Biomedical subjects

Sonia Franco

Publications and source records attributed to Sonia Franco.

At least 19 recordsLinked to original sources

PubMed2006

Pathways that suppress programmed DNA breaks from progressing to chromosomal breaks and translocations.

Guarding the genome against internal and external assaults requires the coordinated interaction of multiple cellular networks to sense, respond to, and repair breaks in chromosomal DNA. Both external factors such as ionizing radiation or internal events like oxidative damage can cause DNA double stranded breaks (DSBs). DSBs are also part of the normal lymphocyte developmental program where they are an integral element of the mechanisms that generate a diverse immune repertoire in the context of V(D)J and immunoglobulin heavy chain (IgH) class switch recombination (CSR). DSBs initiate a cascade of cellular events that direct cells to pause and properly repair potentially lethal chromosomal breaks. Errors in the repair of both general and lymphocyte-specific DSBs can lead to oncogenic chromosomal translocations . Here, we review recent advances in understanding factors and protein complexes involved in the response to DNA DSBs with a focus on the B lymphocyte specific process of CSR.

Animals↗

PubMed2006

Design of new heteroscorpionate ligands and their coordinative ability toward Group 4 transition metals; an efficient synthetic route to obtain enantiopure ligands.

The reaction of different types of bis(pyrazol-1-yl)methane derivatives with Bu(n)Li and alkyl or aryl-containing-isocyanates or isothiocyanates, some of these as chiral reagents, gives rise to the preparation of new heteroscorpionate ligands in the form of the lithium derivatives [Li(NNE)]2 (1-10), although a similar process with trimethylsilyl isocyanate or isothiocyanate gave the complexes [Li(NCX)(bdmpzs)(THF)](X = O, 11; X = S, 12)[bdmpzs = bis(3,5-dimethylpyrazol-1-yl)trimethylsilylmethane]. Compounds 1-8 reacted with [TiCl4(THF)2] or [MCl4](M = Zr, Hf) to give a series of cationic complexes [MCl3{kappa3-NNE(H)}]Cl (13-36) where the heteroscorpionate ligand contains either an acetamide or thioacetamide group resulting from the protonation of the corresponding acetamidate or thioacetamidate. However, under appropriate experimental conditions neutral Ti complexes were isolated-namely [TiClx(NMe2)3-x(S-mbbpam)](37-39)[S-mbbpam =(S)-(-)-N-alpha-methylbenzyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamidate]. Finally, two alkoxide-containing titanium complexes [TiClx(OR)3-x(S-mbbpamH)]Cl (40-41) were also prepared. The structures of these complexes have been determined by spectroscopic methods and, in addition, the X-ray crystal structures of 1, 12, and 19 were also established.

Journal Article↗

PubMed2006

53BP1 and p53 synergize to suppress genomic instability and lymphomagenesis.

p53-binding protein 1 (53BP1) participates in the cellular response to DNA double-stranded breaks where it associates with various DNA repair/cell cycle factors including the H2AX histone variant. Mice deficient for 53BP1 (53BP1(-/-)) are sensitive to ionizing radiation and immunodeficient because of impaired Ig heavy chain class switch recombination. Here we show that, as compared with p53(-/-) mice, 53BP1(-/-)/p53(-/-) animals more rapidly develop tumors, including T cell lymphomas and, at lower frequency, B lineage lymphomas, sarcomas, and teratomas. In addition, T cells from animals deficient for both 53BP1 and p53 (53BP1(-/-)/p53(-/-)) display elevated levels of genomic instability relative to T cells deficient for either 53BP1 or p53 alone. In contrast to p53(-/-) T cell lymphomas, which routinely display aneuploidy but not translocations, 53BP1(-/-)/p53(-/-) thymic lymphomas fall into two distinct cytogenetic categories, with many harboring clonal translocations (40%) and the remainder showing aneuploidy (60%). We propose that 53BP1, in the context of p53 deficiency, suppresses T cell lymphomagenesis through its roles in both cell-cycle checkpoints and double-stranded break repair.

Animals↗

PubMed2006

Genomic instability and aging-like phenotype in the absence of mammalian SIRT6.

The Sir2 histone deacetylase functions as a chromatin silencer to regulate recombination, genomic stability, and aging in budding yeast. Seven mammalian Sir2 homologs have been identified (SIRT1-SIRT7), and it has been speculated that some may have similar functions to Sir2. Here, we demonstrate that SIRT6 is a nuclear, chromatin-associated protein that promotes resistance to DNA damage and suppresses genomic instability in mouse cells, in association with a role in base excision repair (BER). SIRT6-deficient mice are small and at 2-3 weeks of age develop abnormalities that include profound lymphopenia, loss of subcutaneous fat, lordokyphosis, and severe metabolic defects, eventually dying at about 4 weeks. We conclude that one function of SIRT6 is to promote normal DNA repair, and that SIRT6 loss leads to abnormalities in mice that overlap with aging-associated degenerative processes.

Aging↗

PubMed2006

MDC1 maintains genomic stability by participating in the amplification of ATM-dependent DNA damage signals.

MDC1 functions in checkpoint activation and DNA repair following DNA damage. To address the physiological role of MDC1, we disrupted the MDC1 gene in mice. MDC1-/- mice recapitulated many phenotypes of H2AX-/- mice, including growth retardation, male infertility, immune defects, chromosome instability, DNA repair defects, and radiation sensitivity. At the molecular level, H2AX, MDC1, and ATM form a positive feedback loop, with MDC1 directly mediating the interaction between H2AX and ATM. MDC1 binds phosphorylated H2AX through its BRCT domain and ATM through its FHA domain. Through these interactions, MDC1 accumulates activated ATM flanking the sites of DNA damage, facilitating further ATM-dependent phosphorylation of H2AX and the amplification of DNA damage signals. In the absence of MDC1, many downstream ATM signaling events are defective. These results suggest that MDC1, as a signal amplifier of the ATM pathway, is vital in controlling proper DNA damage response and maintaining genomic stability.

Adaptor Proteins, Signal Transducing↗

PubMed2006

H2AX prevents DNA breaks from progressing to chromosome breaks and translocations.

Histone H2AX promotes DNA double-strand break (DSB) repair and immunoglobulin heavy chain (IgH) class switch recombination (CSR) in B-lymphocytes. CSR requires activation-induced cytidine deaminase (AID) and involves joining of DSB intermediates by end joining. We find that AID-dependent IgH locus chromosome breaks occur at high frequency in primary H2AX-deficient B cells activated for CSR and that a substantial proportion of these breaks participate in chromosomal translocations. Moreover, activated B cells deficient for ATM, 53BP1, or MDC1, which interact with H2AX during the DSB response, show similarly increased IgH locus breaks and translocations. Thus, our findings implicate a general role for these factors in promoting end joining and thereby preventing DSBs from progressing into chromosomal breaks and translocations. As cellular p53 status does not markedly influence the frequency of such events, our results also have implications for how p53 and the DSB response machinery cooperate to suppress generation of lymphomas with oncogenic translocations.

Animals↗

PubMed2005

Clinical evidences of GM3 (NeuGc) ganglioside expression in human breast cancer using the 14F7 monoclonal antibody labelled with (99m)Tc.

The relevance of certain gangliosides in tumour growth and metastatic dissemination has been well documented, reasons for considering these molecules as potential targets for cancer immunotherapy and diagnosis. GM3(NeuGc) ganglioside is particularly interesting due to its restrictive expression in normal human tissues according to immunohistochemical studies, using either polyclonal or monoclonal antibodies. But both immunohistochemical and biochemical methods have strongly suggested its over-expression in human breast tumours. Nevertheless, the lack of a direct evidence of this antigenic display in human breast cancer has kept the subject controversial. For the first time, we described herein the "in vivo" detection of GM3(NeuGc) ganglioside in human breast primary tumours using a radioimmunoscintigraphic technique with 14F7, a highly specific anti-GM3(NeuGc) ganglioside monoclonal antibody, labelled with (99m)Tc. In an open, prospective Phase I/II clinical trial, including women diagnosed in stage II breast cancer, the 14F7 monoclonal antibody accumulation in tumours at doses of 0.3 (n=5), 1 (n=5) and 3 mg (n=4) was evaluated. Noteworthy, the immunoscintigraphic study showed antibody accumulation in 100% of patients' tumours for the 1 mg dose group. In turn, the radioimmunoconjugate injected at doses of 0.3 mg or 3 mg of the antibody, was uptaken by 60 and 33.3% of breast tumours, respectively. "In vivo" immune recognition of GM3(NeuGc) in breast tumours reinforces the value of this peculiar target for cancer immunotherapy.

Adolescent↗

PubMed2005

Effectors of mammalian telomere dysfunction: a comparative transcriptome analysis using mouse models.

Critical telomere shortening in the absence of telomerase in late generation Terc-/- mice (G3 Terc-/-) or loss of telomere capping due to abrogation of the DNA repair/telomere binding protein Ku86 (Ku86-/- mice) results in telomere dysfunction and organismal premature aging. Here, we report on genome-wide transcription in mouse G3 Terc-/-, Ku86-/- and G3 Terc-/-/Ku86-/- germ cells using high-density oligonucleotide microarrays. Although a few transcripts are modulated specifically in Ku86- or Terc-deficient cells, the observed transcriptional response is mainly inductive and qualitatively similar for all three genotypes, with highest transcriptional induction observed in double mutant G3 Terc-/-/Ku86-/- cells compared with either single mutant. Analysis of 92 known genes induced in G3 Terc-/-/Ku86-/- germ cells compared with wild-type cells shows predominance of genes involved in cell adhesion, cell-to-cell and cell-to-matrix communication, as well as increased metabolic turnover and augmented antioxidant responses. In addition, the data presented in this study support the view that telomere dysfunction induces a robust compensatory response to rescue impaired germ cell function through the induction of survival signals related to the PI3-kinase pathway, as well as by the coordinated upregulation of transcripts that are essential for mammalian spermatogenesis.

Animals↗

PubMed2005

DNA repair, genome stability, and aging.

Aging can be defined as progressive functional decline and increasing mortality over time. Here, we review evidence linking aging to nuclear DNA lesions: DNA damage accumulates with age, and DNA repair defects can cause phenotypes resembling premature aging. We discuss how cellular DNA damage responses may contribute to manifestations of aging. We review Sir2, a factor linking genomic stability, metabolism, and aging. We conclude with a general discussion of the role of mutant mice in aging research and avenues for future investigation.

Animals↗

PubMed2005

Telomere length predicts embryo fragmentation after in vitro fertilization in women--toward a telomere theory of reproductive aging in women.

OBJECTIVE: Telomeres are DNA repeats which cap and protect chromosome ends, facilitate homologue pairing and chiasmata formation during early meiosis, and shorten with cell division and exposure to reactive oxygen to mediate aging. Early germ cells contain telomerase, a reverse transcriptase which adds telomeres to 3-prime DNA ends, but telomerase activity declines in oocytes, fixing telomere length earlier during development. Experimentally induced telomere shortening in mice disrupts meiosis, impairs chiasmata formation, halts embryonic cell cycles, and promotes apoptosis in embryos, a phenotype which mimics reproductive senescence in women. Ethical constraints limit study of human embryos to nondestructive assays, such as morphologic evaluation under transmission optics, but cytoplasmic fragmentation is a reliable marker of apoptosis. STUDY DESIGN: Study design consisted of observational study of effect of telomere length in human eggs on cytoplasmic fragmentation, and on other morphologic features of preimplantation embryos. To test the hypothesis that telomere shortening triggers apoptosis in human embryos, we evaluated telomere length as a predictor of cytoplasmic fragmentation in embryos from women undergoing in vitro fertilization. RESULTS: Telomere length negatively predicted fragmentation in day 3 preimplantation embryos, after controlling for patient age and basal follicle stimulating hormone level. Telomere length did not predict other features of preimplantation embryo morphology. CONCLUSION: The finding that telomere length in human eggs predicts cytoplasmic fragmentation in embryos provides evidence that telomere shortening induces apoptosis in human preimplantation embryos, consistent with a telomere theory of reproductive senescence in women.

Adult↗

PubMed2005

Mammalian SIRT1 limits replicative life span in response to chronic genotoxic stress.

The Saccharomyces cerevisiae chromatin silencing factor Sir2 suppresses genomic instability and extends replicative life span. In contrast, we find that mouse embryonic fibroblasts (MEFs) deficient for SIRT1, a mammalian Sir2 homolog, have dramatically increased resistance to replicative senescence. Extended replicative life span of SIRT1-deficient MEFs correlates with enhanced proliferative capacity under conditions of chronic, sublethal oxidative stress. In this context, SIRT1-deficient cells fail to normally upregulate either the p19(ARF) senescence regulator or its downstream target p53. However, upon acute DNA damage or oncogene expression, SIRT1-deficient cells show normal p19(ARF) induction and cell cycle arrest. Together, our findings demonstrate an unexpected SIRT1 function in promoting replicative senescence in response to chronic cellular stress and implicate p19(ARF) as a downstream effector in this pathway.

Animals↗

PubMed2004

Telomere dynamics in Fancg-deficient mouse and human cells.

A number of DNA repair proteins also play roles in telomere metabolism. To investigate whether the accelerated telomere shortening reported in Fanconi anemia (FA) hematopoietic cells relates to a direct role of the FA pathway in telomere maintenance, we have analyzed telomere dynamics in Fancg-deficient mouse and human cells. We show here that both hematopoietic (stem and differentiated bone marrow cells, B and T lymphocytes) and nonhematopoietic (germ cells, mouse embryonic fibroblasts [MEFs]) Fancg(-/-) mouse cells display normal telomere length, normal telomerase activity, and normal chromosome end-capping, even in the presence of extensive clastogen-induced cytogenetic instability (mitomycin C [MMC], gamma-radiation). In addition, telomerase-deficient MEFs with humanlike telomere length and decreased Fancg expression (G5 Terc(-/-)/Fancg shRNA3 MEFs) display normal telomere maintenance. Finally, early-passage primary fibroblasts from patients with FA of complementation group G as well as primary human cells with reduced FANCG expression (FANCG shRNA IMR90 cells) show no signs of telomere dysfunction. Our observations indicate that accelerated telomere shortening in patients with FA is not due to a role of FANCG at telomeres but instead may be secondary to the disease. These findings suggest that telomerase-based therapies could be useful prophylactic agents in FA aplastic anemia by preserving their telomere reserve in the context of the disease.

Animals↗

PubMed2004

Telomere shortening and chromosomal instability abrogates proliferation of adult but not embryonic neural stem cells.

Chromosome integrity is essential for cell viability and, therefore, highly proliferative cell types require active telomere elongation mechanisms to grow indefinitely. Consistently, deletion of telomerase activity in a genetically modified mouse strain results in growth impairments in all highly proliferative cell populations analyzed so far. We show that telomere attrition dramatically impairs the in vitro proliferation of adult neural stem cells (NSCs) isolated from the subventricular zone (SVZ) of telomerase-deficient adult mice. Reduced proliferation of postnatal neurogenic progenitors was also observed in vivo, in the absence of exogenous mitogenic stimulation. Strikingly, severe telomere erosion resulting in chromosomal abnormalities and nuclear accumulation of p53 did not affect the in vitro proliferative potential of embryonic NSCs. These results suggest that intrinsic differences exist between embryonic and adult neural progenitor cells in their response to telomere shortening, and that some populations of tissue-specific stem cells can bypass DNA damage check points.

Animals↗

PubMed2004

Irregular telomeres impair meiotic synapsis and recombination in mice.

Telomere shortening can lead to chromosome instability, replicative senescence, and apoptosis in both somatic and male germ cells. To study roles for mammalian telomeres in homologous pairing and recombination, we characterized effects of telomere shortening on spermatogenesis and oogenesis in late-generation telomerase-deficient mice. We show that shortened telomeres of late-generation telomerase-deficient mice impair meiotic synapsis and decrease recombination, in particular, in females. In response to telomere shortening, male germ cells mostly undergo apoptosis, whereas female germ cells preferentially arrest in early meiosis, suggesting sexually dimorphic surveillance mechanisms for telomere dysfunction during meiosis in mice. Further, meiocytes of late-generation telomerase-deficient females with shortened telomeres, bred with early-generation males harboring relatively long telomeres, exhibit severely impaired chromosome pairing and synapsis and reduced meiotic recombination. These findings imply that functional telomeres are important in mammalian meiotic synapsis and recombination.

Animals↗

PubMed2004

Long-term molecular and cellular stability of human neural stem cell lines.

Human Neural Stem Cells (hNSCs) are excellent candidates for in vitro and in vivo molecular, cellular, and developmental research, and also for ex-vivo gene transfer and cell therapy in the nervous system. However, hNSCs are mortal somatic cells, and thus invariably enter an irreversible growth arrest after a finite number of cell divisions in culture. It has been proposed that this is due to telomere shortening. Here, we show that long-term cultured (up to 4 years) v-myc perpetuated hNSC lines do preserve short but stable and homogeneous telomeres (TRF and Q-FISH determinations). hNSC lines (but not strains) express high levels of telomerase activity, which is activated by v-myc, as demonstrated here. Telomerase activity is not constitutive, becoming non-detectable after differentiation (in parallel to v-myc down-regulation). hNSC lines also maintain a stable cell cycle length, mitotic potential, differentiation and neuron generation capacity, and do not express senescence-associated beta-galactosidase over years, as studied here. These data, collectively, help to explain the immortal nature of v-myc-perpetuated hNSC lines, and to establish them as excellent research tools for basic and applied neurobiological and translational studies.

Cell Culture Techniques↗

PubMed2003

Short telomeres protect from diet-induced atherosclerosis in apolipoprotein E-null mice.

By imposing a replicative defect in most somatic cells, gradual telomere attrition during aging is thought to progressively impair cellular function and viability and may contribute to age-related disease. Immune cells play important roles in all phases of atherosclerosis, a multifactorial disease that prevails within the elderly. Because shorter telomeres have been found in circulating blood leukocytes of human patients with advanced coronary atherosclerosis, it has been suggested that telomere shortening may predispose the organism to atheroma development. In this study, we assessed the impact of telomere attrition on atherogenesis induced by dietary cholesterol in apolipoprotein E (apoE)-deficient mice, a well-established model of experimental atherosclerosis that recapitulates important aspects of the human disease. Our study shows that late-generation mice doubly deficient in apoE and telomerase RNA experience telomere attrition and a substantial reduction of atherosclerosis compared with control mice with intact telomerase, in spite of sustained hypercholesterolemia in response to the atherogenic diet. Short telomeres impaired the proliferation of both lymphocytes and macrophages, an important step in atherosclerosis development. Therefore, telomere exhaustion resulting in replicative immunosenescence may serve as a mechanism for restricting atheroma progression.

Animals↗

PubMed2003

Porphyrin-aminoquinoline conjugates as telomerase inhibitors.

A series of metalloporphyrins was prepared in order to target the G-quadruplex structure of telomeric DNA for the design of antitelomerase compounds. The initial cationic tetramethylpyridiniumyl porphyrin was modified by the replacement of one or two methylpyridiniumyl groups by one or two 4-aminoquinoline moieties, at the meso position, in order to increase the cell penetration and the quadruplex affinity. The porphyrins were either metallated by manganese or by nickel. The degradation of quadruplex DNA was assayed in vitro with the manganese redox-active derivatives. All porphyrins complexes were capable of inhibiting the telomerase enzyme with IC50 values in the micromolar range (TRAP assay).

Aminoquinolines↗

PubMed2003

Ablation of telomerase and telomere loss leads to cardiac dilatation and heart failure associated with p53 upregulation.

Cardiac failure is a frequent cause of death in the aging human population. Telomere attrition occurs with age, and is proposed to be causal for the aging process. To determine whether telomere shortening leads to a cardiac phenotype, we studied heart function in the telomerase knockout mouse, Terc-/-. We studied Terc-/- mice at the second, G2, and fifth, G5, generation. Telomere shortening in G2 and G5 Terc-/- mice was coupled with attenuation in cardiac myocyte proliferation, increased apoptosis and cardiac myocyte hypertrophy. On a single-cell basis, telomere shortening was coincidental with increased expression of p53, indicating the presence of dysfunctional telomeres in cardiac myocytes from G5 Terc-/- mice. The impairment in cell division, the enhanced cardiac myocyte death and cellular hypertrophy, are concomitant with ventricular dilation, thinning of the wall and cardiac dysfunction. Thus, inhibition of cardiac myocyte replication provoked by telomere shortening, results in de-compensated eccentric hypertrophy and heart failure in mice. Telomere shortening with age could also contribute to cardiac failure in humans, opening the possibility for new therapies.

Animals↗