Senior researcher: Dr. Daniel Mertens & Dr. Stephan Wolf in collaboration with Prof. Dr. Hartmut Döhner & Dr. Stefan Stilgenbauer, University of Ulm, Germany
Elucidation of the 13q14.3 tumor suppressor mechanism
Blood-smear of a B-CLL patient. In this Papenheim-stain, lymphocytes with a dark red colour can be easily distinguished from red blood cells (light red). In B-CLL, the number of lymphocytes is drastically increased.
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A variety of tumors, predominantly leukemias and lymphomas, show loss of a defined genomic region localized in chromosomal band 13q14.3. Thus, a tumor suppressor mechanism has been postulated in this region which encompasses approximately 500 kbp.
To identify this tumor suppressor mechanism, all genes localized in this genomic region were identified and isolated by several groups. None of the genes identified has been funcrtionally characterized yet. Interestingly, the majority of genes localized in this critical region are probably not translated into proteins, but rather exert their function as non-coding RNAs (ncRNAs). In addition, several genes overlap in opposite direction, forming antisense transcripts.
Sequence-analysis of a B-CLL patient. In order to identify the tumorsuppressor gene responsible for the pathogenesis of B-CLL, candidate genes are analysed for point mutations in B-CLL patients. Shown is a short sequence of 20 basepairs derived from DNA of a B-CLL patients. The critical region in chromosomal band 13q14.3 under investigation spans roughly 400.00 base pairs.
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The next step was to test these isolated genes for loss-of-function mutations in tumor patients in order to identify the tumor-relevant gene. No such mutations were found in any of the laboratories involved in the 13q14.3 gene-hunt up to now. However, we could show a significant downregulation of the majority of genes localized in this critical region in tumor samples, pointing to an epigenetic tumor suppressor mechanism. In addition we assume a multigenic pathomechanims involving several of the candidate genes. Therefore, the molecular function of the candidate genes is currently characterized in more detail.
Taqman-Analysis. In a realtime-PCR, the accumulation of DNA in a reaction tube can be visualized in realtime. With this methodology, gene expression or DNA-modifications like DNA-methylation can be detected using very small quantities of sample material. Shown is the increase in fluorescence (y-axis) in PCR-reactions with different amounts of template during the reaction cycles (x-axis).
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Funding
This project is funded by the 'Bundesministerium für Bildung und Forschung'. (www.bmbf.de)
Publications in this field
- Down-regulation of candidate tumor suppressor genes within chromosome band 13q14.3 is independent of the DNA methylation pattern in B-cell chronic lymphocytic leukemia.
- B-cell neoplasia associated gene with multiple splicing (BCMS): the candidate B-CLL gene on 13q14 comprises more than 560 kb covering all critical regions.
- Distinct gene expression patterns in chronic lymphocytic leukemia defined by usage of specific VH genes.
- Ala228 variant of trail receptor 1 affecting the ligand binding site is associated with chronic lymphocytic leukemia, mantle cell lymphoma, prostate cancer, head and neck squamous cell carcinoma and bladder cancer.
- Evidence for distinct pathomechanisms in genetic subgroups of chronic lymphocytic leukemia revealed by quantitative expression analysis of cell cycle, activation, and apoptosis-associated genes.
- Translocation t(X;11)(q13;q23) in B-cell chronic lymphocytic leukemia disrupts two novel genes.
- BCMSUN, a candidate gene for B-cell chronic lymphocytic leukemia and mantle-cell lymphoma, has an independently expressed homolog on 1p22-p31, BCMSUN-like.
- BCL10 is not the gene inactivated by mutation in the 1p22 deletion region in mantle cell lymphoma.