DNA polymerase α-primase facilitates PARP inhibitor-induced fork acceleration and protects BRCA1-deficient cells against ssDNA gaps.

PARP inhibitors (PARPi), known for their ability to induce replication gaps and accelerate replication forks, have become potent agents in anticancer therapy. However, the molecular mechanism underlying PARPi-induced fork acceleration has remained elusive. Here, we show that the first PARPi-induced effect on DNA replication is an increased replication fork rate, followed by a secondary reduction in origin activity.

The cellular Notch1 protein promotes KSHV reactivation in an Rta-dependent manner.

Unlabelled: The cellular Notch signal transduction pathway is intimately associated with infections by Kaposi's sarcoma-associated herpesvirus (KSHV) and other gamma-herpesviruses. RBP-Jk, the cellular DNA binding component of the canonical Notch pathway, is the key Notch downstream effector protein in virus-infected and uninfected animal cells. Reactivation of KSHV from latency requires the viral lytic switch protein, Rta, to form complexes with RBP-Jk on numerous sites within the viral DNA.

Emetine blocks DNA replication via proteosynthesis inhibition not by targeting Okazaki fragments.

DNA synthesis of the leading and lagging strands works independently and cells tolerate single-stranded DNA generated during strand uncoupling if it is protected by RPA molecules. Natural alkaloid emetine is used as a specific inhibitor of lagging strand synthesis, uncoupling leading and lagging strand replication. Here, by analysis of lagging strand synthesis inhibitors, we show that despite emetine completely inhibiting DNA replication: it does not induce the generation of single-stranded DNA and chromatin-bound RPA32 (CB-RPA32).

Cannabidiol-induced activation of the metallothionein pathway impedes anticancer effects of disulfiram and its metabolite CuET.

Disulfiram (DSF), an established alcohol-aversion drug, is a candidate for repurposing in cancer treatment. DSF's antitumor activity is supported by preclinical studies, case reports, and small clinical trials; however, ongoing clinical trials of advanced-stage cancer patients encounter variable results. Here, we show that one reason for the inconsistent clinical effects of DSF may reflect interference by other drugs.

A herpesvirus transactivator and cellular POU proteins extensively regulate DNA binding of the host Notch signaling protein RBP-Jκ to the virus genome.

Reactivation of Kaposi's sarcoma-associated herpesvirus (KSHV) from latency requires the viral transactivator Rta to contact the host protein Jκ recombination signal-binding protein (RBP-Jκ or CSL). RBP-Jκ normally binds DNA sequence-specifically to determine the transcriptional targets of the Notch-signaling pathway, yet Notch alone cannot reactivate KSHV. We previously showed that Rta stimulates RBP-Jκ DNA binding to the viral genome.

KSHV and the Role of Notch Receptor Dysregulation in Disease Progression.

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of two human cancers, Kaposi's Sarcoma (KS) and primary effusion lymphoma (PEL), and a lymphoproliferation, Multicentric Castleman's Disease (MCD). Progression to tumor development in KS is dependent upon the reactivation of the virus from its latent state. We, and others, have shown that the Replication and transcriptional activator (Rta) protein is the only viral gene product that is necessary and sufficient for viral reactivation.

An easily transfectable cell line that produces an infectious reporter virus for routine and robust quantitation of Kaposi's sarcoma-associated herpesvirus reactivation.

Reactivation of Kaposi's sarcoma-associated herpesvirus (KHSV; also known as Human herpesvirus (HHV)-8) from latency is associated with progression to disease. The primary experimental models for studying KSHV reactivation are B lymphocyte cell lines derived from patients with primary effusion lymphoma (PEL). PEL models have remained essential tools for understanding molecular details of latency and reactivation, yet they have shortcomings.

KSHV reactivation and novel implications of protein isomerization on lytic switch control.

In Kaposi's sarcoma-associated herpesvirus (KSHV) oncogenesis, both latency and reactivation are hypothesized to potentiate tumor growth. The KSHV Rta protein is the lytic switch for reactivation. Rta transactivates essential genes via interactions with cofactors such as the cellular RBP-Jk and Oct-1 proteins, and the viral Mta protein.

Histone deacetylase classes I and II regulate Kaposi's sarcoma-associated herpesvirus reactivation.

In primary effusion lymphoma (PEL) cells infected with latent Kaposi's sarcoma-associated herpesvirus (KSHV), the promoter of the viral lytic switch gene, Rta, is organized into bivalent chromatin, similar to cellular developmental switch genes. Histone deacetylase (HDAC) inhibitors (HDACis) reactivate latent KSHV and dramatically remodel the viral genome topology and chromatin architecture. However, reactivation is not uniform across a population of infected cells.

The cellular peptidyl-prolyl cis/trans isomerase Pin1 regulates reactivation of Kaposi's sarcoma-associated herpesvirus from latency.

Kaposi's sarcoma-associated herpesvirus (KSHV) causes Kaposi's sarcoma and primary effusion lymphoma. KSHV-infected cells are predominantly latent, with a subset undergoing lytic reactivation. Rta is the essential lytic switch protein that reactivates virus by forming transactivation-competent complexes with the Notch effector protein RBP-Jk and promoter DNA.

Chromatin immunoprecipitation and microarray analysis reveal that TFIIB occupies the SL RNA gene promoter region in Trypanosoma brucei chromosomes.

RNA polymerase II (RNAP-II) synthesizes the m(7)G-capped Spliced Leader (SL) RNA and most protein-coding mRNAs in trypanosomes. RNAP-II recruitment to DNA usually requires a set of transcription factors that make sequence-specific contacts near transcriptional start sites within chromosomes. In trypanosomes, the transcription factor TFIIB is necessary for RNAP-II-dependent SL RNA transcription.

KSHV Rta Promoter Specification and Viral Reactivation.

Viruses are obligate intracellular pathogens whose biological success depends upon replication and packaging of viral genomes, and transmission of progeny viruses to new hosts. The biological success of herpesviruses is enhanced by their ability to reproduce their genomes without producing progeny viruses or killing the host cells, a process called latency. Latency permits a herpesvirus to remain undetected in its animal host for decades while maintaining the potential to reactivate, or switch, to a productive life cycle when host conditions are conducive to generating viral progeny.

An alternative Kaposi's sarcoma-associated herpesvirus replication program triggered by host cell apoptosis.

Kaposi's sarcoma-associated herpesvirus (KSHV) is linked to several neoplastic diseases: Kaposi's sarcoma, primary effusion lymphoma (PEL), and multicentric Castleman's disease (MCD). KSHV replicates actively, via a controlled gene expression program, but can also remain latent. It had been thought that the transition from latent to lytic replication was controlled exclusively by the replication and transcription activator protein RTA (open reading frame 50 [ORF50] gene product).

Kaposi's sarcoma-associated herpesvirus Rta tetramers make high-affinity interactions with repetitive DNA elements in the Mta promoter to stimulate DNA binding of RBP-Jk/CSL.

Kaposi's sarcoma-associated herpesvirus (KSHV; also known as human herpesvirus 8 [HHV-8]) is the etiologic agent of Kaposi's sarcoma (KS) and lymphoproliferative diseases. We previously demonstrated that the KSHV lytic switch protein Rta stimulates DNA binding of the cellular RBP-Jk/CSL protein, the nuclear component of the Notch pathway, on Rta target promoters. In the current study, we define the promoter requirements for formation of transcriptionally productive Rta/RBP-Jk/DNA complexes.

Convergence of Kaposi's sarcoma-associated herpesvirus reactivation with Epstein-Barr virus latency and cellular growth mediated by the notch signaling pathway in coinfected cells.

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiologic agent of primary effusion lymphoma (PEL). All PEL cell lines are infected with KSHV, and 70% are coinfected with Epstein-Barr virus (EBV). KSHV reactivation from latency requires promoter-specific transactivation by the KSHV Rta protein through interactions with RBP-Jk (CSL), the cellular DNA-binding component of the Notch signal transduction pathway.

Identification of direct transcriptional targets of the Kaposi's sarcoma-associated herpesvirus Rta lytic switch protein by conditional nuclear localization.

Lytic reactivation from latency is critical for the pathogenesis of Kaposi's sarcoma-associated herpesvirus (KSHV). We previously demonstrated that the 691-amino-acid (aa) KSHV Rta transcriptional transactivator is necessary and sufficient to reactivate the virus from latency. Viral lytic cycle genes, including those expressing additional transactivators and putative oncogenes, are induced in a cascade fashion following Rta expression.

Promoter- and cell-specific transcriptional transactivation by the Kaposi's sarcoma-associated herpesvirus ORF57/Mta protein.

The Kaposi's sarcoma-associated herpesvirus (KSHV) Mta protein, encoded by open reading frame 57, is a transactivator of gene expression that is essential for productive viral replication. Previous studies have suggested both transcriptional and posttranscriptional roles for Mta, but little is known regarding Mta's transcriptional function. In this study, we demonstrate that Mta cooperates with the KSHV lytic switch protein, Rta, to reactivate KSHV from latency, but Mta has little effect on reactivation when expressed alone.

Direct interactions of Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8 ORF50/Rta protein with the cellular protein octamer-1 and DNA are critical for specifying transactivation of a delayed-early promoter and stimulating viral reactivation.

The Kaposi's sarcoma-associated herpesvirus (KSHV) delayed-early K-bZIP promoter contains an ORF50/Rta binding site whose sequence is conserved with the ORF57 promoter. Mutation of the site in the full-length K-bZIP promoter reduced Rta-mediated transactivation by greater than 80%. The K-bZIP element contains an octamer (Oct) binding site that overlaps the Rta site and is well conserved with Oct elements found in the immediate-early promoters of herpes simplex virus type 1(HSV-1).

Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8 ORF50/Rta lytic switch protein functions as a tetramer.

The Kaposi's sarcoma-associated herpesvirus open reading frame 50 (ORF50) protein (called Rta), is necessary and sufficient for reactivation of the virus from latency. We previously demonstrated that a truncated mutant of ORF50 lacking its C-terminal transcriptional activation domain, called ORF50DeltaSTAD, formed mixed multimers with wild-type (WT) ORF50 and functioned as a dominant negative inhibitor of reactivation. For this report, we investigated the requirements for multimerization of ORF50/Rta in transactivation and viral reactivation.

Kaposi's Sarcoma-associated herpesvirus lytic switch protein stimulates DNA binding of RBP-Jk/CSL to activate the Notch pathway.

Kaposi's sarcoma-associated herpesvirus (KSHV) lytic switch protein, Rta, is a ligand-independent inducer of the Notch signal transduction pathway, and KSHV cannot reactivate from latency in cells null for the Notch target protein RBP-Jk. Here we show that Rta promotes DNA binding of RBP-Jk, a mechanism that is fundamentally different from that established for the RBP-Jk-activating proteins, Notch intracellular domain (NICD) and Epstein-Barr virus EBNA2. Although constitutively active RBP-Jk and NICD do not transactivate KSHV promoters independently, cotransfection of an Rta mutant lacking its transactivation domain robustly restores transcriptional activation.