p16(INK4A) positively regulates p21(WAF1) expression by suppressing AUF1-dependent mRNA decay

Exploring cellular senescence in the musculoskeletal system: Any insights for biomarkers discovery?

The locomotor system comprises skeletal muscles and bones with active metabolism and cellular turnover. Chronic locomotor system disorders gradually arising with aging are inversely associated with the correct function of bone and muscles. Senescent cells appear more frequently in advanced ages or pathological conditions, and the accumulation of senescent cells in muscle tissue negatively correlates with muscle regeneration, which is crucial for maintaining strength and preventing frailty. Senescence in the bone microenvironment, osteoblasts, and osteocytes affects bone turnover favoring osteoporosis. It is likely that in response to injury and age-related damage over the lifetime, a subset of niche cells accumulates oxidative stress and DNA damage beyond the threshold that primes the onset of cellular senescence. These senescent cells may acquire resistance to apoptosis that, combined with the weakened immune system, results in impaired clearance of senescent cells and their accumulation. The secretory profile of senescent cells causes local inflammation, further spreading senescence in neighboring niche cells and impairing tissue homeostasis. The resulting impairment of turnover/tissue repair in the musculoskeletal system reduces the efficiency of the organ in response to environmental needs that finally lead to functional decline. Management of the musculoskeletal system at the cellular level can benefit the quality of life and reduce early aging. This work discusses current knowledge of cellular senescence of musculoskeletal tissues to conclude with biologically active biomarkers effective enough to reveal the underlying mechanisms of tissue flaws at the earliest possible.

Senescent cardiomyocytes contribute to cardiac dysfunction following myocardial infarction

Myocardial infarction is a leading cause of morbidity and mortality. While reperfusion is now standard therapy, pathological remodelling leading to heart failure remains a clinical problem. Cellular senescence has been shown to contribute to disease pathophysiology and treatment with the senolytic navitoclax attenuates inflammation, reduces adverse myocardial remodelling and results in improved functional recovery. However, it remains unclear which senescent cell populations contribute to these processes. To identify whether senescent cardiomyocytes contribute to disease pathophysiology post-myocardial infarction, we established a transgenic model in which p16 (CDKN2A) expression was specifically knocked-out in the cardiomyocyte population. Following myocardial infarction, mice lacking cardiomyocyte p16 expression demonstrated no difference in cardiomyocyte hypertrophy but exhibited improved cardiac function and significantly reduced scar size in comparison to control animals. This data demonstrates that senescent cardiomyocytes participate in pathological myocardial remodelling. Importantly, inhibition of cardiomyocyte senescence led to reduced senescence-associated inflammation and decreased senescence-associated markers within other myocardial lineages, consistent with the hypothesis that cardiomyocytes promote pathological remodelling by spreading senescence to other cell-types. Collectively this study presents the demonstration that senescent cardiomyocytes are major contributors to myocardial remodelling and dysfunction following a myocardial infarction. Therefore, to maximise the potential for clinical translation, it is important to further understand the mechanisms underlying cardiomyocyte senescence and how to optimise senolytic strategies to target this cell lineage.

Biomarkers of aging

Aging biomarkers are a combination of biological parameters to (i) assess age-related changes, (ii) track the physiological aging process, and (iii) predict the transition into a pathological status. Although a broad spectrum of aging biomarkers has been developed, their potential uses and limitations remain poorly characterized. An immediate goal of biomarkers is to help us answer the following three fundamental questions in aging research: How old are we? Why do we get old? And how can we age slower? This review aims to address this need. Here, we summarize our current knowledge of biomarkers developed for cellular, organ, and organismal levels of aging, comprising six pillars: physiological characteristics, medical imaging, histological features, cellular alterations, molecular changes, and secretory factors. To fulfill all these requisites, we propose that aging biomarkers should qualify for being specific, systemic, and clinically relevant.

St18 specifies globus pallidus projection neuron identity in MGE lineage

The medial ganglionic eminence (MGE) produces both locally-projecting interneurons, which migrate long distances to structures such as the cortex as well as projection neurons that occupy subcortical nuclei. Little is known about what regulates the migratory behavior and axonal projections of these two broad classes of neurons. We find that St18 regulates the migration and morphology of MGE neurons in vitro. Further, genetic loss-of-function of St18 in mice reveals a reduction in projection neurons of the globus pallidus pars externa. St18 functions by influencing cell fate in MGE lineages as we observe a large expansion of nascent cortical interneurons at the expense of putative GPe neurons in St18 null embryos. Downstream of St18, we identified Cbx7, a component of Polycomb repressor complex 1, and find that it is essential for projection neuron-like migration but not morphology. Thus, we identify St18 as a key regulator of projection neuron vs. interneuron identity.

Pancreatic Cancer and Cellular Senescence: Tumor Microenvironment under the Spotlight

Pancreatic ductal adenocarcinoma (PDAC) has one of the most dismal prognoses of all cancers due to its late manifestation and resistance to current therapies. Accumulating evidence has suggested that the malignant behavior of this cancer is mainly influenced by the associated strongly immunosuppressive, desmoplastic microenvironment and by the relatively low mutational burden. PDAC develops and progresses through a multi-step process. Early in tumorigenesis, cancer cells must evade the effects of cellular senescence, which slows proliferation and promotes the immune-mediated elimination of pre-malignant cells. The role of senescence as a tumor suppressor has been well-established; however, recent evidence has revealed novel pro-tumorigenic paracrine functions of senescent cells towards their microenvironment. Understanding the interactions between tumors and their microenvironment is a growing research field, with evidence having been provided that non-tumoral cells composing the tumor microenvironment (TME) influence tumor proliferation, metabolism, cell death, and therapeutic resistance. Simultaneously, cancer cells shape a tumor-supportive and immunosuppressive environment, influencing both non-tumoral neighboring and distant cells. The overall intention of this review is to provide an overview of the interplay that occurs between senescent and non-senescent cell types and to describe how such interplay may have an impact on PDAC progression. Specifically, the effects and the molecular changes occurring in non-cancerous cells during senescence, and how these may contribute to a tumor-permissive microenvironment, will be discussed. Finally, senescence targeting strategies will be briefly introduced, highlighting their potential in the treatment of PDAC.

A novel lncRNA derived from an ultraconserved region: lnc-uc.147, a potential biomarker in luminal A breast cancer

The human genome contains 481 ultraconserved regions (UCRs), which are genomic stretches of over 200 base pairs conserved among human, rat, and mouse. The majority of these regions are transcriptionally active (T-UCRs), and several have been found to be differentially expressed in tumours. Some T-UCRs have been functionally characterized, but of those few have been associated to breast cancer (BC). Using TCGA data, we found 302 T-UCRs related to clinical features in BC: 43% were associated with molecular subtypes, 36% with oestrogen-receptor positivity, 17% with HER2 expression, 12% with stage, and 10% with overall survival. The expression levels of 12 T-UCRs were further analysed in a cohort of 82 Brazilian BC patients using RT-qPCR. We found that uc.147 is high expressed in luminal A and B patients. For luminal A, a subtype usually associated with better prognosis, high uc.147 expression was associated with a poor prognosis and suggested as an independent prognostic factor. The lncRNA from uc.147 (lnc-uc.147) is located in the nucleus. Northern blotting results show that uc.147 is a 2,8 kb monoexonic trancript, and its sequence was confirmed by RACE. The silencing of uc.147 increases apoptosis, arrests cell cycle, and reduces cell viability and colony formation in BC cell lines. Additionally, we identifed 19 proteins that interact with lnc-uc.147 through mass spectrometry and demonstrated a high correlation of lnc-uc.147 with the neighbour gene expression and miR-18 and miR-190b. This is the first study to analyse the expression of all T-UCRs in BC and to functionally assess the lnc-uc.147.

Toxicity and Anti-Proliferative Properties of Anisomeles indica Ethanol Extract on Cervical Cancer HeLa Cells and Zebrafish Embryos

In this study, we showed that crude extract of Anisomeles indica (AI-EtE) expressed its toxicity to HeLa cells with an IC50 dose of 38.8 µg/mL and to zebrafish embryos with malformations, lethality and hatching inhibition at 72-hpf at doses higher than 75 µg/mL. More interestingly, flow cytometry revealed that AI-EtE significantly promoted the number of cells entering apoptotic. Accordingly, the transcript levels of BAX, CASPASE-8, and CASPASE-3 in the cells treated with AI-EtE at IC50 dose were 1.55-, 1.62-, and 2.45-fold higher than those in the control cells, respectively. Moreover, treatment with AI-EtE caused cell cycle arrest at the G1 phase in a p53-independent manner. Particularly, percentages of AI-EtE-treated cells in G1, S, G2/M were, respectively 85%, 6.7% and 6.4%; while percentages of control cells in G1, S, G2/M were 64%, 15% and 19%, respectively. Consistent with cell cycle arrest, the expressions of CDKN1A and CDNK2A in AI-EtE-treated cells were up-regulated 1.9- and 1.64-fold, respectively. Significantly, treatment with AI-EtE also decreased anchorage-independent growth of HeLa cells. In conclusion, we suggest that Anisomeles indica can be considered as a medicinal plant with a possible use against cervical cancer cells; however, the used dose should be carefully monitored, especially when applying to pregnant women.

Hyaluronan-binding protein 1 (HABP1) overexpression triggers induction of senescence in fibroblasts cells

Hyaluronan-binding protein 1 (HABP1), a multi-compartmental, multi-functional protein has a wide range of functions, which can be attributed to its ability to associate with a variety of cellular ligands. Earlier we have reported that HABP1 overexpression in rat normal fibroblasts (F-HABP07) shows chronic generation of reactive oxygen species (ROS), induction of autophagy, and apoptosis. However, a significant proportion of cells remained viable after the majority went through apoptosis from 60 to 72 h. In this study, an attempt has been made to delineate the cellular events in the declined population of surviving cells. It has been elucidated here that, these cells at later time points of growth, that is, 72 and 84 h, not only appeared to shrink but also are devoid of autophagic vacuoles and displayed polyploidy. F-HABP07 cells exhibited an altered cytoskeletal structure from their parental cell line F111, assumed to be caused upon inhibition of actin polymerization and decrease in IQ motif-containing GTPase activating protein 1 (IQGAP1), a key protein associated with maintenance of cytoskeletal integrity. Enhanced expression and nuclear localization of AKT observed in F-HABP07 cells appears to be contributing toward the maintenance of high ROS levels in these cells and also potentially modulating the IQGAP1 activity. These observations, in fact have been considered to result in sustained DNA damage, which then leads to increased expression of p53 and activation of p21 and carry out the cellular events responsible for senescence. Subsequent assessment of the presence of positive β-gal staining and enhanced expression of p16^INK4a in F-HABP07, confirmed that HABP1 overexpressing fibroblasts undergo senescence.

Immunohistochemical detection of senescence markers in human sarcomas

INTRODUCTION

Senescent cells in tumors are not inert cells but exert bystander effects by developing secretory phenotypes affecting the extracellular matrix and interfering the biological behavior of adjacent tumor cells.

MATERIALS AND METHODS

We assessed putative senescent cell content in a series of human sarcomas, using in parallel markers related to cell proliferation (Ki67), DNA damage (γH2Ax), lipofuscin detection (SenTraGor®) and two cyclin-dependent kinase CDK-inhibitors (p16/INK4a and p21/cip/waf21).

RESULTS

Necrosis was directly linked with the size of tumors (p = 0.02, r = 0.25), number of mitosis (p = 0.05, r = 0.21) and inversely with the expression of γH2Ax (p = 0.01, r = 0.28). Smaller tumors (less than 3 cm) had a higher p16 expression (p = 0.07); Moreover, in group analysis, tumors with lack of expression of p16 had significantly higher necrosis score (p = 0.03). Linear regression analysis showed that p21 expression was strongly and directly related with MIB1 (p < 0.0001, r = 0.44) and with Lipofuscin expression (p = 0.02, r = 0.26).

CONCLUSION

Senescence markers are extensively expressed in human sarcomas and correlated with histopathological features. However, p16, p21 and Lipofuscin expression show different patterns, suggesting that these markers may detect different senescence phenotypes. In addition, our data suggest that the novel marker SenTraGor® may detect phenotypes of senescent cells involving p21 activation.

AUF1 positively controls angiogenesis through mRNA stabilization-dependent up-regulation of HIF-1α and VEGF-A in human osteosarcoma

Osteosarcoma is the most common malignant bone tumor in children, adolescents, and young adults. This pleiomorphic tumor depends on new blood vessel development, also known as angiogenesis, for tumor growth and metastasis. Therefore, it’s of utmost importance to identify the key genes and pathways that regulate this pro-metastatic process in order to develop more efficient therapies. Here, we have shown that the RNA-binding protein AUF1 positively regulates the expression of the pro-angiogenic factor VEGF-A and its positive regulator HIF-1alpha through direct binding and stabilization of their mRNAs. This effect is mediated through the seeding sequence of the AUF1 protein in the VEGF-A and HIF-1alpha 3’UTR sequences. As a consequence, the expression of the 3 genes was highly correlative in various osteosarcoma cell lines, and AUF1 enhanced the pro-angiogenic capabilities of osteosarcoma cells both in vitro and in vivo. Indeed, while inhibition of AUF1 using specific siRNA suppressed the pro-angiogenic effects of osteosarcoma cells, ectopic expression of AUF1 enhanced the pro-angiogenic effect in a VEGF-A-dependent manner. Therefore, in the era of targeted therapy, anti-angiogenic therapies targeting AUF1 could provide effective methods for treating osteosarcoma.

Two ways of escaping from oxidative RNA damage: Selective degradation and cell death

Reactive oxygen species (ROS) are produced during normal cellular metabolism, and various oxidized compounds are formed by the ROS attack. Among oxidized bases, 8-oxo-7,8-dihydroguanine (8-oxoG) is most abundant and seems important with respect to the maintenance and transfer of genetic information. The accumulation of 8-oxoG in messenger RNA may cause errors during codon-anticodon pairing in the translation process, which may result in the synthesis of abnormal proteins. Organisms that use oxygen as the source of energy production must therefore have some mechanisms to eliminate the deleterious effects of RNA oxidation. Recently, we found two protein factors, AUF1 and PCBP1, which each have a different binding capacity to oxidized RNA. Evidence demonstrated that AUF1 is involved in the specific degradation of oxidized RNA, and that PCBP1 has a function of inducing cell death to eliminate severely damaged RNA.

Umbilical Mononuclear Cells and Fibroblast Interaction Downregulate the Expression of Cell Cycle Negative Control Genes

The human umbilical cord blood (HUCB) is an excellent source of adult stem cells, having the benefit of being younger than the bone marrow stem cells. The role of stem cells in the lesion repair mechanism is still being studied. We evaluated the capability of HUCB to interfere into the fibroblast dedifferentiation plasticity through cocultivation. Direct and indirect cocultures were maintained for 24, 48, and 72 hours. Coculture viability was evaluated by MTT assay. The messenger RNA was extracted, and the expression of p16 and p21 genes was estimated by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). The direct or indirect contact did not interfere with fibroblast cell viability. However, these direct and indirect contacts reduced the expression of p16 and p21 genes. A sigmoidal curve was applied to adjust gene expression against time, and a mathematical function was established for gene expression according to cell culture type. These results suggest that the differentiated cells were influenced by immature cells (HUCB) either by the direct contact or by signaling molecules, which alter their behavior and plasticity. Therefore our data may contribute to paracrine effects other than the commonly known to be responsible for the repair of lesions in stem cell therapy.

Hallmarks of Cellular Senescence

Cellular senescence is a permanent state of cell cycle arrest that promotes tissue remodeling during development and after injury, but can also contribute to the decline of the regenerative potential and function of tissues, to inflammation, and to tumorigenesis in aged organisms. Therefore, the identification, characterization, and pharmacological elimination of senescent cells have gained attention in the field of aging research. However, the nonspecificity of current senescence markers and the existence of different senescence programs strongly limit these tasks. Here, we describe the molecular regulators of senescence phenotypes and how they are used for identifying senescent cells in vitro and in vivo. We also highlight the importance that these levels of regulations have in the development of therapeutic targets.

Inhibition of enhancer of zeste homolog 2 increases the expression of p16 and suppresses the proliferation and migration of ovarian carcinoma cells in vitro and in vivo

Enhancer of zeste homolog 2 (EZH2) is a histone methyltransferase, which targets histone H3 lysine 27. Studies have reported that EZH2 is involved in the development of several types of tumor, including ovarian cancer. p16, a well-known cell cycle regulator, has been demonstrated to be a tumor suppressor gene in a variety of malignant cells. However, the regulatory association between EZH2 and p16 in ovarian cancer remains to be fully elucidated. The present study aimed to determine whether EZH2 is involved in the development of ovarian cancer by regulating the expression of p16. An EZH2 short hairpin RNA (shRNA) lentiviral vector was constructed and used for transducing A2780 and SKOV3 ovarian cancer cell lines. The expression levels of EZH2 and p16 in the ovarian cancer cells were detected using a reverse transcription-quantitative polymerase chain reaction and western blot analyses, respectively. The function of the inhibition of EZH2 in cell proliferation and migration were determined using a CCK-8 assay and Transwell assay. In addition, a nude mouse xenograft model was used to determine the function of EZH2 and p16 in the formation of ovarian cancer in vivo. The results revealed that the inhibition of EZH2 increased the expression of p16, and suppressed the proliferation and migration capabilities of ovarian cancer in vitro. The downregulated expression of EZH2 suppressed ovarian tumor formation in vivo. The results of the study revealed that p16 was negatively regulated by EZH2 in ovarian cancer, and that p16 and EZH2 are important in the tumorigenesis of ovarian cancer. EZH2 and p16 represent potential biomarkers for the diagnosis of ovarian cancer and as targets for ovarian cancer gene therapy.

Expression of the tumor suppressor gene p16, and lymph node metastasis in patients with ovarian cancer

This study examined the relationship between the expression of p16, a tumor suppressor gene, and lymph node metastasis, as well as patient prognosis, in cases with ovarian cancer. SKOV-3, an ovarian cancer cell line, and IOSE80, a normal human ovarian cell line, were selected for testing. Western blot analysis was used to detect the p16 expression in ovarian cell culture samples. In the study, 20 cases with normal ovarian tissue and 64 cases with ovarian cancer tissue, including 38 cases with lymph node metastasis and 26 cases without lymph node metastasis, were also selected for testing. Immunohistochemical techniques were used to detect the expression of p16 protein in ovarian tissue samples. The influence of p16 protein on SKOV-3 cell invasion ability was studied using p16 gene high-expression vector transfection. Clinical and prognosis data were summarized and the influence of p16 on patient prognosis was analyzed through Kaplan-Meier single-factor survival analysis. The results showed that p16 expression in SKOV-3 was decreased significantly compared with that in IOSE80. The positive rate of p16 protein expression in ovarian cancer tissue was notably decreased compared with that in normal ovarian tissue. The positive rate of p16 protein expression in ovarian cancer tissue of patients with lymph node metastasis was significantly decreased compared with that of patients without lymph node metastasis. Therefore, transfection of the p16 gene significantly inhibited the protein expression and invasion ability of p16 in SKOV-3. Correlation analyses between p16 and survival prognosis demonstrated that lower expression of p16 was negatively correlated with the prognosis of patients with ovarian cancer. Overall, the abnormal expression of p16 in ovarian cancer is associated with an increased invasion ability of ovarian cancer and the lower expression of p16 in tissue samples indicates a poor prognosis in patients with ovarian cancer.

Inhibitory Effect of Ginseng on Breast Cancer Cell Line Growth Via Up-Regulation of Cyclin Dependent Kinase Inhibitor, p21 and p53

Objective:

Breast cancer is global female health problem worldwide. Most of the currently used agents for breast cancer treatment have toxic side-effects. Ginseng root, an oriental medicine, has many health benefits and may exhibit direct anti-cancer properties. This study was performed to assess the effects of ginseng on breast cancer cell lines.

Materials and Methods:

Cytotoxicity of ginseng extract was measured by MTT assay after exposure of MDA-MB-231, MCF-10A and MCF-7 breast cancer cells to concentrations of 0.25, 0.5, 1, 1.5, 2 and 2.5 mg/well. Expression levels of p21WAF, p16INK4A, Bcl-2, Bax and P53 genes were analyzed by quantitative real time PCR.

Results:

The treatment resulted in inhibition of cell proliferation in a dose-and time-dependent manner. p53, p21WAF1and p16INK4A expression levels were up-regulated in ginseng treated MDA-MB-231 and MCF-7 cancer cells compared to untreated controls and in MCF-10A cells. The expression levels of Bcl2 in the MDA-MB-231 and MCF-7 cells were down-regulated. In contrast, that of Bax was significantly up-regulated.

Conclusion:

The results of this study revealed that ginseng may inhibit breast cancer cell growth by activation of the apoptotic pathway.

Rapamycin safeguards lymphocytes from DNA damage accumulation in vivo

Several studies reported the benefits of switching from anticalcineurins to mTOR inhibitors to avoid cancer occurrence after organ transplantation. The purpose of our study was to determine in vivo biological markers to explain these benefits. Cellular changes related to cellular senescence and DNA damage were analyzed in peripheral blood lymphocytes. Thirty-five kidney transplanted patients receiving anticalcineurins were investigated: 17 patients were proposed to switch to rapamycin and 18 patients with similar age and transplantation duration, continued anticalcineurins. Rapamycin effects were studied one year after the switch. Thirteen healthy volunteers and 18 hemodialyzed patients were evaluated as control. Compared with the healthy group, hemodialyzed and transplanted patients exhibited a significant decrease in telomere length, an increase in p16(INK4A) mRNA expression and in lymphocytes with 53BP1 foci. A destabilization of the shelterin complexes was suggested by a significant TIN2 mRNA decrease in transplanted patients compared with controls and a significant increase in TRF1, TRF2 and POT1 expression in switch-proposed patients compared with the non-switched subgroup. Rapamycin treatment resulted in a significant decrease in DNA damage and a slight TIN2 increase. In vitro experiments strengthened in vivo results showing that rapamycin but not FK506 induced a significant DNA damage decrease and TIN2 expression increase compared with controls. The roles of rapamycin in the decrease in DNA damage in vivo and the rescue of shelterin gene expression are demonstrated for the first time. These data provide new insights into understanding of how rapamycin may overcome genomic injuries.

Oxidative challenge enhances REGγ-proteasome-dependent protein degradation

Elimination of oxidized proteins is important to cells as accumulation of damaged proteins causes cellular dysfunction, disease, and aging. Abundant evidence shows that the 20S proteasome is largely responsible for degradation of oxidative proteins in both ubiquitin-dependent and ubiquitin-independent pathways. However, the role of the REGγ-proteasome in degrading oxidative proteins remains unclear. Here, we focus on two of the well-known REGγ-proteasome substrates, p21(Waf1/Cip1) and hepatitis C virus (HCV) core protein, to analyze the impact of oxidative stress on REGγ-proteasome functions. We demonstrate that REGγ-proteasome is essential for oxidative stress-induced rapid degradation of p21 and HCV proteins. Silencing REGγ abrogated this response in multiple cell lines. Furthermore, pretreatment with proteasome inhibitor MG132 completely blunted oxidant-induced p21 degradation, indicating a proteasome-dependent action. Cellular oxidation promoted REGγ-proteasome-dependent trypsin-like activity by enhancing the interaction between REGγ and 20S proteasome. Antioxidant could counteract oxidation-induced protein degradation, indicating that REGγ-proteasome activity may be regulated by redox state. This study provides further insights into the actions of a unique proteasome pathway in response to an oxidative stress environment, implying a novel molecular basis for REGγ-proteasome functions in antioxidation.

NaCl pretreatment attenuates H.pylori-induced DNA damage and exacerbates proliferation of gastric epithelial cells (GES-1)

Background

Both H. pylori infection and high salt (NaCl) diet are risks of gastric cancer, however, the interaction pattern of the two is not very clear. Our objective was to investigate the effects of NaCl-pretreated H. pylori on DNA damage and proliferation of gastric epithelial cell (GES-1).

Methods

GES-1 cells were co-cultured with H.pylori or NaCl-pretreated H. pylori (with 30% NaCl) for 24 h. The morphological changes of all cells were observed by inverted phase contrast microscopy and transmission electron microscopy. Oxidative DNA damage was examined by immunofluorescence. Alterations in mitochondrial membrane potential and apoptosis rate were detected by flow cytometry and western blot, and expression of Ki-67, PCNA and P21 were evaluated using the immunocytochemical staining.

Results

GES-1 cells co-cultured with NaCl-pretreated H.pylori exhibited morphological changes and oxidative DNA damage. Although no significant disruption of the mitochondrial membrane potential (ΔΨm) and apoptotic rate were observed compared with control groups, there were significant decreased in Bax and Caspase3 proteins and increased in Bcl-2 protein in GES-1 cells infected with H. pylori³⁰ when compared with GES-1 cells cultured with H. pylori. In addition, we found a proliferative effect on GES-1 cells with an increased expression of Ki-67 and PCNA as well as a decreased p21 expression, through which the cells may acquire the potential for malignant transformation.

Conclusion

NaCl-pretreated H. pylori possessed the ability to cause cell injury and promote proliferation in gastric epithelial cells.

p16(INK4A) inhibits the pro-metastatic potentials of osteosarcoma cells through targeting the ERK pathway and TGF-β1

Extracellular signal-regulated kinase (ERK) is a downstream component of the evolutionarily conserved mitogen-activated protein kinase-signaling pathway, which controls the expression of a plethora of genes implicated in various physiological processes. This pathway is often hyper-activated by mutations or abnormal extracellular signaling in different types of human cancer, including the most common primary malignant bone tumor osteosarcomas. p16(INK4A) is an important tumor suppressor gene frequently lost in osteosarcomas, and is associated with the progression of these malignancies. We have shown, here, that the ERK1/2 protein kinase is also activated by p16(INK4A) down-regulation in osteosarcoma cells and normal human as well as mouse cells. This inhibitory effect is associated with the suppression of the upstream kinase MEK1/2, and is mediated via the repression of miR-21-5p and the consequent up-regulation of the MEK/ERK antagonist SPRY2 in osteosarcoma cells. Furthermore, we have shown that p16(INK4) inhibits the migration/invasion abilities of these cells through miR-21-5p-dependent inhibition of ERK1/2. In addition, we present clear evidence that p16(INK4) represses the paracrine pro-migratory effect of osteosarcoma cells on stromal fibroblasts through the inhibition of the TGF-β1 expression/secretion. This effect is also ERK1/2-dependent, indicating that in addition to their cell-autonomous actions, p16(INK4) and ERK1/2 have also non-cell-autonomous cancer-related functions. Together, these results indicate that the tumor suppressor p16(INK4) protein represses the carcinogenic process of osteosarcoma cells not only as a cell cycle regulator, but also as a negative regulator of pro-carcinogenic/-metastatic pathways. This indicates that targeting the ERK pathway is of utmost therapeutic value.

Role of Auf1 in elimination of oxidatively damaged messenger RNA in human cells

In aerobically growing cells, in which reactive oxygen species are produced, the guanine base of RNA is oxidized to 8-oxo-7,8-dihydroguanine, which induces alterations in gene expression. Here we show that the human Auf1 protein, also called HNRNPD, binds specifically to RNA containing this oxidized base and may be involved in cellular processes associated with managing the problems caused by RNA oxidation. Auf1-deficient cells were constructed from human HeLa and Nalm-6 lines using two different targeting procedures. Both types of Auf1-deficient cells are viable, but exhibit growth retardation. The stability of messenger RNA for four different housekeeping genes was determined in Auf1-deficient and -proficient cells, treated with or without hydrogen peroxide. The level of oxidized messenger RNA was considerably higher in Auf1-deficient cells than in Auf1-proficient cells. Auf1 may play a role in the elimination of oxidized RNA, which is required for the maintenance of proper gene expression under conditions of oxidative stress.

MicroRNA-141 and microRNA-146b-5p inhibit the prometastatic mesenchymal characteristics through the RNA-binding protein AUF1 targeting the transcription factor ZEB1 and the protein kinase AKT

miR-141 and miR-146b-5p are two important tumor suppressor microRNAs, which control several cancer-related genes and processes. In the present report, we have shown that these microRNAs bind specific sites at the 3'-untranslated region (UTR) of the mRNA-binding protein AUF1, leading to its down-regulation. This inverse correlation between the levels of these microRNAs and AUF1 has been identified in various osteosarcoma cell lines. Additionally, we present clear evidence that AUF1 promotes mesenchymal features in osteosarcoma cells and that miR-141 and miR-146b-5p suppress this prometastatic process through AUF1 repression. Indeed, both microRNAs suppressed the invasion/migration and proliferation abilities of osteosarcoma cells through inhibiting the AKT protein kinase in an AUF1-dependent manner. We have also shown that AUF1 binds to and stabilizes the mRNA of the AKT activator phosphoinositide-dependent kinase-1 (PDK1). Furthermore, miR-141 and miR-146b-5p positively regulate the epithelial markers (E-cadherin and Epcam) and repress the mesenchymal markers (N-cadherin, Vimentin, Twist2, and ZEB1). These effects were mediated via the repression of the epithelial-to-mesenchymal inducer ZEB1 through targeting AUF1, which binds the 3'-UTR of the ZEB1 mRNA and reduces its turnover. These results indicate that at least some tumor suppressor functions of miR-141 and miR-146b-5p are mediated through the repression of the oncogenic potentials of AUF1. Therefore, these 3'-UTR-directed post-transcriptional gene expression regulators constitute promising new targets for diagnostic and/or therapeutic interventions.

The cyclin-dependent kinase inhibitor p16INK4a physically interacts with transcription factor Sp1 and cyclin-dependent kinase 4 to transactivate microRNA-141 and microRNA-146b-5p spontaneously and in response to ultraviolet light-induced DNA damage

p16(INK4a) is a tumor suppressor protein involved in several stress-related cellular responses, including apoptosis. Recent lines of evidence indicate that p16(INK4a) is also a modulator of gene expression. However, the molecular mechanisms underlying this novel function are still obscure. Here, we present clear evidence that p16(INK4a) modulates the levels of various microRNAs, with marked positive effect on miR-141 and miR-146b-5p. This effect is mediated through the formation of the p16-CDK4-Sp1 heterocomplex, which binds to Sp1 consensus-binding motifs present in the promoters of miR-141 and miR-146b-5p, and it enables their transcription. In addition, we have shown that p16(INK4a) interacts with Sp1 through the fourth ankyrin repeat, which is crucial for Sp1 binding to the miR-141 and miR-146b-5p promoters and their transcriptional activation. The physiological importance of this association was revealed by the inability of cancer-related p16(INK4a) mutants to interact with Sp1. Moreover, we have shown p16-CDK4-Sp1-dependent up-regulation of miR-141 and miR-146b-5p following UV light-induced DNA damage and the role of these two microRNAs in mediating p16-related induction of apoptosis in response to this genotoxic stress. Together, these results indicate that p16(INK4a) associates with CDK4 not only to inhibit the cell cycle but also to enable the transcription of two important onco-microRNAs, which act as downstream effectors.

The molecular balancing act of p16(INK4a) in cancer and aging

p16(INK4a), located on chromosome 9p21.3, is lost among a cluster of neighboring tumor suppressor genes. Although it is classically known for its capacity to inhibit cyclin-dependent kinase (CDK) activity, p16(INK4a) is not just a one-trick pony. Long-term p16(INK4a) expression pushes cells to enter senescence, an irreversible cell-cycle arrest that precludes the growth of would-be cancer cells but also contributes to cellular aging. Importantly, loss of p16(INK4a) is one of the most frequent events in human tumors and allows precancerous lesions to bypass senescence. Therefore, precise regulation of p16(INK4a) is essential to tissue homeostasis, maintaining a coordinated balance between tumor suppression and aging. This review outlines the molecular pathways critical for proper p16(INK4a) regulation and emphasizes the indispensable functions of p16(INK4a) in cancer, aging, and human physiology that make this gene special.