Identification of the cellular origin and "stemness" phenotype of malignant rhabdoid tumours (MRT) may represent a new therapeutic approach in paediatric oncology
introduction: Malignant Rhabdoid Tumours (MRT) arc especially lethal cancers that predominantly occur in infants and young ehildrcn. MRT arc caused by biallelic inactivation of a single gene; SMARCB I which is a component of SWI/S F chromatin remodelling complex. The tumours can be found almost ever...
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| Format: | Thesis Book |
| Language: | English |
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| Summary: | introduction: Malignant Rhabdoid Tumours (MRT) arc especially lethal cancers that predominantly occur in infants and young ehildrcn. MRT arc caused by biallelic inactivation of a single gene; SMARCB I which is a component of SWI/S F chromatin remodelling complex. The tumours can be found almost everywhere in the body and the cell of origin for MRT is still unknown. Expression profiling of primary MRT demonstrates strong overexpression of a large number of stemness/self-renewal genes (PBTG, unpublished). Previous studies have shown that expression of these genes arc deregulated by SMARCB I and/or larger SWI/SNF complex. Therefore, this project was aimed to uncover the potential cell of origin and to examine if expression of sci f-renewal genes could potentially contribute towards disease aggressiveness. The understanding of other mechanisms involved in MRT tumourigenesis is essential to identify therapeutic targets that can improve the outcomes of MRT patients. Methods: I performed a meta-analysis cross-referencing expression profiles from primary MRT(n= 119), and functional models in which SMARCBI was re-exprcsscd (n=5 lines) with expression profiles from multiple candidate stem cell types including epithelial, embryonal, neural, mesenchymal and neural crest (n= 446). I developed a Icntiviral CRISPRlCas9 system to efficicntly model Smarcb l mutation in primary candidate cells of origin ex vivo. To undcrstand how SMARCB I loss is capable of hijacking active stcmncss/self-rencwal machinery to initiate MRT tumourigenesis, an integrated data analysis was performed to identify stcmness/self-renewal genes whose expression are SMA RCB I-dependcnt, by eross-refercncing a manually curatcd stemness/self-renewal gene list with existing RNA-seq data from primary MRT and MRT cell lincs with and without re-cxprcssion of SMARCB I and with CRlSPRlCas9 genome¬wide screening data from MRT cells with and without rc-cxpression of SMARCB I. Finally, the expression ofstcmness/sclf-rcncwal genes and their re\cvance as a therapeutic target in MRT, specifically the protein BMII, was studied using shRNA and a small molecular inhibitor. Results: Bioinformatic analysis of potential cells of origin suggests three putative candidate cell populations within the family of neural crest ( C), neural progenitor and mesenchymal stem cells. The extent of transcriptional overlap clearly reflects differences in tumour location and molecular subgroup. Unlike most cells tested, early neural crest (NC) cells tolerated Smarcb l mutation and conferred proliferative advantage resembling human MRT molecularly and immunophenotypically. From my integrated bioinfonnatic analysis of self-renewallstemness, BMJI was identified as a functional SMARCB l¬dependent gene. Here. I show that targeted disruption of BMII by shRNA or pharmacologic inhibition using PTC209 strongly impairs MRT cell growth, suppresses tumour cell self-renewal, induces apoptosis and senescence. Using functional gene expression analysis, I found that BMJI knockdown in MRT cells transcriptionally activates critical genes in MRTsuch asp2l,pl6 and CD44. Conclusion: Our findings suggest C cells as a potential cell of origin for MRT. I describe a system for ranking putative cells of origin and a practical means for inducing Smarcb l mutations ex vivo. Furthennore, I show evidence that subtypes within MRT have different cells of origin. Here, I also establish the role of BMJI in self-renewal and survival of MRT cells. In addition, I show that the effects of BMl I knockdown recapitulates the effect of SMARCBl re-expression in MRT cells, dcmonstrating an attractive therapeutic target for MRT. |
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| Physical Description: | xxiii, 377 leaves: illustrations (some colour); 31 cm. |
| Bibliography: | Includes bibliographical references (leaves 351-377) |