Suppression of DNA-damage checkpoint signaling by Rsk-mediated phosphorylation of Mre11.

Ataxia telangiectasia mutant (ATM) is an S/T-Q-directed kinase that is critical for the cellular response to double-stranded breaks (DSBs) in DNA. Following DNA damage, ATM is activated and recruited by the MRN protein complex [meiotic recombination 11 (Mre11)/DNA repair protein Rad50/Nijmegen breakage syndrome 1 proteins] to sites of DNA damage where ATM phosphorylates multiple substrates to trigger cell-cycle arrest. In cancer cells, this regulation may be faulty, and cell division may proceed even in the presence of damaged DNA. We show here that the ribosomal s6 kinase (Rsk), often elevated in cancers, can suppress DSB-induced ATM activation in both Xenopus egg extracts and human tumor cell lines. In analyzing each step in ATM activation, we have found that Rsk targets loading of MRN complex components onto DNA at DSB sites. Rsk can phosphorylate the Mre11 protein directly at S676 both in vitro and in intact cells and thereby can inhibit the binding of Mre11 to DNA with DSBs. Accordingly, mutation of S676 to Ala can reverse inhibition of the response to DSBs by Rsk. Collectively, these data point to Mre11 as an important locus of Rsk-mediated checkpoint inhibition acting upstream of ATM activation.

Telomere disruption results in non-random formation of de novo dicentric chromosomes involving acrocentric human chromosomes.

Genome rearrangement often produces chromosomes with two centromeres (dicentrics) that are inherently unstable because of bridge formation and breakage during cell division. However, mammalian dicentrics, and particularly those in humans, can be quite stable, usually because one centromere is functionally silenced. Molecular mechanisms of centromere inactivation are poorly understood since there are few systems to experimentally create dicentric human chromosomes. Here, we describe a human cell culture model that enriches for de novo dicentrics. We demonstrate that transient disruption of human telomere structure non-randomly produces dicentric fusions involving acrocentric chromosomes. The induced dicentrics vary in structure near fusion breakpoints and like naturally-occurring dicentrics, exhibit various inter-centromeric distances. Many functional dicentrics persist for months after formation. Even those with distantly spaced centromeres remain functionally dicentric for 20 cell generations. Other dicentrics within the population reflect centromere inactivation. In some cases, centromere inactivation occurs by an apparently epigenetic mechanism. In other dicentrics, the size of the alpha-satellite DNA array associated with CENP-A is reduced compared to the same array before dicentric formation. Extra-chromosomal fragments that contained CENP-A often appear in the same cells as dicentrics. Some of these fragments are derived from the same alpha-satellite DNA array as inactivated centromeres. Our results indicate that dicentric human chromosomes undergo alternative fates after formation. Many retain two active centromeres and are stable through multiple cell divisions. Others undergo centromere inactivation. This event occurs within a broad temporal window and can involve deletion of chromatin that marks the locus as a site for CENP-A maintenance/replenishment.

Redeeming Faustus: Tracing the pacts of Mariken and Faust from the 1500s to the present

<p>This dissertation uncovers and analyzes the complicated history of the devil’s pact in literature from approximately 1330 to 2015, focusing primarily on texts written in German and Dutch. That the tale of the pact with the devil (the so-called Faustian bargain) is one of the most durable and pliable literary themes is undeniable. Yet for too long, the success of Johann Wolfgang von Goethe’s Faust I (1808) decisively shaped scholarship on early devil’s pact tales, leading to a misreading of the texts with Goethe’s concerns being projected onto the earliest manifestations. But Goethe’s Faust really only borrows from the original Faust his name; the two characters could not be more different. Furthermore, Faustus was not the only early pact-maker character and his tale was neither limited to the German language nor to the Protestant faith. Among others, tales written in Dutch about a female, Catholic, latemedieval pact-maker, Mariken van Nieumeghen (1515), illustrate this. This dissertation seeks to redeem the early modern Faustus texts from its misreading and to broaden the scholarship on the literature of the devil’s pact by considering the Mariken and Faust traditions together.</p> <p>The first chapter outlines the beginnings of pact literature as a Catholic phenomenon, considering the tales of Theophilus and Pope Joan alongside Mariken of Nijmegen. The second chapter turns to the original Faust tale, the Historia von D. Johann Fausten (1587), best read as a Lutheran response to the Catholic pact literature in the wake of the Reformation. In the third chapter, this dissertation offers a new, united reading of the early modern Faust tradition. The fourth and fifth chapters trace the literary preoccupation with the pacts of both Mariken and Faustus from the late early modern to the present. <p>The dissertation traces the evolution of these two bodies of literature and provides an in-depth analysis and comparison of the two that has not been done before. It argues for a more global literary scholarship that considers texts across multiple languages and one that takes into consideration the rich body of material of the pact tradition.</p>