Identification of a novel factor that interacts with an immunoglobulin heavy-chain promoter and stimulates transcription in conjunction with the lymphoid cell-specific factor OTF2

Functional human endogenous retroviral LTR transcription start sites are located between the R and U5 regions

Human endogenous retroviruses (HERVs) occupy about 5% of human DNA and are thought to be remnants of ancient retroviral infections of human ancestors' germ cells. HERVs can modify expression of host cell genes through their cis-regulatory elements concentrated in their long terminal repeats (LTRs). Although numerous HERV-related RNAs were identified in the human transcriptome, for most of them, it remains unclear whether they are LTR-promoted or read-through products initiated from neighboring genomic promoters. Here, we describe mapping of transcriptional start sites within solitary and proviral LTRs of the HERV-K (HML-2) human-specific subfamily of endogenous retroviruses. Surprisingly, the transcription was initiated predominantly from the very 3' termini of the LTR R regions. The data presented here may shed light on adaptive coevolution of human endogenous retroviruses with their host cells.

Somatic Mutations Within the Untranslated Regions of Rearranged Ig Genes in a Case of Classical Hodgkin’s Disease as a Potential Cause for the Absence of Ig in the Lymphoma Cells

Hodgkin–Reed-Sternberg (H-RS) cells are clonal B cells carrying Ig gene rearrangements. However, in situ hybridization methods failed to demonstrate Ig gene expression in H-RS cells of classical Hodgkin’s disease (HD). Because somatic mutations rendering potentially functional Ig gene rearrangements nonfunctional were detected in some cases of the disease, it was speculated that H-RS cells in classical HD may have lost the ability to express antigen receptor as a rule. Recently, we established a novel cell line (L1236) from H-RS cells of a patient with mixed cellularity subtype of HD. L1236 cells harbor a potentially functional VH1 and a potentially functional Vκ3 gene rearrangement. However, no antibody expression was detected. To show potential reasons for this lack of Ig expression, we analyzed the genomic organization of the Ig genes and their transcription in the primary and cultivated H-RS cells of this patient. The H-RS cells were found to have switched their isotype to IgG4, confirming their mature B-cell nature. By amplifying cDNA from L1236 cells as well as from frozen biopsy material transcripts of the Vκ3 and the VH1 gene rearrangement were detected for both sources of cDNA. However, Northern blot hybridization of L1236 RNA failed to demonstrate VH1 and Vκ3 transcripts, indicating only a low level of transcription. Sequence analysis of the promoter and leader regions of the VH1 gene rearrangement from L1236 cells as well as from lymphoma-affected tissue showed a somatic mutation in the conserved octamer motif of the promoter region. Somatic mutations were also detected within the 3′ splice site of the leader intron and adjacent nucleotides in the rearranged Vκ light chain gene, leading to aberrant splicing. These mutations might prevent the generation of adequate amounts of functional Ig gene transcripts as template for translation into protein. Thus, mutations in H-RS cells that prevent Ig gene expression might also be located outside the coding region of the Ig genes.

Somatic Mutations Within the Untranslated Regions of Rearranged Ig Genes in a Case of Classical Hodgkin’s Disease as a Potential Cause for the Absence of Ig in the Lymphoma Cells

Hodgkin–Reed-Sternberg (H-RS) cells are clonal B cells carrying Ig gene rearrangements. However, in situ hybridization methods failed to demonstrate Ig gene expression in H-RS cells of classical Hodgkin’s disease (HD). Because somatic mutations rendering potentially functional Ig gene rearrangements nonfunctional were detected in some cases of the disease, it was speculated that H-RS cells in classical HD may have lost the ability to express antigen receptor as a rule. Recently, we established a novel cell line (L1236) from H-RS cells of a patient with mixed cellularity subtype of HD. L1236 cells harbor a potentially functional VH1 and a potentially functional Vκ3 gene rearrangement. However, no antibody expression was detected. To show potential reasons for this lack of Ig expression, we analyzed the genomic organization of the Ig genes and their transcription in the primary and cultivated H-RS cells of this patient. The H-RS cells were found to have switched their isotype to IgG4, confirming their mature B-cell nature. By amplifying cDNA from L1236 cells as well as from frozen biopsy material transcripts of the Vκ3 and the VH1 gene rearrangement were detected for both sources of cDNA. However, Northern blot hybridization of L1236 RNA failed to demonstrate VH1 and Vκ3 transcripts, indicating only a low level of transcription. Sequence analysis of the promoter and leader regions of the VH1 gene rearrangement from L1236 cells as well as from lymphoma-affected tissue showed a somatic mutation in the conserved octamer motif of the promoter region. Somatic mutations were also detected within the 3′ splice site of the leader intron and adjacent nucleotides in the rearranged Vκ light chain gene, leading to aberrant splicing. These mutations might prevent the generation of adequate amounts of functional Ig gene transcripts as template for translation into protein. Thus, mutations in H-RS cells that prevent Ig gene expression might also be located outside the coding region of the Ig genes.

Diverse transcription factors are involved in the quantitative regulation of transcriptional activation of kappa promoters

Immunoglobulin kappa promoters show sequence divergence but conserved function between different subgroups. Here we show that three separate 5' elements are required for synergistic stimulation of transcription with the decamer in a kappa promoter. These sites are a 5' E-box, a 3' AT-rich region in the pentadecamer (pd) element, and the kappa-Y element. Elf-1 is a novel kappa-Y element ligand induced upon mitogenic stimulation of resting B lymphocytes. Furthermore, the 5' E2A-like E-box in the pd element could be substituted by an upstream stimulatory factor motif with conservation of function. Thus, the synergistic activation requirements of kappa transcription is strictly dependent on the quantitative presence of transcription factor-binding motifs 5' of the decamer, but these differ qualitatively in that they may bind an array of proteins with conserved function.