To determine the extent to which the co-occurrence of chronic obstructive pulmonary disease (COPD) and cognitive impairment affect adverse health outcomes in older adults.
Multi-center longitudinal cohort study.
California, Pennsylvania, Maryland, and North Carolina.
Three thousand ninety-three community-dwelling adults aged ≥65 from the Cardiovascular Health Study. Four hundred thirty-one participants had chronic obstructive pulmonary disease (COPD) at study baseline.
Follow-up began at the second CHS visit and continued for three years. Spirometric criteria for airflow limitation served to establish COPD, using the Lambda-Mu-Sigma method, which accounts for age-related changes in lung function. Cognitive impairment was evaluated by the modified Mini Mental State Exam and claims data. Outcomes were respiratory-related and all-cause hospitalizations and death.
Participants with co-existing COPD and cognitive impairment had the highest rates of respiratory-related (adjusted hazard ratio [HR]=4.10, 95%CI=1.86–9.05) and all-cause hospitalizations (HR= 1.34, 95%CI=1.00–1.80) and death (HR=2.29, 95%CI=1.18–4.45). In particular, individuals with both conditions had a 48% higher rate of all-cause hospitalizations (adjusted synergy index [SI]=1.48, 95%CI=0.19–11.31) and nearly a three-fold higher rate of death (SI=2.74, 95%CI=0.43–17.32) than the sum of risks for each respective outcome associated with having COPD or cognitive impairment alone. However, tests for interaction were not statistically significant for the presence of synergism between both conditions relative to any of the outcomes. Therefore, we cannot conclude that the combined effect of COPD and cognitive impairment is greater than additive.
Co-existing COPD and cognitive impairment have an additive effect on respiratory-related and all-cause hospitalizations and death. Optimizing outcomes in older adults with COPD and cognitive impairment will require that we determine how to improve concurrent management of both conditions.
Chronic obstructive pulmonary disease; cognitive impairment; health outcomes; hospitalizations; disability; death
Dysfunctional telomeres limit cellular proliferative capacity by activating the p53-p21– and p16INK4a-Rb–dependent DNA damage responses (DDRs). The p16INK4a tumor suppressor accumulates in aging tissues, is a biomarker for cellular senescence, and limits stem cell function in vivo. While the activation of a p53-dependent DDR by dysfunctional telomeres has been well documented in human cells and mouse models, the role for p16INK4a in response to telomere dysfunction remains unclear. Here, we generated protection of telomeres 1b p16–/– mice (Pot1bΔ/Δ;p16–/–) to address the function of p16INK4a in the setting of telomere dysfunction in vivo. We found that deletion of p16INK4a accelerated organ impairment and observed functional defects in highly proliferative organs, including the hematopoietic system, small intestine, and testes. Pot1bΔ/Δ;p16–/– hematopoietic cells exhibited increased telomere loss, increased chromosomal fusions, and telomere replication defects. p16INK4a deletion enhanced the activation of the ATR-dependent DDR in Pot1bΔ/Δ hematopoietic cells, leading to p53 stabilization, increased p21-dependent cell cycle arrest, and elevated p53-dependent apoptosis. In contrast to p16INK4a, deletion of p21 did not activate ATR, rescued proliferative defects in Pot1bΔ/Δ hematopoietic cells, and significantly increased organismal lifespan. Our results provide experimental evidence that p16INK4a exerts protective functions in proliferative cells bearing dysfunctional telomeres.
Dysfunctional telomeres arising either through natural attrition due to telomerase deficiency or by the removal of telomere binding proteins are recognized as double stranded breaks (DSBs). Repair of DSBs is crucial for the maintenance of genome stability. In mammals, DSBs are repaired by either error prone nonhomologous end joining (NHEJ) or error free homologous recombination (HR) and can be visualized as chromosomal fusions.
Conserved metallo β-Lactamase and β-CASP (CPSF-Artemis-Snm1-Pso2) domain nuclease family member SNM1B/Apollo is a shelterin-associated protein that localizes to telomeres through its interaction with TRF2. To study its in vivo role, we generated a knockout of SNM1B/Apollo in a mouse model. Snm1B/Apollo homozygous null mice die at birth with developmental delay and defects in multiple organ systems. Cell proliferation defects were observed in Snm1B/Apollo mutant mouse embryonic fibroblasts (MEFs) owing to high levels of telomeric end-to-end fusions. Deficiency of the nonhomologous end-joining (NHEJ) factor Ku70, but not p53, rescued the developmental defects and lethality observed in Snm1B/Apollo mutant mice as well as the impaired proliferation of Snm1B/Apollo-deficient MEFs. These findings demonstrate that SNM1B/Apollo is required to protect telomeres against NHEJ-mediated repair, which results in genomic instability and the consequent multi-organ developmental failure. Although Snm1B/Apollo-deficient MEFs exhibited high levels of apoptosis, abrogation of p53-dependent programmed cell death did not rescue the multi-organ developmental failure in the mice.
chromosome instability; Ku; mouse model; nonhomologous end-joining; SNM1B/Apollo; telomeres
Telomere dysfunctions, rendered through replicative attrition of telomeric DNA or due to the inhibition of shelterin components, are recognized as DNA double stranded breaks (DSBs) by the DNA damage repair (DDR) pathway. This leads to the activation of DNA damage checkpoint sensors including the Mre11-Rad50-Nbs1 (MRN) complex, γ-H2AX and 53BP1, the ATM and ATR signal transducing kinases and downstream effectors including Chk1, Chk2 and p53. Robust DNA damage response signals at dysfunctional telomeres, achieved by complete deletion of TRF2 or by expressing dominant negative mutant TPP1ΔRD, can be detected by their association with γ-H2AX and 53BP1 forming “telomere dysfunction induced foci (TIFs)”. Induction of TIFs at telomeres provides an opportunity to quantify the extent of telomere dysfunction and monitor the signaling pathways.
DNA damage; Telomere dysfunction; Telomere induced foci; Telomere-FISH
Human carcinomas arise through the acquisition of genetic changes that endow precursor cancer cells with a critical threshold of cancer-relevant genetic lesions. This complex genomic alterations confer upon precursor cancer cells the ability to grow indefinitely and to metastasize to distant sites. One important mechanism underlying a cell’s tumorigenic potential is the status of its telomere. Telomeres are G-rich simple repeat sequences that serve to prevent chromosomal ends from being recognized as DNA double-strand breaks (DSBs). Dysfunctional telomeres resemble DSBs, leading to the formation of dicentric chromosomes that fuel high degrees of genomic instability. In the setting of an intact p53 pathway, this instability promotes cellular senescence, a potent tumor suppressor mechanism. However, rare cells that stochastically lose p53 function emerge from this sea of genomic instability and progress towards cancer. In this review, we describe the use of mouse models to probe the impact of dysfunctional telomeres on tumor initiation and suppression.
Repressor activator protein 1 (RAP1) is the most highly conserved telomere protein. It is involved in protecting chromosome ends in fission yeast, promoting gene silencing in Saccharomyces cerevisiae while in Kluyveromyces lactis it is required to repress homology directed recombination (HDR) at telomeres. Since mammalian RAP1 requires TRF2 for stable expression, its role in telomere function has remained obscure. To understand how RAP1 plays such diverse functions at telomeres, we solved the crystal or solution structures of the C-terminal RCT domains of RAP1 from multiple organisms in complex with their respective protein-binding partners. Our comparative structural analysis establishes the RCT domain of RAP1 as an evolutionarily conserved protein-protein interaction module. In mammalian and fission yeast cells, this module interacts with TRF2 and Taz1, respectively, targeting RAP1 to chromosome ends for telomere end protection. While RAP1 repress NHEJ at fission yeast telomeres, at mammalian telomeres it is required to repress HDR. In contrast, S. cerevisiae RAP1 utilizes the RCT domain to recruit Sir3 to telomeres to mediate gene silencing. Together, our results reveal that depending on the organism, the evolutionarily conserved RAP1 RCT motif plays diverse functional roles at telomeres.
Long lived organisms such as humans have evolved several intrinsic tumor suppressor mechanisms to combat the slew of oncogenic somatic mutations that constantly arise in proliferating stem cell compartments. One of these anti-cancer barriers is the telomere, a specialized nucleoprotein that caps the ends of eukaryotic chromosome. Impaired telomere function activates the canonical DNA damage response pathway that engages p53 to initiate apoptosis or replicative senescence. Here, we discuss how p53-dependent senescence induced by dysfunctional telomeres may be as potent as apoptosis in suppressing tumorigenesis in vivo.
Recent studies have expanded the functions of vitamin D to a possible role in pulmonary function. Our objective was to examine the relationship between serum 25-hydroxyvitamin D (25[OH]D), serum parathyroid hormone, and pulmonary function in older women.
We examined the relationship of serum 25(OH)D and parathyroid hormone with pulmonary function (forced expiratory volume in one second [FEV1], forced vital capacity [FVC], and FEV1/FVC ratio) in a cross-sectional study of 646 moderately to severely disabled women, 65 years or more, living in the community in Baltimore, Maryland, who participated in the Women’s Health and Aging Study I.
Overall, median (25th, 75th percentile) serum 25-hydroxyvitamin D concentrations were 19.9 (14.7, 26.7) ng/mL. Serum 25(OH)D was positively associated with FEV1 (p = .03), FVC (p = .18), and FEV1/FVC (p = .04) in multivariable linear regression models adjusting for age, race, education, smoking, height, physical activity, cognition, interleukin-6, chronic diseases, and other potential confounders. In the same models, serum parathyroid hormone was not significantly associated with FEV1, FVC, or FEV1/FVC.
These findings support the idea that vitamin D deficiency is independently associated with poor pulmonary function in older disabled women.
Aging; Lung function; Parathyroid hormone; Vitamin D; Women
The linear nature of eukaryotic chromosomes leaves natural ends susceptible to triggering DNA damage responses. Telomeres are specialized nucleoprotein structures that comprise the “end zone” of chromosomes. Besides having a specialized sequences and structures, there are six resident proteins at telomeres that play a prominent role in protecting chromosome ends. In the review, we will discuss this team of proteins called shelterin and how they are involved in regulating DNA damage signaling, repair and replication at telomeres.
telomere; shelterin; DNA damage response; NHEJ
TPP1, a component of the mammalian shelterin complex, plays essential roles in telomere maintenance. It forms a heterodimer with POT1 to repress ATR-dependent DNA damage signaling at telomeres, and recruits telomerase to chromosome ends. Here we show that the E3 ubiquitin ligase RNF8 localizes to and promotes the accumulation of DNA damage proteins 53BP1 and γ-H2AX to uncapped telomeres. TPP1 is unstable in the absence of RNF8, resulting in telomere shortening and chromosome fusions via the alternative non-homologous end joining (A-NHEJ)-mediated DNA repair pathway. The RNF8 ubiquitin ligase RING domain is essential for TPP1 stability and retention at telomeres. RNF8 physically interacts with TPP1 to generate Ubc13-dependent K63 polyubiquitin chains that stabilizes TPP1 at telomeres. The conserved TPP1 lysine residue 233 is essential for RNF8-mediated TPP1 ubiquitylation and localization to telomeres. Our results demonstrate that TPP1 is a novel substrate for RNF8, and suggest a previously unrecognized role for RNF8 in telomere end protection. We propose a model in which engagement of classical vs. A-NHEJ repair pathways at dysfunctional telomeres is controlled by the ubiquitin ligase functions of RNF8.
To determine the relative effect of five chronic conditions on four representative universal health outcomes.
Cardiovascular Health Study.
Five thousand two hundred and ninety-eight community-living participants aged 65 and older.
Multiple regression and Cox models were used to determine the effect of heart failure (HF), chronic obstructive pulmonary disease (COPD), osteoarthritis, depression, and cognitive impairment on self-rated health, 12 basic and instrumental activities of daily living (ADLs and IADLs), six-item symptom burden scale, and death.
Each condition adversely affected self-rated health (P<.001) and ADLs and IADLs (P<.001). For example, persons with HF performed 0.70 ± 0.08 fewer ADLs and IADLs than those without; persons with depression and persons with cognitive impairment performed 0.59 ± 0.04 and 0.58 ± 0.06 fewer activities, respectively, than those without these conditions. Depression, HF, COPD, and osteoarthritis were associated with 1.18 ± 0.04, 0.40 ± 0.08, 0.40 ± 0.05, and 0.57 ± 0.03 more symptoms, respectively, in individuals with these conditions than in those without. HF (hazard ratio (HR) = 2.84, 95% confidence interval (CI) = 1.97–4.10), COPD (2.62, 95% CI = 1.94–3.53), cognitive impairment (2.05, 95% CI = 1.47–2.85), and depression (1.47, 95% CI = 1.08–2.01) were each associated with death within 2 years. Several paired combinations of conditions had synergistic effects on ADLs and IADLs. For example, individuals with HF plus depression performed 2.0 fewer activities than persons with neither condition, versus the 1.3 fewer activities expected from adding the effects of the two conditions together.
Universal health outcomes may provide a common metric for measuring the effects of multiple conditions and their treatments. The varying effects of the conditions across universal outcomes could inform care priorities.
multiple chronic conditions; patient-reported outcomes; universal health outcomes
Telomere maintenance in cycling cells relies on both DNA replication and capping by the protein complex shelterin. Two single-stranded DNA (ssDNA)-binding proteins, replication protein A (RPA) and protection of telomere 1 (POT1) play critical roles in DNA replication and telomere capping, respectively. While RPA binds to ssDNA in a non-sequence-specific manner, POT1 specifically recognizes singlestranded TTAGGG telomeric repeats. Loss of POT1 leads to aberrant accumulation of RPA at telomeres and activation of the ataxia telangiectasia and Rad3-related kinase (ATR)-mediated checkpoint response, suggesting that POT1 antagonizes RPA binding to telomeric ssDNA. The requirement for both POT1 and RPA in telomere maintenance and the antagonism between the two proteins raises the important question of how they function in concert on telomeric ssDNA. Two interesting models were proposed by recent studies to explain the regulation of POT1 and RPA at telomeres. Here, we discuss how these models help unravel the coordination, and also the antagonism, between POT1 and RPA during the cell cycle.
RPA; POT1; telomere; ATR; checkpoint
Frailty is associated with a pro-inflammatory state, which has been characterized by elevated levels of systemic inflammatory biomarkers, but has not been related to the number of co-existing chronic diseases associated with inflammation. We sought to determine the extent to which a higher number of inflammatory-related diseases is associated with frailty and to identify the most common disease patterns associated with being frail in older adults. We performed binomial regression analyses to assess whether a higher count of inflammatory-related diseases increases the probability of frailty using data from the Women's Health and Aging Studies I and II, companion cohorts composed of 70–79-year-old community-dwelling older women in Baltimore, Maryland (n=620). An increase of one inflammatory-related disease was associated log-linearly with frailty (Prevalence Ratio (PR)=2.32, 95% Confidence Interval (CI)=1.85–2.92). After adjusting for age, race, education, and smoking status, the probability of frailty remained significant (PR=1.97, 95%CI=1.52–2.55). In the frail population, chronic kidney disease (CKD) and depressive symptoms (Prevalence=22.9%, 95%CI=14.2–34.8%); CVD and depressive symptoms (21.7%, 95%CI=13.2–33.5%); CKD and anemia (18.7%, 95%CI=11.1–29.7%); cardiovascular disease (CVD), CKD, and pulmonary disease (10.7%, 95%CI=5.2–21.0%); CKD, anemia, and depressive symptoms (8.7%, 95%CI=3.9–18.2%); and CVD, anemia, pulmonary disease, and depressive symptoms (5.0%, 95%CI=1.6–14.4%) were among the most frequent disease combinations. Their prevalence percentages were significantly higher in the frail versus non-frail women. A higher inflammatory-related disease count, perhaps reflecting a greater pro-inflammatory burden, increases the likelihood of frailty. Shared mechanisms among specific disease combinations may further contribute to this risk.
comorbidity; inflammation; frailty
Nuclear lamins are usually classified as A-type (lamins A and C) or B-type (lamins B1 and B2). A-type lamins have been implicated in multiple genetic diseases but are not required for cell growth or development. In contrast, B-type lamins have been considered essential in eukaryotic cells, with crucial roles in DNA replication and in the formation of the mitotic spindle. Knocking down the genes for B-type lamins (LMNB1, LMNB2) in HeLa cells has been reported to cause apoptosis. In the current study, we created conditional knockout alleles for mouse Lmnb1 and Lmnb2, with the goal of testing the hypothesis that B-type lamins are crucial for the growth and viability of mammalian cells in vivo. Using the keratin 14-Cre transgene, we bred mice lacking the expression of both Lmnb1 and Lmnb2 in skin keratinocytes (Lmnb1Δ/ΔLmnb2Δ/Δ). Lmnb1 and Lmnb2 transcripts were absent in keratinocytes of Lmnb1Δ/ΔLmnb2Δ/Δ mice, and lamin B1 and lamin B2 proteins were undetectable. But despite an absence of B-type lamins in keratinocytes, the skin and hair of Lmnb1Δ/ΔLmnb2Δ/Δ mice developed normally and were free of histological abnormalities, even in 2-year-old mice. After an intraperitoneal injection of bromodeoxyuridine (BrdU), similar numbers of BrdU-positive keratinocytes were observed in the skin of wild-type and Lmnb1Δ/ΔLmnb2Δ/Δ mice. Lmnb1Δ/ΔLmnb2Δ/Δ keratinocytes did not exhibit aneuploidy, and their growth rate was normal in culture. These studies challenge the concept that B-type lamins are essential for proliferation and vitality of eukaryotic cells.
To determine the extent to which disease-related symptoms and impairments, which constitute measures of disease severity or targets of therapy, account for the associations between chronic diseases and universal health outcomes.
Cardiovascular Health Study (CHS) and Health ABC.
5,654 CHS, and 2,706 Health ABC, members.
Diseases included heart failure (HF), chronic obstructive pulmonary disease (COPD), osteoarthritis, and cognitive impairment. The universal health outcomes included self-rated health, basic and instrumental activities of daily living (BADLs-IADLs), and death. Disease-related symptoms/impairments included HF symptoms and ejection fraction (EF) for HF; Dyspnea Scale and FEV1 for COPD; joint pain for osteoarthritis, and executive function for cognitive impairment.
The diseases were associated with the universal health outcomes (p<0.001) except osteoarthritis with death (both cohorts) and cognitive impairment with self-rated health (Health ABC). Symptoms/impairments accounted for ≥30% of each disease’s effect on the universal health outcomes. In CHS, for example, HF, compared with no HF, was associated with one fewer (0.918) BADLs-IADL performed without difficulty; 27% of this effect was accounted for by HF symptoms, only 5% by EF. The hazard ratio for death with HF was 6.5 (95% CI, 4.7, 8.9) with 40% accounted for by EF and only 14% by HF symptoms.
Disease-related symptoms/impairments accounted for much of the significant associations between the 4 chronic diseases and the universal health outcomes. Results support considering universal health outcomes as common metrics across diseases in clinical decision-making, perhaps by targeting the disease-related symptoms/impairments that contribute most strongly to the effect of the disease on the universal health outcomes.
chronic diseases; universal health outcomes; patient-reported outcomes; clinical decision-making
Lamin B1 is essential for neuronal migration and progenitor proliferation during the development of the cerebral cortex. The observation of distinct phenotypes of Lmnb1- and Lmnb2-knockout mice and the differences in the nuclear morphology of cortical neurons in vivo suggest that lamin B1 and lamin B2 play distinct functions in the developing brain.
Neuronal migration is essential for the development of the mammalian brain. Here, we document severe defects in neuronal migration and reduced numbers of neurons in lamin B1–deficient mice. Lamin B1 deficiency resulted in striking abnormalities in the nuclear shape of cortical neurons; many neurons contained a solitary nuclear bleb and exhibited an asymmetric distribution of lamin B2. In contrast, lamin B2 deficiency led to increased numbers of neurons with elongated nuclei. We used conditional alleles for Lmnb1 and Lmnb2 to create forebrain-specific knockout mice. The forebrain-specific Lmnb1- and Lmnb2-knockout models had a small forebrain with disorganized layering of neurons and nuclear shape abnormalities, similar to abnormalities identified in the conventional knockout mice. A more severe phenotype, complete atrophy of the cortex, was observed in forebrain-specific Lmnb1/Lmnb2 double-knockout mice. This study demonstrates that both lamin B1 and lamin B2 are essential for brain development, with lamin B1 being required for the integrity of the nuclear lamina, and lamin B2 being important for resistance to nuclear elongation in neurons.
Hutchinson–Gilford progeria syndrome (HGPS) is caused by a mutant prelamin A, progerin, that terminates with a farnesylcysteine. HGPS knock-in mice (LmnaHG/+) develop severe progeria-like disease phenotypes. These phenotypes can be ameliorated with a protein farnesyltransferase inhibitor (FTI), suggesting that progerin's farnesyl lipid is important for disease pathogenesis and raising the possibility that FTIs could be useful for treating humans with HGPS. Subsequent studies showed that mice expressing non-farnesylated progerin (LmnanHG/+ mice, in which progerin's carboxyl-terminal –CSIM motif was changed to –SSIM) also develop severe progeria, raising doubts about whether any treatment targeting protein prenylation would be particularly effective. We suspected that those doubts might be premature and hypothesized that the persistent disease in LmnanHG/+ mice could be an unanticipated consequence of the cysteine-to-serine substitution that was used to eliminate farnesylation. To test this hypothesis, we generated a second knock-in allele yielding non-farnesylated progerin (LmnacsmHG) in which the carboxyl-terminal –CSIM motif was changed to –CSM. We then compared disease phenotypes in mice harboring the LmnanHG or LmnacsmHG allele. As expected, LmnanHG/+ and LmnanHG/nHG mice developed severe progeria-like disease phenotypes, including osteolytic lesions and rib fractures, osteoporosis, slow growth and reduced survival. In contrast, LmnacsmHG/+ and LmnacsmHG/csmHG mice exhibited no bone disease and displayed entirely normal body weights and survival. The frequencies of misshapen cell nuclei were lower in LmnacsmHG/+ and LmnacsmHG/csmHG fibroblasts. These studies show that the ability of non-farnesylated progerin to elicit disease depends on the carboxyl-terminal mutation used to eliminate protein prenylation.
Maintenance of telomeres requires both DNA replication and telomere ‘capping’ by shelterin. These two processes employ two single-stranded DNA (ssDNA)-binding proteins, replication protein A (RPA) and protection of telomeres 1 (POT1). Although RPA and POT1 each have a critical role at telomeres, how they function in concert is not clear. POT1 ablation leads to activation of the ataxia telangiectasia and Rad3-related (ATR) checkpoint kinase at telomeres1, 2, suggesting that POT1 antagonizes RPA binding to telomeric ssDNA. Unexpectedly, we found that purified POT1 and its functional partner TPP1 are unable to efficiently prevent RPA binding to telomeric ssDNA. In cell extracts, we identified a novel activity that specifically displaces RPA, but not POT1, from telomeric ssDNA. Using purified protein, we show that the heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) recapitulates the RPA displacing activity. The RPA displacing activity is inhibited by the telomeric repeat-containing RNA (TERRA) in early S phase, but is then unleashed in late S phase when TERRA levels decline at telomeres3. Interestingly, TERRA also promotes POT1 binding to telomeric ssDNA by removing hnRNPA1, suggesting that the reaccumulation of TERRA after S phase helps to complete the RPA-to-POT1 switch on telomeric ssDNA. Together, our data suggest that hnRNPA1, TERRA, and POT1 act in concert to displace RPA from telomeric ssDNA following DNA replication, and promote telomere capping to preserve genomic integrity.
Misrepair of DNA double-strand breaks (DSBs) produced by the V(D)J recombinase (the RAG1/RAG2 proteins) at immunoglobulin (Ig) and T cell receptor (Tcr) loci has been implicated in pathogenesis of lymphoid malignancies in humans1 and in mice2–7. Defects in DNA damage response factors such as ATM and combined deficiencies in classical nonhomologous end joining (NHEJ) and p53 predispose to RAG-initiated genomic rearrangements and lymphomagenesis2–11. Although we showed previously that RAG1/RAG2 shepherd the broken DNA ends to classical NHEJ for proper repair12,13, roles for the RAG proteins in preserving genomic stability remain poorly defined. Here we show that the RAG2 C-terminus, although dispensable for recombination14,15, is critical for maintaining genomic stability. Thymocytes from “core” Rag2 homozygotes (Rag2c/c mice) show dramatic disruption of Tcrα/δ locus integrity. Furthermore, all Rag2c/c p53−/− mice, unlike Rag1c/c p53−/− and p53−/− animals, rapidly develop thymic lymphomas bearing complex chromosomal translocations, amplifications, and deletions involving the Tcrα/δ and Igh loci. We also find these features in lymphomas from Atm−/− mice. We show that, like ATM-deficiency3, core RAG2 severely destabilizes the RAG post-cleavage complex. These results reveal a novel genome guardian role for RAG2 and suggest that similar “end release/end persistence” mechanisms underlie genomic instability and lymphomagenesis in Rag2c/c p53−/− and Atm−/− mice.
Aurora kinase A (Aurora-A) is known to regulate genomic instability and tumorigenesis in multiple human cancers. The underlying mechanism, however, is not fully understood. We examined the molecular mechanism of Aurora-A regulation in human ovarian cancer.
Retrovirus-mediated small hairpin RNA (shRNA) was used to silence the expression of Aurora-A in the ovarian cancer cell lines SKOV3, OVCA432, and OVCA433. Immunofluorescence, Western blotting, flow cytometry, cytogenetic analysis, and animal assay were used to test centrosome amplification, cell cycle alteration, apoptosis, DNA damage response, tumor growth, and genomic instability. Immunostaining of BRCA2 and Aurora-A was done in ovarian, pancreatic, breast, and colon cancer samples.
Knockdown of Aurora-A reduced centrosome amplification, malformation of mitotic spindles, and chromosome aberration, leading to decreased tumor growth. Silencing Aurora-A attenuated cell cycle progression and enhanced apoptosis and DNA damage response by restoring p21, pRb, and BRCA2 expression. Aurora-A was inversely correlated with BRCA2 in high-grade ovarian serous carcinoma, breast cancer, and pancreatic cancer. In high-grade ovarian serous carcinoma, positive expression of BRCA2 predicted increased overall and disease-free survival, whereas positive expression of Aurora-A predicted poor overall and disease-free survival (P < 0.05). Moreover, an increased Aurora-A to BRCA2 expression ratio predicted poor overall survival (P = 0.047) compared with a decreased Aurora-A to BRCA2 expression ratio.
Aurora-A regulates genomic instability and tumorigenesis through cell cycle dysregulation and BRCA2 suppression. The negative correlation between Aurora-A and BRCA2 exists in multiple cancers, whereas the expression ratio of Aurora-A to BRCA2 predicts ovarian cancer patient outcome.
The modification of proteins with farnesyl or geranylgeranyl lipids, a process called protein prenylation, facilitates interactions of proteins with membrane surfaces. Protein prenylation is carried out by a pair of cytosolic enzymes, protein farnesyltransferase (FTase) and protein geranylgeranyltransferase type I (GGTase-I). FTase and GGTase-I have attracted interest as therapeutic targets for both cancer and progeria, but very little information exists on the importance of these enzymes for homeostasis of normal tissues. One study actually suggested that FTase is entirely dispensable. To explore the importance of the protein prenyltransferases for normal tissues, we used conditional knockout alleles for Fntb and Pggt1b (which encode the β-subunits of FTase and GGTase-I, respectively) and a keratin 14–Cre transgene to create mice lacking FTase or GGTase-I in skin keratinocytes. Keratinocyte-specific Fntb knockout mice were viable but developed severe alopecia. Although hair follicles appeared normal during development, they were morphologically abnormal after birth, and ultrastructural and immunohistochemical studies revealed many apoptotic cells. The interfollicular epidermis of Fntb-deficient mice appeared normal; however, keratinocytes from these mice could not proliferate in culture. As expected, non-farnesylated prelamin A and non-farnesylated DNAJA1 accumulated in Fntb-deficient keratinocytes. Keratinocyte-specific Pggt1b knockout mice survived development but died shortly after birth. Like Fntb-deficient keratinocytes, Pggt1b-deficient keratinocytes did not proliferate in culture. Thus, both FTase and GGTase-I are required for the homeostasis of skin keratinocytes.
Developing interventions to prevent frailty in older adults is a priority as it increases the risk for disability, institutionalization, and death. Single chronic inflammatory diseases are known to increase the risk of frailty. Identification of comorbid inflammatory diseases that synergistically might heighten this risk would provide further insight into therapeutic approaches to prevent frailty. The study aims were to characterize whether there are specific inflammatory disease pairs that are associated with frailty and to determine whether the risk of frailty is affected by synergistic interactions between these inflammatory diseases.
Data were from the Women's Health and Aging Studies I and II and complementary cohorts of community-dwelling women aged 70–79 years from Baltimore, Maryland (n = 620). Multivariable logistic regression analyses were performed to evaluate the relationships between these diseases and frailty.
Among the frail (11.3%), 15.2% had both depressive symptoms and anemia and 14.5% had pulmonary disease and anemia. The risk of frailty was synergistically increased in those with depressive symptoms and anemia (adjusted risk ratios = 11.93, 95% confidence interval [CI] 4.10–34.76) and those with pulmonary disease and anemia (risk ratios = 5.57, 95% CI 2.14–14.48), compared with those without either disease in each pair. The attributable proportions of frail cases due to interaction between the diseases of each pair were 0.56 (95% CI 0.07–1.05) and 0.61 (95% CI 0.18–1.05), respectively.
Synergistic interactions between specific inflammatory diseases may heighten the risk of frailty. These findings suggest that a common etiologic pathway may exist among co-occurring inflammatory diseases and that their improved comanagement may be an approach to reducing frailty.
Frailty; Comorbidity; Inflammation
The proliferative potential of eukaryotic cells is critically dependent upon the maintenance of functional telomeres, the protein-DNA complexes that cap the ends of chromosomes. A paper published in this issue of Aging describes that the telomere protein tankyrase 1 regulates DNA damage responses at telomeres.
Histone acetyltransferases (HATs) play important roles in gene regulation and DNA repair by influencing the accessibility of chromatin to transcription factors and repair proteins. Here we show that deletion of Gcn5 leads to telomere dysfunction in mouse and human cells. Biochemical studies reveal that depletion of Gcn5 or ubiquitin specific protease 22 (Usp22), which is another bona fide component of the Gcn5-containing SAGA complex, increases ubiquitination and turnover of TRF1, a primary component of the telomeric shelterin complex. Inhibition of the proteasome or over expression of USP22 opposes this effect. The USP22 deubiquitinating module requires association with SAGA complexes for activity, and we find that depletion of Gcn5 compromises this association in mammalian cells. Thus, our results indicate that Gcn5 regulates TRF1 levels through effects on Usp22 activity and SAGA integrity.