RESUMEN
Maintaining proteostasis is key to resisting stress and promoting healthy aging. Proteostasis is necessary to preserve stem cell function, but little is known about the mechanisms that regulate proteostasis during stress in stem cells, and whether disruptions of proteostasis contribute to stem cell aging is largely unexplored. We determined that ex-vivo-cultured mouse and human hematopoietic stem cells (HSCs) rapidly increase protein synthesis. This challenge to HSC proteostasis was associated with nuclear accumulation of Hsf1, and deletion of Hsf1 impaired HSC maintenance ex vivo. Strikingly, supplementing cultures with small molecules that enhance Hsf1 activation partially suppressed protein synthesis, rebalanced proteostasis, and supported retention of HSC serial reconstituting activity. Although Hsf1 was dispensable for young adult HSCs in vivo, Hsf1 deficiency increased protein synthesis and impaired the reconstituting activity of middle-aged HSCs. Hsf1 thus promotes proteostasis and the regenerative activity of HSCs in response to culture stress and aging.
Asunto(s)
Células Madre Hematopoyéticas , Proteostasis , Envejecimiento , Animales , Senescencia Celular , Ratones , Factores de TranscripciónRESUMEN
BRAF inhibitors can delay the progression of metastatic melanoma, but resistance usually emerges, leading to relapse. Drugs simultaneously targeting two or more pathways essential for cancer growth could slow or prevent the development of resistant clones. Here, we identified pyridinyl imidazole compounds SB202190, SB203580, and SB590885 as dual inhibitors of critical proliferative pathways in human melanoma cells bearing the V600E activating mutation of BRAF kinase. We found that the drugs simultaneously disrupt the BRAF V600E-driven extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) activity and the mechanistic target of rapamycin complex 1 (mTORC1) signaling in melanoma cells. Pyridinyl imidazole compounds directly inhibit BRAF V600E kinase. Moreover, they interfere with the endolysosomal compartment, promoting the accumulation of large acidic vacuole-like vesicles and dynamic changes in mTOR signaling. A transient increase in mTORC1 activity is followed by the enrichment of the Ragulator complex protein p18/LAMTOR1 at contact sites of large vesicles and delocalization of mTOR from the lysosomes. The induced disruption of the endolysosomal pathway not only disrupts mTORC1 signaling, but also renders melanoma cells sensitive to endoplasmic reticulum (ER) stress. Our findings identify new activities of pharmacologically relevant small molecule compounds and provide a biological rationale for the development of anti-melanoma therapeutics based on the pyridinyl imidazole core.
RESUMEN
Low protein synthesis is a feature of somatic stem cells that promotes regeneration in multiple tissues. Modest increases in protein synthesis impair stem cell function, but the mechanisms by which this occurs are largely unknown. We determine that low protein synthesis within hematopoietic stem cells (HSCs) is associated with elevated proteome quality in vivo. HSCs contain less misfolded and unfolded proteins than myeloid progenitors. Increases in protein synthesis cause HSCs to accumulate misfolded and unfolded proteins. To test how proteome quality affects HSCs, we examine Aarssti/sti mice that harbor a tRNA editing defect that increases amino acid misincorporation. Aarssti/sti mice exhibit reduced HSC numbers, increased proliferation, and diminished serial reconstituting activity. Misfolded proteins overwhelm the proteasome within Aarssti/sti HSCs, which is associated with increased c-Myc abundance. Deletion of one Myc allele partially rescues serial reconstitution defects in Aarssti/sti HSCs. Thus, HSCs are dependent on low protein synthesis to maintain proteostasis, which promotes their self-renewal.
Asunto(s)
Autorrenovación de las Células , Células Madre Hematopoyéticas/citología , Células Madre Hematopoyéticas/metabolismo , Proteoma/metabolismo , Animales , Ratones Endogámicos C57BL , Células Progenitoras Mieloides/metabolismo , Complejo de la Endopetidasa Proteasomal/metabolismo , Biosíntesis de Proteínas , Estabilidad Proteica , Desplegamiento Proteico , Proteínas Proto-Oncogénicas c-myc/metabolismo , Edición de ARN/genética , ARN de Transferencia/genética , UbiquitinaciónRESUMEN
Maintenance of human embryonic stem cells (hESCs) with stable genome is important for their future use in cell replacement therapy and disease modeling. Our understanding of the mechanisms maintaining genomic stability of hESC and our ability to modulate them is essential in preventing unwanted mutation accumulation during their in vitro cultivation. In this study, we show the DNA damage response mechanism in hESCs is composed of known, yet unlikely components. Clustered oxidative base damage is converted into DNA double-strand breaks (DSBs) by base excision repair (BER) and then quickly repaired by ligase (Lig)3-mediated end-joining (EJ). If there is further induction of clustered oxidative base damage by irradiation, then BER-mediated DSBs become essential in triggering the checkpoint response in hESCs. hESCs limit the mutagenic potential of Lig3-mediated EJ by DNA break end protection involving p53 binding protein 1 (53BP1), which results in fast and error-free microhomology-mediated repair and a low mutant frequency in hESCs. DSBs in hESCs are also repaired via homologous recombination (HR); however, DSB overload, together with massive end protection by 53BP1, triggers competition between error-free HR and mutagenic nonhomologous EJ.-Kohutova, A., Raska, J., Kruta, M., Seneklova, M., Barta, T., Fojtik, P., Jurakova, T., Walter, C. A., Hampl, A., Dvorak, P., Rotrekl, V. Ligase 3-mediated end-joining maintains genome stability of human embryonic stem cells.
Asunto(s)
Roturas del ADN de Doble Cadena/efectos de la radiación , Reparación del ADN por Unión de Extremidades/fisiología , ADN Ligasa (ATP)/metabolismo , Reparación del ADN/fisiología , Inestabilidad Genómica , Células Madre Embrionarias Humanas/fisiología , Proteínas de Unión a Poli-ADP-Ribosa/metabolismo , Células Cultivadas , Reparación del ADN por Unión de Extremidades/efectos de la radiación , ADN Ligasa (ATP)/genética , Reparación del ADN/efectos de la radiación , Recombinación Homóloga , Células Madre Embrionarias Humanas/citología , Humanos , Proteínas de Unión a Poli-ADP-Ribosa/genéticaRESUMEN
Recent data on Duchenne muscular dystrophy (DMD) show myocyte progenitor's involvement in the disease pathology often leading to the DMD patient's death. The molecular mechanism underlying stem cell impairment in DMD has not been described. We created dystrophin-deficient human pluripotent stem cell (hPSC) lines by reprogramming cells from two DMD patients, and also by introducing dystrophin mutation into human embryonic stem cells via CRISPR/Cas9. While dystrophin is expressed in healthy hPSC, its deficiency in DMD hPSC lines induces the release of reactive oxygen species (ROS) through dysregulated activity of all three isoforms of nitric oxide synthase (further abrev. as, NOS). NOS-induced ROS release leads to DNA damage and genomic instability in DMD hPSC. We were able to reduce both the ROS release as well as DNA damage to the level of wild-type hPSC by inhibiting NOS activity.
Asunto(s)
Distrofina/deficiencia , Inestabilidad Genómica , Células Madre Pluripotentes Inducidas/metabolismo , Distrofia Muscular de Duchenne/genética , Óxido Nítrico Sintasa de Tipo III/metabolismo , Óxido Nítrico Sintasa de Tipo II/metabolismo , Óxido Nítrico Sintasa de Tipo I/metabolismo , Línea Celular , Distrofina/genética , Humanos , Células Madre Pluripotentes Inducidas/patología , Estrés Oxidativo , Especies Reactivas de Oxígeno/metabolismoRESUMEN
Ageing of haematopoietic stem cells (HSCs) contributes to deficits in the aged haematopoietic system. HSC decline is driven in part by DNA damage accumulation; yet, how ageing impacts the acute DNA damage response (DDR) of HSCs is poorly understood. We show that old HSCs exhibit diminished ATM activity and attenuated DDR, leading to elevated clonal survival in response to a range of genotoxins that was underwritten by diminished apoptotic priming. Distinct HSC subsets exhibited ageing-dependent and subtype-dependent differences in apoptotic priming and survival in response to DNA damage. The defective DDR of old HSCs was non-cell autonomous, as ATM signalling and clonal survival in response to DNA damage could be restored to levels observed in young HSCs post-transplantated into young recipients. These data indicate that defective DDR and diminished apoptotic priming provide a selective advantage to old HSCs that may contribute to mutation accrual and disease predisposition.
Asunto(s)
Apoptosis , Senescencia Celular , Daño del ADN , Reparación del ADN , Células Madre Hematopoyéticas/enzimología , Factores de Edad , Animales , Proteínas de la Ataxia Telangiectasia Mutada/genética , Proteínas de la Ataxia Telangiectasia Mutada/metabolismo , Células Cultivadas , Trasplante de Células Madre Hematopoyéticas , Células Madre Hematopoyéticas/patología , Masculino , Ratones Endogámicos C57BL , Transducción de Señal , Factores de TiempoRESUMEN
The rapid proliferation and unlimited self-renewal of embryonic stem cells depends upon a permissive chromatin landscape that enables hypertranscription. In this issue of Cell Stem Cell, Bulut-Karslioglu et al. report that euchromatin and transcriptional output are enhanced by protein synthesis in embryonic stem cells (Bulut-Karslioglu et al., 2018).
Asunto(s)
Cromatina , Células Madre Embrionarias , Biosíntesis de ProteínasRESUMEN
The genomic destabilization associated with the adaptation of human embryonic stem cells (hESCs) to culture conditions or the reprogramming of induced pluripotent stem cells (iPSCs) increases the risk of tumorigenesis upon the clinical use of these cells and decreases their value as a model for cell biology studies. Base excision repair (BER), a major genomic integrity maintenance mechanism, has been shown to fail during hESC adaptation. Here, we show that the increase in the mutation frequency (MF) caused by the inhibition of BER was similar to that caused by the hESC adaptation process. The increase in MF reflected the failure of DNA maintenance mechanisms and the subsequent increase in MF rather than being due solely to the accumulation of mutants over a prolonged period, as was previously suggested. The increase in the ionizing-radiation-induced MF in adapted hESCs exceeded the induced MF in nonadapted hESCs and differentiated cells. Unlike hESCs, the overall DNA maintenance in iPSCs, which was reflected by the MF, was similar to that in differentiated cells regardless of the time spent in culture and despite the upregulation of several genes responsible for genome maintenance during the reprogramming process. Taken together, our results suggest that the changes in BER activity during the long-term cultivation of hESCs increase the mutagenic burden, whereas neither reprogramming nor long-term propagation in culture changes the MF in iPSCs.
Asunto(s)
Sitios Genéticos , Hipoxantina Fosforribosiltransferasa/genética , Células Madre Pluripotentes Inducidas/metabolismo , Tasa de Mutación , Diferenciación Celular/efectos de la radiación , Línea Celular , Rayos gamma , Humanos , Hipoxantina Fosforribosiltransferasa/metabolismo , Células Madre Pluripotentes Inducidas/citologíaRESUMEN
The inevitable accumulation of chromosomal abnormalities in human embryonic stem cells (hESCs) during in vitro expansion represents a considerable obstacle for cell replacement therapies. To determine the source of chromosomal abnormalities, we examined hESCs maintained in culture for over 55 months for defects in telomere maintenance and DNA repair. Although prolonged culture affected neither telomerase activity nor nonhomologous end joining, the efficiency of base excision repair (BER) was significantly decreased and correlated with reduced expression of apurinic/apyrimidinic endonuclease 1 (APE1), the major nuclease required for BER. Interestingly, the expression of other BER enzymes was unchanged. Addition of human recombinant APE1 protein to nuclear extracts from late passage hESCs increased BER efficiency to the level typical of early passage hESCs. The link between BER and double-strand breaks (DSB) was demonstrated by decreased DSB release after downregulation of APE1 in early passage hESCs via siRNA. Correspondingly lower APE1 level in late passage hESC resulted in slower and less intensive but long lasting DSB release upon ionizing radiation (IR). Downregulation of APE1 in early passage hESCs also led to approximately 30% decrease in γ-H2AX signaling following IR, similar to that in late passage hESCs. We suggest that downregulation of APE1 significantly contributes to the failure of BER during long-term culture of hESCs, and further that BER failure is one of the factors affecting the genomic instability of hESCs by altering BER-dependent DSB release and cell cycle/checkpoint signaling.