Immunoglobulin diversification in B cell malignancies: internal splicing of heavy chain variable region as a by-product of somatic hypermutation.
In this study we describe alternative splicing of somatically mutated immunoglobulin (Ig) variable heavy chain (V(H)) genes in three distinct primary B cell non-Hodgkin's lymphomas (B-NHL). In two V4-34 expressing lymphomas, ie a post-germinal center type B cell chronic lymphocytic leukemia (B-CLL) and a follicular lymphoma (FL), internally spliced V(H) gene transcripts were found in which a sequence stretch of 116 bp between the framework region 1 (FR1) and complementarity determining region 2 (CDR2) had been deleted. We provide evidence that for this alternative IgV(H) mRNA processing a known cryptic 5' splice donor site and a previously unidentified cryptic 3' splice acceptor site were used. Site-directed mutagenesis showed that the cryptic 3' splice acceptor site had been activated by specific somatic point mutations. The B-CLL further harbored a triplication of the rearranged JH3 gene segment including the putative N region and part of the JH3-JH4 intron sequence. This triplication probably took place via a repeated mechanism of DNA double strand break followed by homologous recombination, a mechanism which was recently proposed also involved in the somatic hypermutation process and is compatible with the post-germinal center derivation of this B-CLL. Finally, in a V4-34 expressing diffuse large B cell lymphoma, we observed alternative IgV(H) mRNA processing using the same cryptic 5' splice donor site and the normal splice acceptor site of the CH1-C(mu) exon. The significance of alternative IgV(H) processing in B cell malignancies and as a potential mechanism of somatic Ig diversification is discussed.
Bende
R J
RJ
Department of Pathology, Academic Medical Center, Amsterdam, The Netherlands.
Aarts
W M
WM
Pals
S T
ST
van Noesel
C J M
CJ
D000368:Aged; D017398:Alternative Splicing / Q000235:genetics*; D001483:Base Sequence; D022801:Complementarity Determining Regions / Q000235:genetics; D016384:Consensus Sequence; D017931:DNA Primers / Q000737:chemistry; D004273:DNA, Neoplasm / Q000378:metabolism; D005260:Female; D005803:Genes, Immunoglobulin; D006801:Humans; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D007135:Immunoglobulin Variable Region / Q000235:genetics*; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D016133:Polymerase Chain Reaction; D012334:RNA, Neoplasm / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid
D022801:Complementarity Determining Regions; D017931:DNA Primers; D004273:DNA, Neoplasm; D007143:Immunoglobulin Heavy Chains; D007135:Immunoglobulin Variable Region; D012334:RNA, Neoplasm