Estrogen Receptor-Mediated Repression of Target Genes: Mechanism of Action, and Biological Significance

Estrogen-bound estrogen receptor (ER) can regulate the transcription of a large number of genes. Although estrogen represses as many genes as it induces, induction has been studied in detail while the repression mechanisms remain largely unknown. In this study we characterized several estrogen-repressed ERα target genes that are directly repressed by estrogen in breast cancer cells. Interestingly, many repressed genes are tumor suppressor genes, playing critical roles in cell cycle inhibition and/or apoptosis. One gene that particularly piqued our interest is Reprimo (RPRM) because of its robust repression in a number of cell lines, and its role as a cell cycle inhibitor. Additionally, it is highly methylated in a variety of cancers including breast cancer and maps to a locus that displays loss of heterozygosity, suggesting that it may be a tumor suppressor gene. As a result, E2-mediated repression of this gene may be a crucial step in the progression of breast cancer. We did show that RPRM decrease (by siRNA) enhances estrogen-mediated S-phase entry, strongly suggesting a biological role of its repression. RPRM was actively and strongly repressed by estrogen and this repression was not due to a quicker turnover of the RPRM mRNA by estrogen. E2-mediated repression of RPRM levels did not require new protein synthesis since it is also repressed in the presence of the translation inhibitor, cycloheximide. We find that estrogen repression of RPRM requires a tripartite interplay between ERα, FoxA1, and HDAC7 as knockdown of these proteins abrogates its repression. Remarkably, silencing of HDAC7 significantly relieved repression of the majority of eleven estrogen-repressed genes tested. Further examination of the interplay between HDAC7 and ERα revealed that HDAC7 can interact with ERα and repress its transcriptional activity in a deacetylase-independent manner. Chromatin immunoprecipitation assays demonstrate that ERα, FoxA1, and HDAC7 are all recruited to a cis-regulatory enhancer (-4.8 kb) in the RPRM gene in the presence of estrogen, which was associated with a release of RNA Pol II from the proximal promoter. Repression requires FoxA1 to be recruited to an epigenetic signature characterized by H3K4 mono- and di-methylation. In summary, we have uncovered a unique requirement for a deacetylase-independent function of HDAC7 in estrogen repression of genes such as RPRM.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 4136.

Analysis of SAFB1 and SAFB2 Knockout Mice Reveals Non-Redundant Functions of the Two Estrogen Receptor Co-Repressor Paralogs

The Scaffold Attachment Factor B1 (SAFB1) and B2 (SAFB2) have been shown to be involved in chromatin organization, transcriptional regulation, and RNA processing. The paralogs SAFB1 and SAFB2 share 74% similarity at the amino acid level, with up to 98% similarity in some functional domains. These functional domains include DNA and RNA-binding domains, and a C-terminal repression domain. We have previously shown that SAFB1 and SAFB2 function as estrogen receptor (ER) corepressors – they directly bind to ER, and repress its transcriptional activity. There is also evidence that both proteins play a role in breast cancer; their shared chromosomal locus on chromosome 19p13 displays high rates of LOH, and protein loss was associated with worse survival of breast cancer patients.To understand the roles of SAFB1 and SAFB2 in development and function of hormone responsive tissues, we generated gene-specific knockout (KO) mouse models. Deletion of SAFB1 resulted in a high degree of embryonic and perinatal lethality. Surviving SAFB1 KO mice displayed severe growth retardation associated with low serum IGF-I levels, male infertility and female subfertility. In contrast, SAFB2 KO mice were born at the expected Mendelian ratio and did not show any obvious defects in growth or fertility. Initial gross pathology analysis has not yet revealed any significant defects.Since the SAFB proteins are known to play a role in estrogen response, we analyzed mammary gland development in the two mouse models. Young virgin SAFB1 KO mice showed delayed mammary gland development with a significantly reduced number of terminal end buds and decreased outgrowth compared to wild type (WT) controls. This was likely a result of delayed puberty, due to low IGF-I levels, since at the four month time point, mammary gland growth was restored in the virgin SAFB1 KO mice to that seen in WT controls. Interestingly, the KO glands exhibited increased alveolar development and side branching. To measure proliferation directly, we performed mammary gland transplantation experiments, thereby excluding secondary effects due to systemic defects. These studies showed a significant increase in proliferation in SAFB1 KO glands compared to WT control glands. In contrast to the SAFB1-null mice, we did not observe any obvious mammary gland defects in pubertal or adult SAFB2-null mice. However, mammary glands from aged virgin SAFB2 mice (1.5 years old) showed extensive side branching and precocious development of alveolar buds resembling glands of late pregnant mice. This was associated with increased proliferation of alveolar cells in the SAFB2 KO glands.In summary, genetic ablation of the ER co-repressors SAFB1 and SAFB2 results in defects in mammary gland development. In general, the two mouse models have very different phenotypes, revealing diverse and non-redundant functions of SAFB1 and SAFB2, findings that were unexpected based on their high sequence similarity. We are currently performing additional studies to finalize characterization of the in vivo phenotypes, focusing on hormone responsive tissues, and also to understand the mechanism underlying the observed phenotypes.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 2162.

Mode-locked 2 mum laser with highly thulium-doped silicate fiber

We report self-starting passively mode-locked fiber lasers with a saturable absorber mirror using a piece of 30-cm-long newly developed highly thulium (Tm)-doped silicate glass fibers. The mode-locked pulses operate at 1980 nm with duration of 1.5 ps and energy of 0.76 nJ. This newly developed Tm-doped silicate fiber exhibits a slope efficiency of 68.3%, an amplified spontaneous emission spectrum bandwidth (FWHM) of 92 nm, and a gain per unit length of greater than 2 dB/cm. To the best of our knowledge, it is the first demonstration of mode-locked 2 mum fiber laser using shorter than 1-m-long active fiber, which paves the way for the demonstration of mode-locked fiber laser at 2 mum with gigahertz fundamental repetition rate.

Depletion of CD4+CD25+ regulatory T cells enhances natural killer T cell-mediated anti-tumour immunity in a murine mammary breast cancer model

Both invariant natural killer T (NK T) cells and CD4(+)CD25(+) T regulatory cells (T(regs)) regulate the immune system to maintain homeostasis. In a tumour setting, NK T cells activated by alpha-galactosylceramide (alpha-GalCer) execute anti-tumour activity by secreting cytokines. By contrast, T(regs) intrinsically suppress antigen-specific immune responses and are often found to be elevated in tumour patients. In this study, we have shown that T(regs) regulate NK T cell function negatively in vitro, suggesting a direct interaction between these cell types. In a murine mammary tumour model, we demonstrated that administration of either alpha-GalCer or anti-CD25 antibody alone markedly suppressed tumour formation and pulmonary metastasis, and resulted in an increase in the survival rate up to 44% (from a baseline of 0%). When treatments were combined, depletion of T(regs) boosted the anti-tumour effect of alpha-GalCer, and the survival rate jumped to 85%. Our results imply a potential application of combining T(reg) cell depletion with alpha-GalCer to stimulate NK T cells for cancer therapy.

Craniopharyngiomas in the posterior fossa: a rare subgroup, diagnosis, management and outcomes

OBJECTIVE

Craniopharyngiomas with predominant pars in the posterior fossa are very rare and extremely overlooked. The clinical features, diagnosis and management are different from their sellar/suprasellar counterparts. The purpose of this study was to explore the differing characteristics of posterior fossa craniopharyngiomas.

METHODS

Seven patients with pathologically proven craniopharyngiomas located in the posterior fossa were retrospectively investigated. The clinical data and radiographic findings were presented and analysed.

RESULTS

The primary presentations included headache, diplopia, ataxia and hearing loss. All tumours were located in the retrochiasmatic area, and five of seven displayed a retroinfundibulum growth pattern. The predominant components of the tumours were located in the unilateral cerebellopontine angle (CPA) in six cases, and the bilateral CPA in one case. Total tumour resection was accomplished in five patients. There were transient cranial nerve deficits in three patients, and CSF leakage in one patient. Six patients fully recovered to normal conditions, but one patient had tumour regrowth and had to undergo a secondary resection.

CONCLUSIONS

Posterior fossa craniopharyngiomas are rare and may be considered an independent subgroup of classifications. Tumours arising from the sellar region and extending to the posterior fossa present with their own unusual set of characteristics. These tumours can be radically and safely removed with a combined supra- and intratentorial approach.

High pressure Raman investigations of multiferroic BiFeO(3)

We have reported a Raman scattering investigation of bismuth ferrite (BiFeO(3)) under high pressure up to 50 GPa. Distinct changes in the Raman spectra show evidence for three pressure-induced structural transitions. The abrupt frequency redshifts of the Raman modes near 300 cm(-1) at around 3 GPa are attributed to the modulation of the FeO(6) octahedral tilts. The disappearance of the modes below 250 cm(-1) at 8.6 GPa, together with the enhancement of the two modes in the range of 300-400 cm(-1), indicate the phase transition from the rhombohedral to orthorhombic symmetry. Afterward, the E-3 and E-4 modes disappear at 44.6 GPa, pointing to the occurrence of the orthorhombic-cubic phase transition, which is consistent with the previous postulate that an orthorhombic-cubic transition takes place across the metal-insulator transition at high pressures.

Effective Verdet constant in a terbium-doped-core phosphate fiber

The concept of an effective Verdet constant is proposed and experimentally validated. The effective Verdet constant of light propagation in a fiber includes contributions from the materials in both the core and the cladding. It is measured in a 25 wt.% terbium-doped-core phosphate fiber to be -6.2+/-0.4 rad/(Tm) at 1,053 nm, which is six times larger than silica fiber. The result agrees well with Faraday rotation theory in optical fiber.

Anthracyclines in basal breast cancer: The NCIC-CTG trial MA5 comparing adjuvant CMF to CEF

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Background: MA5 randomized premenopausal women with node-positive early breast cancers to cyclophosphamide- methotrexate-fluorouracil (CMF) or cyclophosphamide-epirubicin-fluorouracil (CEF) adjuvant chemotherapy. This and other trials have shown that adjuvant regimens containing anthracyclines confer significant survival benefit to breast cancer patients. Meta-analyses have revealed most benefit in women with HER2(+) or TOPO2 (+) tumors. Population-based data suggest that patients with a core basal phenotype (negative for hormone receptors and HER2, positive for CK5/6 or EGFR) conversely have worse survival on anthracycline containing vs. CMF regimens. Here we test the hypothesis specified a priori that for basal breast cancers anthracyclines may be inferior, using data from MA5. Methods: From 710 patients in MA5, blocks suitable for tissue microarray construction were recovered for 549. Immunohistochemistry for ER, PR, HER2, Ki67, CK5/6 and EGFR was obtained, allowing stratification of 511 cases into intrinsic biological subtypes by published methods (Cheang MC et al. Clin Cancer Res 2008;14:1368–76). Prespecified analyses were conducted independently by the NCIC- CTG statistical centre. Results: In the CEF arm, patients with core basal tumors had a hazard ratio of 1.8 (log rank p=0.02) for overall survival (OS) relative to the other biological subtypes. In the CMF arm, there was no significant difference (HR 0.9, p = 0.7). The interaction between core basal status and treatment was borderline significant (p=0.06). Relapse free survival differences did not reach significance. Conclusions: Data from this randomized trial supports the hypothesis that anthracycline containing adjuvant chemotherapy regimens are inferior to adjuvant CMF in women with basal breast cancer.

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No significant financial relationships to disclose.