Resistance to antiestrogen therapy remains a significant problem in breast cancer. Low expression of inhibitor of growth 4 (ING4) in primary tumors has been correlated with increased rates of recurrence in estrogen receptor-positive (ER+) breast cancer patients, suggesting a role for ING4 in ER signaling. This study provides evidence that ING4 inhibits ER activity. ING4 overexpression increased the sensitivity of T47D and MCF7 ER+ breast cancer cells to hormone deprivation. ING4 attenuated maximal estrogen-dependent cell growth without affecting the dose-response of estrogen. These results indicated that ING4 functions as a noncompetitive inhibitor of estrogen signaling and may inhibit estrogen-independent ER activity. Supportive of this, treatment with fulvestrant but not tamoxifen rendered T47D cells sensitive to hormone deprivation as did ING4 overexpression. ING4 did not affect nuclear ER alpha protein expression, but repressed selective ER-target gene transcription. Taken together, these results demonstrated that ING4 inhibited estrogen-independent ER activity, suggesting that ING4-low breast tumors recur faster due to estrogen-independent ER activity that renders tamoxifen less effective. This study puts forth fulvestrant as a proposed therapy choice for patients with ING4-low ER+ breast tumors.

Interferon regulatory factor-1 (IRF-1) is a transcription factor and tumour suppressor, involved in many diverse cellular processes including immune responses and growth regulation. An interesting feature of IRF-1 is that it can both activate and repress gene expression, possibly by acting with co-activator or co-repressor proteins. In a previous phage display assay, a homologous peptide to the known repressor protein, zinc finger 350 (ZNF350), was found to bind to the C-terminus of IRF-1. ZNF350, also known as ZBRK1 (Zinc finger and BRCA1-interacting protein with KRAB domain-1), is a member of the Krüppel-associated box (KRAB)-containing zinc finger (KZF) proteins, which is a group of the widely distributed transcriptional repression proteins in mammals. ZNF350 has previously been shown to repress the expression of a number of genes including ANG1 and GADD45A, often in complex with other proteins. This study confirms the direct interaction between IRF-1 and ZNF350 and identifies key residues, including the LXXLL repression motif within the C-terminus of IRF-1, necessary for the binding interface. The two proteins have additionally been shown to interact within a cellular environment, shown by using techniques including immunoprecipitation and a proximity ligation assay. In addition, the ZNF350/IRF-1 complex formation appears to occur in the basal state of the cell, as opposed to in response to cellular stress such as viral infection or DNA damage. On the basis of ZNF350 being a negative regulator of transcription, a novel technique was developed to identify putative targets of both ZNF350 and IRF-1. This involved an initial bioinformatics screen using candidate IRF-1 binding site data obtained from CENTIPEDE, an algorithm that combines genome sequence information, with cell-specific experimental data to map bound TF binding sites. This allowed for the identification of novel target genes that contained the ZNF350 consensus binding site, GGGxxCAGxxxTTT, within close proximity to an IRF-1 consensus site, such as the immune response gene IL-12A. Lastly, a peptide phage display screen was combined with high-throughput sequencing to identify other potential binding partners of ZNF350 and perhaps help to understand the mechanism by which transcriptional repression is controlled by complex formation.

No description available.

No description available.

En mamíferos, así como en plantas, mutaciones en AND helicasas/ATPasas del la família SNF2, no solo afectan a la estructura de la cromatina, sino que también afectan al patrón global de la metilación del ADN. Sugiriendo una relación funcional entre la estructura de la cromatina y la epigenética. El complejo NuRD, el cual posee una ATPasa de la familía SNF2, está relacionado con la represión de la transcripción y en el remodelamiento de la cromatina. Nuestro laboratorio demostró que la proteína leucémica PML-RARα reprime la transcripción de sus genes diana por el reclutamiento de DNMTs y el complejo PRC2. En esta tesis, demostramos una relación directa del complejo NuRD en la represión génica y en los cambios epigenéticos en la leucemia promielocítica aguda (APL). Mostramos que PML-RARα se une y recluta NuRD a sus genes diana, incluyendo el gen supresor de tumores RAR2, facilitando que el complejo de Polycomb se reclute y metile la lisina 27 de la histona H3. Tratamiento con Acido Retinóico (RA), el qual se utiliza en pacientes, reduce la ocupación de NuRD en células leucémicas. Eliminando NuRD no solo provoca que las histonas no se deacetilen y que la cromatina no se compacte, sino que también provoca que tanto la metilación del ADN y de las histonas no se produzca, así como la represión génica del gen RAR2, favoreciendo la diferenciación celular. Nuestros resultados caracterizan un nuevo papel del complejo NuRD en el establecimiento de los patrones epigenéticos en APL, demostrando una relación esencial entre la estructura de la cromatina y epigenética durante el desarrollo de la leucemia, pudiéndose aplicar a la terapia de esta enfermedad. / In mammals, as in plants, mutations in SNF2-like DNA helicases/ATPases were shown to affect not only chromatin structure but also global methylation patterns, suggesting a potential functional link between chromatin structure and epigentic marks. The SNF2-like containing NuRD complex is involved in gene transcriptional repression and chromatin remodeling. We have previously shown that the leukemogenic protein PMLRARα represses target genes through recruitment of DNMTs and Polycomb complex. In this thesis, we demonstrate a direct role of the NuRD complex in aberrant gene repression and transmission of epigenetic repressive marks in acute promyelocytic leucemia (APL). We show that PML-RARα binds and recruits NuRD to target genes, including to the tumor-suppressor gene RAR2. In turn, the NuRD complex facilitates Polycomb binding and histone methylation at lysine 27. Retinoic acid treatment reduced the promoter occupancy of the NuRD complex. Knock-down of the NuRD complex in leukemic cells not only prevented histone deacetylation and chromatin compaction, but also impaired DNA and histone methylation as well as stable silencing, thus favoring cellular differentiation. These results unveil an important role for NuRD in the establishment of altered epigenetic marks in APL, demonstrating an essential link between chromatin structure and epigenetics in leukemogenesis that could be exploited for therapeutic intervention.