Clustered somatic mutations in and around first exon of non-rearranged c-myc in Burkitt lymphoma with t(8;22) translocation.

We have examined the restriction map of the c-myc gene in 15 BL cell lines carrying the variant t(8;22) translocation in which c-myc is known to remain on chromosome 8. Using 3 restriction enzymes cutting outside the c-myc domain (EcoRI, BamHI, HindIII), we found no evidence for a c-myc/Ig lambda rearrangement in 14 BL cell lines. In the last one, BL 37, the 3' flanking region was rearranged corresponding to the already identified breakpoint located 400 pb downstream from the c-myc gene (9). Using 4 restriction enzymes cutting inside the c-myc gene (PvuII, PstI, SacI, HincII) we looked for discrete abnormalities within the gene limits, and we found in 9 BL cell lines several abolished and created sites, compatible with multiple independent somatic mutations. They are significantly clustered in the 5' non coding region, with a striking prevalence at the end of exon 1. The role of mutations in the non-coding first exon region for the deregulation of c-myc expression is discussed.     

Translocation of oncogene c-sis from chromosome 22 to chromosome 11 in a Ewing sarcoma-derived cell line.

Somatic cell hybrids, obtained after fusion of translocation (11;22)-positive Ewing sarcoma cells and Chinese hamster fibroblasts, were assayed for the presence of immunoglobulin C lambda, Philadelphia chromosome breakpoint cluster region, and c-sis oncogene sequences. It was found that c-sis was translocated from chromosome 22 to chromosome 11 in the Ewing sarcoma cells used, indicating that the breakpoint must be proximal to this locus. Moreover, we found that the chromosome 22-linked C lambda and breakpoint cluster region sequences are not translocated. This result confirms an earlier cytogenetic observation that the Ewing sarcoma-associated breakpoint in chromosome 22 is distal to those observed in translocation (8;22)-positive Burkitt lymphoma and in Philadelphia chromosome-positive chronic myeloid leukemia.     

Rearrangement of the c-myc proto-oncogene locus in a cell line of T-lymphoblastic origin

A molecular rearrangement of the proto-oncogene c-myc located downstream of the exon III 3' end has been found in a cell line derived from KE37 cell line established from an acute T-lymphoblastic leukemia. This rearrangement resulted from a chromosomal translocation t(8; 14)(q24; q11). Since the 14q11 chromosomal band has been found to be involved in several T-cell leukemias and lymphomas, the importance of the rearrangement of c-myc discovered in the KE37 cell line lies in the possibility of analyzing chromosome 14 DNA near the breakpoint involved in the translocation.     

Molecular cloning of a DNA fragment from human chromosome 14(14q11) involved in T-cell malignancies.

To isolate DNA segments specific to chromosome band 14q11, which has been implicated in a number of human T-cell malignancies, a genomic DNA library was prepared from a variant cell subline of the human lymphoblastic KE37 cell line. This subline (KE37-R) bears a t(8;14) (q24;q11) translocation, and the breakpoint on the resulting chromosome 8q+ has been located at the 3' end of the third c-myc exon. Three molecular clones were isolated by screening the library with a c-myc exon 3 probe, and one of them (lambda K40) was analyzed in detail. It contains a 15-kb insert consisting of 4.5 kb of sequence from chromosome 8 (e.g., downstream of c-myc exon 3) and sequences from chromosome 14. The origin of these latter sequences was established by hybridizing DNA from chromosomes sorted by flow cytometry to a lambda K40 subclone containing only chromosome 14 presumptive sequences and by Southern blot analysis of rodent X human somatic hybrid cell DNA with the same probe. No cross-hybridization was found between the lambda K40 clone and a cDNA clone for the alpha chain T-cell receptor gene which is also located in 14q11. A preliminary survey of DNAs from human T-cell malignancies with a probe corresponding to chromosome 14 sequences of lambda K40 clone revealed for some of them restriction patterns different from those of the germ line DNA. The fact that the rearrangement observed in a leukemic patient was not found in DNA from lymphocytes obtained during remission excluded any polymorphism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chromosomal orientation of the lambda light chain locus: V lambda is proximal to C lambda in 22q11.

We have demonstrated that the chromosomal breakpoint at 22q11 of a Burkitt lymphoma cell line (PA682) with an 8;22 translocation interrupts the variable region of the lambda light chain locus. In these cells, all of the C lambda and some V lambda sequences translocate to the 8q+ chromosome whereas some V lambda sequences remain on the 22q-. These results indicate that the lambda light chain locus on the long arm of chromosome 22 is oriented such that V lambda is proximal to C lambda.     

c-myc and immunoglobulin kappa light chain constant genes are on the 8q+ chromosome of three Burkitt lymphoma lines with t(2;8) translocations.

We have determined the localization of c-myc and the immunoglobulin kappa light chain genes on the 8q+/2p- chromosomes of the three Burkitt lymphoma lines BL21, LY66 and LY91 with t(2;8) translocation by in situ hybridization. BL21 is characterized by a complex translocation in which a piece of chromosome 9 appears to be located between the fragments of chromosome 8 and 2 on the 8q+ chromosome. Our data indicate that in all three cell lines the c-myc gene is located on the 8q+ chromosome proximal to the breakpoint in band 8q24. In all cell lines examined the cluster of kappa variable genes has remained on the 2p- chromosome. In LY91 cells the major part of the joining region remained on 2p-, while the joining region has moved to 8q+ in the cell lines BL21 and LY66. In all three cell lines the constant kappa light chain gene was found on the 8q+ chromosome. The fact that an essentially identical pattern was found in the cell line BL21, with the complex translocation, suggests that the insertion of the piece of chromosome 9 into the 8q+ chromosome might be a secondary event. Our present data fit into the concept that in all Burkitt lymphoma lines investigated so far, including cases with t(8;14) and the variant translocations t(2;8) and t(8;22), the c-myc gene becomes situated at the 5' side of an immunoglobulin constant gene. This may have implications for the generation of somatic mutations in the coding and non-coding part of the c-myc gene.     

Genetic recombination in a chromosomal translocation t(2;8)(p11;q24) of a Burkitt's lymphoma cell line, KOBK101

We analyzed a chromosomal translocation, t(2;8)(p11;q24), in a Burkitt's lymphoma cell line, KOBK101. The translocation reciprocally occurred between a site about 150 bp upstream from the J5 segment in the Ig kappa-encoding gene on chromosome 2 and the A-rich end of an Alu repetitive element located far downstream from the c-myc gene on chromosome 8. Short segments of both parental chromosomes were deleted at the rearrangement site. A sequence related to the heptamer recognition signal for the V-J recombination of Ig genes and a topoisomerase I-recognition sequence were detected at the breakpoints. The V-J recombination occurred on both chromosome 2 and the translocated chromosome 2p- at the J3 and J4 segments, respectively. The J region on the translocated chromosomes was mutated, as compared with that on the untranslocated chromosome, while the Alu element and its upstream sequence were conserved. These results suggest the following aspects to the chromosomal translocation of this cell line. A V-J recombination seems to have occurred at the proximal end of the J4 segment first, and then the translocation took place in the region between the J4 and J5 segments. The translocation may have been mediated by the functions of topoisomerase I and the Alu repetitive sequence located at the breakpoint, although the possibility cannot be ruled out that the recombination machinery for Ig gene rearrangements functioned irregularly.     

Mapping by chromosome sorting of several gene probes, including c-myc, to the derivative chromosomes of a 3;8 translocation associated with familial renal cancer

In eight members of a single family a constitutional translocation t(3;8) (p14.2;q24.1) is associated with the development of renal cancer. Chromosomes isolated from a cell line established from a subject with this translocation were analysed in flow with a fluorescence-activated cell sorter (FACS II). Nearly six million chromosomes from the flow karyotype region containing the der(8) and 5.5 million from the region containing the der(3) were sorted, the DNA extracted, digested with EcoRI, size fractionated by electrophoresis, and transferred to nitrocellulose. Hybridization with gene probes for c-mos, which has been localized to 8q11-q22 and somatostatin, which has been mapped to 3q28, confirmed that the sorted fractions contained, respectively, the der(8) and der(3) chromosomes. The cellular oncogenes c-raf-1 (3p25) and c-myc (8q24) were found to be translocated to the der(8) and der(3) chromosomes, respectively. The possible role that the relocation of c-myc might have on the development of renal carcinoma in carriers of this 3;8 translocation was further studied by analysis of the region surrounding the c-myc gene. By the use of cosmid cloning, no rearrangement 31 Kb 5'(or 19 Kb 3') of the translocated gene was found, indicating that the break-point is not immediately adjacent to c-myc. In an associated study, the DNA fragment D3S2 from chromosome 3 was found to map to 3p14.2-pter. This assignment in conjunction with published somatic cell hybrid data enabled D3S2 to be mapped more precisely to the interval 3p14.2-3p21.     

Breakage on chromosome 2 brings the Ck gene to a region 3' of c-myc in a Burkitt's lymphoma line carrying a (2;8) translocation

We have shown using in situ hybridization that the constant region of the kappa light chain immunoglobulin gene (Ck) is translocated from chromosome 2 to chromosome 8 in Burkitt's lymphoma cells with a (2;8) translocation. The Ck gene then ends up adjacent to and on the 3' side of c-myc. The breakpoint probably falls between the gene for the variable region of the kappa light chain (Vk) and the Ck gene.