Rearrangement of the MLL gene in acute lymphoblastic and acute myeloid leukemias with 11q23 chromosomal translocations

ALL-1 partial duplication in acute leukemia

The ALL-1 gene, located on chromosome band 11q23, is fused to a variety of other genes by reciprocal chromosomal translocations present in 5-10% of human acute leukemias. We have recently reported the detection by Southern blot of ALL-1 gene rearrangements in adult patients with acute myeloid leukemia lacking cytogenetic evidence of 11q23 translocations. These include 2 of 19 patients with normal karyotypes as well as 3 of 4 patients with trisomy 11. To characterize the abnormal ALL-1 genes, we cloned the ALL-1 rearrangements from two patients with trisomy 11. Characterization of the clones, together with Southern blot analysis, indicates that the ALL-1 rearrangement in both patients is the result of a direct tandem duplication of a portion of the ALL-1 gene spanning exons 2-6. The partial ALL-1 duplication is also detected by Southern blot analysis in a patient with a normal karyotype. RNA PCR and DNA sequence analysis show that the partially duplicated ALL-1 gene is transcribed into mRNA capable of encoding a partially duplicated protein. Partial duplication of ALL-1, in which a portion of a putative protooncogene is fused with itself, represents an additional genetic mechanism for leukemogenesis. Our findings suggest that the presence of trisomy in malignancy may sometimes indicate the partial duplication of a cellular protooncogene.

Polymerase chain reaction-based methods for the detection of mutations in oncogenes and tumor suppressor genes

Altered expression of oncogenes and tumor suppressor genes, the normal function of which is to regulate cell growth and differentiation, represents a central event in the pathogenesis of human cancer. Aberrant expression of these genes is often a result of a mutational event. In vitro amplification of DNA with the polymerase chain reaction (PCR) has enormously increased the sensitivity of the methods to detect mutations. These PCR-based techniques have thus become invaluable in the elucidation of the mechanisms of carcinogenesis as well as in molecular genetics. In addition, the precise definition of a mutation at the molecular level can be a very valuable adjunct to the diagnosis and classification of malignancies as well as to their prognostic assessment. In this article several PCR-based strategies are outlined, their applicability in the detection of different types of mutations is discussed, and finally the application of these techniques in fresh and archival tissues is presented.

Fusion of PDGF receptor beta to a novel ets-like gene, tel, in chronic myelomonocytic leukemia with t(5;12) chromosomal translocation

Chronic myelomonocytic leukemia (CMML) is a myelodysplastic syndrome characterized by abnormal clonal myeloid proliferation and by progression to acute myelogenous leukemia (AML). CMML thus offers an opportunity to study early genetic events in the transition to AML. A recently recognized subgroup of CMML has a t(5;12)(q33;p13) balanced translocation. We report that the consequence of the t(5;12) translocation is expression of a fusion transcript in which the tyrosine kinase domain of the platelet-derived growth factor receptor beta (PDGFR beta) on chromosome 5 is coupled to a novel ets-like gene, tel, on chromosome 12. The tel-PDGFR beta fusion demonstrates the oncogenic potential of PDGFR beta and may provide a paradigm for early events in the pathogenesis of AML.

DNA rearrangements and altered transcripts of the MLL gene in a human T-ALL cell line Karpas 45 with a t(X;11) (q13;q23) translocation

Translocations involving chromosome band 11q23 are found in both lymphoid and myeloid leukemias as well as in lymphomas, in these translocations. The chromosomes most frequently involved in reciprocal translocations include chromosomes 4, 6, 9, and 19, and we and others have reported that chromosomes 1, 2, 10, 15, 17, 18, 22, and X are also involved. In the cell line Karpas 45, which has a t(X;11) (q13;q23) translocation, we report here that the MLL gene is rearranged and that there are two altered transcripts of MLL that come from the der(11) chromosome.

Detection of chromosome 11q23 involving translocations by pulsed field gel electrophoresis

Translocations involving chromosome band 11q23 are associated with acute lymphocytic and myelomonocytic leukemias with poor clinical prognosis. Pulsed-field gel electrophoresis (PFGE) was used to characterize the breakpoint region that has been mapped within a 300-kb fragment between the genes CD3G and PBGD. Using CD3G as a marker on SfuI-restricted DNA separated by PFGE, we detected a rearrangement involving 11q23 in the cell line B1 with a t(4;11) and in the leukemic cells of two patients, one with a t(2;11) and one with a t(11;19). In comparison, lymphoblastoid cell lines established from normal peripheral blood lymphocytes of these two patients had a normal karyotype and showed germline configuration, thus excluding RFL polymorphisms. Digestion of DNA with BssHII or SalI showed heterogeneity of 11q23 involving breakpoints. A rearrangement in the t(4;11) containing lymphoma cell line Karpas422 was seen only with the chromosome 4 probe KIT on SalI-digested DNA. PFGE is a reliable method for the mapping and detection of complex breakpoint regions. The breakpoints on 11q23 involve different introns of the highly spliced HRX/ALL-1/MLL gene.

Epipodophyllotoxins in the treatment of childhood cancer

We reported marked biologic activity with the epipodophyllotoxins in phase I/II studies of childhood cancer conducted in the 1970s. We have since extensively used the combination of teniposide and ara-C in the treatment of acute lymphoblastic leukemia (ALL). Initially we treated patients with refractory disease and found that the combination lacked clinical cross-resistance with standard antileukemic drugs. This formed a rationale to move teniposide and/or etoposide to front-line therapy of childhood ALL. The superior results projected for our last trial, an overall cure rate of about 75%, are attributable in part to early use of epipodophyllotoxins. This class of agents is also used extensively in the treatment of newly diagnosed childhood solid tumors, including neuroblastoma, medulloblastoma, rhabdomyosarcoma, and germ-cell tumors. Secondary leukemias following treatment with epipodophyllotoxins have been reported in a small subset of patients. Current data show that the most important risk factor is the schedule of drug delivery, which has led to appropriate protocol modifications.

Cytogenetic and molecular analysis of pediatric neoplasms: diagnostic and clinical implications

Recurring chromosome changes, particularly those closely associated with specific subtypes of tumors, have provided critical clues to the location of the genes involved in the genesis of these tumors. These, in turn, have led to the cloning of these genes, especially those located at translocation breakpoints in leukemias, lymphomas, and sarcomas. The immediate consequence of the cloning of these genes is to provide DNA probes for various diagnostic tests, including standard Southern blot analysis, the polymerase chain reaction, and fluorescence in situ hybridization. Because many of these chromosome rearrangements are associated with either an improved or a poorer survival, karyotypic abnormalities provide prognostic information. In the future, more sophisticated understanding of the genes involved and of the nature of their altered function should lead to improved therapy.