The MN1-TEL fusion protein, encoded by the translocation (12;22)(p13;q11) in myeloid leukemia, is a transcription factor with transforming activity

The Tel gene (or ETV6) is the target of the translocation (12;22)(p13;q11) in myeloid leukemia. TEL is a member of the ETS family of transcription factors and contains the pointed protein interaction (PNT) domain and an ETS DNA binding domain (DBD). By contrast to other chimeric proteins that contain TEL's PNT domain, such as TEL-platelet-derived growth factor beta receptor in t(5;12)(q33;p13), MN1-TEL contains the DBD of TEL. The N-terminal MN1 moiety is rich in proline residues and contains two polyglutamine stretches, suggesting that MN1-TEL may act as a deregulated transcription factor. We now show that MN1-TEL type I, unlike TEL and MN1, transforms NIH 3T3 cells. The transforming potential depends on both N-terminal MN1 sequences and a functional TEL DBD. Furthermore, we demonstrate that MN1 has transcription activity and that MN1-TEL acts as a chimeric transcription factor on the Moloney sarcoma virus long terminal repeat and a synthetic promoter containing TEL binding sites. The transactivating capacity of MN1-TEL depended on both the DBD of TEL and sequences in MN1. MN1-TEL contributes to leukemogenesis by a mechanism distinct from that of other chimeric proteins containing TEL.

The human homologue of yeast CRM1 is in a dynamic subcomplex with CAN/Nup214 and a novel nuclear pore component Nup88

The oncogenic nucleoporin CAN/Nup214 is essential in vertebrate cells. Its depletion results in defective nuclear protein import, inhibition of messenger RNA export and cell cycle arrest. We recently found that CAN associates with proteins of 88 and 112 kDa, which we have now cloned and characterized. The 88 kDa protein is a novel nuclear pore complex (NPC) component, which we have named Nup88. Depletion of CAN from the NPC results in concomitant loss of Nup88, indicating that the localization of Nup88 to the NPC is dependent on CAN binding. The 112 kDa protein is the human homologue of yeast CRM1, a protein known to be required for maintenance of correct chromosome structure. This human CRM1 (hCRM1) localized to the NPC as well as to the nucleoplasm. Nuclear overexpression of the FG-repeat region of CAN, containing its hCRM1-interaction domain, resulted in depletion of hCRM1 from the NPC. In CAN-/- mouse embryos lacking CAN, hCRM1 remained in the nuclear envelope, suggesting that this protein can also bind to other repeat-containing nucleoporins. Lastly, hCRM1 shares a domain of significant homology with importin-beta, a cytoplasmic transport factor that interacts with nucleoporin repeat regions. We propose that hCRM1 is a soluble nuclear transport factor that interacts with the NPC.

Interaction of cellular proteins with the leukemia specific fusion proteins DEK-CAN and SET-CAN and their normal counterpart, the nucleoporin CAN

The recurrent chromosomal translocation (6;9) is associated with acute myeloid leukemia and results in expression of the DEK-CAN fusion protein. This oncoprotein consists of almost the entire DEK protein fused to the C-terminal two-thirds of the CAN protein. In much the same way, CAN is fused to SET in a patient with acute undifferentiated leukemia, producing a SET-CAN fusion protein. Interestingly, CAN is associated with the nuclear pore complex (NPC) and we recently established its crucial role in nucleocytoplasmic transport processes and cell cycle progression. As a first step in the biochemical analysis of the oncogenic mechanism associated with translocation (6;9), we set out to identify proteins that interact with CAN and its fusion proteins. We found that two proteins specifically co-immunoprecipitate with CAN. One had a molecular mass of 88 kDa protein (CC88) and was determined to associate with the central region of CAN that contains several protein interaction motifs. A second protein of 112 kDa (CC112) was found to interact with the C-terminal nucleoporin-specific repeat of CAN, a region that is supposed to function in nucleocytoplasmic transport. CC112 also interacts with the DEK-CAN and SET-CAN fusion proteins. This finding suggests that CC112 may contribute an essential function to the leukemogenic effect of DEK-CAN and SET-CAN.

Relocation of the carboxyterminal part of CAN from the nuclear envelope to the nucleus as a result of leukemia-specific chromosome rearrangements

Fusion genes encoding the 3' part of the can gene are implicated in two types of leukemia. The dek-can fusion gene is present in t(6;9) acute myeloid leukemia and the set-can fusion gene is present in one case of acute undifferentiated leukemia. In order to obtain leads towards the molecular basis of these diseases, we have studied the cellular localization of the DEK-CAN and SET-CAN fusion proteins and their normal counterparts. DEK-CAN and SET-CAN were localized exclusively in the nucleus, and also DEK and SET were found to be nuclear proteins. However, CAN was mainly located at the nuclear and cytoplasmic face of the nuclear envelope. This observation is in accordance with the presence of an amino acid repeat in the C-terminal part of CAN, common to the family of nucleoporins. The C-terminal part also contains a nuclear location domain as shown by deletion analysis. This domain may be important for the presence of CAN at the nucleoplasmic side of the nuclear envelope. The relocation of the carboxyterminal part of CAN due to DEK-CAN and SET-CAN may reinforce a nuclear function of the CAN protein.

Translocation (12;22) (p13;q11) in myeloproliferative disorders results in fusion of the ETS-like TEL gene on 12p13 to the MN1 gene on 22q11

In myeloid and lymphoid leukemias recurrent chromosomal aberrations can be detected in chromosome region 12p13. We characterized the genes involved in t(12;22) (p13;q11) in two patients with myeloid leukemia and one with myelodysplastic syndrome (MDS). MN1, a gene on chromosome 22q11 was shown to be fused to TEL, a member of the family of ETS transcription factors on chromosome 12p13. The translocation results in transcription of the reciprocal fusion mRNAs, MN1-TEL and TEL-MN1, of which MN1-TEL is likely to encode an aberrant transcription factor containing the ETS DNA-binding domain of TEL. In addition to fusion of TEL to the PDGF beta receptor in t(5;12) in chronic myelomonocytic leukemia (CMML), our data suggest that the involvement of this protein in myeloid leukemogenesis could be dual; its isolated protein-protein dimerization and DNA-binding domains may be crucial for the oncogenic activation of functionally different fusion proteins.

Translocation t(6;9) in acute non-lymphocytic leukaemia results in the formation of a DEK-CAN fusion gene

The t(6;9) that characterizes a specific subtype of ANLL fuses the 3' part of a gene located on chromosome 9q34, CAN, to the 5' part of a gene located on chromosome 6p23, DEK. On the 6p- chromosome, the resulting DEK-CAN fusion gene is transcribed into a leukaemia-specific 5.5 kb chimaeric mRNA that encodes a putative DEK-CAN fusion protein. No transcription could be detected from the reciprocal CAN-DEK fusion on chromosome 9q+. Analysis of 17 t(6;9) ANLL cases showed that the translocation breakpoints occur in a single intron of 7.5 kb in the CAN gene (ICB9) and in a single intron of 9 kb in the DEK gene (ICB6). As a result, the presence of a t(6;9) in blood or bone marrow cells can be faithfully diagnosed by Southern blotting. Moreover, the result of the translocation is an invariable DEK-CAN transcript, which can be sensitively monitored by RNA-PCR. Surprisingly, a SET-CAN fusion gene was found in leukaemic cells from a patient with AUL. Like CAN, SET is located on chromosome 9q34, which explains the apparently normal karyotype of the leukaemic cells. The occurrence of a SET-CAN fusion gene indicates that CAN may be the relevant oncogene involved in leukaemogenesis, and that activation of CAN can be effectuated through fusion of its 3' part to either DEK or SET. As yet, the function of CAN, DEK or SET is unknown. None of the proteins shows consistent homology to any known protein sequences. However, preliminary localization data and analysis of sequence motifs suggested that DEK-CAN may have a role in transcription regulation. CAN contains several dimerization domains and a repeated motif that can function as an ancillary DNA-binding domain. DEK and SET are non-related proteins, but they share a stretch of acidic amino acids, which is also present in the fusion proteins.

Characterization of the translocation breakpoint sequences of two DEK-CAN fusion genes present in t(6;9) acute myeloid leukemia and a SET-CAN fusion gene found in a case of acute undifferentiated leukemia

The t(6;9) associated with a subtype of acute myeloid leukemia (AML) was shown to generate a fusion between the 3' part of the CAN gene on chromosome 9 and the 5' part of the DEK gene on chromosome 6. The same part of the CAN gene appeared to be involved in a case of acute undifferentiated leukemia (AUL) as well, where it was fused to the SET gene. Genomic sequences around the translocation breakpoint were determined in two t(6;9) samples and in the case of the SET-CAN fusion. Although coexpression of myeloid markers and terminal deoxynucleotidyl transferase was shown to be one of the characteristics of t(6;9) AML, no addition of random nucleotides at the translocation breakpoint could be found. In addition, the breakpoint regions did not reveal heptamer-nonamer sequences, purine-pyrimidine tracts, a chi-octamer motif, or Alu repeats. The sequence in which the translocation breakpoints occurred was enriched in A/T. Notably, the specific introns in which clustering of breakpoints occurs in DEK and CAN both contain a LINE-I element. As LINE-I elements occur with a moderate frequency in the human genome, the presence of such an element in both breakpoint regions may be more than coincidental and may play a role in the translocation process.

Can, a putative oncogene associated with myeloid leukemogenesis, may be activated by fusion of its 3' half to different genes: characterization of the set gene

The translocation (6;9)(p23;q34) in acute nonlymphocytic leukemia results in the formation of a highly consistent dek-can fusion gene. Translocation breakpoints invariably occur in single introns of dek and can, which were named icb-6 and icb-9, respectively. In a case of acute undifferentiated leukemia, a breakpoint was detected in icb-9 of can, whereas no breakpoint could be detected in dek. Genomic and cDNA cloning showed that instead of dek, a different gene was fused to can, which was named set. set encodes transcripts of 2.0 and 2.7 kb that result from the use of alternative polyadenylation sites. Both transcripts contain the open reading frame for a putative SET protein with a predicted molecular mass of 32 kDa. The set-can fusion gene is transcribed into a 5-kb transcript that contains a single open reading frame predicting a 155-kDa chimeric SET-CAN protein. The SET sequence shows homology with the yeast nucleosome assembly protein NAP-I. The only common sequence motif of SET and DEK proteins is an acidic region. SET has a long acidic tail, of which a large part is present in the predicted SET-CAN fusion protein. The set gene is located on chromosome 9q34, centromeric of c-abl. Since a dek-can fusion gene is present in t(6;9) acute myeloid leukemia and a set-can fusion gene was found in a case of acute undifferentiated leukemia, we assume that can may function as an oncogene activated by fusion of its 3' part to dek, set, or perhaps other genes.

The translocation (6;9), associated with a specific subtype of acute myeloid leukemia, results in the fusion of two genes, dek and can, and the expression of a chimeric, leukemia-specific dek-can mRNA

The translocation (6;9) is associated with a specific subtype of acute myeloid leukemia (AML). Previously, it was found that breakpoints on chromosome 9 are clustered in one of the introns of a large gene named Cain (can). cDNA probes derived from the 3' part of can detect an aberrant, leukemia-specific 5.5-kb transcript in bone marrow cells from t(6;9) AML patients. cDNA cloning of this mRNA revealed that it is a fusion of sequences encoded on chromosome 6 and 3' can. A novel gene on chromosome 6 which was named dek was isolated. In dek the t(6;9) breakpoints also occur in one intron. As a result the dek-can fusion gene, present in t(6;9) AML, encodes an invariable dek-can transcript. Sequence analysis of the dek-can cDNA showed that dek and can are merged without disruption of the original open reading frames and therefore the fusion mRNA encodes a chimeric DEK-CAN protein of 165 kDa. The predicted DEK and CAN proteins have molecular masses of 43 and 220 kDa, respectively. Sequence comparison with the EMBL data base failed to show consistent homology with any known protein sequences.

Unique fusion of bcr and c-abl genes in Philadelphia chromosome positive acute lymphoblastic leukemia

The Philadelphia (Ph) chromosome, the product of t(9:22), is the cytogenetic hallmark of chronic myelogenous leukemia. The c-abl oncogene on chromosome 9 is translocated to the Ph chromosome and linked to a breakpoint cluster region (bcr), which is part of a large bcr gene. This results in the formation of a bcr-c-abl fusion gene, which is transcribed into an 8.5 kb chimeric mRNA encoding a 210 kd bcr-c-abl fusion protein. The Ph chromosome is also found in acute lymphoblastic leukemia (Ph+ ALL). Although the c-abl is translocated and a new 190 kd c-abl protein has been identified, no breakpoints are observed in the bcr (Ph+bcr- ALL). Here we show that in Ph+bcr- ALL, breakpoints in chromosome 22 occur within the same bcr gene, but more 5' of the bcr. Cloning of a chimeric bcr-c-abl cDNA demonstrates that the fusion gene is transcribed into a 7 kb mRNA, encoding a novel fusion protein.

The incidence of hepatic hamartomas in tuberous sclerosis. Evaluation by ultrasonography

Our series of tuberous sclerosis patients consisted of 23 children between 6 and 16 years of age and of 13 patients between 16 and 48 years of age. In the former group the incidence of multiple hepatic haemangiomas, estimated by grey-scale ultrasonography, is 13%, whereas this incidence is 23% in the group of older patients. The sign might be important for genetic counselling in formes frustes.