142 research outputs found
HYPOTHESIS Open Access
Hepatic autophagy is differentially regulated in periportal and pericentral zones- a general mechanism relevant for other tissues
FOXO transcription factors directly activate bim gene expression and promote apoptosis in sympathetic neurons
Developing sympathetic neurons die by apoptosis when deprived of NGF. BIM, a BH3-only member of the BCL-2 family, is induced after NGF withdrawal in these cells and contributes to NGF withdrawal–induced death. Here, we have investigated the involvement of the Forkhead box, class O (FOXO) subfamily of Forkhead transcription factors in the regulation of BIM expression by NGF. We find that overexpression of FOXO transcription factors induces BIM expression and promotes death of sympathetic neurons in a BIM-dependent manner. In addition, we find that FKHRL1 (FOXO3a) directly activates the bim promoter via two conserved FOXO binding sites and that mutation of these sites abolishes bim promoter activation after NGF withdrawal. Finally, we show that FOXO activity contributes to the NGF deprivation–induced death of sympathetic neurons
Transduction of a dominant-negative H-Ras into human eosinophils attenuates extracellular signal-regulated kinase activation and interleukin-5-mediated cell viability
Inhibition of eosinophil apoptosis by exposure
to interleukin-5 (IL-5) is associated
with the development of tissue eosinophilia
and may contribute to the
inflammation characteristic of asthma.
Analysis of the signaling events associated
with this process has been hampered
by the inability to efficiently manipulate
eosinophils by the introduction of
active or inhibitory effector molecules.
Evidence is provided, using a dominantnegative
N17 H-Ras protein (dn-H-Ras)
and MEK inhibitor U0126, that activation
of the Ras-Raf-MEK-ERK pathway plays a
determining role in the prolongation of
eosinophil survival by IL-5. For these
studies, a small region of the human
immunodeficiency virus Tat protein, a protein
transduction domain known to enter
mammalian cells efficiently, was fused to
the N-terminus of dn-H-Ras. The Tat-dn-HRas
protein generated from this construct
transduced isolated human blood
eosinophils at more than 95% efficiency.
When Tat-dn-H-Ras-transduced eosinophils
were treated with IL-5, they exhibited
a time- and dosage-dependent reduction
in extracellular regulated kinase 1
and 2 activation and an inhibition of p90
Rsk1 phosphorylation and IL-5-mediated
eosinophil survival in vitro. In contrast,
Tat-dn-H-Ras did not inhibit CD11b upregulation
or STAT5 tyrosine phosphorylation.
These data demonstrate that Tat
dominant-negative protein transduction
can serve as an important and novel tool
in studying primary myeloid cell signal
transduction in primary leukocytes and
can implicate the Ras-Raf-MEK-ERK pathway
in IL-5-initiated eosinophil survival
FKHR-L1 can act as a critical effector of cell death induced by cytokine withdrawal: protein kinase B–enhanced cell survival through maintenance of mitochondrial integrity
Survival signals elicited by cytokines include the activation of phosphatidylinositol 3-kinase (PI3K), which in turn promotes the activation of protein kinase B (PKB). Recently, PKB has been demonstrated to phosphorylate and inactivate forkhead transcription factor FKHR-L1, a potent inducer of apoptosis. To explore the mechanisms underlying the induction of apoptosis after cytokine withdrawal or FKHR-L1 activation, we used a cell line in which FKHR-L1 activity could be specifically induced. Both cytokine withdrawal and FKHR-L1 activation induced apoptosis, which was preceded by an upregulation in p27KIP1 and a concomitant decrease in cells entering the cell cycle. Induction of apoptosis by both cytokine withdrawal and activation of FKHR-L1 correlated with the disruption of mitochondrial membrane integrity and cytochrome c release. This was preceded by upregulation of the pro-apoptotic Bcl-2 family member Bim. Ectopic expression of an inhibitory mutant of FKHR-L1 substantially reduced the levels of apoptosis observed after cytokine withdrawal. Activation of PKB alone was sufficient to promote cell survival, as measured by maintenance of mitochondrial integrity and the resultant inhibition of effector caspases. Furthermore, hematopoietic stem cells isolated from Bim−/− mice exhibited reduced levels of apoptosis upon inhibition of PI3K/PKB signaling
Identification and characterization of CKLiK, a novel granulocyteCa^(++)/calmodulin-dependent kinase
Human granulocytes are characterized
by a variety of specific effector functions
involved in host defense. Several widely
expressed protein kinases have been implicated
in the regulation of these effector
functions. A polymerase chain reaction-
based strategy was used to identify novel
granulocyte-specific kinases.Anovel protein
kinase complementary DNA with an
open reading frame of 357 amino acids
was identified with homology to calciumcalmodulin-
dependent kinase I (CaMKI).
This has been termed CaMKI-like kinase
(CKLiK). Analysis of CKLiK messenger
RNA (mRNA) expression in hematopoietic
cells demonstrated an almost exclusive
expression in human polymorphonuclear
leukocytes (PMN). Up-regulation
of CKLiK mRNA occurs during neutrophilic
differentiation of CD341 stem cells.
CKLiK kinase activity was dependent on
Ca11 and calmodulin as analyzed by in
vitro phosphorylation of cyclic adenosine
monophosphate responsive element
modulator (CREM). Furthermore, CKLiKtransfected
cells treated with ionomycin
demonstrated an induction of CREbinding
protein (CREB) transcriptional activity
compared to control cells. Additionally,
CaMK-kinasea enhanced CKLiK activity.
In vivo activation of CKLiK was
shown by addition of interleukin (IL)-8
to a myeloid cell line stably expressing
CKLiK. Furthermore inducible activation
of CKLiK was sufficient to induce
extracellular signal-related kinase (ERK)
mitogen-activated protein (MAP) kinase
activity. These data identify a novel
Ca11/calmodulin-dependent PMNspecific
kinase that may play a role in
Ca11-mediated regulation of human
granulocyte functions
Context-Specific Effects of TGF-β/SMAD3 in Cancer Are Modulated by the Epigenome.
The transforming growth factor beta (TGF-β) signaling pathway exerts opposing effects on cancer cells, acting as either a tumor promoter or a tumor suppressor. Here, we show that these opposing effects are a result of the synergy between SMAD3, a downstream effector of TGF-β signaling, and the distinct epigenomes of breast-tumor-initiating cells (BTICs). These effects of TGF-β are associated with distinct gene expression programs, but genomic SMAD3 binding patterns are highly similar in the BTIC-promoting and BTIC-suppressing contexts. Our data show cell-type-specific patterns of DNA and histone modifications provide a modulatory layer by determining accessibility of genes to regulation by TGF-β/SMAD3. LBH, one such context-specific target gene, is regulated according to its DNA methylation status and is crucial for TGF-β-dependent promotion of BTICs. Overall, these results reveal that the epigenome plays a central and previously overlooked role in shaping the context-specific effects of TGF-β in cancer.S.J.V. was supported by a grant from the Dutch Cancer Foundation (KWF).This is the final version of the article. It was first available from Elsevier via http://dx.doi.org/10.1016/j.celrep.2015.11.04
FoxO3a regulates erythroid differentiation and induces BTG1, an activator of protein arginine methyl transferase 1
Erythropoiesis requires tight control of expansion, maturation, and survival of erythroid progenitors. Because activation of phosphatidylinositol-3-kinase (PI3K) is required for erythropoietin/stem cell factor–induced expansion of erythroid progenitors, we examined the role of the PI3K-controlled Forkhead box, class O (FoxO) subfamily of Forkhead transcription factors. FoxO3a expression and nuclear accumulation increased during erythroid differentiation, whereas untimely induction of FoxO3a activity accelerated differentiation of erythroid progenitors to erythrocytes. We identified B cell translocation gene 1 (BTG1)/antiproliferative protein 2 as a FoxO3a target gene in erythroid progenitors. Promoter studies indicated BTG1 as a direct target of FoxO3a. Expression of BTG1 in primary mouse bone marrow cells blocked the outgrowth of erythroid colonies, which required a domain of BTG1 that binds protein arginine methyl transferase 1. During erythroid differentiation, increased arginine methylation coincided with BTG1 expression. Concordantly, inhibition of methyl transferase activity blocked erythroid maturation without affecting expansion of progenitor cells. We propose FoxO3a-controlled expression of BTG1 and subsequent regulation of protein arginine methyl transferase activity as a novel mechanism controlling erythroid expansion and differentiation
SOX4 can redirect TGF-β-mediated SMAD3-transcriptional output in a context-dependent manner to promote tumorigenesis.
Expression of the transcription factor SOX4 is often elevated in human cancers, where it generally correlates with tumor-progression and poor-disease outcome. Reduction of SOX4 expression results in both diminished tumor-incidence and metastasis. In breast cancer, TGF-β-mediated induction of SOX4 has been shown to contribute to epithelial-to-mesenchymal transition (EMT), which controls pro-metastatic events. Here, we identify SMAD3 as a novel, functionally relevant SOX4 interaction partner. Genome-wide analysis showed that SOX4 and SMAD3 co-occupy a large number of genomic loci in a cell-type specific manner. Moreover, SOX4 expression was required for TGF-β-mediated induction of a subset of SMAD3/SOX4-co-bound genes regulating migration and extracellular matrix-associated processes, and correlating with poor-prognosis. These findings identify SOX4 as an important SMAD3 co-factor controlling transcription of pro-metastatic genes and context-dependent shaping of the cellular response to TGF-β. Targeted disruption of the interaction between these factors may have the potential to disrupt pro-oncogenic TGF-β signaling, thereby impairing tumorigenesis
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