E2F1 and FOXO3 are two transcription factors that have been shown to participate in cellular senescence. Previous report reveals that E2F1 enhanced cellular senescence in human fibroblast cells, while FOXO transcription factors play against senescence by regulation reactive oxygen species scavenging proteins. However, their functional interplay has been unclear. Here we use E2F1 knockout Murine Embryonic Fibroblasts (MEFs), knockdown RNAi constructs, and ectopic expression of E2F1 to show that it functions by negatively regulating FOXO3. E2F1 attenuates FOXO3-mediated expression of MnSOD and Catalase without affecting FOXO3 protein stability, subcellular localization, or phosphorylation by Akt. We mapped the interaction between E2F1 and FOXO3 to a region including the DNA binding domain of E2F1 and the C-terminal transcription-activation domain of FOXO3. We propose that E2F1 inhibits FOXO3-dependent transcription by directly binding FOXO3 in the nucleus and preventing activation of its target genes. Moreover, knockdown of the C. elegans E2F1 ortholog efl-1 significantly extends lifespan in a manner that requires the activity of the C. elegans FOXO gene daf-16. We conclude that there is an evolutionarily conserved signaling connection between E2F1 and FOXO3, which regulates cellular senescence and aging by regulating the activity of FOXO3. We speculate that drugs and/or therapies that inhibit this physical interaction might be good candidates for reducing cellular senescence and increasing longevity.
Previous studies have shown that the Hippo pathway effector yes-associated protein (YAP) plays an important role in maintaining stem cell proliferation. However, the precise molecular mechanism of YAP in regulating murine embryonic neural stem cells (NSCs) remains largely unknown. Here, we show that bone morphogenetic protein-2 (BMP2) treatment inhibited the proliferation of mouse embryonic NSCs, that YAP was critical for mouse NSC proliferation, and that BMP2 treatment-induced inhibition of mouse NSC proliferation was abrogated by YAP knockdown, indicating that the YAP protein mediates the inhibitory effect of BMP2 signaling. Additionally, we found that BMP2 treatment reduced YAP nuclear translocation, YAP-TEAD interaction, and YAP-mediated transactivation. BMP2 treatment inhibited YAP/TEAD-mediated Cyclin D1 (ccnd1) expression, and knockdown of ccnd1 abrogated the BMP2-mediated inhibition of mouse NSC proliferation. Mechanistically, we found that Smad1/4, effectors of BMP2 signaling, competed with YAP for the interaction with TAED1 and inhibited YAP's cotranscriptional activity. Our data reveal mechanistic cross talk between BMP2 signaling and the Hippo-YAP pathway in murine NSC proliferation, which may be exploited as a therapeutic target in neurodegenerative diseases and aging.
Hypertrophic cardiomyopathy (HCM) is a leading cause of heart failure and sudden death in adolescents and young adults. Recently, the role of the Hippo/YAP pathway has been investigated in the pathogenesis of HCM, although the detailed molecular mechanisms largely remain elusive. In this study, we demonstrated an up-regulation of YAP mRNA and protein levels in both HCM patient samples and transverse aortic constriction murine models as well as reduced phosphorylation of YAP at serine 127 accompanied by increased transcription of YAP-mediated genes in hypertrophic heart tissues. The cardiomyocyte-specific transgene of human YAP induced cardiac hypertrophy and increased fetal gene expression in the heart. In primary cultured murine cardiomyocytes, ectopic expression of YAP resulted in increased cellular size, whereas the knockdown of YAP reduced the cell size induced by phenylephrine treatment. Interestingly, both mRNA and protein levels of MST1, the kinase upstream of YAP, were dramatically decreased. Further experiments showed that transcription factor FOXO3 binds to the MST1 promoter and that the PI3 K/Akt/FOXO3 signaling pathway regulates MST1 expression. Our findings define the alteration of the Hippo/YAP pathway in the development of HCM. The exploitation of this pathway may provide a novel therapeutic avenue for this disease.
PD (Parkinson's disease) is a complex disorder that is associated with neuronal loss or dysfunction caused by genetic risks, environmental factors and advanced aging. It has been reported that DJ-1 mutations rendered neurons sensitive to oxidative damage, which led to the onset of familiar PD. However, the molecular mechanism is still unclear. In the present study we show that DJ-1 interacts with RACK1 (receptor of activated C kinase 1) and increases its dimerization and protein stability. The DJ-1 transgene protects cortical neurons from H2O2-induced apoptosis, and this protective effect is abrogated by knocking down RACK1. Similarly, deletion of DJ-1 in cortical neurons increases the sensitivity to H2O2, and the damage can be significantly rescued by DJ-1 or DJ-1/RACK1 co-transfection, but not by RACK1 alone. We observed further that the interaction of DJ-1 and RACK1 is disrupted by H2O2 or MPP+ (1-methyl-4-phenylpyridinium) treatment, and the protein levels of DJ-1 and RACK1 decreased in neurodegenerative disease models. Taken together, the DJ-1-RACK1 complex protects neurons from oxidative stress-induced apoptosis, with the implication that DJ-1 and RACK1 might be novel targets in the treatment of neurodegenerative diseases.
Pigs are ideal organ donors for xenotransplantation and an excellent model for studying human diseases, such as neurodegenerative disease. Transcription activator-like effector nucleases (TALENs) are used widely for gene targeting in various model animals. Here, we developed a strategy using TALENs to target the GGTA1, Parkin and DJ-1 genes in the porcine genome using Large White porcine fibroblast cells without any foreign gene integration. In total, 5% (2/40), 2.5% (2/80), and 22% (11/50) of the obtained colonies of fibroblast cells were mutated for GGTA1, Parkin, and DJ-1, respectively. Among these mutant colonies, over 1/3 were bi-allelic knockouts (KO), and no off-target cleavage was detected. We also successfully used single-strand oligodeoxynucleotides to introduce a short sequence into the DJ-1 locus. Mixed DJ-1 mutant colonies were used as donor cells for somatic cell nuclear transfer (SCNT), and three female piglets were obtained (two were bi-allelically mutated, and one was mono-allelically mutated). Western blot analysis showed that the expression of the DJ-1 protein was disrupted in KO piglets. These results imply that a combination of TALENs technology with SCNT can efficiently generate bi-allelic KO pigs without the integration of exogenous DNA. These DJ-1 KO pigs will provide valuable information for studying Parkinson's disease.
Adult neurogenesis is thought to be crucial for preserving cognitive functions, which is tightly controlled by various epigenetic regulators. As the methyltransferase of histone H3K27, the role of Ezh2 in neurogenesis of adult mice and its mechanism of action are largely unknown. Here, we show that Ezh2 is expressed in actively dividing neural stem cells (NSCs)/progenitor cells as well as mature neurons, but not in quiescent NSCs in the subgranular zone. The deletion of Ezh2 in NSCs/progenitor cells results in a reduction in progenitor cell proliferation. Furthermore, we found that Ezh2 regulates progenitor cell proliferation by suppressing Pten expression and promoting the activation of Akt-mTOR. Moreover, the loss of Ezh2 in progenitor cells leads to a decrease in the number of neurons, which was observed by long-term tracing. Strikingly, conditional knockout of Ezh2 ultimately results in impairments in spatial learning and memory, contextual fear memory, and pattern separation. Our findings demonstrate the essential role of Ezh2 in the proliferation of progenitor cells, thus providing insight into the molecular mechanisms of adult neurogenesis in preserving cognitive functions.
Foxp3 expression and regulatory T cell (Treg) development are critical for maintaining dominant tolerance and preventing autoimmune diseases. Human MST1 deficiency causes a novel primary immunodeficiency syndrome accompanied by autoimmune manifestations. However, the mechanism by which Mst1 controls immune regulation is unknown. In this article, we report that Mst1 regulates Foxp3 expression and Treg development/function and inhibits autoimmunity through modulating Foxo1 and Foxo3 (Foxo1/3) stability. We have found that Mst1 deficiency impairs Foxp3 expression and Treg development and function in mice. Mechanistic studies reveal that Mst1 enhances Foxo1/3 stability directly by phosphorylating Foxo1/3 and indirectly by attenuating TCR-induced Akt activation in peripheral T cells. Our studies have also shown that Mst1 deficiency does not affect Foxo1/3 cellular localization in CD4 T cells. In addition, we show that Mst1(-/-) mice are prone to autoimmune disease, and mutant phenotypes, such as overactivation of naive T cells, splenomegaly, and autoimmune pathological changes, are suppressed in Mst1(-/-) bone marrow chimera by cotransplanted wt Tregs. Finally, we demonstrate that Mst1 and Mst2 play a partially redundant role in Treg development and autoimmunity. Our findings not only identify Mst kinases as the long-searched-for factors that simultaneously activate Foxo1/3 and inhibit TCR-stimulated Akt downstream of TCR signaling to promote Foxp3 expression and Treg development, but also shed new light on understanding and designing better therapeutic strategies for MST1 deficiency-mediated human immunodeficiency syndrome.
Telomerase contributes to cell proliferation and survival through both telomere-dependent and telomere-independent mechanisms. In this report, we discovered that endoplasmic reticulum (ER) stress transiently activates the catalytic components of telomerase (TERT) expression in human cancer cell lines and murine primary neural cells. Importantly, we show that depletion of hTERT sensitizes cells to undergo apoptosis under ER stress, whereas increased hTERT expression reduces ER stress-induced cell death independent of catalytically active enzyme or DNA damage signaling. Our findings establish a functional link between ER stress and telomerase, both of which have important implications in the pathologies associated with aging and cancer.
Transcription coactivator Yes-associated protein (YAP) plays an important role in the regulation of cell proliferation and apoptosis. Here, we identify a new role of YAP in the regulation of cellular senescence. We find that the expression levels of YAP proteins decrease following the replication-induced cellular senescence in IMR90 cells. Silencing of YAP inhibits cell proliferation and induces premature senescence. In additional experiments, we observe that cellular senescence induced by YAP deficiency is TEAD- and Rb/p16/p53-dependent. Furthermore, we show that Cdk6 is a direct downstream target gene of YAP in the regulation of cellular senescence, and the expression of Cdk6 is through the YAP-TEAD complex. Ectopic expression of Cdk6 rescued YAP knockdown-induced senescence. Finally, we find that downregulation of YAP in tumor cells increases senescence in response to chemotherapeutic agents, and YAP or Cdk6 expression rescues cellular senescence. Taken together, our findings define the critical role of YAP in the regulation of cellular senescence and provide a novel insight into a potential chemotherapeutic avenue for tumor suppression.
Skeletal muscle undergoes rapid atrophy upon denervation and the underlying mechanisms are complicated. FOXO3a has been implicated as a major mediator of muscle atrophy, but how its subcellular location and activity is controlled during the pathogenesis of muscle atrophy remains largely unknown. MST1 (Mammalian Sterile 20-like kinase 1) is identified as a central component of the Hippo signaling pathway. MST1 has been shown to mediate phosphorylation of FOXO3a at Ser207. Whether this MST1-FOXO signaling cascade exerts any functional consequence on cellular homeostasis remains to be investigated.
Chromatin remodeling processes are among the most important regulatory mechanisms in controlling cell proliferation and regeneration. Drosophila intestinal stem cells (ISCs) exhibit self-renewal potentials, maintain tissue homeostasis, and serve as an excellent model for studying cell growth and regeneration. In this study, we show that Brahma (Brm) chromatin-remodeling complex is required for ISC proliferation and damage-induced midgut regeneration in a lineage-specific manner. ISCs and enteroblasts exhibit high levels of Brm proteins; and without Brm, ISC proliferation and differentiation are impaired. Importantly, the Brm complex participates in ISC proliferation induced by the Scalloped-Yorkie transcriptional complex and that the Hippo (Hpo) signaling pathway directly restricted ISC proliferation by regulating Brm protein levels by inducing caspase-dependent cleavage of Brm. The cleavage resistant form of Brm protein promoted ISC proliferation. Our findings highlighted the importance of Hpo signaling in regulating epigenetic components such as Brm to control downstream transcription and hence ISC proliferation. DOI:http://dx.doi.org/10.7554/eLife.00999.001.
The insulin-like signaling pathway maintains a relatively short wild-type lifespan in Caenorhabditis elegans by phosphorylating and inactivating DAF-16, the ortholog of the FOXO transcription factors of mammalian cells. DAF-16 is phosphorylated by the AKT kinases, preventing its nuclear translocation. Calcineurin (PP2B phosphatase) also limits the lifespan of C. elegans, but the mechanism through which it does so is unknown. Herein, we show that TAX-6•CNB-1 and UNC-43, the C. elegans Calcineurin and Ca(2+)/calmodulin-dependent kinase type II (CAMKII) orthologs, respectively, also regulate lifespan through DAF-16. Moreover, UNC-43 regulates DAF-16 in response to various stress conditions, including starvation, heat or oxidative stress, and cooperatively contributes to lifespan regulation by insulin signaling. However, unlike insulin signaling, UNC-43 phosphorylates and activates DAF-16, thus promoting its nuclear localization. The phosphorylation of DAF-16 at S286 by UNC-43 is removed by TAX-6•CNB-1, leading to DAF-16 inactivation. Mammalian FOXO3 is also regulated by CAMKIIA and Calcineurin. DOI:http://dx.doi.org/10.7554/eLife.00518.001.
The Hippo/MST1 signaling pathway plays an important role in the regulation of cell proliferation and apoptosis. As a major downstream target of the Hippo/MST1 pathway, YAP2 (Yes-associated protein 2) functions as a transcriptional cofactor that has been implicated in many biological processes, including organ size control and cancer development. MST1/Lats kinase inhibits YAP2s nuclear accumulation and transcriptional activity through inducing the phosphorylation at serine 127 and the sequential association with 14-3-3 proteins. However, the dephosphorylation of YAP2 is not fully appreciated.
Oxidative stress influences cell survival and homeostasis, but the mechanisms underlying the biological effects of oxidative stress remain to be elucidated. The protein kinase MST1 (mammalian Ste20-like kinase 1) plays a major role in oxidative stress-induced cell death in primary mammalian neurons. However, the mechanisms that regulate MST1 in oxidative stress responses remain largely unknown. In the present study, we demonstrate that the protein kinase c-Abl phosphorylates MST1 at Y433, which triggers the stabilization and activation of MST1. Inhibition of c-Abl promotes the degradation of MST1 through C terminus of Hsc70-interacting protein (CHIP)-mediated ubiquitination, and thereby attenuates cell death. Oxidative stress induces the c-Abl-dependent tyrosine phosphorylation of MST1 and increases the interaction between MST1 and FOXO3 (Forkhead box O3), thereby activating the MST1-FOXO signaling pathway, leading to cell death in both primary culture neurons and rat hippocampal neurons. The identification of the c-Abl tyrosine kinase as a novel upstream activator of MST1 suggests that the c-Abl-MST1 signaling cascade plays an important role in cellular responses to oxidative stress.
E2F1 promotes DNA damage-induced apoptosis and the post-translational modifications of E2F1 play an important role in the regulation of E2F1-mediated cell death. Here, we found that Set9 and LSD1 regulate E2F1-mediated apoptosis upon DNA damage. Set9 methylates E2F1 at lysine 185, a conserved residue in the DNA-binding domain of E2F family proteins. The methylation of E2F1 by Set9 leads to the stabilization of E2F1 and up-regulation of its proapoptotic target genes p73 and Bim, and thereby induces E2F1-mediated apoptosis in response to genotoxic agents. We also found that LSD1 demethylates E2F1 at lysine 185 and reduces E2F1-mediated cell death. The identification of the methylation/demethylation of E2F1 by Set9/LSD1 suggests that E2F1 is dynamically regulated by epigenetic enzymes in response to DNA damage.
Mammalian Sterile 20-like kinase 1 (MST1) protein kinase plays an important role in the apoptosis induced by a variety of stresses. The MST1 is a serine/threonine kinase that is activated upon apoptotic stimulation, which in turn activates its downstream targets, JNK/p38, histone H2B and FOXO. It has been reported that overexpression of MST1 initiates apoptosis by activating p53. However, the molecular mechanisms underlying MST1-p53 signaling during apoptosis are unclear. Here, we report that MST1 promotes genotoxic agent-induced apoptosis in a p53-dependent manner. We found that MST1 increases p53 acetylation and transactivation by inhibiting the deacetylation of Sirtuin 1 (Sirt1) and its interaction with p53 and that Sirt1 can be phosphorylated by MST1 leading to the inhibition of Sirt1 activity. Collectively, these findings define a novel regulatory mechanism involving the phosphorylation of Sirt1 by MST1 kinase which leads to p53 activation, with implications for our understanding of signaling mechanisms during DNA damage-induced apoptosis.
We examined the role and molecular mechanism of cADPR action on Ca(2+) spark properties in mouse bladder smooth muscle. Dialysis of cADPR with patch pipettes increased frequency and amplitude of spontaneous transient out currents (STOCs) to 6.1+/-0.87 currents/min from 1.2+/-0.36 currents/min (control) and to 179.8+/-48.7pA from 36.4+/-22.6pA (control), respectively, in wildtype (WT) cells, and the effects of cADPR on STOCs were significantly blocked by JVT-591, a RYR2 stabilizer. In contrast, no significant changes were observed in FKBP12.6 null cells. Further studies indicated that Ca(2+) spark properties were altered by cADPR in WT but not FKBP12.6 null cells, namely, Ca(2+) spark frequency was increased by about 3.4-fold, peak Ca(2+) (F/F0) increased to 1.72+/-0.57 from 1.56+/-0.13, size increased to 2.86+/-0.26 microM from 1.92+/-0.14 microM, rise time and half-time decay were prolonged 1.6-fold and 2.3-fold, respectively, in WT cells. Furthermore, in the presence of thapsigargin cADPR still altered Ca(2+) spark properties, and cADPR increased F/F0 without affecting Ca(2+) spark decay time in voltage clamping cells. Dissociation studies demonstrated that application of cADPR resulted in significant removal of FKBP12.6 proteins from sarcoplasmic reticulum (SR) microsomes, and that treatment of the RyR2 immunoprecipitation complexes with cADPR or FK506 disrupted the interaction between RyR2 and FKBP12.6. Finally, cADPR altered SR Ca(2+) load in WT myocytes but not in FKBP12.6-null myocytes. Taken together, these results suggest that Ca(2+) release induced by cADPR is mediated by FKBP12.6 proteins in mouse bladder smooth muscle.
Protein kinases play an important role in the maintenance of homeostasis between cell survival and apoptosis. Deregulation of these kinases leads to various pathological manifestations, such as cancer and neurodegenerative diseases. The MST1 encodes a serine/threonine kinase that is activated upon apoptotic stimulation, which in turn phosphorylates its downstream targets, Histone H2B and FOXO. However, the upstream regulators of MST1 kinase have been poorly studied. In this study, we report that JNK (c-Jun N-terminal kinase) phosphorylates MST1 at serine 82, which leads to the enhancement of MST1 activation. Accordingly, the activation of MST1 phosphorylates FOXO3 at serine 207 and promotes cell death. The inhibition of JNK kinase per se attenuates MST1 activity and nuclear translocation as well as MST1-induced apoptosis. We also find the S82A (serine mutated to alanine) diminishes MST1 activation and its effect on the FOXO transcription activity. Collectively, these findings define the novel feedback regulation of MST1 kinase activation by its putative substrate, JNK, with implication for our understanding of the signaling mechanism during cell death.
The protein kinase mammalian sterile 20-like kinase 1 (MST1) is a mammalian homologue of the Drosophila hippo and plays a critical role in regulation of programmed cell death. MST1 exerts pro-apoptotic function through cleavage, autophosphorylation-Thr(183) and subsequent translocation to the nucleus where it phosphorylates a number of molecules, including LATS1/2, FOXO, JNK, and histone H2B. Here, we show that the cleavage of MST1 is inhibited by the phosphatidylinositol 3-kinase/Akt pathway. Akt interacts with MST1 and phosphorylates a highly conserved residue threonine 120 of MST1, which leads to inhibition of its kinase activity and nuclear translocation as well as the autophosphorylation of Thr(183). Phospho-MST1-Thr(120) failed to activate downstream targets FOXO3a and JNK. Further, inverse correlation between pMST1-Thr(120) and pMST1-Thr(183) was observed in human ovarian tumors. These findings indicate that the phosphorylation of MST1-Thr(120) by Akt could be a major mechanism of regulation of the Hippo/MST1 pathway by cell survival signaling.
The protein kinase mammalian Sterile 20-like kinase 1 (MST1) plays a critical role in the regulation of cell death. Recent studies suggest that MST1 mediates oxidative stress-induced neuronal cell death by phosphorylating the transcription factor FOXO3 at serine 207, a site that is conserved in other FOXO family members. Here, we show that MST1-induced phosphorylation of FOXO1 at serine 212, corresponding to serine 207 in FOXO3, disrupts the association of FOXO1 with 14-3-3 proteins. Accordingly, MST1 mediates the nuclear translocation of FOXO1 in primary rat cerebellar granule neurons that are deprived of neuronal activity. We also find a requirement for MST1 in cell death of granule neurons upon withdrawal of growth factors and neuronal activity, and MST1 induces cell death in a FOXO1-dependent manner. Finally, we show that the MST1-regulatory, scaffold protein Nore1 is required for survival factor deprivation induced neuronal death. Collectively, these findings define MST1-FOXO1 signaling as an important link survival factor deprivation-induced neuronal cell death with implications for our understanding of brain development and neurological diseases.
Interleukin-22 (IL-22), an IL-10 family cytokine, mediates the crosstalk between leukocytes and epithelial cells. Previous studies reported that IL-22 expresses in mouse brain, and the rat PC12 cells are responsive to IL-22 stimulation. However, the biological roles of IL-22 in neuronal cells remain largely unknown. We show here that IL-22 activates Stat3, p38 mitogen-activated protein kinases (MAPK), and Akt pathways and inhibits Erk/MAPK pathway in naïve PC12 cells. We further demonstrate that IL-22 protects naïve PC12 cells from serum starvation-induced cell death via the Jak1/Stat3 and Akt pathways. We also show that IL-22 has no effects on naïve PC12 cell proliferation and cannot protect naïve PC12 cells from 1-methyl-4-phenylpyridinium (MPP(+))-induced cytotoxicity. However, IL-22 exerts a dose-dependent protective effect on MPP(+)-induced neurodegeneration in nerve growth factor-differentiated PC12 cells. Overall, our data suggest that IL-22 might play a role in neurological processes. To our knowledge, this is the first report showing that IL-22 confers a neuroprotective function, which may provide a new therapeutic option for treatment of neurodegenerative diseases.
The Forkhead box O (FOXO) family transcription factors play critical roles in a series of cellular processes, including the cell cycle, cell death, metabolism, and oxidative stress resistance. FOXO proteins are subject to several post-translational modifications, which are closely related to their activity. In this paper, we review the post-translational modifications of FOXOs and their biological functions.
Mutations in DJ-1/PARK7 (Parkinson protein 7) have been identified as a cause of autosomal-recessive PD (Parkinsons disease) and the antioxidant property of DJ-1 has been shown to be involved in the regulation of mitochondrial function and neuronal cell survival. In the present study, we first found that the DJ-1 transgene mitigated MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-induced DA (dopamine) neuron cell death and cell loss. We then observed that the protein levels of DJ-1 were significantly decreased, whereas levels of Fis1 [fission 1 (mitochondrial outer membrane) homologue] were noticeably increased in the striatum of MPTP-treated mice. In addition to our identification of RNF5 (RING-finger protein-5) as an E3-ligase for Fis1 ubiquitination, we demonstrated the involvement of the DJ-1/Akt/RNF5 signalling pathway in the regulation of Fis1 proteasomal degradation. In other experiments, we found that Akt1 enhances the mitochondrial translocation and E3-ligase activity of RNF5, leading to Fis1 degradation. Together, the identification of Fis1 degradation by DJ-1 signalling in the regulation of oxidative stress-induced neuronal cell death supplies a novel mechanism of DJ-1 in neuronal protection with the implication of DJ-1 in a potential therapeutic avenue for PD.
PHF20 is a multidomain protein and subunit of a lysine acetyltransferase complex that acetylates histone H4 and p53 but whose function is unclear. Using biochemical, biophysical and cellular approaches, we determined that PHF20 is a direct regulator of p53. A Tudor domain in PHF20 recognized p53 dimethylated at Lys370 or Lys382 and a homodimeric form of this Tudor domain could associate with the two dimethylated sites on p53 with enhanced affinity, indicating a multivalent interaction. Association with PHF20 promotes stabilization and activation of p53 by diminishing Mdm2-mediated p53 ubiquitylation and degradation. PHF20 contributes to upregulation of p53 in response to DNA damage, and ectopic expression of PHF20 in different cell lines leads to phenotypic changes that are hallmarks of p53 activation. Overall our work establishes that PHF20 functions as an effector of p53 methylation that stabilizes and activates p53.
Alzheimers disease (AD) is the most common neurodegenerative disease among elderly people worldwide. Several genes have been validated to be associated with AD, and calcium homeostasis modulator 1 (Calhm1) is the latest suspected one. To investigate the biological and pathological function of Calhm1 systematically, we generated a Calhm1 conventional knockout mouse. However, both the male and female of elderly Calhm1 knockout (KO) mice showed similar ability to their wild type littermates in spatial learning and memory retrieving. Surprisingly, we found that Calhm1 mRNA could not be detected in mouse brains at different ages, although it is expressed in the human brain tissues. We further found that CpG islands (CGIs) of both mouse and human Calhm1 were hypermethylated, whereas CGI of mouse Calhm2 was hypomethylated. In addition, transcriptional active marker H3K4Di occupied on promoters of human Calhm1 and mouse Calhm2 at a considerable level in brain tissues, while the occupancy of H3K4Di on promoter of mouse Calhm1 was rare. In sum, we found that mouse Calhm1 was of rare abundance in brain tissues. So it might not be suitable to utilize the knockout murine model to explore biological function of Calhm1 in the pathogenesis of AD.
Mammalian Ste20-like kinases (MSTs) are the mammalian homologue of Drosophila hippo and play critical roles in regulation of cell death, organ size control, proliferation and tumorigenesis. MSTs exert pro-apoptotic function through cleavage, autophosphorylation and in turn phosphorylation of downstream targets, such as Histone H2B and FOXO (Forkhead box O). Previously we reported that protein kinase c-Abl mediates oxidative stress-induced neuronal cell death through phosphorylating MST1 at Y433, which is not conserved among mammalian MST2, Drosophila Hippo and C.elegans cst-1/2.
FOXO transcription factors have a critical role in oxidative stress-induced neuronal cell death. A variety of post-translational modifications of FOXO family proteins have been reported, including phosphorylation, acetylation, ubiqutination and recently arginine methylation. Here, we demonstrate that the methyltransferase Set9 methylates FOXO3 at lysine 270. Methylation of FOXO3 leads to the inhibition of its DNA-binding activity and transactivation. Accordingly, lysine methylation reduces oxidative stress-induced and FOXO3-mediated Bim expression and neuronal apoptosis in neurons. Collectively, these findings define a novel modification of FOXO3 and show that lysine methylation negatively regulates FOXO3-mediated transcription and neuronal apoptosis.
The human gene PTPN11, which encodes the non-receptor protein tyrosine phosphatase of Src homology phosphotyrosine phosphatase 2 (Shp2), has been previously well interpreted as a proto-oncogene in a variety of malignancies. However, the tumor suppressor role of Shp2 has also been reported. The present study was conducted to investigate the role of Shp2 expression and its associated clinical manifestations in hepatocellular carcinoma (HCC).
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