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Mastermind-Like 1 Is Ubiquitinated: Functional Consequences for Notch Signaling.

Farshbaf M, Lindberg MJ, Truong A, Bevens Z, Chambers E, Pournara A, Wallberg AE, White JB - PLoS ONE (2015)

Bottom Line: We also show that p300 stimulates ubiquitination and that Notch inhibits ubiquitination.Therefore, we speculate that ubiquitination of MAML1 might be a mechanism to maintain low levels of the protein until needed for transcriptional activation.Our data supports the notion that a precise and tight regulation of the Notch pathway is required for this signaling pathway.

View Article: PubMed Central - PubMed

Affiliation: From the Department of Biological Sciences, San José State University, San José, California, United States of America.

ABSTRACT
Early studies demonstrated the involvement of ubiquitination of the Notch intracellular domain for rapid turnover of the transcriptional complex at Notch target genes. It was shown that this ubiquitination was promoted by the co-activator Mastermind like 1 (MAML1). MAML1 also contains numerous lysine residues that may also be ubiquitinated and necessary for protein regulation. In this study, we show that over-expressed MAML1 is ubiquitinated and identify eight conserved lysine residues which are required for ubiquitination. We also show that p300 stimulates ubiquitination and that Notch inhibits ubiquitination. Furthermore, we show that a mutant MAML1 that has decreased ubiquitination shows increased output from a HES1 reporter gene assay. Therefore, we speculate that ubiquitination of MAML1 might be a mechanism to maintain low levels of the protein until needed for transcriptional activation. In summary, this study identifies that MAML1 is ubiquitinated in the absence of Notch signaling to maintain low levels of MAML1 in the cell. Our data supports the notion that a precise and tight regulation of the Notch pathway is required for this signaling pathway.

No MeSH data available.


Related in: MedlinePlus

Overview of Notch Signaling in the Nucleus.(A) In the absence of the NICD, Notch target genes remain in a repressed state through interaction of CBF1 with corepressor complexes (SMRT and HDAC1). (B) Release of the NICD from the cell membrane results in nuclear translocation and recruitment of MAML1, p300, and CDK8. CDK8 phosphorylates the NICD in the PEST domain as indicated by the lollipop structures. (C) Phosphorylation is thought to recruit the ubiquitin ligase Fbw7 to poly-ubiquitinate (boxes) the NICD, thereby signaling for degradation and shut off of target gene activation.
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pone.0134013.g001: Overview of Notch Signaling in the Nucleus.(A) In the absence of the NICD, Notch target genes remain in a repressed state through interaction of CBF1 with corepressor complexes (SMRT and HDAC1). (B) Release of the NICD from the cell membrane results in nuclear translocation and recruitment of MAML1, p300, and CDK8. CDK8 phosphorylates the NICD in the PEST domain as indicated by the lollipop structures. (C) Phosphorylation is thought to recruit the ubiquitin ligase Fbw7 to poly-ubiquitinate (boxes) the NICD, thereby signaling for degradation and shut off of target gene activation.

Mentions: The Notch signaling pathway is an evolutionarily conserved system found in all metazoans and it plays an important role in developmental and disease processes by influencing proliferation, differentiation, self-renewal and apoptosis [1, 2]. In mammals, there are four Notch receptors. The Notch receptor is a protease-activated transcription factor located on the cell membrane. Interaction with a ligand results in cleavage releasing the intracellular domain (NICD). The NICD enters the nucleus and forms a complex with CSL (CBF1, Suppressor of Hairless, and Lag-1) enhancer-binding proteins and MAML1 to activate target genes. The ternary complex (CSL, NICD, and MAML1) is believed essential for activation of target genes (Fig 1). MAML1 was initially identified as a protein involved in the Notch pathway in D. Melanogaster [3, 4]. In mammals, there are three family members (MAML1-3) [5]. The most well characterized interactions have been shown between Notch 1 (N1ICD) and MAML1.


Mastermind-Like 1 Is Ubiquitinated: Functional Consequences for Notch Signaling.

Farshbaf M, Lindberg MJ, Truong A, Bevens Z, Chambers E, Pournara A, Wallberg AE, White JB - PLoS ONE (2015)

Overview of Notch Signaling in the Nucleus.(A) In the absence of the NICD, Notch target genes remain in a repressed state through interaction of CBF1 with corepressor complexes (SMRT and HDAC1). (B) Release of the NICD from the cell membrane results in nuclear translocation and recruitment of MAML1, p300, and CDK8. CDK8 phosphorylates the NICD in the PEST domain as indicated by the lollipop structures. (C) Phosphorylation is thought to recruit the ubiquitin ligase Fbw7 to poly-ubiquitinate (boxes) the NICD, thereby signaling for degradation and shut off of target gene activation.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4520489&req=5

pone.0134013.g001: Overview of Notch Signaling in the Nucleus.(A) In the absence of the NICD, Notch target genes remain in a repressed state through interaction of CBF1 with corepressor complexes (SMRT and HDAC1). (B) Release of the NICD from the cell membrane results in nuclear translocation and recruitment of MAML1, p300, and CDK8. CDK8 phosphorylates the NICD in the PEST domain as indicated by the lollipop structures. (C) Phosphorylation is thought to recruit the ubiquitin ligase Fbw7 to poly-ubiquitinate (boxes) the NICD, thereby signaling for degradation and shut off of target gene activation.
Mentions: The Notch signaling pathway is an evolutionarily conserved system found in all metazoans and it plays an important role in developmental and disease processes by influencing proliferation, differentiation, self-renewal and apoptosis [1, 2]. In mammals, there are four Notch receptors. The Notch receptor is a protease-activated transcription factor located on the cell membrane. Interaction with a ligand results in cleavage releasing the intracellular domain (NICD). The NICD enters the nucleus and forms a complex with CSL (CBF1, Suppressor of Hairless, and Lag-1) enhancer-binding proteins and MAML1 to activate target genes. The ternary complex (CSL, NICD, and MAML1) is believed essential for activation of target genes (Fig 1). MAML1 was initially identified as a protein involved in the Notch pathway in D. Melanogaster [3, 4]. In mammals, there are three family members (MAML1-3) [5]. The most well characterized interactions have been shown between Notch 1 (N1ICD) and MAML1.

Bottom Line: We also show that p300 stimulates ubiquitination and that Notch inhibits ubiquitination.Therefore, we speculate that ubiquitination of MAML1 might be a mechanism to maintain low levels of the protein until needed for transcriptional activation.Our data supports the notion that a precise and tight regulation of the Notch pathway is required for this signaling pathway.

View Article: PubMed Central - PubMed

Affiliation: From the Department of Biological Sciences, San José State University, San José, California, United States of America.

ABSTRACT
Early studies demonstrated the involvement of ubiquitination of the Notch intracellular domain for rapid turnover of the transcriptional complex at Notch target genes. It was shown that this ubiquitination was promoted by the co-activator Mastermind like 1 (MAML1). MAML1 also contains numerous lysine residues that may also be ubiquitinated and necessary for protein regulation. In this study, we show that over-expressed MAML1 is ubiquitinated and identify eight conserved lysine residues which are required for ubiquitination. We also show that p300 stimulates ubiquitination and that Notch inhibits ubiquitination. Furthermore, we show that a mutant MAML1 that has decreased ubiquitination shows increased output from a HES1 reporter gene assay. Therefore, we speculate that ubiquitination of MAML1 might be a mechanism to maintain low levels of the protein until needed for transcriptional activation. In summary, this study identifies that MAML1 is ubiquitinated in the absence of Notch signaling to maintain low levels of MAML1 in the cell. Our data supports the notion that a precise and tight regulation of the Notch pathway is required for this signaling pathway.

No MeSH data available.


Related in: MedlinePlus