Phenotypic Screen Identifies a Small Molecule Modulating ERK2 and Promoting Stem Cell Proliferation

Stem cells display a fundamentally different mechanism of proliferation control when compared to somatic cells. Uncovering these mechanisms would maximize the impact in drug discovery with a higher translational applicability. The unbiased approach used in phenotype-based drug discovery (PDD) programs can offer a unique opportunity to identify such novel biological phenomenon. Here, we describe an integrated phenotypic screening approach, employing a combination of in vitro and in vivo PDD models to identify a small molecule increasing stem cell proliferation. We demonstrate that a combination of both in vitro and in vivo screening models improves hit identification and reproducibility of effects across various PDD models. Using cell viability and colony size phenotype measurement we characterize the structure activity relationship of the lead molecule, and identify that the small molecule inhibits phosphorylation of ERK2 and promotes stem cell proliferation. This study demonstrates a PDD approach that employs combinatorial models to identify compounds promoting stem cell proliferation.

Understanding cytoskeleton regulators in glioblastoma multiforme for therapy design

The cellular cytoskeleton forms the primary basis through which a cell governs the changes in size, shape, migration, proliferation, and forms the primary means through which the cells respond to their environment. Indeed, cell and tissue morphologies are used routinely not only to grade tumors but also in various high-content screening methods with an aim to identify new small molecules with therapeutic potential. This study examines the expression of various cytoskeleton regulators in glioblastoma multiforme (GBM). GBM is a very aggressive disease with a low life expectancy even after chemo- and radiotherapy. Cancer cells of GBM are notorious for their invasiveness, ability to develop resistance to chemo- and radiotherapy, and to form secondary site tumors. This study aims to gain insight into cytoskeleton regulators in GBM cells and to understand the effect of various oncology drugs, including temozolomide, on cytoskeleton regulators. We compare the expression of various cytoskeleton regulators in GBM-derived tumor and normal tissue, CD133-postive and -negative cells from GBM and neural cells, and GBM stem-like and differentiated cells. In addition, the correlation between the expression of cytoskeleton regulators with the clinical outcome was examined to identify genes associated with longer patient survival. This was followed by a small molecule screening with US Food and Drug Administration (FDA)-approved oncology drugs, and its effect on cellular cytoskeleton was compared to treatment with temozolomide. This study identifies various groups of cytoskeletal regulators that have an important effect on patient survival and tumor development. Importantly, this work highlights the advantage of using cytoskeleton regulators as biomarkers for assessing prognosis and treatment design for GBM.

Abstract A23: Epigenetic Cis-regulatory interactions in HIF1a-activated melanocytes

Melanoma tumors are heterogeneous lesions that progress through distinct cellular phenotypes exhibiting either highly proliferative or invasive cell state gene expression signatures (SOX10+ vs. TGFB+ pathways, respectively) as disease progression occurs. It is appreciated that even within a single tumor, individual cells respond to hypoxic conditions through Hypoxia Inducible Factor 1a (HIF1a) activation, leading to gene expression that promotes invasive cell properties. Regulation of gene expression integrates the binding of intrinsic cell lineage factors and general transcription machinery to key cis-regulatory DNA sequences that are epigenetically defined. In order to identify the cis-regulatory sequences that are utilized in a cell's response to HIF1a activation, we have established an integrated regulatory dataset from melan-Ink4a-ARF-/- immortalized mouse melanocytes. This dataset includes Dnase1 HS regions, enhancer regions marked by H3K4me1 and EP300 co-binding, ChIP-Seq for the transcription factors HIF1a and SOX10, and RNA-SEQ datasets under proliferative and HIF1a-activated growth conditions. We are evaluating HIF1a binding regions in order to identify the cis-regulatory sequences utilized to regulate gene expression, identify the key factors engaged at these sites, and assess the role that DNA variation has in modulating factor binding and gene transcription in the switch from proliferative to hypoxic cell signaling conditions. By identifying the epigenetic cis-regulatory interactions that occur as a result of HIF1a activation, we hypothesize that we will highlight pathways important for melanoma progression that may be relevant to future therapeutics.

Citation Format: Stacie Loftus, Julie Cronin, Temesgen Fufa, Andrew McCallion, Gregory Crawford, William Pavan. Epigenetic Cis-regulatory interactions in HIF1a-activated melanocytes. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Melanoma: From Biology to Therapy; Sep 20-23, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(14 Suppl):Abstract nr A23.

Abstract 2941: Rapid changes in chromatin structure in response to extracellular signals

Immediate early genes (IEGs) are well known to be rapidly and transiently induced at high levels of expression in response to various extracellular signals such as growth factors. These rapid changes in the transcriptional state of this class of genes raised questions regarding the role of higher order chromatin structure in this transient event of inducible gene expression. In these studies, we compared the degree of chromatin condensation in Jurkat cells before and after mitogen stimulation of c-fos, a well-known IEG. Soluble chromatin obtained from unstimulated and stimulated cells were collected for a sucrose gradient sedimentation assay in order to separate chromatin fibers by means of size and more importantly by the extent of structural condensation of the chromatin. Real time-PCR analysis of c-fos was then used as a tool to quantify the distribution of open and closed chromatin fibers across the collected fractions obtained from the sucrose gradients. The results suggested a major decondensation of the chromatin fiber at the c-fos gene upon stimulation. The unfolding of the chromatin structure upon stimulation is paired with a dramatic increase in histone acetylation as detected by chromatin immunoprecipiation (ChIP) at the promoter region. Histone hyperacetylation is known to cause destabilization of the higher order chromatin structure leading to an increase in chromatin accessibility as clearly shown in our DNase hypersensitivity studies. Taken together, we have detected a rapid decondensation of the chromatin fiber, which is believed to facilitate the rapid transcriptional response to extracellular signals. Our current interest lies in obtaining further information regarding the molecular events that are more directly related to destabilization of the higher order chromatin structure upon mitogen stimulation. Testing of various molecular candidates involved in chromatin destabilizing events include phosphorylation of linker histone H1, recruitment of histone variants and dramatic histone modications such as ADP-polyribosylation at the c-fos promoter region. A more detailed understanding on the rapid decondensation of the chromatin fiber would provide valuable information regarding the cascade of events that must take place in response to stress or extracellular signals.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2941.

Transcriptional autoregulation by BRCA1

The BRCA1 gene product plays numerous roles in regulating genome integrity. Its role in assembling supermolecular complexes in response to DNA damage has been extensively studied; however, much less is understood about its role as a transcriptional coregulator. Loss or mutation is associated with hereditary breast and ovarian cancers, whereas altered expression occurs frequently in sporadic forms of breast cancer, suggesting that the control of BRCA1 transcription might be important to tumorigenesis. Here, we provide evidence of a striking linkage between the roles for BRCA1 as a transcriptional coregulator with control of its expression via an autoregulatory transcriptional loop. BRCA1 assembles with complexes containing E2F-1 and RB to form a repressive multicomponent transcriptional complex that inhibits BRCA1 promoter transcription. This complex is disrupted by genotoxic stress, resulting in the displacement of BRCA1 protein from the BRCA1 promoter and subsequent upregulation of BRCA1 transcription. Cells depleted of BRCA1 respond by upregulating BRCA1 transcripts, whereas cells overexpressing BRCA1 respond by downregulating BRCA1 transcripts. Tandem chromatin immmunoprecipitation studies show that BRCA1 is regulated by a dynamic coregulatory complex containing BRCA1, E2F1, and Rb at the BRCA1 promoter that is disrupted by DNA-damaging agents to increase its transcription. These results define a novel transcriptional mechanism of autoregulated homeostasis of BRCA1 that selectively titrates its levels to maintain genome integrity in response to genotoxic insult.