 5' flanking sequences from the two genes show several regions of high homology. The alignment of both sequences enabled us to predict that similarly, to the human, the mouse gene contains two alternative first exons (Ia and Ib). Remarkably, in both species, the proximal region of the tissue-specific exon Ia (i.e. gene segment -122 to +1) contains two GATA-motifs (at -65 and -33) and one SP-1 consensus binding site (-59). Mobility shift assays demonstrate that GATA proteins are able to interact with both GATA-motifs in a sequence specific fashion, but with different efficiencies. Moreover transfection studies show that the GATA-1 protein directly mediates tal-1 transcription by interacting with the -122/+1 fragment, defined as a minimal promoter in erythroid cells. Mutagenesis of the promoter establishes that the -33 GATA-binding site present in this fragment is critical for tal-1 expression in erythroid cells, but by itself does not lead to full promoter activity. Indeed, further mutations show that the second -65 GATA-binding site and the binding motif for SP1 (-59) significantly contribute to the overall activity of the proximal tal-1 promoter. Altogether, our data provide evidence that GATA-1 cooperates with the transcription factor SP1 to mediate the erythroid-specific expression of the tal-1 gene.

The BCMA gene, preferentially expressed during B lymphoid maturation, is bidirectionally transcribed

In a previous study of a t(4;16)(q26;p13) translocation, found in a human malignant T-cell lymphoma the BCMA gene, located on chromosome band 16p13.1, has been characterized. In this study we show that the BCMA gene is organized into three exons and its major initiation transcription site is located 69 nucleotides downstream of a TATA box. RNase protection assays demonstrated that the BCMA gene is preferentially expressed in mature B cells, suggesting a role for this gene in the B-cell developmental process. A cDNA complementary to the BCMA cDNA was cloned and sequenced and its presence was assessed by RNase protection assay and anchor-PCR amplification. This antisense-BCMA RNA is transcribed from the same locus as BCMA, and exhibits mRNA characteristic features, e.g. polyadenylation and splicing. It also contains an ORF encoding a putative 115 aa polypeptide, presenting no homology with already known sequences. RNase protection assays demonstrated the simultaneous expression of natural sense and antisense-BCMA transcripts in the majority of human B-cell lines tested.