Biomedical subjects

Marc Therrien

Publications and source records attributed to Marc Therrien.

7 recordsLinked to original sources

PubMed2006

Alphabet, a Ser/Thr phosphatase of the protein phosphatase 2C family, negatively regulates RAS/MAPK signaling in Drosophila.

Signal transduction through the RAS/mitogen-activated protein kinase (MAPK) pathway depends on a diverse collection of proteins regulating positively and negatively signaling flow. We previously conducted a genetic screen in Drosophila to identify novel components of this signaling pathway. Here, we present the identification and characterization of a new gene, alphabet (alph), whose activity negatively regulates RAS/MAPK-dependent developmental processes in Drosophila and this, at a step downstream or in parallel to RAS. alph encodes a protein phosphatase 2C (PP2C) family member closely related to the mammalian PP2C alpha and beta isoforms. Interestingly, although alph gene product does not appear to be essential for viability, its elimination leads to weak but significant developmental defects reminiscent of an overactivated RAS/MAPK pathway. Consistent with this interpretation, strong genetic interactions are observed between alph alleles and mutations in bona fide components of the pathway. Together, this work identifies a PP2C of the alpha/beta subfamily as a novel negative regulator of the RAS/MAPK pathway and suggests that these evolutionarily conserved enzymes play a similar role in other metazoans. Finally, despite the relatively large size of the PP2C gene family in metazoans, this study represents only the second genetic characterization of a PP2C in these organisms.

Animals↗

PubMed2006

A KSR/CNK complex mediated by HYP, a novel SAM domain-containing protein, regulates RAS-dependent RAF activation in Drosophila.

RAF is a critical effector of the small GTPase RAS in normal and malignant cells. Despite intense scrutiny, the mechanism regulating RAF activation remains partially understood. Here, we show that the scaffold KSR (kinase suppressor of RAS), a RAF homolog known to assemble RAF/MEK/ERK complexes, induces RAF activation in Drosophila by a mechanism mediated by its kinase-like domain, but which is independent of its scaffolding property or putative kinase activity. Interestingly, we found that KSR is recruited to RAF prior to signal activation by the RAF-binding protein CNK (connector enhancer of KSR) in association with a novel SAM (sterile alpha motif) domain-containing protein, named Hyphen (HYP). Moreover, our data suggest that the interaction of KSR to CNK/HYP stimulates the RAS-dependent RAF-activating property of KSR. Together, these findings identify a novel protein complex that controls RAF activation and suggest that KSR does not only act as a scaffold for the MAPK (mitogen-activated protein kinase) module, but may also function as a RAF activator. By analogy to catalytically impaired, but conformationally active B-RAF oncogenic mutants, we discuss the possibility that KSR represents a natural allosteric inducer of RAF catalytic function.

Adaptor Proteins, Signal Transducing↗

PubMed2006

Assessment of seated postural control in children: comparison of a force platform versus a pressure mapping system.

OBJECTIVE: To establish the validity and reliability of a pressure mapping system to measure seated postural control in children. DESIGN: A concurrent validity and reliability study. SETTING: Gait and posture laboratory of a rehabilitation center. PARTICIPANTS: Thirteen able-bodied children volunteers. INTERVENTION: Measurements were taken on a seating simulator in quiet sitting and while reaching. The localization of the center of pressure (COP) in the anteroposterior and mediolateral directions was measured simultaneously by means of a pressure mapping system and a force platform. MAIN OUTCOME MEASURES: Concurrent validity was first assessed by Pearson and Spearman correlation coefficients and then by Student paired t tests and Wilcoxon signed-rank test (P<.05) on the range and root mean square (RMS) amplitudes of COP. Reliability was evaluated using intraclass correlation coefficients and coefficients of variation. RESULTS: The COP signals were significantly correlated between both instruments for the RMS and range in both tasks and directions (mean r> or =.87) and for the time series while reaching (r> or =.99), as well as during quiet sitting (r> or =65). Both instruments showed generally fair to good reliability in quiet sitting and excellent reliability when reaching. CONCLUSIONS: The pressure mapping system can detect the COP displacement as effectively as the force platform. In a clinical context, it could help in the evaluation of seated stability and also help in evaluating the efficacy of seating components for wheelchair users.

Adolescent↗

PubMed2005

Src42 binding activity regulates Drosophila RAF by a novel CNK-dependent derepression mechanism.

Connector enhancer of KSR (CNK), an essential component of Drosophila receptor tyrosine kinase/mitogen-activated protein kinase pathways, regulates oppositely RAF function. This bimodal property depends on the N-terminal region of CNK, which integrates RAS activity to stimulate RAF and a bipartite element, called the RAF-inhibitory region (RIR), which binds and inhibits RAF catalytic activity. Here, we show that the repressive effect of the RIR is counteracted by the ability of Src42 to associate, in an RTK-dependent manner, with a conserved region located immediately C-terminal to the RIR. Strikingly, we found that several cnk loss-of-function alleles have mutations clustered in this area and provide evidence that these mutations impair Src42 binding. Surprisingly, the derepressing effect of Src42 does not appear to involve its catalytic function, but critically depends on the ability of its SH3 and SH2 domains to associate with CNK. Together, these findings suggest that the integration of RTK-induced RAS and Src42 signals by CNK as a two-component input is essential for RAF activation in Drosophila.

Adaptor Proteins, Signal Transducing↗

PubMed2003

Bimodal regulation of RAF by CNK in Drosophila.

Connector enhancer of KSR (CNK) is a multidomain-containing protein previously identified as a positive regulator of the RAS/MAPK pathway in Drosophila. Using transfection experiments and an RNAi-based rescue assay in Drosophila S2 cells, we demonstrate that CNK has antagonistic properties with respect to RAF activity. We show that CNK's N-terminal region contains two domains (SAM and CRIC) that are essential for RAF function. Unexpectedly, we also report that the C-terminal region of CNK contains a short bipartite element that strongly inhibits RAF catalytic function. Interestingly, CNK's opposite properties appear to prevent signaling leakage from RAF to MEK in the absence of upstream signals, but then transforms into a potent RAF activator upon signal activation. Together, these findings suggest that CNK not only participates in the elusive RAF activation process, but might also contribute to the switch-like behavior of the MAPK module.

Adaptor Proteins, Signal Transducing↗

PubMed2002

MAP kinase module: the Ksr connection.

Ksr has been genetically defined as a component of the Ras/MAP kinase pathway, but its role has been unclear. New studies now provide evidence that Ksr is important for signal transmission within the MAP kinase module, where it apparently acts as a location-regulated scaffold connecting MEK to Raf.

Animals↗

PubMed2002

KSR is a scaffold required for activation of the ERK/MAPK module.

Mechanisms that regulate signal propagation through the ERK/MAPK pathway are still poorly understood. Several proteins are suspected to play critical roles in this process. One of these is Kinase Suppressor of Ras (KSR), a component previously identified in RAS-dependent genetic screens in Drosophila and Caenorhabditis elegans. Here, we show that KSR functions upstream of MEK within the ERK/MAPK module. In agreement with this, we found that KSR facilitates the phosphorylation of MEK by RAF. We further show that KSR associates independently with RAF and MEK, and that these interactions lead to the formation of a RAF/MEK complex, thereby positioning RAF in close proximity to its substrate MEK. These findings suggest that KSR functions as a scaffold that assembles the RAF/MEK functional pair.

Animals↗