Instruct: Given a scientific claim, retrieve documents that support or refute the claim.
Query: Forkhead 0 (fox0) transcription factors are involved in apoptosis.
The forkhead O (FoxO) family of transcription factors participates in diverse physiologic processes, including induction of cell-cycle arrest, stress resistance, differentiation, apoptosis, and metabolism. Several recent studies indicate that FoxO-dependent signaling is required for long-term regenerative potential of the hematopoietic stem cell (HSC) compartment through regulation of HSC response to physiologic oxidative stress, quiescence, and survival. These observations link FoxO function in mammalian systems with the evolutionarily conserved role of FoxO in promotion of stress resistance and longevity in lower phylogenetic systems. Furthermore, these findings have implications for aging in higher organisms and in malignant stem cell biology, and suggest that FoxOs may play an important role in the maintenance and integrity of stem cell compartments in a broad spectrum of tissues.
Organisms are constantly challenged by stresses and privations and require adaptive responses for their survival. The forkhead box O (FOXO) transcription factor DAF-16 (hereafter referred to as DAF-16/FOXO) is a central nexus in these responses, but despite its importance little is known about how it regulates its target genes. Proteomic identification of DAF-16/FOXO-binding partners in Caenorhabditis elegans and their subsequent functional evaluation by RNA interference revealed several candidate DAF-16/FOXO cofactors, most notably the chromatin remodeller SWI/SNF. DAF-16/FOXO and SWI/SNF form a complex and globally co-localize at DAF-16/FOXO target promoters. We show that specifically for gene activation, DAF-16/FOXO depends on SWI/SNF, facilitating SWI/SNF recruitment to target promoters, to activate transcription by presumed remodelling of local chromatin. For the animal, this translates into an essential role for SWI/SNF in DAF-16/FOXO-mediated processes, in particular dauer formation, stress resistance and the promotion of longevity. Thus, we give insight into the mechanisms of DAF-16/FOXO-mediated transcriptional regulation and establish a critical link between ATP-dependent chromatin remodelling and lifespan regulation.
The promyelocytic leukaemia zinc finger (Plzf) protein (encoded by the gene Zfp145) belongs to the POZ/zinc-finger family of transcription factors. Here we generate Zfp145−/− mice and show that Plzf is essential for patterning of the limb and axial skeleton. Plzf inactivation results in patterning defects affecting all skeletal structures of the limb, including homeotic transformations of anterior skeletal elements into posterior structures. We demonstrate that Plzf acts as a growth-inhibitory and pro-apoptotic factor in the limb bud. The expression of members of the abdominal b (Abdb) Hox gene complex, as well as genes encoding bone morphogenetic proteins (Bmps), is altered in the developing limb of Zfp145−/− mice. Plzf regulates the expression of these genes in the absence of aberrant polarizing activity and independently of known patterning genes. Zfp145−/− mice also exhibit anterior-directed homeotic transformation throughout the axial skeleton with associated alterations in Hox gene expression. Plzf is therefore a mediator of anterior-to-posterior (AP) patterning in both the axial and appendicular skeleton and acts as a regulator of Hox gene expression.
The YAP transcription coactivator has been implicated as an oncogene and is amplified in human cancers. Recent studies have established that YAP is phosphorylated and inhibited by the Hippo tumor suppressor pathway. Here we demonstrate that the TEAD family transcription factors are essential in mediating YAP-dependent gene expression. TEAD is also required for YAP-induced cell growth, oncogenic transformation, and epithelial-mesenchymal transition. CTGF is identified as a direct YAP target gene important for cell growth. Moreover, the functional relationship between YAP and TEAD is conserved in Drosophila Yki (the YAP homolog) and Scalloped (the TEAD homolog). Our study reveals TEAD as a new component in the Hippo pathway playing essential roles in mediating biological functions of YAP.
Apoptosis that proceeds via the mitochondrial pathway involves mitochondrial outer membrane permeabilization (MOMP), responsible for the release of cytochrome c and other proteins of the mitochondrial intermembrane space. This essential step is controlled and mediated by proteins of the Bcl-2 family. The proapoptotic proteins Bax and Bak are required for MOMP, while the antiapoptotic Bcl-2 proteins, including Bcl-2, Bcl-xL, Mcl-1, and others, prevent MOMP. Different proapoptotic BH3-only proteins act to interfere with the function of the antiapoptotic Bcl-2 members and/or activate Bax and Bak. Here, we discuss an emerging view, proposed by Certo et al. in this issue of Cancer Cell, on how these interactions result in MOMP and apoptosis.
The airways of the lung develop through a reiterative process of branching morphogenesis that gives rise to the intricate and extensive surface area required for postnatal respiration. The forkhead transcription factors Foxp2 and Foxp1 are expressed in multiple foregut-derived tissues including the lung and intestine. In this report, we show that loss of Foxp2 in mouse leads to defective postnatal lung alveolarization, contributing to postnatal lethality. Using in vitro and in vivo assays, we show that T1alpha, a lung alveolar epithelial type 1 cell-restricted gene crucial for lung development and function, is a direct target of Foxp2 and Foxp1. Remarkably, loss of a single Foxp1 allele in addition to complete loss of Foxp2 results in increased severity of morphological defects in mutant lungs and leads to perinatal loss of all Foxp2(-/-);Foxp1(+/-) mice. Expression of N-myc and Hop, crucial regulators of lung development, is compromised in Foxp2(-/-);Foxp1(+/-) mutants. In addition to the defects in lung development, esophageal muscle development is disrupted in Foxp2(-/-);Foxp1(+/-) embryos, a tissue where Foxp2 and Foxp1 are co-expressed. These data identify Foxp2 and Foxp1 as crucial regulators of lung and esophageal development, underscoring the necessity of these transcription factors in the development of anterior foregut-derived tissues and demonstrating functional cooperativity between members of the Foxp1/2/4 family in tissues where they are co-expressed.
Hypoxia is a common cause of cell death and is implicated in many disease processes including stroke and chronic degenerative disorders. In response to hypoxia, cells express a variety of genes, which allow adaptation to altered metabolic demands, decreased oxygen demands, and the removal of irreversibly damaged cells. Using polymerase chain reaction–based suppression subtractive hybridization to find genes that are differentially expressed in hypoxia, we identified the BH3-only Bcl-2 family protein Noxa. Noxa is a candidate molecule mediating p53-induced apoptosis. We show that Noxa promoter responds directly to hypoxia via hypoxia-inducible factor (HIF)-1α. Suppression of Noxa expression by antisense oligonucleotides rescued cells from hypoxia-induced cell death and decreased infarction volumes in an animal model of ischemia. Further, we show that reactive oxygen species and resultant cytochrome c release participate in Noxa-mediated hypoxic cell death. Altogether, our results show that Noxa is induced by HIF-1α and mediates hypoxic cell death.
The E2F transcription factors have emerged as critical apoptotic effectors. Herein we report that the E2F family member E2F3a can be induced by DNA damage through transcriptional and posttranslational mechanisms. We demonstrate that the posttranslational induction of human E2F3a is dependent on the checkpoint kinases. Moreover, we show that human E2F3a is a substrate for the checkpoint kinases (chk kinases) and that mutation of the chk phosphorylation site eliminates the DNA damage inducibility of the protein. Furthermore, we demonstrate that E2F1 and E2F2 are transcriptionally induced by DNA damage in an E2f3-dependent manner. Finally, using both in vitro and in vivo approaches, we establish that E2f3 is required for DNA damage-induced apoptosis. Thus, our data reveal the novel ability of E2f3 to function as a master regulator of the DNA damage response.
The ability of progenitor cells to exit the cell cycle is essential for proper embryonic development and homeostasis, but the mechanisms governing cell cycle exit are still not fully understood. Here, we tested the requirement for the retinoblastoma (Rb) protein and its family members p107 and p130 in G0/G1 arrest and differentiation in mammalian cells. We found that Rb family triple knockout (TKO) mouse embryos survive until days 9-11 of gestation. Strikingly, some TKO cells, including in epithelial and neural lineages, are able to exit the cell cycle in G0/G1 and differentiate in teratomas and in culture. This ability of TKO cells to arrest in G0/G1 is associated with the repression of key E2F target genes. Thus, G1 arrest is not always dependent on Rb family members, which illustrates the robustness of cell cycle regulatory networks during differentiation and allows for the identification of candidate pathways to inhibit the expansion of cancer cells with mutations in the Rb pathway.
Proteostasis is critical for maintaining cell function and proteome stability may play an important role in human embryonic stem cell (hESC) immortality. Notably, hESC populations exhibit a high assembly of active proteasomes, a key node of the proteostasis network. FOXO4, an insulin/IGF-1 responsive transcription factor, regulates proteasome activity in hESCs. We find that loss of FOXO4 reduces the potential of hESCs to differentiate into neural lineages. Therefore, FOXO4 crosses evolutionary boundaries and links hESC function to invertebrate longevity modulation.
Ex-FABP, an extracellular fatty acid binding lipocalin, is physiologically expressed by differentiating chicken chondrocytes and myoblasts. Its expression is enhanced after cell treatment with inflammatory stimuli and repressed by anti-inflammatory agents, behaving as an acute phase protein. Chicken liver fragments in culture show enhanced protein expression after bacterial endotoxin treatment. To investigate the biological role of Ex-FABP, we stably transfected proliferating chondrocytes with an expression vector carrying antisense oriented Ex-FABP cDNA. We observed a dramatic loss of cell viability and a strong inhibition of cell proliferation and differentiation. When chondrocytes were transfected with the antisense oriented Ex-FABP cDNA we observed that Ex-FABP down-modulation increased apoptotic cell number. Myoblasts transfected with the same expression vector showed extensive cell death and impaired myotube formation. We suggest that Ex-FABP acts as a constitutive survival protein and that its expression and activation are fundamental to protect chondrocytes from cell death.
The aim of this study was to investigate the mechanism through which Sphingosine kinase-1 (SPHK1) exerts its anti-apoptosis activity in glioma cancer cells. We here report that dysregulation of SPHK1 alters the sensitivity of glioma to apoptosis both in vitro and in vivo. Further mechanistic study examined the expression of Bcl-2 family members, including Bcl-2, Mcl-1, Bax and Bim, in SPHK1-overexpressing glioma cells and revealed that only pro-apoptotic Bim was downregulated by SPHK1. Moreover, the transcriptional level of Bim was also altered by SPHK1 in glioma cells. We next confirmed the correlation between SPHK1 and Bim expression in primary glioma specimens. Importantly, increasing SPHK1 expression in glioma cells markedly elevated Akt activity and phosphorylated inactivation of FOXO3a, which led to downregulation of Bim. A pharmacological approach showed that these effects of SPHK1 were dependent on phosphatidylinositol 3-kinase (PI3K). Furthermore, effects of SPHK1 on Akt/FOXO3a/Bim pathway could be reversed by SPHK1 specific RNA interference or SPHK1 inhibitor. Collectively, our results indicate that regulation of the Akt/FOXO3a/Bim pathway may be a novel mechanism by which SPHK1 protects glioma cells from apoptosis, thereby involved in glioma tumorigenesis.
Oxidative stress influences cell survival and homeostasis, but the mechanisms underlying the biological effects of oxidative stress remain to be elucidated. Here, we demonstrate that the protein kinase MST1 mediates oxidative-stress-induced cell death in primary mammalian neurons by directly activating the FOXO transcription factors. MST1 phosphorylates FOXO proteins at a conserved site within the forkhead domain that disrupts their interaction with 14-3-3 proteins, promotes FOXO nuclear translocation, and thereby induces cell death in neurons. We also extend the MST-FOXO signaling link to nematodes. Knockdown of the C. elegans MST1 ortholog CST-1 shortens life span and accelerates tissue aging, while overexpression of cst-1 promotes life span and delays aging. The cst-1-induced life-span extension occurs in a daf-16-dependent manner. The identification of the FOXO transcription factors as major and evolutionarily conserved targets of MST1 suggests that MST kinases play important roles in diverse biological processes including cellular responses to oxidative stress and longevity.
The cell-positional incidence of both spontaneous and damage-induced apoptosis of epithelial cells was assessed in longitudinal sections of the crypts of small intestine and colon of BDF1 mice. This was compared, using immunohistochemistry, with the pattern of expression of bcl-2, a suppressor of apoptosis. In the small intestine, apoptosis was maximal around cell position 4 from the base of the crypt; this closely corresponds to the position considered to contain the stem cells. In the colon, however, apoptosis was not confined to the area considered to harbour the stem cells (position 1 and 2). Instead, apoptosis was attenuated and distributed along the length of the crypt. Some cells at the base of murine colonic crypts expressed bcl-2 protein, whereas bcl-2 was absent in the crypts of the small intestine. Most pertinently, bcl-2 was absent from small intestinal crypt cells at positions 4-5 (the stem cell region). The importance of the expression of bcl-2 to the attenuation of apoptosis in stem cells was confirmed by analysis of the levels of both spontaneous and induced apoptosis in homozygously bcl-2 null C57BL/6 mice: in colonic crypts the level of spontaneous apoptosis rose significantly, and selectively at the base of the crypt, in comparison with crypts from wild-type animals. In contrast, there was no rise in spontaneous apoptosis in the small intestinal crypts from the bcl-2 null animals. Analysis of sections of human colon and small intestine also showed that expression of bcl-2 was confined to the base of the colonic crypt. The attenuation of apoptosis by bcl-2 in the region of the stem cells of the colonic crypts may dispose these to neoplastic transformation. Indeed, analysis of human carcinomas revealed expression of bcl-2, which in some samples was reciprocal with the expression of p53.
Immature T cells and some T cell hybridomas undergo apoptotic cell death when activated through the T cell receptor complex, a phenomenon that is probably related to antigen induced negative selection of developing T cells. This activation-induced apoptosis depends on active protein and RNA synthesis in the dying cells, although none of the genes required for this process have previously been identified. Antisense oligonucleotides corresponding to c-myc block the constitutive expression of c-Myc protein in T cell hybridomas and interfere with all aspects of activation-induced apoptosis without affecting lymphokine production in these cells. These data indicate that c-myc expression is a necessary component of activation-induced apoptosis.
Asymmetric cell division and apoptosis (programmed cell death) are two fundamental processes that are important for the development and function of multicellular organisms. We have found that the processes of asymmetric cell division and apoptosis can be functionally linked. Specifically, we show that asymmetric cell division in the nematode Caenorhabditis elegans is mediated by a pathway involving three genes, dnj-11 MIDA1, ces-2 HLF, and ces-1 Snail, that directly control the enzymatic machinery responsible for apoptosis. Interestingly, the MIDA1-like protein GlsA of the alga Volvox carteri, as well as the Snail-related proteins Snail, Escargot, and Worniu of Drosophila melanogaster, have previously been implicated in asymmetric cell division. Therefore, C. elegans dnj-11 MIDA1, ces-2 HLF, and ces-1 Snail may be components of a pathway involved in asymmetric cell division that is conserved throughout the plant and animal kingdoms. Furthermore, based on our results, we propose that this pathway directly controls the apoptotic fate in C. elegans, and possibly other animals as well.
The recently identified Fas antigen (Ag) is a cell surface molecule that can mediate apoptosis. The cytoplasmic product of proto-oncogene bcl-2 has been shown to prolong the cellular survival by inhibiting apoptosis. To elucidate the physiologic significance of expression of both molecules, we examined the expression of Fas Ag and bcl-2 on blood leukocyte populations and evaluated their sensitivity to the cytolytic action of anti-Fas antibody. Although Fas Ag was expressed on a fraction of lymphocytes, both neutrophils and monocytes expressed Fas Ag constitutively. In contrast, there was marked difference among these leukocytes regarding bcl-2 expression. Lymphocytes expressed bcl-2 intensely, but monocytes showed weaker bcl-2 expression, and neutrophils were essentially absent for bcl-2 expression. Seemingly reflecting this lack of bcl-2-expression, neutrophils more easily underwent apoptotic cell death in vitro as compared with monocytes and lymphocytes. We showed that anti-Fas antibody affectively accelerated apoptotic cell death in neutrophils. However, the apoptosis-inducing effect of anti-Fas antibody was minimal on monocytes, and lymphocytes were resistant to this antibody. These results suggest that anti-Fas-mediated cell death may, in part, be determined by bcl-2 expression status in Fas+ lymphoid and hematopoietic cells.
The Sir2 deacetylase modulates organismal life-span in various species. However, the molecular mechanisms by which Sir2 increases longevity are largely unknown. We show that in mammalian cells, the Sir2 homolog SIRT1 appears to control the cellular response to stress by regulating the FOXO family of Forkhead transcription factors, a family of proteins that function as sensors of the insulin signaling pathway and as regulators of organismal longevity. SIRT1 and the FOXO transcription factor FOXO3 formed a complex in cells in response to oxidative stress, and SIRT1 deacetylated FOXO3 in vitro and within cells. SIRT1 had a dual effect on FOXO3 function: SIRT1 increased FOXO3's ability to induce cell cycle arrest and resistance to oxidative stress but inhibited FOXO3's ability to induce cell death. Thus, one way in which members of the Sir2 family of proteins may increase organismal longevity is by tipping FOXO-dependent responses away from apoptosis and toward stress resistance.
Although the essential role of the adaptor protein SLP-65 in pre-B cell differentiation is established, the molecular mechanism underlying its function is poorly understood. In this study, we uncover a link between SLP-65–dependent signaling and the phosphoinositide-3-OH kinase (PI(3)K)–protein kinase B (PKB)–Foxo pathway. We show that the forkhead box transcription factor Foxo3a promotes light chain rearrangement in pre-B cells. Our data suggest that PKB suppresses light chain recombination by phosphorylating Foxo proteins, whereas reconstitution of SLP-65 function counteracts PKB activation and promotes Foxo3a and Foxo1 activity in pre-B cells. Together, these data illuminate a molecular function of SLP-65 and identify a key role for Foxo proteins in the regulation of light chain recombination, receptor editing and B cell selection.
OBJECTIVE A20 is a TNF-inducible primary response gene, which has been found to have antiapoptotic function in several cancer cells. This study investigates A20 expression in human glioma tissues and four glioma cell lines, and its effect on tumorigenesis of glioma cells and a mouse tumor model. METHODS Human glioma tissue samples and cells were subject to reverse transcription-PCR (RT-PCR), western blotting and immunohistochemistry. Glioma cells was tested by flow cytometry. A xenograft tumor model in mice was utilized to examine the knock-down effect of specific A20 siRNAs on tumorigenesis. RESULTS A20 was overexpressed in clinical glioma tissue samples (63.9%) and correlated with clinical staging. All four human glioma cell lines expressed A20, among which U87 displayed the strongest expression signals. Inhibiting A20 expression by siRNAs in vitro reduced the growth rates of glioma cells and resulted in G1/S arrest and increased apoptosis. In a mouse tumor model, local administration of siRNA significantly suppressed solid tumor growth. CONCLUSIONS A20 was overexpressed both in human glioma tissues and cell lines, and inhibiting A20 expression greatly slowed tumor cell growth in culture and in mice. These findings indicated that A20 is involved in tumorigenesis of human glioma, and may serve as a future therapeutic target.
Genome endoreduplication during mammalian development is a rare event for which the mechanism is unknown. It first appears when fibroblast growth factor 4 (FGF4) deprivation induces differentiation of trophoblast stem (TS) cells into the nonproliferating trophoblast giant (TG) cells required for embryo implantation. Here we show that RO3306 inhibition of cyclin-dependent protein kinase 1 (CDK1), the enzyme required to enter mitosis, induced differentiation of TS cells into TG cells. In contrast, RO3306 induced abortive endoreduplication and apoptosis in embryonic stem cells, revealing that inactivation of CDK1 triggers endoreduplication only in cells programmed to differentiate into polyploid cells. Similarly, FGF4 deprivation resulted in CDK1 inhibition by overexpressing two CDK-specific inhibitors, p57/KIP2 and p21/CIP1. TS cell mutants revealed that p57 was required to trigger endoreduplication by inhibiting CDK1, while p21 suppressed expression of the checkpoint protein kinase CHK1, thereby preventing induction of apoptosis. Furthermore, Cdk2(-/-) TS cells revealed that CDK2 is required for endoreduplication when CDK1 is inhibited. Expression of p57 in TG cells was restricted to G-phase nuclei to allow CDK activation of S phase. Thus, endoreduplication in TS cells is triggered by p57 inhibition of CDK1 with concomitant suppression of the DNA damage response by p21.
Polyhomeotic-like 3 (PHC3) is a ubiquitously expressed member of the polycomb gene family and part of the human polycomb complex hPRC-H. We found that in normal cells PHC3 associated with both hPRC-H complex components and with the transcription factor E2F6. In differentiating and confluent cells, PHC3 and E2F6 showed nuclear colocalization in a punctate pattern that resembled the binding of polycomb bodies to heterochromatin. This punctate pattern was not seen in proliferating cells suggesting that PHC3 may be part of an E2F6-polycomb complex that has been shown to occupy and silence target promoters in G0. Previous loss of heterozygosity (LoH) analyses had shown that the region containing PHC3 underwent frequent LoH in primary human osteosarcoma tumors. When we examined normal bone and human osteosarcoma tumors, we found loss of PHC3 expression in 36 of 56 osteosarcoma tumors. Sequence analysis revealed that PHC3 was mutated in nine of 15 primary osteosarcoma tumors. These findings suggest that loss of PHC3 may favor tumorigenesis by potentially disrupting the ability of cells to remain in G0.
Tet-mediated DNA oxidation is a recently identified mammalian epigenetic modification, and its functional role in cell-fate transitions remains poorly understood. Here, we derive mouse embryonic fibroblasts (MEFs) deleted in all three Tet genes and examine their capacity for reprogramming into induced pluripotent stem cells (iPSCs). We show that Tet-deficient MEFs cannot be reprogrammed because of a block in the mesenchymal-to-epithelial transition (MET) step. Reprogramming of MEFs deficient in TDG is similarly impaired. The block in reprogramming is caused at least in part by defective activation of key miRNAs, which depends on oxidative demethylation promoted by Tet and TDG. Reintroduction of either the affected miRNAs or catalytically active Tet and TDG restores reprogramming in the knockout MEFs. Thus, oxidative demethylation to promote gene activation appears to be functionally required for reprogramming of fibroblasts to pluripotency. These findings provide mechanistic insight into the role of epigenetic barriers in cell-lineage conversion.
The mechanisms underlying the silencing of alternative fate potentials in very early B cell precursors remain unclear. Using gain- and loss-of-function approaches together with a synthetic Zinc-finger polypeptide (6ZFP) engineered to prevent transcription factor binding to a defined cis element, we show that the transcription factor EBF1 promotes B cell lineage commitment by directly repressing expression of the T-cell-lineage-requisite Gata3 gene. Ebf1-deficient lymphoid progenitors exhibited increased T cell lineage potential and elevated Gata3 transcript expression, whereas enforced EBF1 expression inhibited T cell differentiation and caused rapid loss of Gata3 mRNA. Notably, 6ZFP-mediated perturbation of EBF1 binding to a Gata3 regulatory region restored Gata3 expression, abrogated EBF1-driven suppression of T cell differentiation, and prevented B cell differentiation via a GATA3-dependent mechanism. Furthermore, EBF1 binding to Gata3 regulatory sites induced repressive histone modifications across this region. These data identify a transcriptional circuit critical for B cell lineage commitment.
We describe robust induction of autophagy during the reprogramming of mouse fibroblasts to induced pluripotent stem cells by four reprogramming factors (Sox2, Oct4, Klf4 and c-Myc), henceforth 4F. This process occurs independently of p53 activation, and is mediated by the synergistic downregulation of mechanistic target of rapamycin complex 1 (mTORC1) and the induction of autophagy-related genes. The 4F coordinately repress mTORC1, but bifurcate in their regulation of autophagy-related genes, with Klf4 and c-Myc inducing them but Sox2 and Oct4 inhibiting them. On one hand, inhibition of mTORC1 facilitates reprogramming by promoting cell reshaping (mitochondrial remodelling and cell size reduction). On the other hand, mTORC1 paradoxically impairs reprogramming by triggering autophagy. Autophagy does not participate in cell reshaping in reprogramming but instead degrades p62, whose accumulation in autophagy-deficient cells facilitates reprogramming. Our results thus reveal a complex signalling network involving mTORC1 inhibition and autophagy induction in the early phase of reprogramming, whose delicate balance ultimately determines reprogramming efficiency.