Transcriptional activation of polycomb-repressed genes by ZRF1.

Covalent modification of histones is fundamental in orchestrating chromatin dynamics and transcription. One example of such an epigenetic mark is the mono-ubiquitination of histones, which mainly occurs at histone H2A and H2B. Ubiquitination of histone H2A has been implicated in polycomb-mediated transcriptional silencing. However, the precise role of the ubiquitin mark during silencing is still elusive. Here we show in human cell lines that ZRF1 (zuotin-related factor 1) is specifically recruited to histone H2A when it is ubiquitinated at Lys 119 by means of a novel ubiquitin-interacting domain that is located in the evolutionarily conserved zuotin domain. At the onset of differentiation, ZRF1 specifically displaces polycomb-repressive complex 1 (PRC1) from chromatin and facilitates transcriptional activation. A genome-wide mapping of ZRF1, RING1B and H2A-ubiquitin targets revealed its involvement in the regulation of a large set of polycomb target genes, emphasizing the key role ZRF1 has in cell fate decisions. We provide here a model of the molecular mechanism of switching polycomb-repressed genes to an active state.

Progesterone receptor induces bcl-x expression through intragenic binding sites favoring RNA polymerase II elongation.

Steroid receptors were classically described for regulating transcription by binding to target gene promoters. However, genome-wide studies reveal that steroid receptors-binding sites are mainly located at intragenic regions. To determine the role of these sites, we examined the effect of progestins on the transcription of the bcl-x gene, where only intragenic progesterone receptor-binding sites (PRbs) were identified. We found that in response to hormone treatment, the PR is recruited to these sites along with two histone acetyltransferases CREB-binding protein (CBP) and GCN5, leading to an increase in histone H3 and H4 acetylation and to the binding of the SWI/SNF complex. Concomitant, a more relaxed chromatin was detected along bcl-x gene mainly in the regions surrounding the intragenic PRbs. PR also mediated the recruitment of the positive elongation factor pTEFb, favoring RNA polymerase II (Pol II) elongation activity. Together these events promoted the re-distribution of the active Pol II toward the 3'-end of the gene and a decrease in the ratio between proximal and distal transcription. These results suggest a novel mechanism by which PR regulates gene expression by facilitating the proper passage of the polymerase along hormone-dependent genes.

RUNX1 Is Regulated by Androgen Receptor to Promote Cancer Stem Markers and Chemotherapy Resistance in Triple Negative Breast Cancer.

Triple negative breast cancer (TNBC) is an aggressive breast cancer subtype for which no effective targeted therapies are available. Growing evidence suggests that chemotherapy-resistant cancer cells with stem-like properties (CSC) may repopulate the tumor. The androgen receptor (AR) is expressed in up to 50% of TNBCs, and AR inhibition decreases CSC and tumor initiation. Runt-related transcription factor 1 (RUNX1) correlates with poor prognosis in TNBC and is regulated by the AR in prostate cancer. Our group has shown that RUNX1 promotes TNBC cell migration and regulates tumor gene expression. We hypothesized that RUNX1 is regulated by the AR and that both may work together in TNBC CSC to promote disease recurrence following chemotherapy. Chromatin immunoprecipitation sequencing (ChIP-seq) experiments in MDA-MB-453 revealed AR binding to RUNX1 regulatory regions. RUNX1 expression is upregulated by dihydrotestosterone (DHT) in MDA-MB-453 and in an AR+-TNBC HCI-009 patient-derived xenograft (PDX) tumors (p < 0.05). RUNX1 is increased in a CSC-like experimental model in MDA-MB-453 and SUM-159PT cells (p < 0.05). Inhibition of RUNX1 transcriptional activity reduced the expression of CSC markers. Interestingly, RUNX1 inhibition reduced cell viability and enhanced paclitaxel and enzalutamide sensitivity. Targeting RUNX1 may be an attractive strategy to potentiate the anti-tumor effects of AR inhibition, specifically in the slow-growing CSC-like populations that resist chemotherapy which lead to metastatic disease.

Glucocorticoid alternative effects on proliferating and differentiated mammary epithelium are associated to opposite regulation of cell-cycle inhibitor expression.

Glucocorticoids influence post-natal mammary gland development by sequentially controlling cell proliferation, differentiation, and apoptosis. In the mammary gland, it has been demonstrated that glucocorticoid treatment inhibits epithelial apoptosis in post-lactating glands. In this study, our first goal was to identify new glucocorticoid target genes that could be involved in generating this effect. Expression profiling, by microarray analysis, revealed that expression of several cell-cycle control genes was altered by dexamethasone (DEX) treatment after lactation. Importantly, it was determined that not only the exogenous synthetic hormone, but also the endogenous glucocorticoids regulated the expression of these genes. Particularly, we found that the expression of cell cycle inhibitors p21CIP1, p18INK4c, and Atm was differentially regulated by glucocorticoids through the successive stages of mammary gland development. In undifferentiated cells, DEX treatment induced their expression and reduced cell proliferation, while in differentiated cells this hormone repressed expression of those cell cycle inhibitors and promoted survival. Therefore, differentiation status determined the effect of glucocorticoids on mammary cell fate. Particularly, we have determined that p21CIP1 inhibition would mediate the activity of these hormones in differentiated mammary cells because over-expression of this protein blocked DEX-induced apoptosis protection. Together, our data suggest that the multiple roles played by glucocorticoids in mammary gland development and function might be at least partially due to the alternative roles that these hormones play on the expression of cell cycle regulators.

Active Surveillance of Asymptomatic, Presymptomatic, and Oligosymptomatic SARS-CoV-2-Infected Individuals in Communities Inhabiting Closed or Semi-closed Institutions.

Background: The high COVID-19 dissemination rate demands active surveillance to identify asymptomatic, presymptomatic, and oligosymptomatic (APO) SARS-CoV-2-infected individuals. This is of special importance in communities inhabiting closed or semi-closed institutions such as residential care homes, prisons, neuropsychiatric hospitals, etc., where risk people are in close contact. Thus, a pooling approach-where samples are mixed and tested as single pools-is an attractive strategy to rapidly detect APO-infected in these epidemiological scenarios. Materials and Methods: This study was done at different pandemic periods between May 28 and August 31 2020 in 153 closed or semi-closed institutions in the Province of Buenos Aires (Argentina). We setup pooling strategy in two stages: first a pool-testing followed by selective individual-testing according to pool results. Samples included in negative pools were presumed as negative, while samples from positive pools were re-tested individually for positives identification. Results: Sensitivity in 5-sample or 10-sample pools was adequate since only 2 Ct values were increased with regard to single tests on average. Concordance between 5-sample or 10-sample pools and individual-testing was 100% in the Ct ≤ 36. We tested 4,936 APO clinical samples in 822 pools, requiring 86-50% fewer tests in low-to-moderate prevalence settings compared to individual testing. Conclusions: By this strategy we detected three COVID-19 outbreaks at early stages in these institutions, helping to their containment and increasing the likelihood of saving lives in such places where risk groups are concentrated.

Glucocorticoids uncover a critical role for ASH2L on BCL-X expression regulation in leukemia cells.

Targeting the apoptosis machinery is a promising therapeutic approach in myeloid malignancies. BCL2L1 is a well-known glucocorticoid-responsive gene and a key apoptosis regulator that, when over-expressed, can contribute to tumor development, progression and therapeutic resistance. Moreover, synthetic glucocorticoids, like dexamethasone, are frequently used in the treatment of hematopoietic diseases due to its pro-apoptotic properties. We report here that the trithorax protein ASH2L, considered one of the core subunits of H3K4-specific MLL/SET methyltransferase complexes, contributes to anti-apoptotic BCL-XL over-expression and cell survival in patient-derived myeloid leukemia cells. We find that the unliganded glucocorticoid receptor (uGR) and ASH2L interact in a common protein complex through a chromatin looping determined by uGR and ASH2L binding to BCL2L1 specific +58 HRE and promoter region, respectively. Upon addition of dexamethasone, GR and ASH2L recruitment is reduced, BCL-XL expression diminishes and apoptosis is induced consequently. Overall, our findings indicate that uGR and ASH2L may act as key regulatory players of BCL- XL upregulation in AML cells.

Mechanisms involved in tissue-specific apopotosis regulated by glucocorticoids.

Physiological cell turnover is under the control of a sharp and dynamic balance of different homeostatic mechanisms such as the equilibrium between cell proliferation and cell death. These mechanisms play an important role in maintaining normal tissue function and architecture. It is well known that apoptosis is the prevalent mode of physiological cell loss in most tissues. Steroid hormones like glucocorticoids have been identified as key signals controlling cell turnover by modulating programmed cell death in a tissue- and cell-specific manner. In this sense, several reports have demonstrated that glucocorticoids are able to induce apoptosis in cells of the hematopoietic system such as monocytes, macrophages, and T lymphocytes. In contrast, they protect against apoptotic signals evoked by cytokines, cAMP, tumor suppressors, in glandular cells such as the mammary gland epithelia, endometrium, hepatocytes, ovarian follicular cells, and fibroblasts. Although several studies have provided significant information on hormone-dependent apoptosis in an specific tissue, a clearly defined pathway that mediates cell death in response to glucocorticoids in different cell types is still misunderstood. The scope of this review is held to those mechanisms by which glucocorticoids control apoptosis, emphasizing tissue-specific expression of genes that are involved in the apoptotic pathway.

Role of 3'-5'-cyclic adenosine monophosphate on the epidermal growth factor dependent survival in mammary epithelial cells.

Epidermal growth factor (EGF) has been suggested to play a key role in the maintenance of epithelial cell survival during lactation. Previously, we demonstrated that EGF dependent activation of PI3K pathway prevents apoptosis in confluent murine HC11 cells cultured under low nutrient conditions. The EGF protective effect is associated with increased levels of the antiapoptotic protein Bcl-XL. Here, we identify the EGF-dependent mechanism involved in cell survival that converges in the regulation of bcl-X expression by activated CREB. EGF induces Bcl-XL expression through activation of a unique bcl-X promoter, the P1; being not only the PI3K/AKT signaling pathway but also the increase in cAMP levels and the concomitant PKA/CREB activation necessary for both bcl-XL upregulation and apoptosis avoidance. Results presented in this work suggest the existence of a novel connection between the EGF receptor and the adenylate cyclase that would have an impact in preventing apoptosis under low nutrient conditions.

RUNX1 and FOXP3 interplay regulates expression of breast cancer related genes.

Runx1 participation in epithelial mammary cells is still under review. Emerging data indicates that Runx1 could be relevant for breast tumor promotion. However, to date no studies have specifically evaluated the functional contribution of Runx1 to control gene expression in mammary epithelial tumor cells. It has been described that Runx1 activity is defined by protein context interaction. Interestingly, Foxp3 is a breast tumor suppressor gene. Here we show that endogenous Runx1 and Foxp3 physically interact in normal mammary cells and this interaction blocks Runx1 transcriptional activity. Furthermore we demonstrate that Runx1 is able to bind to R-spondin 3 (RSPO3) and Gap Junction protein Alpha 1 (GJA1) promoters. This binding upregulates Rspo3 oncogene expression and downregulates GJA1 tumor suppressor gene expression in a Foxp3-dependent manner. Moreover, reduced Runx1 transcriptional activity decreases tumor cell migration properties. Collectively, these data provide evidence of a new mechanism for breast tumor gene expression regulation, in which Runx1 and Foxp3 physically interact to control mammary epithelial cell gene expression fate. Our work suggests for the first time that Runx1 could be involved in breast tumor progression depending on Foxp3 availability.

Involvement of Bax protein in the prevention of glucocorticoid-induced thymocytes apoptosis by melatonin.

The antiapoptotic effect of melatonin has been described in several systems. In this study, the antagonistic effect of the methoxyindole on dexamethasone-induced apoptosis in mouse thymocytes was examined. Melatonin decreased both DNA fragmentation, and the number of annexin V-positive cells incubated in the presence of dexamethasone. Analysis of the expression of the members of the Bcl-2 family indicated that the synthetic glucocorticoid increased Bax protein levels without affecting the levels of Bcl-2, Bcl-XL, Bcl-XS, or Bak. This effect correlated with an increase in thymocytes bax mRNA levels. Dexamethasone also increased the release of cytochrome C from mitochondria. All of these effects were reduced in the presence of melatonin, which was ineffective per se on these parameters. In addition, the involvement of cAMP on glucocorticoid/melatonin antagonism was examined. Both melatonin and dexamethasone decreased the levels of this nucleotide in mouse thymocytes, indicating that the antagonistic action between both hormones involves a cAMP-independent pathway. In summary, the present results suggest that the antiapoptotic effect of melatonin on glucocorticoid-treated thymocytes would be a consequence of an inhibition of the mitochondrial pathway, presumably through the regulation of Bax protein levels.

Role of UTX in retinoic acid receptor-mediated gene regulation in leukemia.

Human UTX, a member of the Jumonji C family of proteins, associates with mixed-lineage leukemia 3/4 complexes. Stimulation with retinoic acid leads to the recruitment of UTX-containing complexes to HOX genes, which results in demethylation of histone H3 lysine 27 and concomitant methylation of histone H3 lysine 4. Here, we show that UTX interacts with the retinoic acid receptor α (RARα) and that this interaction is essential for proper differentiation of leukemic U937 cells in response to retinoic acid. UTX occupies the promoters of several RAR target genes and regulates their transcriptional output by modulating ASH2L complex recruitment. Overexpression of UTX in promyelocytic NB4 cells results in enhanced cellular differentiation upon retinoic acid treatment. Our results show that UTX is important for RAR-mediated transcription and provide insight into the critical role of cross talk between histone H3 lysine 4 methylation and histone H3 lysine 27 demethylation during cellular differentiation.

Glucocorticoids repress bcl-X expression in lymphoid cells by recruiting STAT5B to the P4 promoter.

The bcl-X gene plays a critical role in apoptosis. Six different isoforms generated by tissue-specific promoter usage and alternative splicing were described. Some of them exert opposite effects on cell death. In mammary epithelial cells glucocorticoids induce bcl-X expression and increase the ratio bcl-X(L) (antiapoptotic)/bcl-X(S) (apoptotic) by activating P4 promoter, which contains two hormone response elements. Here we show that, on mouse thymocytes and T lymphocyte derivative S49 cells, glucocorticoids inhibited transcription from P4 and decreased the ratio bcl-X(L)/bcl-X(S) favoring apoptosis. Upon hormonal treatment, glucocorticoid receptor (GR), steroid receptor coactivator-1, and RNA polymerase II were transiently recruited to P4 promoter, whereas STAT5B was also recruited but remained bound. Concomitant with the release of GR, silencing mediator for retinoic acid receptor and thyroid hormone receptor and histone deacetylase 3 were recruited, histone H3 was deacetylated, and RNA polymerase II left the promoter. Inhibition of STAT5 activity reverted glucocorticoid repression to activation of transcription and was accompanied by stable recruitment of GR and RNA polymerase II to P4.