Separation of telomere protection from length regulation by two different point mutations at amino acid 492 of RTEL1.

RTEL1 is an essential DNA helicase that plays multiple roles in genome stability and telomere length regulation. A variant of RTEL1 with a lysine at position 492 is associated with short telomeres in , while a conserved methionine at this position is found in , which has ultra-long telomeres. In humans, a missense mutation at this position ( ) causes a fatal telomere biology disease termed Hoyeraal-Hreidarsson syndrome (HHS).

A cyclin D1 intrinsically disordered domain accesses modified histone motifs to govern gene transcription.

The essential G-cyclin, CCND1, is frequently overexpressed in cancer, contributing to tumorigenesis by driving cell-cycle progression. D-type cyclins are rate-limiting regulators of G-S progression in mammalian cells via their ability to bind and activate CDK4 and CDK6. In addition, cyclin D1 conveys kinase-independent transcriptional functions of cyclin D1.

Telomouse-a mouse model with human-length telomeres generated by a single amino acid change in RTEL1.

Telomeres, the ends of eukaryotic chromosomes, protect genome integrity and enable cell proliferation. Maintaining optimal telomere length in the germline and throughout life limits the risk of cancer and enables healthy aging. Telomeres in the house mouse, Mus musculus, are about five times longer than human telomeres, limiting the use of this common laboratory animal for studying the contribution of telomere biology to aging and cancer.

Parkin ubiquitination of Kindlin-2 enables mitochondria-associated metastasis suppression.

Mitochondria are signaling organelles implicated in cancer, but the mechanisms are elusive. Here, we show that Parkin, an E3 ubiquitination (Ub) ligase altered in Parkinson's disease, forms a complex with the regulator of cell motility, Kindlin-2 (K2), at mitochondria of tumor cells. In turn, Parkin ubiquitinates Lys581 and Lys582 using Lys48 linkages, resulting in proteasomal degradation of K2 and shortened half-life from ∼5 h to ∼1.

Functional Interactions of Telomerase Reverse Transcriptase with the Three-Way Junction and the Template Domains of Telomerase RNA.

The ribonucleoprotein telomerase contains two essential components: telomerase RNA (TER) and telomerase reverse transcriptase (TERT, Est2 in yeast). A small portion of TER, termed the template, is copied by TERT onto the chromosome ends, thus compensating for sequence loss due to incomplete DNA replication and nuclease action. Although telomerase RNA is highly divergent in sequence and length across fungi and mammals, structural motifs essential for telomerase function are conserved.

Telomere dysfunction implicates POT1 in patients with idiopathic pulmonary fibrosis.

Exonic sequencing identified a family with idiopathic pulmonary fibrosis (IPF) containing a previously unreported heterozygous mutation in POT1 p.(L259S). The family displays short telomeres and genetic anticipation.

POT1-TPP1 binding stabilizes POT1, promoting efficient telomere maintenance.

Telomeric POT1-TPP1 binding is critical to telomere maintenance and disruption of this complex may lead to cancer. Current data suggests a reduction of intracellular POT1 levels in the absence of TPP1. Here we provide evidence of POT1 plasticity that contributes to its lack of stability in the absence of TPP1 binding.

Pol α-primase dependent nuclear localization of the mammalian CST complex.

The human CST complex composed of CTC1, STN1, and TEN1 is critically involved in telomere maintenance and homeostasis. Specifically, CST terminates telomere extension by inhibiting telomerase access to the telomeric overhang and facilitates lagging strand fill in by recruiting DNA Polymerase alpha primase (Pol α-primase) to the telomeric C-strand. Here we reveal that CST has a dynamic intracellular localization that is cell cycle dependent.

Targeting ACSS2 with a Transition-State Mimetic Inhibits Triple-Negative Breast Cancer Growth.

Acetyl-CoA is a vitally important and versatile metabolite used for many cellular processes including fatty acid synthesis, ATP production, and protein acetylation. Recent studies have shown that cancer cells upregulate acetyl-CoA synthetase 2 (ACSS2), an enzyme that converts acetate to acetyl-CoA, in response to stresses such as low nutrient availability and hypoxia. Stressed cancer cells use ACSS2 as a means to exploit acetate as an alternative nutrient source.

Endogenous Cyclin D1 Promotes the Rate of Onset and Magnitude of Mitogenic Signaling via Akt1 Ser473 Phosphorylation.

Cyclin D1 encodes the regulatory subunit of a holoenzyme that phosphorylates RB and functions as a collaborative nuclear oncogene. The serine threonine kinase Akt plays a pivotal role in the control of cellular metabolism, survival, and mitogenic signaling. Herein, Akt1-mediated phosphorylation of downstream substrates in the mammary gland is reduced by cyclin D1 genetic deletion and is induced by mammary-gland-targeted cyclin D1 overexpression.

POT1-TPP1 telomere length regulation and disease.

Telomeres are DNA repeats at the ends of linear chromosomes and are replicated by telomerase, a ribonucleoprotein reverse transcriptase. Telomere length regulation and chromosome end capping are essential for genome stability and are mediated primarily by the shelterin and CST complexes. POT1-TPP1, a subunit of shelterin, binds the telomeric overhang, suppresses ATR-dependent DNA damage response, and recruits telomerase to telomeres for DNA replication.

Disruption of ATRX-RNA interactions uncovers roles in ATRX localization and PRC2 function.

Heterochromatin in the eukaryotic genome is rigorously controlled by the concerted action of protein factors and RNAs. Here, we investigate the RNA binding function of ATRX, a chromatin remodeler with roles in silencing of repetitive regions of the genome and in recruitment of the polycomb repressive complex 2 (PRC2). We identify ATRX RNA binding regions (RBRs) and discover that the major ATRX RBR lies within the N-terminal region of the protein, distinct from its PHD and helicase domains.

MFF Regulation of Mitochondrial Cell Death Is a Therapeutic Target in Cancer.

The regulators of mitochondrial cell death in cancer have remained elusive, hampering the development of new therapies. Here, we showed that protein isoforms of mitochondrial fission factor (MFF1 and MFF2), a molecule that controls mitochondrial size and shape, that is, mitochondrial dynamics, were overexpressed in patients with non-small cell lung cancer and formed homo- and heterodimeric complexes with the voltage-dependent anion channel-1 (VDAC1), a key regulator of mitochondrial outer membrane permeability. MFF inserted into the interior hole of the VDAC1 ring using Arg225, Arg236, and Gln241 as key contact sites.

Recent advances with cyclin-dependent kinase inhibitors: therapeutic agents for breast cancer and their role in immuno-oncology.

: Collaborative interactions between several diverse biological processes govern the onset and progression of breast cancer. These processes include alterations in cellular metabolism, anti-tumor immune responses, DNA damage repair, proliferation, anti-apoptotic signals, autophagy, epithelial-mesenchymal transition, components of the non-coding genome or onco-mIRs, cancer stem cells and cellular invasiveness. The last two decades have revealed that each of these processes are also directly regulated by a component of the cell cycle apparatus, cyclin D1.

A non-natural nucleotide uses a specific pocket to selectively inhibit telomerase activity.

Telomerase, a unique reverse transcriptase that specifically extends the ends of linear chromosomes, is up-regulated in the vast majority of cancer cells. Here, we show that an indole nucleotide analog, 5-methylcarboxyl-indolyl-2'-deoxyriboside 5'-triphosphate (5-MeCITP), functions as an inhibitor of telomerase activity. The crystal structure of 5-MeCITP bound to the Tribolium castaneum telomerase reverse transcriptase reveals an atypical interaction, in which the nucleobase is flipped in the active site.

Structural and functional analysis of an OB-fold in human Ctc1 implicated in telomere maintenance and bone marrow syndromes.

The human CST (Ctc1, Stn1 and Ten1) complex binds the telomeric overhang and regulates telomere length by promoting C-strand replication and inhibiting telomerase-dependent G-strand synthesis. Structural and biochemical studies on the human Stn1 and Ten1 complex revealed its mechanism of assembly and nucleic acid binding. However, little is known about the structural organization of the multi-domain Ctc1 protein and how each of these domains contribute to telomere length regulation.

ADAR1 controls apoptosis of stressed cells by inhibiting Staufen1-mediated mRNA decay.

Both p150 and p110 isoforms of ADAR1 convert adenosine to inosine in double-stranded RNA (dsRNA). ADAR1p150 suppresses the dsRNA-sensing mechanism that activates MDA5-MAVS-IFN signaling in the cytoplasm. In contrast, the biological function of the ADAR1p110 isoform, which is usually located in the nucleus, is largely unknown.

Structural and functional analysis of the human POT1-TPP1 telomeric complex.

POT1 and TPP1 are part of the shelterin complex and are essential for telomere length regulation and maintenance. Naturally occurring mutations of the telomeric POT1-TPP1 complex are implicated in familial glioma, melanoma and chronic lymphocytic leukaemia. Here we report the atomic structure of the interacting portion of the human telomeric POT1-TPP1 complex and suggest how several of these mutations contribute to malignant cancer.

Structural Analysis Reveals the Deleterious Effects of Telomerase Mutations in Bone Marrow Failure Syndromes.

Naturally occurring mutations in the ribonucleoprotein reverse transcriptase, telomerase, are associated with the bone marrow failure syndromes dyskeratosis congenita, aplastic anemia, and idiopathic pulmonary fibrosis. However, the mechanism by which these mutations impact telomerase function remains unknown. Here we present the structure of the human telomerase C-terminal extension (or thumb domain) determined by the method of single-wavelength anomalous diffraction to 2.

Structure and function of the telomeric CST complex.

Telomeres comprise the ends of eukaryotic chromosomes and are essential for cell proliferation and genome maintenance. Telomeres are replicated by telomerase, a ribonucleoprotein (RNP) reverse transcriptase, and are maintained primarily by nucleoprotein complexes such as shelterin (TRF1, TRF2, TIN2, RAP1, POT1, TPP1) and CST (Cdc13/Ctc1, Stn1, Ten1). The focus of this review is on the CST complex and its role in telomere maintenance.

SPOP E3 Ubiquitin Ligase Adaptor Promotes Cellular Senescence by Degrading the SENP7 deSUMOylase.

The SPOP gene, which encodes an E3 ubiquitin ligase adaptor, is frequently mutated in a number of cancer types. However, the mechanisms by which SPOP functions as a tumor suppressor remain poorly understood. Here, we show that SPOP promotes senescence, an important tumor suppression mechanism, by targeting the SENP7 deSUMOylase for degradation.

Structural Basis of Telomerase Inhibition by the Highly Specific BIBR1532.

BIBR1532 is a highly specific telomerase inhibitor, although the molecular basis for inhibition is unknown. Here we present the crystal structure of BIBR1532 bound to Tribolium castaneum catalytic subunit of telomerase (tcTERT). BIBR1532 binds to a conserved hydrophobic pocket (FVYL motif) on the outer surface of the thumb domain.

The Telomere Binding Protein Cdc13 and the Single-Stranded DNA Binding Protein RPA Protect Telomeric DNA from Resection by Exonucleases.

The telomere is present at the ends of all eukaryotic chromosomes and usually consists of repetitive TG-rich DNA that terminates in a single-stranded 3' TG extension and a 5' CA-rich recessed strand. A biochemical assay that allows the in vitro observation of exonuclease-catalyzed degradation (resection) of telomeres has been developed. The approach uses an oligodeoxynucleotide that folds to a stem-loop with a TG-rich double-stranded region and a 3' single-stranded extension, typical of telomeres.

Interaction between TBP and Condensin Drives the Organization and Faithful Segregation of Mitotic Chromosomes.

Genome/chromosome organization is highly ordered and controls various nuclear events, although the molecular mechanisms underlying the functional organization remain largely unknown. Here, we show that the TATA box-binding protein (TBP) interacts with the Cnd2 kleisin subunit of condensin to mediate interphase and mitotic chromosomal organization in fission yeast. TBP recruits condensin onto RNA polymerase III-transcribed (Pol III) genes and highly transcribed Pol II genes; condensin in turn associates these genes with centromeres.