Cdc13 OB2 Dimerization Required for Productive Stn1 Binding and Efficient Telomere Maintenance

SummaryCdc13 is an essential yeast protein required for telomere length regulation and genome stability. It does so via its telomere-capping properties and by regulating telomerase access to the telomeres. The crystal structure of the Saccharomyces cerevisiae Cdc13 domain located between the recruitment and DNA binding domains reveals an oligonucleotide-oligosaccharide binding fold (OB2) with unusually long loops extending from the core of the protein. These loops are involved in extensive interactions between two Cdc13 OB2 folds leading to stable homodimerization. Interestingly, the functionally impaired cdc13-1 mutation inhibits OB2 dimerization. Biochemical assays indicate OB2 is not involved in telomeric DNA or Stn1 binding. However, disruption of the OB2 dimer in full-length Cdc13 affects Cdc13-Stn1 association, leading to telomere length deregulation, increased temperature sensitivity, and Stn1 binding defects. We therefore propose that dimerization of the OB2 domain of Cdc13 is required for proper Cdc13, Stn1, Ten1 (CST) assembly and productive telomere capping

Noncommutative probability, matrix models, and quantum orbifold geometry

Inspired by the intimate relationship between Voiculescu's noncommutative probability theory (of type A) and large-N matrix models in physics, we look for physical models related to noncommutative probability theory of type B. These turn out to be fermionic matrix-vector models at the double large-N limit. In the context of string theory, they describe different orbifolded string worldsheets with boundaries. Their critical exponents coincide with that of ordinary string worldsheets, but their renormalised tree-level one-boundary amplitudes differ.Comment: 22 pages, 8 eps figures, LaTeX2.09; title changed, mistakes correcte

The Wasteland of Random Supergravities

We show that in a general \cal{N} = 1 supergravity with N \gg 1 scalar fields, an exponentially small fraction of the de Sitter critical points are metastable vacua. Taking the superpotential and Kahler potential to be random functions, we construct a random matrix model for the Hessian matrix, which is well-approximated by the sum of a Wigner matrix and two Wishart matrices. We compute the eigenvalue spectrum analytically from the free convolution of the constituent spectra and find that in typical configurations, a significant fraction of the eigenvalues are negative. Building on the Tracy-Widom law governing fluctuations of extreme eigenvalues, we determine the probability P of a large fluctuation in which all the eigenvalues become positive. Strong eigenvalue repulsion makes this extremely unlikely: we find P \propto exp(-c N^p), with c, p being constants. For generic critical points we find p \approx 1.5, while for approximately-supersymmetric critical points, p \approx 1.3. Our results have significant implications for the counting of de Sitter vacua in string theory, but the number of vacua remains vast.Comment: 39 pages, 9 figures; v2: fixed typos, added refs and clarification

Cumulant Expansions and the Spin-Boson Problem

The dynamics of the dissipative two-level system at zero temperature is studied using three different cumulant expansion techniques. The relative merits and drawbacks of each technique are discussed. It is found that a new technique, the non-crossing cumulant expansion, appears to embody the virtues of the more standard cumulant methods.Comment: 26 pages, LaTe

MYC regulates fatty acid metabolism through a multigenic program in claudin-low triple negative breast cancer

Background: Recent studies have suggested that fatty acid oxidation (FAO) is a key metabolic pathway for the growth of triple negative breast cancers (TNBCs), particularly those that have high expression of MYC. However, the underlying mechanism by which MYC promotes FAO remains poorly understood. Methods: We used a combination of metabolomics, transcriptomics, bioinformatics, and microscopy to elucidate a potential mechanism by which MYC regulates FAO in TNBC. Results: We propose that MYC induces a multigenic program that involves changes in intracellular calcium signalling and fatty acid metabolism. We determined key roles for fatty acid transporters (CD36), lipases (LPL), and kinases (PDGFRB, CAMKK2, and AMPK) that each contribute to promoting FAO in human mammary epithelial cells that express oncogenic levels of MYC. Bioinformatic analysis further showed that this multigenic program is highly expressed and predicts poor survival in the claudin-low molecular subtype of TNBC, but not other subtypes of TNBCs, suggesting that efforts to target FAO in the clinic may best serve claudin-low TNBC patients. Conclusion: We identified critical pieces of the FAO machinery that have the potential to be targeted for improved treatment of patients with TNBC, especially the claudin-low molecular subtype

Concurrent MEK2 Mutation and BRAF Amplification Confer Resistance to BRAF and MEK Inhibitors in Melanoma

SummaryAlthough BRAF and MEK inhibitors have proven clinical benefits in melanoma, most patients develop resistance. We report a de novo MEK2-Q60P mutation and BRAF gain in a melanoma from a patient who progressed on the MEK inhibitor trametinib and did not respond to the BRAF inhibitor dabrafenib. We also identified the same MEK2-Q60P mutation along with BRAF amplification in a xenograft tumor derived from a second melanoma patient resistant to the combination of dabrafenib and trametinib. Melanoma cells chronically exposed to trametinib acquired concurrent MEK2-Q60P mutation and BRAF-V600E amplification, which conferred resistance to MEK and BRAF inhibitors. The resistant cells had sustained MAPK activation and persistent phosphorylation of S6K. A triple combination of dabrafenib, trametinib, and the PI3K/mTOR inhibitor GSK2126458 led to sustained tumor growth inhibition. Hence, concurrent genetic events that sustain MAPK signaling can underlie resistance to both BRAF and MEK inhibitors, requiring novel therapeutic strategies to overcome it

Myc-mediated transcriptional regulation of the mitochondrial chaperone TRAP1 controls primary and metastatic tumor growth.

The role of mitochondria in cancer continues to be debated, and whether exploitation of mitochondrial functions is a general hallmark of malignancy or a tumor- or context-specific response is still unknown. Using a variety of cancer cell lines and several technical approaches, including siRNA-mediated gene silencing, ChIP assays, global metabolomics and focused metabolite analyses, bioenergetics, and cell viability assays, we show that two oncogenic Myc proteins, c-Myc and N-Myc, transcriptionally control the expression of the mitochondrial chaperone TNFR-associated protein- 1 (TRAP1) in cancer. In turn, this Myc-mediated regulation preserved the folding and function of mitochondrial oxidative phosphorylation (OXPHOS) complex II and IV subunits, dampened reactive oxygen species production, and enabled oxidative bioenergetics in tumor cells. Of note, we found that genetic or pharmacological targeting of this pathway shuts off tumor cell motility and invasion, kills Myc-expressing cells in a TRAP1-dependent manner, and suppresses primary and metastatic tumor growth in vivo. We conclude that exploitation of mitochondrial functions is a general trait of tumorigenesis and that this reliance of cancer cells on mitochondrialOXPHOSpathways could offer an actionable therapeutic target in the clinic

Abstract 1441 : MYC expression promotes lipid metabolism and metabolic plasticity in human mammary epithelial cell

MYC is one of the most commonly mutated and highly amplified oncogenes in human breast cancer. MYC amplifications occur most frequently in triple-negative breast cancers (TNBCs). TNBCs can be divided into two molecular subtypes: basal-like and claudin-low breast cancers. These cancers tend to be extremely aggressive and are strongly associated with disease recurrence, poor prognosis and high mortality. In particular, claudin-low tumors are classified by a loss of tight junctions and cell-to-cell contacts and an enrichment for genes associated with an epithelial-to-mesenchymal transition (EMT) and mammary stem cells (also known as tumor-initiating cells). Despite the high level of disease severity, there are no targeted therapies for claudin-low TNBCs. To address this unmet need, we utilized human mammary epithelial cells (HuMECs) that express oncogenic levels of MYC and a mutant MYC (T58A) to characterize the behavioral and metabolic changes that occur during the formation of MYC-driven breast cancers. We found that MYC regulates the expression of genes associated with cell stemness, EMT, lipid metabolism, and calcium (Ca2+) signaling and that the expression of this gene signature promotes cell growth, survival, migration, and metabolic plasticity. The gene signature of MYC-expressing HuMECs highly correlates with the gene signature of claudin-low breast cancers, therefore highlighting the relevance of our HuMEC model to human claudin-low breast cancer. We found the major drivers underlying the MYC-dependent changes in cell behavior to be stimulation of Ca2+ signaling and strong activation of lipid metabolism. Ca2+ signaling is stimulated through the MYC-dependent repression of Ca2+ efflux mechanisms; elevated cytosolic Ca2+ then consequently stimulates a Ca2+/calmodulin kinase kinase 2 (CAMKK2)/AMPK signaling axis that activates fatty acid scavenging and transport, as well as β-oxidation. Enhanced lipid metabolism thereby provides the necessary biomass (fatty acids) for phospholipid biosynthesis and energy (ATP) to support the metabolically demanding processes of cell growth, proliferation, and migration. In all, our findings provide a strong rationale for targeting lipid metabolism and the Ca2+/CAMKK2/AMPK signaling axis in MYC-driven, and potentially claudin-low, breast cancers

Co-circulation of Four Human Coronaviruses (HCoVs) in Queensland Children with Acute Respiratory Tract Illnesses in 2004

Acute respiratory illnesses (ARIs) with unconfirmed infectious aetiologies peak at different times of the year. Molecular diagnostic assays reduce the number of unconfirmed ARIs compared to serology- or culture-based techniques. Screening of 888 inpatient and outpatient respiratory specimens spanning late autumn through to early spring, 2004, identified the presence of a human coronavirus (HCoV) on 74 occasions (8.3% of all specimens and 26.3% of all respiratory virus detections). Prevalence peaked in August (late winter in the southern hemisphere) when they were detected in 21.9% of specimens tested. HCoV-HKU1 and HCoV-OC43 comprised 82.4% of all HCoVs detected. Positive specimens were used to develop novel reverse transcriptase real-time PCRs (RT-rtPCRs) for HCoV detection. An objective clinical severity score was assigned to each positive HCoV patient. Severity scores were similar to those from a random selection of young children who were positive for respiratory syncytial virus at a different time but from the same specimen population. During the cooler months of 2004, sensitive and specific RT-rtPCRs identified the concurrent circulation of all four HCoVs, a quarter of which co-occurred with another virus and most of which were from children under the age of two years