Extracellular Signal-Regulated Kinase 1c (ERK1c), a Novel 42-Kilodalton ERK, Demonstrates Unique Modes of Regulation, Localization, and Function

ABSTRACT Extracellular signal-regulated kinases (ERKs) are signaling molecules that regulate many cellular processes. We have previously identified an alternatively spliced 46-kDa form of ERK1 that is expressed in rats and mice and named ERK1b. Here we report that the same splicing event in humans and monkeys causes, due to sequence differences in the inserted introns, the production of an ERK isoform that migrates together with the 42-kDa ERK2. Because of the differences of this isoform from ERK1b, we named it ERK1c. We found that its expression levels are about 10% of ERK1. ERK1c seems to be expressed in a wide variety of tissues and cells. Its activation by MEKs and inactivation by phosphatases are slower than those of ERK1, which is probably the reason for its differential regulation in response to extracellular stimuli. Unlike ERK1, ERK1c undergoes monoubiquitination, which is increased with elevated cell density concomitantly with accumulation of ERK1c in the Golgi apparatus. Elevated cell density also causes enhanced Golgi fragmentation, which is facilitated by overexpression of native ERK1c and is prevented by dominant-negative ERK1c, indicating that ERK1c mediates cell density-induced Golgi fragmentation. The differential regulation of ERK1c extends the signaling specificity of MEKs after stimulation by various extracellular stimuli.

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Signaling diversity enabled by Rap1-regulated plasma membrane ERK with distinct temporal dynamics

eLife ◽

10.7554/elife.57410 ◽

2020 ◽

Vol 9 ◽

Author(s):

Jeremiah Keyes ◽

Ambhighainath Ganesan ◽

Olivia Molinar-Inglis ◽

Archer Hamidzadeh ◽

Jinfan Zhang ◽

...

Keyword(s):

Plasma Membrane ◽

Temporal Dynamics ◽

Resonance Energy Transfer ◽

Resonance Energy ◽

Signaling Specificity ◽

Temporal Regulation ◽

Cellular Processes ◽

Extracellular Signal ◽

Transient Activity ◽

Erk Activity

A variety of different signals induce specific responses through a common, extracellular-signal regulated kinase (ERK)-dependent cascade. It has been suggested that signaling specificity can be achieved through precise temporal regulation of ERK activity. Given the wide distrubtion of ERK susbtrates across different subcellular compartments, it is important to understand how ERK activity is temporally regulated at specific subcellular locations. To address this question, we have expanded the toolbox of Förster Resonance Energy Transfer (FRET)-based ERK biosensors by creating a series of improved biosensors targeted to various subcellular regions via sequence specific motifs to measure spatiotemporal changes in ERK activity. Using these sensors, we showed that EGF induces sustained ERK activity near the plasma membrane in sharp contrast to the transient activity observed in the cytoplasm and nucleus. Furthermore, EGF-induced plasma membrane ERK activity involves Rap1, a noncanonical activator, and controls cell morphology and EGF-induced membrane protrusion dynamics. Our work strongly supports that spatial and temporal regulation of ERK activity is integrated to control signaling specificity from a single extracellular signal to multiple cellular processes.

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Regulation and function of the RSK family of protein kinases

Biochemical Journal ◽

10.1042/bj20110289 ◽

2011 ◽

Vol 441 (2) ◽

pp. 553-569 ◽

Cited By ~ 206

Author(s):

Yves Romeo ◽

Xiaocui Zhang ◽

Philippe P. Roux

Keyword(s):

Single Family ◽

Protein Substrates ◽

Cellular Processes ◽

Downstream Effectors ◽

Extracellular Signal ◽

New Findings ◽

Activation Mechanisms ◽

Ribosomal S6 Kinase ◽

And Function ◽

Novel Protein

The RSK (90 kDa ribosomal S6 kinase) family comprises a group of highly related serine/threonine kinases that regulate diverse cellular processes, including cell growth, proliferation, survival and motility. This family includes four vertebrate isoforms (RSK1, RSK2, RSK3 and RSK4), and single family member orthologues are also present in Drosophila and Caenorhabditis elegans. The RSK isoforms are downstream effectors of the Ras/ERK (extracellular-signal-regulated kinase) signalling pathway. Significant advances in the field of RSK signalling have occurred in the past few years, including several new functions ascribed to the RSK isoforms, the discovery of novel protein substrates and the implication of different RSK isoforms in cancer. Collectively, these new findings increase the diversity of biological functions regulated by RSK, and highlight potential new directions of research. In the present paper, we review the structure, expression and activation mechanisms of the RSK isoforms, and discuss their physiological roles on the basis of established substrates and recent discoveries.

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Increased extracellular signal regulated kinases phosphorylation in the adrenal gland in response to chronic ACTH treatment

Journal of Endocrinology ◽

10.1677/joe.1.06961 ◽

2007 ◽

Vol 192 (3) ◽

pp. 647-658 ◽

Cited By ~ 16

Author(s):

Jorge G Ferreira ◽

Célia D Cruz ◽

Delminda Neves ◽

Duarte Pignatelli

Keyword(s):

Cell Proliferation ◽

Mek Inhibitor ◽

Nuclear Antigen ◽

Dependent Manner ◽

Cellular Processes ◽

Extracellular Signal ◽

Extracellular Stimuli ◽

Corticosterone Release

ACTH released from the pituitary acts through activation of cAMP/PKA in adrenocortical cells stimulating steroidogenesis. Although ACTH was originally thought to have anti-proliferative effects on the adrenal, recently it has been described that it could also have proliferative effects acting through other signalling cascades. This is also relevant in humans given the increased levels of ACTH occurring together with adrenal cortex hyperplasia observed in Cushing’s disease and possibly in other situations such as chronic stress. One of the signalling pathways regulating cell proliferation is the extracellular signal regulated kinase (ERKs) pathway. ERKs are members of the MAPK family of cascades. They are activated by extracellular stimuli such as growth factors and mitogens, become phosphorylated through MEK1/2 and regulate a diversity of cellular processes such as proliferation and differentiation. Until now, no study addressed the effects of chronic ACTH administration on the activation of ERKs in vivo. Using rats submitted to different ACTH dosages as well as variable durations, we determined if ACTH induced ERKs activation and by establishing a parallelism with proliferating cell nuclear antigen (PCNA) expression, we aimed to demonstrate a role of ACTH-induced ERKs activation in cell proliferation. Blood was collected for hormonal analysis and the role of ACTH-induced ERKs activation in the stimulation of steroidogenesis was also studied. We confirmed that ACTH increased adrenal weight and corticosterone levels when compared with control or dexamethasone-treated animals. We also demonstrated that ACTH increases ERKs activation and PCNA expression in a time- and dose-dependent manner. When ERKs activation was blocked by the use of a specific MEK inhibitor (PD98059), there was a decrease in ACTH-induced corticosterone release and PCNA expression. We conclude that chronic ACTH induces ERKs activation and that this plays an important role in the induction of cell proliferation as well as steroidogenesis.

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Alternative Splicing of MAPKs in the Regulation of Signaling Specificity

Cells ◽

10.3390/cells10123466 ◽

2021 ◽

Vol 10 (12) ◽

pp. 3466

Author(s):

Galia Maik-Rachline ◽

Inbal Wortzel ◽

Rony Seger

Keyword(s):

Cell Fate ◽

Mitogen Activated Protein Kinase ◽

Signaling Specificity ◽

Cellular Processes ◽

Extracellular Signals ◽

Mapk Cascades ◽

Mitogen Activated Protein ◽

Extracellular Stimuli ◽

Alternatively Spliced

The mitogen-activated protein kinase (MAPK) cascades transmit signals from extracellular stimuli to a variety of distinct cellular processes. The MAPKKs in each cascade specifically phosphorylate and activate their cognate MAPKs, indicating that this step funnels various signals into a seemingly linear pathway. Still, the effects of these cascades vary significantly, depending on the identity of the extracellular signals, which gives rise to proper outcomes. Therefore, it is clear that the specificity of the signals transmitted through the cascades is tightly regulated in order to secure the desired cell fate. Indeed, many regulatory components or processes that extend the specificity of the cascades have been identified. Here, we focus on a less discussed mechanism, that is, the role of distinct components in each tier of the cascade in extending the signaling specificity. We cover the role of distinct genes, and the alternatively spliced isoforms of MAPKKs and MAPKs, in the signaling specificity. The alternatively spliced MEK1b and ERK1c, which form an independent signaling route, are used as the main example. Unlike MEK1/2 and ERK1/2, this route’s functions are limited, including mainly the regulation of mitotic Golgi fragmentation. The unique roles of the alternatively spliced isoforms indicate that these components play an essential role in determining the proper cell fate in response to distinct stimulations.

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Signaling Diversity Enabled by Rap1-Regulated Plasma Membrane ERK with Distinct Temporal Dynamics

10.1101/781716 ◽

2019 ◽

Author(s):

Jeremiah Keyes ◽

Ambhighainath Ganesan ◽

Olivia Molinar-Inglis ◽

Archer Hamidzadeh ◽

Megan Ling ◽

...

Keyword(s):

Plasma Membrane ◽

Temporal Dynamics ◽

Membrane Protrusion ◽

Signaling Specificity ◽

Temporal Regulation ◽

Cellular Processes ◽

Extracellular Signal ◽

Transient Activity ◽

Kinase Cascade ◽

Erk Activity

AbstractA variety of different signals induce specific responses through a common, ERK-dependent kinase cascade. It has been suggested that signaling specificity can be achieved through precise temporal regulation of ERK activity. Given the wide distrubtion of ERK susbtrates across different subcellular compartments, it is important to understand how ERK activity is temporally regulated at specific subcellular locations. To address this question, we have expanded the toolbox of FRET-based ERK biosensors by creating a series of improved biosensors targeted to various subcellular regions via sequence specific motifs to measure spatiotemporal changes in ERK enzymatic activity. Using these sensors, we showed that EGF induces sustained ERK activity near the plasma membrane in sharp contrast to the transient activity observed in the cytopolasm and nucleus. Furthermore, EGF-induced plasma membrane ERK activity involves Rap1, a noncanonical activator, and controls cell morphology and EGF-induced membrane protrusion dynamics. Our work strongly supports that spatial and temporal regulation of ERK activity is integrated to control signaling specificity from a single extracellular signal to multiple cellular processes.

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Bend, Push, Stretch: Remarkable Structure and Mechanics of Single Intermediate Filaments and Meshworks

Cells ◽

10.3390/cells10081960 ◽

2021 ◽

Vol 10 (8) ◽

pp. 1960

Author(s):

K. Tanuj Sapra ◽

Ohad Medalia

Keyword(s):

Intermediate Filaments ◽

Eukaryotic Cell ◽

Coiled Coils ◽

Cellular Functions ◽

Mechanical Pressure ◽

Mechanical Feature ◽

Cellular Processes ◽

Nuclear Lamins ◽

Filament Networks ◽

And Function

The cytoskeleton of the eukaryotic cell provides a structural and functional scaffold enabling biochemical and cellular functions. While actin and microtubules form the main framework of the cell, intermediate filament networks provide unique mechanical properties that increase the resilience of both the cytoplasm and the nucleus, thereby maintaining cellular function while under mechanical pressure. Intermediate filaments (IFs) are imperative to a plethora of regulatory and signaling functions in mechanotransduction. Mutations in all types of IF proteins are known to affect the architectural integrity and function of cellular processes, leading to debilitating diseases. The basic building block of all IFs are elongated α-helical coiled-coils that assemble hierarchically into complex meshworks. A remarkable mechanical feature of IFs is the capability of coiled-coils to metamorphize into β-sheets under stress, making them one of the strongest and most resilient mechanical entities in nature. Here, we discuss structural and mechanical aspects of IFs with a focus on nuclear lamins and vimentin.

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Differential Regulation of Gonadotropins as Revealed by Transcriptomes of Distinct LH and FSH Cells of Fish Pituitary

International Journal of Molecular Sciences ◽

10.3390/ijms22126478 ◽

2021 ◽

Vol 22 (12) ◽

pp. 6478

Author(s):

Lian Hollander-Cohen ◽

Matan Golan ◽

Berta Levavi-Sivan

Keyword(s):

Follicle Stimulating Hormone ◽

Differential Regulation ◽

Receptor Expression ◽

Hormone Regulation ◽

Fish Reproduction ◽

Cell Type ◽

Conserved Genes ◽

Transgenic Tilapia ◽

And Function ◽

Direct Regulation

From mammals to fish, reproduction is driven by luteinizing hormone (LH) and follicle-stimulating hormone (FSH) temporally secreted from the pituitary gland. Teleost fish are an excellent model for addressing the unique regulation and function of each gonadotropin cell since, unlike mammals, they synthesize and secrete LH and FSH from distinct cells. Only very distant vertebrate classes (such as fish and birds) demonstrate the mono-hormonal strategy, suggesting a potential convergent evolution. Cell-specific transcriptome analysis of double-labeled transgenic tilapia expressing GFP and RFP in LH or FSH cells, respectively, yielded genes specifically enriched in each cell type, revealing differences in hormone regulation, receptor expression, cell signaling, and electrical properties. Each cell type expresses a unique GPCR signature that reveals the direct regulation of metabolic and homeostatic hormones. Comparing these novel transcriptomes to that of rat gonadotrophs revealed conserved genes that might specifically contribute to each gonadotropin activity in mammals, suggesting conserved mechanisms controlling the differential regulation of gonadotropins in vertebrates.

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Ubiquitin and Ubiquitin-Like Proteins and Domains in Ribosome Production and Function: Chance or Necessity?

International Journal of Molecular Sciences ◽

10.3390/ijms22094359 ◽

2021 ◽

Vol 22 (9) ◽

pp. 4359

Author(s):

Sara Martín-Villanueva ◽

Gabriel Gutiérrez ◽

Dieter Kressler ◽

Jesús de la Cruz

Keyword(s):

Ribosomal Proteins ◽

Ribosome Biogenesis ◽

Ribosome Assembly ◽

Cellular Processes ◽

Substrate Protein ◽

Precursor Proteins ◽

Assembly Factors ◽

Ubiquitin Moiety ◽

And Function

Ubiquitin is a small protein that is highly conserved throughout eukaryotes. It operates as a reversible post-translational modifier through a process known as ubiquitination, which involves the addition of one or several ubiquitin moieties to a substrate protein. These modifications mark proteins for proteasome-dependent degradation or alter their localization or activity in a variety of cellular processes. In most eukaryotes, ubiquitin is generated by the proteolytic cleavage of precursor proteins in which it is fused either to itself, constituting a polyubiquitin precursor, or as a single N-terminal moiety to ribosomal proteins, which are practically invariably eL40 and eS31. Herein, we summarize the contribution of the ubiquitin moiety within precursors of ribosomal proteins to ribosome biogenesis and function and discuss the biological relevance of having maintained the explicit fusion to eL40 and eS31 during evolution. There are other ubiquitin-like proteins, which also work as post-translational modifiers, among them the small ubiquitin-like modifier (SUMO). Both ubiquitin and SUMO are able to modify ribosome assembly factors and ribosomal proteins to regulate ribosome biogenesis and function. Strikingly, ubiquitin-like domains are also found within two ribosome assembly factors; hence, the functional role of these proteins will also be highlighted.

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Extracellular Signal-Regulated Kinase Binds to TFII-I and Regulates Its Activation of the c-fosPromoter

Molecular and Cellular Biology ◽

10.1128/mcb.20.4.1140-1148.2000 ◽

2000 ◽

Vol 20 (4) ◽

pp. 1140-1148 ◽

Cited By ~ 37

Author(s):

Dae-Won Kim ◽

Brent H. Cochran

Keyword(s):

Map Kinase ◽

Transcriptional Activation ◽

Dominant Negative ◽

Binding Motif ◽

Dependent Manner ◽

Consensus Map ◽

Interaction Domain ◽

Extracellular Signal

ABSTRACT We have previously shown that TFII-I enhances transcriptional activation of the c-fos promoter through interactions with upstream elements in a signal-dependent manner. Here we demonstrate that activated Ras and RhoA synergize with TFII-I for c-fospromoter activation, whereas dominant-negative Ras and RhoA inhibit these effects of TFII-I. The Mek1 inhibitor, PD98059 abrogates the enhancement of the c-fos promoter by TFII-I, indicating that TFII-I function is dependent on an active mitogen-activated protein (MAP) kinase pathway. Analysis of the TFII-I protein sequence revealed that TFII-I contains a consensus MAP kinase interaction domain (D box). Consistent with this, we have found that TFII-I forms an in vivo complex with extracellular signal-related kinase (ERK). Point mutations within the consensus MAP kinase binding motif of TFII-I inhibit its ability to bind ERK and its ability to enhance the c-fos promoter. Therefore, the D box of TFII-I is required for its activity on the c-fos promoter. Moreover, the interaction between TFII-I and ERK can be regulated. Serum stimulation enhances complex formation between TFII-I and ERK, and dominant-negative Ras abrogates this interaction. In addition, TFII-I can be phosphorylated in vitro by ERK and mutation of consensus MAP kinase substrate sites at serines 627 and 633 impairs the phosphorylation of TFII-I by ERK and its activity on the c-fos promoter. These results suggest that ERK regulates the activity of TFII-I by direct phosphorylation.

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A disease-associated frameshift mutation in caveolin-1 disrupts caveolae formation and function through introduction of a de novo ER retention signal

Molecular Biology of the Cell ◽

10.1091/mbc.e17-06-0421 ◽

2017 ◽

Vol 28 (22) ◽

pp. 3095-3111 ◽

Cited By ~ 11

Author(s):

Courtney A. Copeland ◽

Bing Han ◽

Ajit Tiwari ◽

Eric D. Austin ◽

James E. Loyd ◽

...

Keyword(s):

Frameshift Mutation ◽

De Novo ◽

Dominant Negative ◽

Caveolin 1 ◽

Protein Levels ◽

C Terminus ◽

Er Retention ◽

And Function ◽

Er Retention Signal ◽

Retention Signal

Caveolin-1 (CAV1) is an essential component of caveolae and is implicated in numerous physiological processes. Recent studies have identified heterozygous mutations in the CAV1 gene in patients with pulmonary arterial hypertension (PAH), but the mechanisms by which these mutations impact caveolae assembly and contribute to disease remain unclear. To address this question, we examined the consequences of a familial PAH-associated frameshift mutation in CAV1, P158PfsX22, on caveolae assembly and function. We show that C-terminus of the CAV1 P158 protein contains a functional ER-retention signal that inhibits ER exit and caveolae formation and accelerates CAV1 turnover in Cav1–/– MEFs. Moreover, when coexpressed with wild-type (WT) CAV1 in Cav1–/– MEFs, CAV1-P158 functions as a dominant negative by partially disrupting WT CAV1 trafficking. In patient skin fibroblasts, CAV1 and caveolar accessory protein levels are reduced, fewer caveolae are observed, and CAV1 complexes exhibit biochemical abnormalities. Patient fibroblasts also exhibit decreased resistance to a hypo-osmotic challenge, suggesting the function of caveolae as membrane reservoir is compromised. We conclude that the P158PfsX22 frameshift introduces a gain of function that gives rise to a dominant negative form of CAV1, defining a new mechanism by which disease-associated mutations in CAV1 impair caveolae assembly.

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