Cellular Senescence In Human Cells Research Articles

The Effect of Telomerase Enzyme on Cell Aging and Cancer Formation-Treatment

Research has made the effects of the telomerase enzyme on both cellular ageing and cancer even more important. Measurement of telomerase activity appears to be a unique marker in addition to known methods for cancer diagnosis and treatment. In addition, numerous studies have shown that the reduction of telomeres shortens the life span of living cells. It is a known fact that cells with shortened lifespan age earlier and predispose to many diseases, especially cancer types. The fact that old cells are the basis for many diseases and young cells are resistant to many diseases has revealed the reality of keeping the cells young in order to prevent diseases. Studies aimed at understanding the activation of the telomerase enzyme on telomeres, have shown that this enzyme will have a positive effect on cellular rejuvenation on living cells, prolong the life span of living cells, thus preventing age-related diseases before they occur, and also making it impossible for many types of cancer that may develop due to old age to occur in the first place. Predictions such as preventing and stopping cellular senescence in human cells, providing cellular rejuvenation by reversing cellular senescence and extending human life span as much as desired are also worthy of further emphasis with the studies carried out.

Microautophagy regulated by STK38 and GABARAPs is essential to repair lysosomes and prevent aging.

Lysosomes are degradative organelles and signaling hubs that maintain cell and tissue homeostasis, and lysosomal dysfunction is implicated in aging and reduced longevity. Lysosomes are frequently damaged, but their repair mechanisms remain unclear. Here, we demonstrate that damaged lysosomal membranes are repaired by microautophagy (a process termed "microlysophagy") and identify key regulators of the first and last steps. We reveal the AGC kinase STK38 as a novel microlysophagy regulator. Through phosphorylation of the scaffold protein DOK1, STK38 is specifically required for the lysosomal recruitment of the AAA+ ATPase VPS4, which terminates microlysophagy by promoting the disassembly of ESCRT components. By contrast, microlysophagy initiation involves non-canonical lipidation of ATG8s, especially the GABARAP subfamily, which is required for ESCRT assembly through interaction with ALIX. Depletion of STK38 and GABARAPs accelerates DNA damage-induced cellular senescence in human cells and curtails lifespan in C. elegans, respectively. Thus, microlysophagy is regulated by STK38 and GABARAPs and could be essential for maintaining lysosomal integrity and preventing aging.

Lamin B receptor (LBR) is involved in the induction of cellular senescence in human cells

Cellular senescence is a phenomenon of irreversible growth arrest in mammalian somatic cells in culture. Various stresses induce cellular senescence and indeed, we have found that excess thymidine effectively induces cellular senescence in human cells. Further, many reports indicate the implication of chromatin proteins in cellular senescence. Here we analysed the role of lamin B receptor (LBR), a nuclear envelope protein that regulates heterochromatin organization, in cellular senescence induced by excess thymidine. We then found that the LBR protein was down-regulated and showed aberrant localization in cells upon induction of cellular senescence by excess thymidine. Additionally, we also found that knock-down of LBR facilitated the induction of cellular senescence by excess thymidine in cancerous HeLa cells, and importantly, it induced cellular senescence in normal human diploid fibroblast TIG-7 cells. These results suggested that decreased LBR function is involved in the induction of cellular senescence in human cells.

Dual roles of ERK1/2 in cellular senescence induced by excess thymidine in HeLa cells

DNA damage response is crucially involved in cellular senescence. We have previously shown that excess thymidine, which stalls DNA replication forks, induces cellular senescence in human cells, and ERK1/2 play a key role in the induction of it. In this study, we found that Chk1 and ERK1/2 were activated to promote cell survival upon addition of excess thymidine. Knockdown of ERK1/2 activated Chk1, and conversely, knockdown of Chk1 activated ERK1/2, which observations suggested a mechanism for compensatory activation of Chk1 and ERK1/2 in the absence of ERK1/2 and Chk1, respectively. We also found that Chk1 functioned mainly at the onset of cellular senescence, and on the other hand, ERK1/2 functioned for a more extended period to induce cellular senescence. Our findings suggested that Chk1 and ERK1/2 were activated to promote cell survival upon addition of excess thymidine, but prolonged activation of ERK1/2 led to cellular senescence. This implies a pleiotropic effect of ERK1/2 in cellular senescence induced by excess thymidine.

Aberrant localization of lamin B receptor (LBR) in cellular senescence in human cells

5-Bromodeoxyuridine (BrdU), a thymidine analogue, induces cellular senescence in mammalian cells. BrdU induces cellular senescence probably through the regulation of chromatin because BrdU destabilizes or disrupts nucleosome positioning and decondenses heterochromatin. Since heterochromatin is tethered to the nuclear periphery through the interaction with the nuclear envelope proteins, we examined the localization of the several nuclear envelope proteins such as lamins, lamin-interacting proteins, nuclear pore complex proteins, and nuclear transport proteins in senescent cells. We have shown here that lamin B receptor (LBR) showed a change in localization in both BrdU-induced and replicative senescent cells.

Integrated Stochastic Model of DNA Damage Repair by Non-homologous End Joining and p53/p21-Mediated Early Senescence Signalling.

Unrepaired or inaccurately repaired DNA damage can lead to a range of cell fates, such as apoptosis, cellular senescence or cancer, depending on the efficiency and accuracy of DNA damage repair and on the downstream DNA damage signalling. DNA damage repair and signalling have been studied and modelled in detail separately, but it is not yet clear how they integrate with one another to control cell fate. In this study, we have created an integrated stochastic model of DNA damage repair by non-homologous end joining and of gamma irradiation-induced cellular senescence in human cells that are not apoptosis-prone. The integrated model successfully explains the changes that occur in the dynamics of DNA damage repair after irradiation. Simulations of p53/p21 dynamics after irradiation agree well with previously published experimental studies, further validating the model. Additionally, the model predicts, and we offer some experimental support, that low-dose fractionated irradiation of cells leads to temporal patterns in p53/p21 that lead to significant cellular senescence. The integrated model is valuable for studying the processes of DNA damage induced cell fate and predicting the effectiveness of DNA damage related medical interventions at the cellular level.

TopBP1 Deficiency Causes an Early Embryonic Lethality and Induces Cellular Senescence in Primary Cells

TopBP1 plays important roles in chromosome replication, DNA damage response, and other cellular regulatory functions in vertebrates. Although the roles of TopBP1 have been studied mostly in cancer cell lines, its physiological function remains unclear in mice and untransformed cells. We generated conditional knock-out mice in which exons 5 and 6 of the TopBP1 gene are flanked by loxP sequences. Although TopBP1-deficient embryos developed to the blastocyst stage, no homozygous mutant embryos were recovered at E8.5 or beyond, and completely resorbed embryos were frequent at E7.5, indicating that mutant embryos tend to die at the peri-implantation stage. This finding indicated that TopBP1 is essential for cell proliferation during early embryogenesis. Ablation of TopBP1 in TopBP1(flox/flox) mouse embryonic fibroblasts and 3T3 cells using Cre recombinase-expressing retrovirus arrests cell cycle progression at the G(1), S, and G(2)/M phases. The TopBP1-ablated mouse cells exhibit phosphorylation of H2AX and Chk2, indicating that the cells contain DNA breaks. The TopBP1-ablated mouse cells enter cellular senescence. Although RNA interference-mediated knockdown of TopBP1 induced cellular senescence in human primary cells, it induced apoptosis in cancer cells. Therefore, TopBP1 deficiency in untransformed mouse and human primary cells induces cellular senescence rather than apoptosis. These results indicate that TopBP1 is essential for cell proliferation and maintenance of chromosomal integrity.

Identification of Plant Extracts that Inhibit Cellular Senescence in Human Fibroblasts, Endothelial Cells, and Vascular Smooth Muscle Cells

To identify plant extracts capable of inhibiting cellular senescence, the effects of plant extracts on adriamycin-induced cellular senescence in human fibroblasts, human umbilical vein endothelial cells (HUVECs), and vascular smooth muscle cells were investigated. After adriamcyin treatment, the effects of plant extracts on cellular senescence were evaluated by measuring senescenceassociated β-galactosidase activity of the cells. Among 799 plant extracts, those from Rhei Rhizoma, Cirsii Radix, and Plantagnis Semen repressed adriamycin-induced cellular senescence in fibroblasts. Extracts of Cinnamomi Cortex and Cinnamomi Cortex Spissus were effective in endothelial cells. Extracts of Euonymi Lignum Suberalatum, Salicis Radicis Cortex, Polygoni aviculari Herba, and Chaenomelis langenariae Radix reduced senescence in vascular smooth muscle cells. These results suggested the effectiveness of plant extracts in reducing cellular senescence of human cells. These plant extracts could be used to develop dietary supplements or cosmetics for modulating tissue aging or aging-associated diseases.

Expression regulation and genomic organization of human polynucleotide phosphorylase, hPNPaseold-35, a Type I interferon inducible early response gene

An overlapping pathway screening (OPS) approach designed to identify and clone genes displaying parallel expression profiles as a function of induction of terminal differentiation and cellular senescence in human cells identified a novel gene old-35. Sequence and functional analysis indicates that old-35 encodes human polynucleotide phosphorylase, hPNPase old-35 . Polynucleotide phosphorylases comprise a family of phosphate dependent 3′–5′ RNA exonucleases implicated in RNA regulation. Treatment of HO-1 human melanoma and additional diverse normal and tumor-derived human cell types with Type I interferon (IFN), IFN-β or IFN-α, induces hPNPase old-35 expression. To provide insights into the regulation of hPNPase old-35 , we cloned and analyzed the promoter region of this gene. These studies demonstrate that IFN-β controls hPNPase old-35 expression by transcriptional modulation rather than by altering mRNA stability. Transcriptional activation of hPNPase old-35 by IFN-β is primarily mediated by the interferon stimulatory response element (ISRE) present in its promoter. Analysis of hPNPase old-35 expression in cell lines defective in various IFN signaling molecules confirms that hPNPase old-35 expression is dependent upon the Janus activated kinase (JAK)/signal transducers and activators of transcription (STAT) pathway. Furthermore, gel shift analyses document that hPNPase old-35 is a direct target of the interferon stimulated gene factor 3 (ISGF3) complex. The hPNPase old-35 gene spans ∼54 kb of genomic DNA and is distributed on 28 exons and 27 introns. hPNPase old-35 maps to 2p15–2p16.1, a region implicated in hereditary nonpolyposis colorectal cancer, Carney complex, Doyne′s honeycomb retinal dystrophy and several other diseases. To provide insights into PNPase function in vivo, we have also cloned the mouse PNPase old-35 cDNA, mPNPase old-35 . Induction of hPNPase old-35 by IFN treatment as well as during differentiation and senescence suggest that this gene may play a significant role in regulating cellular growth and that overlapping gene expression changes, also induced by IFN, may contribute to these important physiological processes.