Mantle cell lymphoma pathogenesis: another turn of the screw to cyclin D1 overexpression
[eng] Mantle cell lymphoma (MCL) is an aggressive lymphoid neoplasm derived from mature B cells characterized by the presence of the t(11;14)(q13;q32) translocation that leads to the overexpression of Cyclin D1. Cyclin D1 plays a well-established role in G1/S progression, although other functions in...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2017 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/122544 |
| Acceso en línea: | https://hdl.handle.net/2445/122544 http://hdl.handle.net/10803/565574 |
| Access Level: | acceso abierto |
| Palabra clave: | Biologia molecular Patologia Cultiu cel·lular Oncologia Molecular biology Pathology Cell culture Oncology |
| Sumario: | [eng] Mantle cell lymphoma (MCL) is an aggressive lymphoid neoplasm derived from mature B cells characterized by the presence of the t(11;14)(q13;q32) translocation that leads to the overexpression of Cyclin D1. Cyclin D1 plays a well-established role in G1/S progression, although other functions including transcription or DNA damage response (DDR) can be regulated by this cyclin. Therefore, the main goal of this thesis is the characterization of the cyclin D1 non-canonical function in MCL and lymphoid cells. Firstly, we analyzed the genomic binding of endogenous cyclin D1 in four MCL cell lines, showing widespread occupancy around the transcription start site of active promoters. Overexpressed cyclin D1 in lymphoblastic cell lines causes a global transcription downmodulation, while cyclin D1 silencing increased the RNA content. In addition, higher levels of cyclin D1 correlated with lower transcription outputs in MCL and multiple myeloma cell lines. We also found that cyclin D1 colocalized with Pol II, but its overexpression increased the RNA polymerase II pausing and decreased elongation. Cyclin D1 overexpressing cells showed higher sensitivity to transcription inhibitors, revealing a synthetic lethality interaction. As expected, MCL and multiple myeloma cell lines displaying higher levels of cyclin D1 were more sensitive to the effects of the drug. Next, we studied the capacity of cyclin D1 to induce DNA replication stress in lymphoblastic cell lines. Cyclin D1 overexpression caused increased cell proliferation, especially the mutant form cyclin D1 T286A that codifies for a more stable protein. However, cyclin D1 overexpressing cells displayed a slower progression through S-phase. The analysis of DNA fibers showed that cyclin D1 overexpression caused DNA replication stress. Indeed, constitutive overexpression of cyclin D1 led to basal DDR activation, which was detected by the induction of γH2AX and pCHK2 phosphoproteins. These results led us to wonder if MCL can display a high, constitutive hyperactivation of DDR in primary samples. Concordantly, 66% showed positive γH2AX staining and 33% of all cases showed a concomitant pCHK2expression. The activation of DDR correlated to worse survival, more chromosome abnormalities, higher proliferation and genetic alterations of genes involved in the DDR. Finally, we aimed to study the potential contribution of altered DNA methylation in the development and/or progression of MCL. To do so, we performed genome-wide methylation profiling of a large cohort of primary MCL tumors and normal lymphoid tissue samples. Primary MCL displayed a heterogeneous methylation pattern dominated by DNA hypomethylation when compared to controls. Annotation analysis of hypermethylated promoters recognized pathways related to cell proliferation. The promoters of WNT pathway inhibitors and several other tumor suppressor genes were shown frequently methylated. A substantial fraction of the genes with promoter hypermethylation showed a significant downregulation of their transcription levels. Furthermore, we identified a subset of tumors with extensive CpG methylation that had an increased proliferation signature, higher number of chromosomal alterations and poor prognosis. Our results suggest that a subset of highly proliferative MCL cases displays a dysregulation of DNA methylation characterized by the accumulation of CpG hypermethylation that may influence the clinical behavior of the tumors. Overall, we have characterized for the first time the new functions that cyclin D1 performs in transcription and replication stress in MCL. The elucidation of these mechanisms may be useful not only for a better understanding of the tumor, but also for improving diagnostic and treatment of MCL patients. A subset of aggressive cases displayed dysregulated DDR and higher methylation levels and were associated with higher proliferation. Our findings suggest that cyclin D1, in addition to its canonical role in cell cycle regulation, plays other functions that may be important for MCL lymphomagenesis. |
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