Paradoxical Signaling Pathways in Developing Thymocytes

ABSTRACT- Thymocytes are subjected to processes of selection during their life in the thymus; negative selection for autoreactive thymocytes and positive selection for self-MHC restricted self-tolerant cells. Interestingly, signals for positive or negative selection originate from the same receptor. More importantly, evidence showed that both death and survival signals are mediated by the MAPK pathway. The degree and order of ERK activation, but not other MAPK proteins, has been found to be different in either cases of cell fate. Therefore, it is suspected that the kinetics of ERK after activation may dictate cell death or survival. There are two important GEF proteins that are involved in Ras/ERK activation, RasGRP and SOS. It is thought that the level, order and kinetics of ERK are influenced upstream by the type of GEF. This review discusses the role of both GEF proteins in positive and negative selection and how this reflects on ERK activation. This article is open POST-PUBLICATION REVIEW. Registered readers (see “For Readers”) may comment by clicking on ABSTRACT on the issue’s contents page.

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Revisiting the evolutionary analysis of mammalian CRISPs reveals positive selection

10.1101/266940 ◽

2018 ◽

Author(s):

Alberto Vicens ◽

Claudia Treviño

Keyword(s):

Positive Selection ◽

Adaptive Evolution ◽

Negative Selection ◽

Secretory Proteins ◽

Evolutionary Analysis ◽

Episodic Selection ◽

Show Evidence ◽

Selection For ◽

Related Proteins

AbstractCysteine-rich secretory proteins (CRISPs) constitute a versatile family, with functions that include being components of reptilian venom and participation in mammalian reproduction. While non-mammalian vertebrates express a single CRISP gene, mammals generally express three CRISP paralogs. A previous study assessing the molecular evolution of vertebrate CRISPs revealed strong positive selection in reptilian CRISP and negative selection in mammalian CRISPs. In this study, we re-assessed molecular adaptation of mammalian CRISPs through an analysis of larger sequence datasets that represent mammalian diversity. Our analyses show evidence of recent episodes of positive selection for all mammalian CRISPs. Intensity of positive selection was heterogeneous both among CRISP paralogs (being stronger in CRISP3 than in CRISP1 and CRISP2) and across functional domains (having more impact on CRD or PR-1 domain). Analysis of episodic selection did not yield strong signatures of adaptive evolution in any particular mammalian group, suggesting that positive selection was more pervasive on mammalian CRISPs. Our findings provide evidence of adaptive evolution in a family of reproduction-related proteins, and offer interesting insights regarding the role of mammalian CRISPs in fertility and speciation.

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Role of hepcidin in oxidative stress and cell death of cultured mouse renal collecting duct cells: protection against iron and sensitization to cadmium

Archives of Toxicology ◽

10.1007/s00204-021-03106-z ◽

2021 ◽

Author(s):

Stephanie Probst ◽

Johannes Fels ◽

Bettina Scharner ◽

Natascha A. Wolff ◽

Eleni Roussa ◽

...

Keyword(s):

Oxidative Stress ◽

Cell Death ◽

Cell Fate ◽

Catalase Activity ◽

Metal Ion ◽

Iron Homeostasis ◽

Collecting Duct ◽

Duct Cell ◽

Plasmid Transfection

AbstractThe liver hormone hepcidin regulates systemic iron homeostasis. Hepcidin is also expressed by the kidney, but exclusively in distal nephron segments. Several studies suggest hepcidin protects against kidney damage involving Fe2+ overload. The nephrotoxic non-essential metal ion Cd2+ can displace Fe2+ from cellular biomolecules, causing oxidative stress and cell death. The role of hepcidin in Fe2+ and Cd2+ toxicity was assessed in mouse renal cortical [mCCD(cl.1)] and inner medullary [mIMCD3] collecting duct cell lines. Cells were exposed to equipotent Cd2+ (0.5–5 μmol/l) and/or Fe2+ (50–100 μmol/l) for 4–24 h. Hepcidin (Hamp1) was transiently silenced by RNAi or overexpressed by plasmid transfection. Hepcidin or catalase expression were evaluated by RT-PCR, qPCR, immunoblotting or immunofluorescence microscopy, and cell fate by MTT, apoptosis and necrosis assays. Reactive oxygen species (ROS) were detected using CellROX™ Green and catalase activity by fluorometry. Hepcidin upregulation protected against Fe2+-induced mIMCD3 cell death by increasing catalase activity and reducing ROS, but exacerbated Cd2+-induced catalase dysfunction, increasing ROS and cell death. Opposite effects were observed with Hamp1 siRNA. Similar to Hamp1 silencing, increased intracellular Fe2+ prevented Cd2+ damage, ROS formation and catalase disruption whereas chelation of intracellular Fe2+ with desferrioxamine augmented Cd2+ damage, corresponding to hepcidin upregulation. Comparable effects were observed in mCCD(cl.1) cells, indicating equivalent functions of renal hepcidin in different collecting duct segments. In conclusion, hepcidin likely binds Fe2+, but not Cd2+. Because Fe2+ and Cd2+ compete for functional binding sites in proteins, hepcidin affects their free metal ion pools and differentially impacts downstream processes and cell fate.

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Genetic control of programmed cell death in the Caenorhabditis elegans hermaphrodite germline

Development ◽

10.1242/dev.126.5.1011 ◽

1999 ◽

Vol 126 (5) ◽

pp. 1011-1022 ◽

Cited By ~ 8

Author(s):

T.L. Gumienny ◽

E. Lambie ◽

E. Hartwieg ◽

H.R. Horvitz ◽

M.O. Hengartner

Keyword(s):

Cell Death ◽

Caenorhabditis Elegans ◽

Germ Cell ◽

Somatic Cell ◽

Cell Fate ◽

Germ Cells ◽

Mapk Pathway ◽

Apoptotic Cell ◽

C Elegans ◽

Pathway Activation

Development of the nematode Caenorhabditis elegans is highly reproducible and the fate of every somatic cell has been reported. We describe here a previously uncharacterized cell fate in C. elegans: we show that germ cells, which in hermaphrodites can differentiate into sperm and oocytes, also undergo apoptotic cell death. In adult hermaphrodites, over 300 germ cells die, using the same apoptotic execution machinery (ced-3, ced-4 and ced-9) as the previously described 131 somatic cell deaths. However, this machinery is activated by a distinct pathway, as loss of egl-1 function, which inhibits somatic cell death, does not affect germ cell apoptosis. Germ cell death requires ras/MAPK pathway activation and is used to maintain germline homeostasis. We suggest that apoptosis eliminates excess germ cells that acted as nurse cells to provide cytoplasmic components to maturing oocytes.

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Positive and negative selection invoke distinct signaling pathways.

Journal of Experimental Medicine ◽

10.1084/jem.184.1.9 ◽

1996 ◽

Vol 184 (1) ◽

pp. 9-18 ◽

Cited By ~ 177

Author(s):

J Alberola-Ila ◽

K A Hogquist ◽

K A Swan ◽

M J Bevan ◽

R M Perlmutter

Keyword(s):

T Cell ◽

Positive Selection ◽

Negative Selection ◽

Mapk Pathway ◽

Cell Receptor ◽

Dominant Negative ◽

Mapk Cascade ◽

Mitogen Activated Protein Kinase ◽

Mitogen Activated Protein

During T cell development, interaction of the T cell receptor (TCR) with cognate ligands in the thymus may result in either maturation (positive selection) or death (negative selection). The intracellular pathways that control these opposed outcomes are not well characterized. We have generated mice expressing dominant-negative Ras (dnRas) and Mek-1 (dMek) transgenes simultaneously, either in otherwise normal animals, or in animals expressing a transgenic TCR, thereby permitting a comprehensive analysis of peptide-specific selection. In this system, thymocyte maturation beyond the CD4+8+ stage is blocked almost completely, whereas negative selection, assessed using an in vitro deletion protocol, is quantitatively intact. This suggests that activation of the mitogen-activated protein kinase (MAPK) cascade is necessary for positive selection, but irrelevant for negative selection. Generation of gamma/delta and of CD4-8- alpha/beta T cells proceeds normally despite blockade of the MAPK cascade. Hence, only cells that mature via conventional, TCR-mediated repertoire selection require activation of the MAPK pathway to complete their maturation.

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ERK: A Double-Edged Sword in Cancer. ERK-Dependent Apoptosis as a Potential Therapeutic Strategy for Cancer

Cells ◽

10.3390/cells10102509 ◽

2021 ◽

Vol 10 (10) ◽

pp. 2509

Author(s):

Reiko Sugiura ◽

Ryosuke Satoh ◽

Teruaki Takasaki

Keyword(s):

Cell Proliferation ◽

Cell Death ◽

Tumor Cell Death ◽

Cancer Treatments ◽

Erk Activation ◽

Cellular Processes ◽

Dual Specificity ◽

Anti Cancer ◽

Dual Specificity Phosphatases

The RAF/MEK/ERK signaling pathway regulates diverse cellular processes as exemplified by cell proliferation, differentiation, motility, and survival. Activation of ERK1/2 generally promotes cell proliferation, and its deregulated activity is a hallmark of many cancers. Therefore, components and regulators of the ERK pathway are considered potential therapeutic targets for cancer, and inhibitors of this pathway, including some MEK and BRAF inhibitors, are already being used in the clinic. Notably, ERK1/2 kinases also have pro-apoptotic functions under certain conditions and enhanced ERK1/2 signaling can cause tumor cell death. Although the repertoire of the compounds which mediate ERK activation and apoptosis is expanding, and various anti-cancer compounds induce ERK activation while exerting their anti-proliferative effects, the mechanisms underlying ERK1/2-mediated cell death are still vague. Recent studies highlight the importance of dual-specificity phosphatases (DUSPs) in determining the pro- versus anti-apoptotic function of ERK in cancer. In this review, we will summarize the recent major findings in understanding the role of ERK in apoptosis, focusing on the major compounds mediating ERK-dependent apoptosis. Studies that further define the molecular targets of these compounds relevant to cell death will be essential to harnessing these compounds for developing effective cancer treatments.

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Use of signals of positive and negative selection to distinguish cancer genes and passenger genes

10.1101/2020.06.04.133199 ◽

2020 ◽

Author(s):

László Bányai ◽

Mária Trexler ◽

Krisztina Kerekes ◽

Orsolya Csuka ◽

László Patthy

Keyword(s):

Negative Selection ◽

Cancer Genomics ◽

Tumor Evolution ◽

Cancer Genes ◽

Cancer Evolution ◽

Human Genes ◽

Strong Negative Selection ◽

Selection For ◽

Inactivating Mutations

AbstractA major goal of cancer genomics is to identify all genes that play critical roles in carcinogenesis. Most approaches focused on genes that are positively selected for mutations that drive carcinogenesis and neglected the role of negative selection. Some studies have actually concluded that negative selection has no role in cancer evolution. In the present work we have re-examined the role of negative selection in tumor evolution through the analysis of the patterns of somatic mutations affecting the coding sequences of human genes. Our analyses have confirmed that tumor suppressor genes are positively selected for inactivating mutations. Oncogenes, however, were found to display signals of both negative selection for inactivating mutations and positive selection for activating mutations. Significantly, we have identified numerous human genes that show signs of strong negative selection during tumor evolution, suggesting that their functional integrity is essential for the growth and survival of tumor cells.

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Vesicular formation regulated by ERK/MAPK pathway mediates human erythroblast enucleation

Blood Advances ◽

10.1182/bloodadvances.2021004859 ◽

2021 ◽

Author(s):

Chao An ◽

Yumin Huang ◽

Mengjia Li ◽

Fumin Xue ◽

Dingrui Nie ◽

...

Keyword(s):

Mapk Pathway ◽

Chromatin Condensation ◽

Erythroid Differentiation ◽

Mitogen Activated Protein Kinase ◽

Rna Seq ◽

Erk Activation ◽

Cytoplasmic Vesicles ◽

Mitogen Activated Protein ◽

Terminal Erythroid Differentiation

Enucleation is a key event in mammalian erythropoiesis responsible for generation of enucleated reticulocytes. While progress is being made in developing mechanistic understanding of enucleation, our understanding of mechanisms for enucleation is still incomplete. Mitogen-activated protein kinase (MAPK) pathway plays diverse roles in biological processes but its role in erythropoiesis is yet to be fully defined. Analysis of RNA-seq data revealed that MAPK pathway is significantly up regulated during human terminal erythroid differentiation. MAPK pathway consists of three major signaling cassettes, MEK/ERK, p38 and c-Jun N-terminal Kinases (JNK). In the present study, we show that amongst these three cassettes, only ERK was significantly up regulated in late stage human erythroblasts. The increased expression of ERK along with its increased phosphorylation suggests a potential role of ERK activation in enucleation. To explore this hypothesis, we treated sorted populations of human orthochromatic erythroblasts with MEK/ERK inhibitor U0126 and found that U0126 inhibited enucleation. In contrast, inhibitors of either p38 or JNK had no effect on enucleation. Mechanistically, U0126 selectively inhibited formation/accumulation of cytoplasmic vesicles and endocytosis of the transferrin receptor without affecting chromatin condensation, nuclear polarization and enucleosome formation. Treatment with vacuolin-1 that induces vacuole formation partially rescued the blockage of enucleation by U0126. Moreover, phosphoproteomic analysis revealed that inactivation of the ERK pathway led to down regulation of endocytic recycling pathway. Collectively, our findings uncovered a novel role of ERK activation in human erythroblast enucleation by modulating vesicle formation and have implications for understanding anemia associated with defective enucleation.

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Timing of gene expression in a cell-fate decision system

10.1101/197103 ◽

2017 ◽

Author(s):

Delphine Aymoz ◽

Carme Solé ◽

Jean-Jerrold Pierre ◽

Marta Schmitt ◽

Eulàlia de Nadal ◽

...

Keyword(s):

Gene Expression ◽

Cell Fate ◽

Mapk Pathway ◽

Single Cells ◽

Cell Fate Decision ◽

Decision System ◽

Mating Partner ◽

Mating Pathway ◽

Fate Decision ◽

Kinetics Of

AbstractDuring development, morphogens provide extracellular cues allowing cells to select a specific fate by inducing complex transcriptional programs. The mating pathway in budding yeast offers simplified settings to understand this process. Pheromone secreted by the mating partner triggers the activity of a MAPK pathway, which results in the expression of hundreds of genes. Using a dynamic expression reporter, we quantified the kinetics of gene expression in single cells upon exogenous pheromone stimulation and in the physiological context of mating. In both conditions, we observed striking differences in the timing of induction of mating-responsive promoters. Biochemical analyses and generation of synthetic promoter variants demonstrated how the interplay between transcription factor binding and nucleosomes contribute to determine the kinetics of transcription in a simplified cell-fate decision system.One Sentence SummaryQuantitative and dynamic single cell measurements in the yeast mating pathway uncover a complex temporal orchestration of gene expression events.

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OXPHOS Promotes Apoptotic Resistance and Persistence in TH17 cells

10.1101/2021.10.01.462812 ◽

2021 ◽

Author(s):

Hanna S. Hong ◽

Nneka E. Mbah ◽

Mengrou Shan ◽

Kristen Loesel ◽

Lin Lin ◽

...

Keyword(s):

T Cells ◽

Cell Death ◽

Cell Fate ◽

Apoptotic Cell ◽

Metabolic Phenotype ◽

Tumor Studies ◽

A Cell

AbstractApoptotic cell death is a cell-intrinsic, immune tolerance mechanism that regulates the magnitude and resolution of T cell-mediated responses. Evasion of apoptosis is critical for the generation of memory T cells, as well as autoimmune T cells, and knowledge of the mechanisms that enable resistance to apoptosis will provide insight into ways to modulate their activity during protective and pathogenic responses. IL-17-producing CD4 T cells (TH17s) are long-lived, memory cells. These features enable their role in host defense, chronic inflammatory disorders, and anti-tumor immunity. A growing number of reports now indicate that TH17s in vivo require mitochondrial oxidative phosphorylation (OXPHOS), a metabolic phenotype that is poorly induced in vitro. To elucidate the role of OXPHOS in TH17 processes, we developed a system to polarize TH17s that metabolically resembled their in vivo counterparts. We discovered that directing TH17s to use OXPHOS promotes mitochondrial fitness, glutamine anaplerosis, and an anti-apoptotic phenotype marked by high BCL-XL and low BIM. Through competitive co-transfer experiments and tumor studies, we further revealed how OXPHOS protects TH17s from cell death while enhancing their persistence in the periphery and tumor microenvironment. Together, our work demonstrates a non-classical role of metabolism in regulating TH17 cell fate and highlights the potential for therapies that target OXPHOS in TH17-driven diseases.

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Thymus-derived Glucocorticoids Regulate Antigen-specific Positive Selection

Journal of Experimental Medicine ◽

10.1084/jem.185.11.2033 ◽

1997 ◽

Vol 185 (11) ◽

pp. 2033-2038 ◽

Cited By ~ 97

Author(s):

Melanie S. Vacchio ◽

Jonathan D. Ashwell

Keyword(s):

Positive Selection ◽

Negative Selection ◽

Cross Linking ◽

Thymocyte Development ◽

Organ Cultures ◽

Specific Loss ◽

Histocompatibility Complex ◽

Glucocorticoid Production ◽

Self Antigen

While it is generally believed that the avidity of the T cell antigen receptor (TCR) for self antigen/major histocompatibility complex (MHC) determines a thymocyte's fate, how the cell discriminates between a stimulus that causes positive selection (survival) and one that causes negative selection (death) is unknown. We have previously demonstrated that glucocorticoids are produced in the thymus, and that they antagonize deletion caused by TCR cross-linking. To examine the role of glucocorticoids during MHC-dependent selection, we examined thymocyte development in organ cultures in which corticosteroid biosynthesis was inhibited. Inhibition of glucocorticoid production in thymi from α/β-TCR transgenic mice resulted in the antigen- and MHC-specific loss of thymocytes that normally recognize self antigen/MHC with sufficient avidity to result in positive selection. Furthermore, inhibition of glucocorticoid production caused an increase in apoptosis only in CD+CD8+ thymocytes bearing transgenic TCRs that recognized self antigen/MHC. These results indicate that the balance of TCR and glucocorticoid receptor signaling influences the antigen-specific thymocyte development by allowing cells with low-to-moderate avidity for self antigen/MHC to survive.

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