Rearrangements and mutations of the LAZ3/BCL6 gene are the most frequent events associated with diffuse large-cell lymphoma, a particular class of non-Hodgkin's lymphomas.
To determine the functional consequences of these alterations, we have analyzed the structure of the rearranged BCL6 alleles and their corresponding RNA and protein species in two DLCL biopsies and one tumor cell line which carried the t(3;14)(q27;q32) translocation involving the BCL6 and immunoglobulin heavy-chain (IgH) loci.
In B cell lymphomas, structural alterations of the BCL-6 promoter region, including chromosome translocation and somatic hypermutation, represent the most frequent genetic lesions associated with non-Hodgkin lymphoma, especially of diffuse large cell lymphoma, a malignancy often derived from germinal centre (GC) B cells.
It has been demonstrated that the BCL-6 gene can be altered by chromosomal rearrangements and by mutations clustering in its 5' noncoding region in a significant fraction of FL and diffuse large cell lymphoma (DLCL).
Our results show that rearrangements of BCL-6 are present in 20% of AIDS-DLCL (5 of 24), including 2 of 8 LNCCL and 3 of 16 LC-IBPL, but in no case of AIDS-SNCCL.
Polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE) and direct DNA sequencing were used to identify mutations in the 5' noncoding region of the BCL-6 gene in a total of 40 cases of diffuse large-cell lymphoma (DLCL) and follicular lymphoma (FL).
When compared with six other DLCL cell lines lacking t(9;14)(p13;q32), the KIS-1 cell line showed an 11-fold overexpression of PAX-5 mRNA and a significantly reduced expression of the p53 gene, which is normally regulated by PAX-5.
Single-strand conformation polymorphism (SSCP) analysis and sequencing of exons 5 through 9 of the p53 tumor-suppressor gene showed a mutation in codon 176 of the DLL but not in the CLL/SLL component in one case where the CLL/SLL and DLL represented different clones.
When compared with six other DLCL cell lines lacking t(9;14)(p13;q32), the KIS-1 cell line showed an 11-fold overexpression of PAX-5 mRNA and a significantly reduced expression of the p53 gene, which is normally regulated by PAX-5.
Deregulation of PAX-5 by translocation of the Emu enhancer of the IgH locus adjacent to two alternative PAX-5 promoters in a diffuse large-cell lymphoma.
When compared with six other DLCL cell lines lacking t(9;14)(p13;q32), the KIS-1 cell line showed an 11-fold overexpression of PAX-5 mRNA and a significantly reduced expression of the p53 gene, which is normally regulated by PAX-5.
Sequential samples of the indolent and transformed phase of three cases showed the presence of p16(INK4a) deletions in the Richter's syndrome but not in the CLL component of two cases, whereas in a follicular lymphoma the deletion was present in both the follicular tumor and in the diffuse large-cell lymphoma.
The BCL1 locus was rearranged in 9 out of 25 (36%) cases of intermediate lymphocytic cell lymphomas (ILL), in 1 out of 8 cases of diffuse small cleaved cell lymphoma, in 1 out of 12 cases of diffuse mixed cell lymphoma, and in 1 out of 21 cases of diffuse large cell lymphoma.
We report here that the BLIMP1 gene is inactivated by structural alterations in 24% (8 out of 34) activated B cell-like diffuse large cell lymphoma (ABC-DLBCL), but not in GC B cell-like (n = 0/37) or unclassified (n = 0/21) DLBCL.
Polymerase chain reaction (PCR) amplification, cloning, and DNA sequencing of complementary determinant region 3 (CDR3) of the Ig-heavy chain gene of one of the two cases in which the Ig gene-rearrangement patterns were different showed nonidentical sequences in the CLL/SLL and DLL components.
The TYMS 6 base pair (bp)(-)6bp- (homozygous for 6bp deletion), IVS6 -68C>T, and 1053C>T genotypes (all in complete linkage disequilibrium) were all inversely associated with NHL (TYMS; odds ratio [OR] = 0.57; 0.34-0.94), particularly with diffuse large cell lymphoma (DLCL; OR = 0.29; 0.10-0.82).