Biomedical subjects

Shen-Hsi Yang

Publications and source records attributed to Shen-Hsi Yang.

11 recordsLinked to original sources

PubMed2010

MAP Kinase: SUMO pathway interactions.

The convergence and coordinated cross talk of different signalling pathways forms a regulatory network which determines the biological outcome to environmental cues. The MAPK pathways are one of the important routes by which extracellular signals are transduced into intracellular responses. Through protein phosphorylation mechanisms, they can play a pivotal role in regulating other posttranslational modifications such as protein acetylation and ubiquitination. In addition, protein sumoylation has emerged as an important pathway which also functions through post-translational modification. The SUMO pathway modulates a diverse range of cellular processes including signal transduction, chromosome integrity, and transcription. Interestingly, recent studies have provided links between the SUMO and MAPK signalling pathways which converge to modulate transcription factor activity. This was first demonstrated by the observation that the activation of the ERK pathway caused de-sumoylation of the transcription factor, Elk-1. Furthermore, a growing number of links are now being made between the MAPK pathway and protein sumoylation. Given the nature of protein sumoylation in diverse biological functions, it is not surprising that the effect of MAPK pathways on sumoylation varies between different proteins. Here, we describe protocols that can be used in studying the cross talk between the MAPK and SUMO pathways, particularly at the level of gene regulation.

Amino Acid Sequence↗

PubMed2006

An extended consensus motif enhances the specificity of substrate modification by SUMO.

Protein modification by SUMO conjugation is an important regulatory event. Sumoylation usually takes place on a lysine residue embedded in the core consensus motif psiKxE. However, this motif confers limited specificity on the sumoylation process. Here, we have probed the roles of clusters of acidic residues located downstream from the core SUMO modification sites in proteins such as the transcription factor Elk-1. We demonstrate that these are functionally important in SUMO-dependent transcriptional repression of Elk-1 transcriptional activity. Mechanistically, the acidic residues are important in enhancing the efficiency of Elk-1 sumoylation by Ubc9. Similar mechanisms operate in other transcription factors and phosphorylation sites can functionally substitute for acidic residues. Thus, an extended sumoylation motif, termed the NDSM (negatively charged amino acid-dependent sumoylation motif), helps define functional SUMO targets. We demonstrate that this extended motif can be used to correctly predict novel targets for SUMO modification.

Amino Acid Motifs↗

PubMed2006

PIASxalpha differentially regulates the amplitudes of transcriptional responses following activation of the ERK and p38 MAPK pathways.

Activation of the MAP kinase pathways leads to changes in gene expression profiles through direct targeting of transcription factors and their coregulators. Here we identify PIASxalpha as a key regulator that determines the differential response of the transcription factor Elk-1 to the ERK and the stress-activated p38 MAP kinase pathways. While PIASxalpha functions as a coactivator to facilitate SUMO and HDAC-2 removal from Elk-1 in response to ERK pathway activation, PIASxalpha acts in the opposite manner to inhibit HDAC-2 and SUMO loss following stress-activated MAP kinase pathway signaling. Thus, PIASxalpha either enhances or dampens down the activation of Elk-1 target genes, depending on the pathway activated. p38 MAP kinase-mediated PIASxalpha phosphorylation allows it to switch between these two alternative modes of operation. Thus, PIASxalpha acts as a key signal integrator that permits different responses from the same transcription factor, depending on the signaling pathway that is activated.

Anisomycin↗

PubMed2006

Convergence of the SUMO and MAPK pathways on the ETS-domain transcription factor Elk-1.

The ETS-domain transcription factor Elk-1 is regulated by phosphorylation in response to activation of the MAPK (mitogen-activated protein kinase) pathways. This phosphorylation triggers a series of molecular events that convert Elk-1 from a transcriptionally silent state into a highly active state and then back to a basal level. At the same time, activation of the ERK (extracellular-signal-regulated kinase) MAPK pathway leads to loss of modification of Elk-1 by SUMO (small ubiquitin-related modifier). As SUMO imparts repressive properties on Elk-1, ERK-mediated SUMO loss leads to de-repression at the same time as the ERK pathway promotes activation of Elk-1. Thus a two-step mechanism is employed to convert Elk-1 into its fully activated state. Here, the molecular events underlying these changes in Elk-1 status, and the role of PIASxalpha [protein inhibitor of activated STAT (signal transducer and activator of transcription) xalpha] as a co-activator that facilitates this process, are discussed.

Animals↗

PubMed2005

PIASx acts as an Elk-1 coactivator by facilitating derepression.

The ETS-domain transcription factor Elk-1 is a MAP kinase-inducible transcriptional activator protein. However, in the basal state, its activity is repressed by SUMO-dependent histone deacetylase (HDAC) recruitment. Relief of this repression accompanies the activation process. Here, we demonstrate that PIASx(alpha) acts to facilitate this derepression process. Members of the PIAS family of proteins can act as E3 enzymes that enhance the sumoylation status of a variety of substrates. However, PIASx-mediated coactivation of Elk-1 occurs in an E3 activity-independent manner. PIASx(alpha) binds to Elk-1 in vivo and enhances its transcriptional activity. The coactivating properties of PIASx(alpha) require Elk-1 to be modified with SUMO and the integrity of the SUMO binding motif in PIASx(alpha). PIASx(alpha) activates Elk-1 through alterations in the HAT/HDAC activities associated with Elk-1. In particular, PIASx(alpha) facilitates the loss of the repressive HDAC-2 from sumoylated Elk-1, a key event in the activation of Elk-1 in response to signalling through the ERK MAP kinase pathway. Our data therefore reveal a novel coactivator function for PIASx(alpha) through reversing SUMO-mediated repression of transcription factor activity.

Acetylation↗

PubMed2004

SUMO promotes HDAC-mediated transcriptional repression.

Recently, SUMO modification has been shown to impart repressive properties on several transcriptional regulatory proteins. Indeed, the ETS domain transcription factor Elk-1 is modified by SUMO, and this modification is reversed by ERK MAP kinase pathway activation. This causes a switch from a repressive to activated state. However, the mechanism(s) of SUMO-mediated transcriptional repression is unclear. Here, we have investigated how sumoylation of Elk-1 leads to transcriptional repression. We demonstrate that sumoylation of Elk-1 results in the recruitment of histone deacetylase activity to promoters. In particular, our data point to a key role for HDAC-2. This recruitment leads to decreased histone acetylation and hence transcriptional repression at Elk-1 target genes. Thus, our data demonstrate an important integration point for two protein-modifying pathways in the cell, the SUMO and deacetylation pathways, that combine to promote transcriptional repression.

Blotting, Western↗

PubMed2003

Transcriptional regulation by the MAP kinase signaling cascades.

A major function of the mitogen-activated protein kinase (MAPK) pathways is to control eukaryotic gene expression programmes in response to extracellular signals. MAPKs directly control gene expression by phosphorylating transcription factors. However, it is becoming clear that transcriptional regulation in response to MAPK signaling is more complex. MAPKs can also target coactivators and corepressors and affect nucleosomal structure by inducing histone modifications. Furthermore, multiple inputs into individual promoters can be elicited by MAPKs by targeting different components of the same coregulatory complex or by triggering different events on the same transcription factor. "Postgenomic approaches" are beginning to impact on our understanding of these gene regulatory networks. In this review, we summarise the current knowledge of MAPK-mediated gene regulation, and focus on how complexities in signaling outcomes are achieved and how this relates to physiological processes.

Animals↗

PubMed2003

MAP kinase phosphorylation-dependent activation of Elk-1 leads to activation of the co-activator p300.

CBP/p300 recruitment to enhancer-bound complexes is a key determinant in promoter activation by many transcription factors. We present a novel mechanism of activating such complexes and show that pre-assembled Elk-1-p300 complexes become activated following Elk-1 phosphorylation by changes in Elk-1-p300 interactions rather than recruitment. It is known that Elk-1 binds to promoter in the absence of stimuli. However, it is unclear how activation of Elk-1 by mitogen-acivated protein kinase (MAPK)-mediated phosphorylation leads to targeted gene transactivation. We show that Elk-1 can interact with p300 in vitro and in vivo in the absence of a stimulus through the Elk-1 C-terminus and the p300 N-terminus. Phosphorylation on Ser383 and Ser389 of Elk-1 by MAPK enhances this basal binding but, most importantly, Elk-1 exhibits new interactions with p300. These interaction changes render a strong histone acetyltransferase activity in the Elk-1-associated complex that could play a critical role in chromatin remodeling and gene activation. The pre-assembly mechanism may greatly accelerate transcription activation, which is important in regulation of expression of immediate-early response genes, in particular those involved in stress responses.

Acetyltransferases↗

PubMed2003

Dynamic interplay of the SUMO and ERK pathways in regulating Elk-1 transcriptional activity.

The ETS domain transcription factor Elk-1 is a direct target of the MAP kinase pathways. Phosphorylation of the Elk-1 transcriptional activation domain by MAP kinases triggers its activation. However, Elk-1 also contains two domains with repressive activities. One of these, the R motif, appears to function by suppressing the activity of the activation domain. Here, we demonstrate that SUMO modification of the R motif is required for this repressive activity. A dynamic interplay exists between the activating ERK MAP kinase pathway and the repressive SUMO pathway. ERK pathway activation leads to both phosphorylation of Elk-1 and loss of SUMO conjugation and, hence, to the loss of the repressive activity of the R motif. Thus, the reciprocal regulation of the activation and repressive activities are coupled by MAP kinase modification of Elk-1.

Animals↗

PubMed2002

The ETS domain transcription factor Elk-1 contains a novel class of repression domain.

The ETS domain transcription factor Elk-1 serves as an integration point for different mitogen-activated protein (MAP) kinase pathways. Phosphorylation of Elk-1 by MAP kinases triggers its activation. However, while the activation process is well understood, its downregulation-inactivation is less well characterized. The ETS DNA-binding domain plays a role in the downregulation of Elk-dependent promoter activity following mitogenic activation by recruiting the mSin3A-HDAC complex. Here we have identified a novel evolutionarily conserved repression domain in Elk-1, termed the R motif, which serves to reduce the basal transcriptional activity of Elk-1 and dampen its response to mitogenic signals. This domain is highly potent and portable and can repress transcription in trans. The R motif is related to the CRD1 repression domain in p300 and can functionally replace this domain and confer p21(waf1/cip1) inducibility on p300. However, the R motif acts in a context-dependent manner and is not p21(waf1/cip1) responsive in Elk-1. Thus, the Elk-1 R motif and the p300 CRD1 motif represent a new class of repression domains that are regulated in a context-dependent manner.

Amino Acid Motifs↗

PubMedDate not supplied

SUMO and transcriptional repression: dynamic interactions between the MAP kinase and SUMO pathways.

SUMO modification of proteins is being increasingly linked with transcriptional repression. We recently demonstrated that SUMO modification also downregulates the transcriptional activity of the ETS-domain transcription factor Elk-1. However, as Elk-1 becomes activated through MAP kinase-mediated phosphorylation, the SUMO modification is lost, providing an elegant molecular switch that promotes the loss of repressive activities at the same time as permitting the recruitment of coactivator proteins. However, the mechanism by which SUMO promotes transcriptional repression remains enigmatic.

Animals↗