Genome instability and epigenetic deregulation in retinoblastoma and osteosarcoma
Retinoblastoma and osteosarcoma are the third and eight most common forms of childhood cancers, respectively. Children with hereditary retinoblastoma -germline mutation in the RB1 gene- are predisposed to osteosarcoma later in their life. Despite recent progress in clinical outcomes in retinoblastoma and osteosarcoma, enucleation remains a frequent treatment for retinoblastoma and the survival rate for osteosarcoma is just over 50%, underscoring the need to identify molecular mechanisms responsible for disease progression and to develop more effective drugs. Previous finding from our laboratory suggest that aE2Fs regulate recruitment of the epigenetic machinery that is required for tumor formation in the absence of the Rb family and that epigenetic deregulation of genes in the absence of Rb is sufficient for retinoblastoma formation. However, while functional loss of RB1 is enough for retinoblastoma formation, osteosarcoma requires inactivation of an additional tumor suppressor, TP53. Through the study of the epigenetic landscape of retinoblastoma and osteosarcoma, in this project we hope to determine why some cell types are more susceptible to tumor formation than other cell types, in particular following RB1 inactivation. We aim to elucidate the role of epigenetics and genome instability in osteosarcomagenesis and how the Rb/E2F pathway participates in this process. The use of integrative analyses of the changes in chromatin organization and gene expression that occur during tumorigenesis will help us identify potential novel therapeutic targets for anticancer treatment.
Role of epigenetic regulators UHRF1 and HELLS in retinoblastoma
In the developing retina, loss of function of the RB1 gene is the rate-limiting step for initiation of hereditary and sporadic retinoblastoma. Preliminary analyses of human and mouse retinoblastoma identified UHRF1 (ubiquitin-like, containing PHD and RING domains 1) and HELLS (helicase, lymphoid specific) proteins that may act as key epigenetic regulators during tumorigenesis, one by bridging DNA methylation and chromatin modification and the other through maintenance of heterochromatin, respectively. The goals of this project are directed toward the study of the downstream genes or pathways, in particular UHRF1 and HELLS that are regulated by RB1 and have the potential to become alternative therapeutic targets for cancer treatment.
Elucidating the RB/E2F pathway targets in the retina and the bone – Loredana Zocchi
RB1 is a tumor suppressor gene and its inactivation causes retinoblastoma, a pediatric tumor that starts in the retina. It is very interesting to note that while RB1 inactivation in the retinal cell of origin drives tumor development, that doesn’t happen in other tissues like the bone, where in order to drive tumor formation (osteosarcoma) osteoblasts require TP53 inactivation. My project is focused on elucidating how the RB/E2Fs binding at target promoters, the epigenetic modifications at target genes, and the RB-binding proteins differ between the two systems. Identifying the RB direct target genes and binding proteins is necessary in order to understand its biological roles in different contexts.
Tissue-specific suceptibility to RB/E2F pathway inactivation – Stephanie Wu
The differential susceptibility of different cells, including retinal and bone cells, to transformation retinal and bone cells, to transformation has raised the interest for the elucidation of the disease mechanism following RB1 inactivation. The perturbation of epigenetic landscape facilitated by downstream effectors following the disruption of the RB/E2F pathway is critical for tumor progression. I’m interested in identifying the key players that drive tumorigenesis under the influence of a dysfunctional RB/E2F pathway, with HELLS and UHRF1 as my primary candidates. Understanding the mechanism of RB/E2F-mediated gene regulation and its role in carcinogenesis will strongly aid the process of developing drugs for anticancer treatment.
Identification of the UHRF1 functional domain critical for tumorigenesis
UHRF1 overexpression is associated with poor prognosis in many cancers. Studies from our research group found that suppression of UHRF1 using shRNA in human retinoblastoma cell lines and orthotopic xenografts leads to reduced survival and diminished tumor growth. From these data, we hypothesize that UHRF1 may be used as a therapeutic target for the treatment of retinoblastoma and other cancers. UHRF1 is a multidomain protein that acts as a key epigenetic regulator by bridging DNA methylation and chromatin modification. It recognizes and binds hemimethylated DNA at replication forks via its YDG domain and recruits DNA methyltransferase 1 (DNMT1) to ensure faithful propagation of the DNA methylation patterns through DNA replication. In addition to its role in maintenance of DNA methylation, it also plays a key role in chromatin modification through its TUDOR-like regions and PHD-type zinc fingers. Furthermore, UHRF1 also has E3 ubiquitin-protein ligase activity. Given the complexity of UHRF1, we must first identify which domain of UHRF1 is paramount for tumorigenesis in order to design a small molecule inhibitor that can interfere with the tumorigenic properties of UHRF1.