Fundación Instituto Leloir

About: Fundación Instituto Leloir is a facility organization based out in Buenos Aires, Argentina. It is known for research contribution in the topics: Dentate gyrus & Neurogenesis. The organization has 702 authors who have published 1052 publications receiving 39299 citations.

Chk1 loss creates replication barriers that compromise cell survival independently of excess origin firing

Abstract: The effectiveness of checkpoint kinase 1 (Chk1) inhibitors at killing cancer cells is considered to be fully dependent on their effect on DNA replication initiation. Chk1 inhibition boosts origin firing, presumably limiting the availability of nucleotides and in turn provoking the slowdown and subsequent collapse of forks, thus decreasing cell viability. Here we show that slow fork progression in Chk1-inhibited cells is not an indirect effect of excess new origin firing. Instead, fork slowdown results from the accumulation of replication barriers, whose bypass is impeded by CDK-dependent phosphorylation of the specialized DNA polymerase eta (Polη). Also in contrast to the linear model, the accumulation of DNA damage in Chk1-deficient cells depends on origin density but is largely independent of fork speed. Notwithstanding this, origin dysregulation contributes only mildly to the poor proliferation rates of Chk1-depleted cells. Moreover, elimination of replication barriers by downregulation of helicase components, but not their bypass by Polη, improves cell survival. Our results thus shed light on the molecular basis of the sensitivity of tumors to Chk1 inhibition.

A quasi-spontaneous amyloid route in a DNA binding gene regulatory domain: The papillomavirus HPV16 E2 protein.

Abstract: The DNA binding domain of papillomavirus E2 proteins is at the center of the regulation of gene transcription and replication of the virus. Its unique fold consists of a β-barrel domain that combines an eight-stranded dimeric β-barrel core interface with two symmetrical DNA binding α-helices and other two helices, packed against the central barrel. Treatment with low amounts of trifluoroethanol readily leads to a mostly β-sheet oligomeric species, with a loss of near-UV circular dichroism signal and increase in its ANS binding capacity, indicating that buried hydrophobic surfaces become accessible to the solvent. This species subsequently undergoes a slow transition into amyloid aggregates as determined by light scattering and Congo red and thioflavin T binding. Electron microscopy shows short amyloid fibers with a curly aspect as the end product. The amyloid route is completely prevented by addition of stoichiometrical amounts of specific DNA, strongly suggesting that unfolding of the DNA binding α-helix is required for the formation of the intermediate. The slow nature of this expanded β-oligomeric species and the availability of several different conformational probes make it an excellent model for investigating amyloid mechanisms. The mild perturbation required for entering an amyloid route is indicative of a preexisting equilibrium. Oligomerization processes are required for the assembly of transcription initiation and DNA replication machineries, where proteins from different viruses must come together with host cell proteins. The E2 protein is a virus-encoded multifunctional master regulator that may exert one of its multiple functions through its ability to oligomerize.

Glycoproteomic characterization of carriers of the CD15/Lewisx epitope on Hodgkin's Reed-Sternberg cells

Abstract: Background: The Lewis x trisaccharide, also referred to as the CD15 antigen, is a diagnostic marker used to distinguish Hodgkin’s lymphoma from other lymphocytic cancers. However, the role of such fucosylated structures remains poorly understood, in part because carriers of Lewis x structures on Hodgkin’s Reed-Sternberg cells have not been identified. Methods: GalMBP, an engineered carbohydrate-recognition protein that binds selectively to oligosaccharides with paired terminal galactose and fucose residues, has been used in conjunction with proteomic and glycomic analysis to identify glycoprotein carriers of Lewis x and related glycan structures in multiple Hodgkin’s Reed-Sternberg cell lines. Results: Multiple glycoproteins that bind to GalMBP and carry CD15/Lewis x have been identified in a panel of six Reed-Sternberg cell lines. The most commonly identified Lewis x -bearing glycoproteins are CD98hc, which was found in all six cell lines tested, and intercellular adhesion molecule-1 and DEC-205, which were detected in five and four of the lines, respectively. Thus, several of the most prominent cell adhesion molecules on the lymphomas carry this characteristic glycan epitope. In addition, the Hodgkin’s Reed-Sternberg cell lines can be grouped into subsets based on the presence or absence of less common Lewis x -bearing glycoproteins. Conclusions: CD98 and intercellular adhesion molecule-1 are major carriers of CD15/Lewis x on Reed-Sternberg cells. Binding of DC-SIGN and other glycan-specific receptors to the Lewis x epitopes on CD98 and intercellular adhesion molecule-1 may facilitate interaction of the lymphoma cells with lymphocytes and myeloid cells in lymph nodes.

A Price to Pay for Adult Neurogenesis

Abstract: We tend to believe that plasticity is what makes brain circuits adaptable to continuous changes in environmental demands and that greater brain plasticity should result in a better ability to cope with the surrounding world. To adapt to everyday life, animals explore, learn, and remember, and these tasks make use of various cortical structures, including the hippocampus. The dentate gyrus, part of the hippocampus, is a remarkable structure in that it is one of two areas of the adult mammalian brain, including the human brain, that continue to generate new neurons throughout postnatal life ( 1 ). It is well established that adult-born neurons integrate into preexisting neuronal networks and participate in information processing ( 2 ). Much evidence accumulated over the past decade supports the hypothesis that adult neurogenesis itself is a type of circuit plasticity required for hippocampus-dependent learning and memory recall. The work by Akers et al. on page 598 of this issue ( 3 ) now shows that adult hippocampal neurogenesis may also promote forgetting.

SPARC Controls Melanoma Cell Plasticity through Rac1.

Abstract: Cell transition to a more aggressive mesenchymal-like phenotype is a hallmark of cancer progression that involves different steps and requires tightly regulated cell plasticity. SPARC (Secreted Protein Acidic and Rich in Cysteine) is a matricellular protein that promotes this transition in various malignant cell types, including melanoma cells. We found that suppression of SPARC expression in human melanoma cells compromised cell migration, adhesion, cytoskeleton structure, and cell size. These changes involved the Akt/mTOR pathway. Re-expression of SPARC or protein addition restored all the cell features. Suppression of SPARC expression was associated with increased Rac1-GTP levels and its membrane localization. Expression of the dominant negative mutant of Rac1 counteracted almost all the changes observed in SPARC-deficient cells. Overall, these data suggest that most of the SPARC-mediated effects occurred mainly through the blockade of Rac1 activity.