Apoptosis is a process that removes unwanted or damaged cells. The biochemical events that mediate apoptotic cell death are generally initiated in one of two ways. In the first instance, death signals are generated at the cell surface. Activation of such cell surface proteins as the tumor necrosis factor-␣ or Fas receptors initiate an apoptotic cascade. Alternatively, the deprivation of many trophic growth factors that act through an interaction with a plasma membrane receptor can similarly result in apoptotic cell death. Our current understanding of the events that follow activation of either the tumor necrosis factor-␣ or Fas receptor envisions an initial premitochondrial phase that involves the Bcl-2 family of pro-and anti-apoptotic proteins and that may or may not require the participation of caspases (1). The mitochondrial phase that follows eventuates in the release of cytochrome c and the consequent activation of caspases, enzymes in which action leads to the variety of phenotypic alterations characteristic of apoptotic cell death. The apoptosis consequent to growth factor deprivation is also held to involve an initial phase mediated by the Bcl-2 family of proteins that again results in cytochrome c release from the mitochondria followed by a caspase-mediated effector phase (2, 3). Signals that result in apoptotic cell death are also generated from within the cell. Staurosporine and taxol are two well known examples of chemicals that induce apoptosis as a result of an interaction with an intracellular target. In most cases, however, the specific target and the earliest events that ensue upon the interaction with the inducing chemical are poorly understood.The best known intracellular target for the induction of apoptosis is, of course, DNA. Physical and chemical agents can damage DNA in a variety of ways and with distinct functional consequences, both immediate and delayed. A number of effects on the integrity of the DNA result in the induction of apoptosis, a response that removes cells that can no longer replicate or that have potentially mutagenic damage. The details as to the mechanism whereby the cell recognizes lesions in the DNA that are not readily repairable and then sets in motion events that result in apoptotic cell death are the subject of considerable research efforts. The most dominant current paradigm places p53 at the center of a process that couples DNA damage to the transcriptional regulation of much of the same pro-and antiapoptotic machinery that is activated by signals originating from the cell surface.The topoisomerase II inhibitor etoposide is an antineoplastic drug that has been widely used to couple DNA damage to apoptosis (4). Topoisomerase II is a nuclear enzyme that functions during both DNA replication and transcription (5). Topoisomerase II prevents "knots" from forming in DNA by allowing the passage of an intact segment of the helical DNA through a transient double strand break (6). Topoisomerase II inhibitors such as etoposide stabilize the complex formed by topoisomerase I...

Non-genetic drug resistance is increasingly recognised in various cancers. Molecular insights into this process are lacking and it is unknown whether stable non-genetic resistance can be overcome. Using single cell RNA-sequencing of paired drug naïve and resistant AML patient samples and cellular barcoding in a unique mouse model of non-genetic resistance, here we demonstrate that transcriptional plasticity drives stable epigenetic resistance. With a CRISPR-Cas9 screen we identify regulators of enhancer function as important modulators of the resistant cell state. We show that inhibition of Lsd1 (Kdm1a) is able to overcome stable epigenetic resistance by facilitating the binding of the pioneer factor, Pu.1 and cofactor, Irf8, to nucleate new enhancers that regulate the expression of key survival genes. This enhancer switching results in the re-distribution of transcriptional co-activators, including Brd4, and provides the opportunity to disable their activity and overcome epigenetic resistance. Together these findings highlight key principles to help counteract non-genetic drug resistance.

Induction of apoptosis in HeLa cells with staurosporine produced a rise in the intracellular pH (pH i)

Summary Atypical 7-transmembrane receptors, often called decoy receptors, act promiscuously as molecular sinks to regulate ligand bioavailability and consequently temper the signaling of canonical G protein-coupled receptor (GPCR) pathways. Loss of mammalian CXCR7, the most recently described decoy receptor, results in postnatal lethality due to aberrant cardiac development and myocyte hyperplasia. Here, we provide the molecular underpinning for this proliferative phenotype by demonstrating that the dosage and signaling of adrenomedullin (Adm = gene, AM = protein)—a mitogenic peptide-hormone required for normal cardiovascular development—is tightly controlled by CXCR7. To this end, Cxcr7−/− mice exhibit gain-of-function cardiac and lymphatic vascular phenotypes which can be reversed upon genetic depletion of adrenomedullin ligand. In addition to identifying a biological ligand accountable for the phenotypes of Cxcr7−/− mice, these results reveal a previously underappreciated role for decoy receptors as molecular rheostats in controlling the timing and extent of GPCR-mediated cardiac and vascular development.

These results suggest that cortical astrocytes can be transformed into GBM and that combined dysregulation of MAPK and PI3K signaling revert G1/S-defective astrocytes to a primitive gene expression state. This genetically-defined, immunocompetent model of proneural GBM will be useful for preclinical development of MAPK/PI3K-targeted, subtype-specific therapies.