Np9 Protein of Human Endogenous Retrovirus K Interacts with Ligand of Numb Protein X

ABSTRACT We have recently identified Np9 as a novel nuclear protein produced by the human endogenous retrovirus K and were able to document the exclusive presence of np9 transcript in tumors and transformed cells. With the aim of studying whether Np9 has a role in tumorigenesis, a systematic search for interacting proteins was performed. Here, we identify the RING-type E3 ubiquitin ligase LNX (ligand of Numb protein X) as an Np9-interacting partner. We furthermore show that the interaction involves N- and C-terminal domains of both proteins and can affect the subcellular localization of LNX. LNX has been reported to target the cell fate determinant and Notch antagonist Numb for proteasome-dependent degradation, thereby causing an increase in transactivational activity of Notch. We document that LNX-interacting Np9, like Numb, is unstable and degraded via the proteasome pathway and that ectopic Numb can stabilize recombinant Np9. Combined, these findings point to the possibility that Np9 affects tumorigenesis through the LNX/Numb/Notch pathway.

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PML Activates Transcription by Protecting HIPK2 and p300 from SCFFbx3-Mediated Degradation

Molecular and Cellular Biology ◽

10.1128/mcb.00897-08 ◽

2008 ◽

Vol 28 (23) ◽

pp. 7126-7138 ◽

Cited By ~ 46

Author(s):

Yutaka Shima ◽

Takito Shima ◽

Tomoki Chiba ◽

Tatsuro Irimura ◽

Pier Paolo Pandolfi ◽

...

Keyword(s):

Transcription Factor ◽

Ubiquitin Ligase ◽

Nuclear Protein ◽

Retinoic Acid Receptor ◽

Activation Of Transcription ◽

Ubiquitin Proteasome ◽

Proteasome Pathway ◽

Retinoic Acid Receptor Α ◽

Transcription Factor Complex

ABSTRACT PML, a nuclear protein, interacts with several transcription factors and their coactivators, such as HIPK2 and p300, resulting in the activation of transcription. Although PML is thought to achieve transcription activation by stabilizing the transcription factor complex, little is known about the underlying molecular mechanism. To clarify the role of PML in transcription regulation, we purified the PML complex and identified Fbxo3 (Fbx3), Skp1, and Cullin1 as novel components of this complex. Fbx3 formed SCFFbx3 ubiquitin ligase and promoted the degradation of HIPK2 and p300 by the ubiquitin-proteasome pathway. PML inhibited this degradation through a mechanism that unexpectedly did not involve inhibition of the ubiquitination of HIPK2. PML, Fbx3, and HIPK2 synergistically activated p53-induced transcription. Our findings suggest that PML stabilizes the transcription factor complex by protecting HIPK2 and p300 from SCFFbx3-induced degradation until transcription is completed. In contrast, the leukemia-associated fusion PML-RARα induced the degradation of HIPK2. We discuss the roles of PML and PML-retinoic acid receptor α, as well as those of HIPK2 and p300 ubiquitination, in transcriptional regulation and leukemogenesis.

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The Drosophila melanogaster Suppressor of deltex Gene, a Regulator of the Notch Receptor Signaling Pathway, Is an E3 Class Ubiquitin Ligase

Genetics ◽

10.1093/genetics/152.2.567 ◽

1999 ◽

Vol 152 (2) ◽

pp. 567-576 ◽

Cited By ~ 13

Author(s):

M Cornell ◽

D A P Evans ◽

R Mann ◽

M Fostier ◽

M Flasza ◽

...

Keyword(s):

Notch Signaling ◽

Signaling Pathway ◽

Cell Fate ◽

Ubiquitin Ligase ◽

Notch Pathway ◽

Notch Receptor ◽

Negative Regulator ◽

Loss Of Function ◽

Wing Vein ◽

Cell Fate Decisions

Abstract During development, the Notch receptor regulates many cell fate decisions by a signaling pathway that has been conserved during evolution. One positive regulator of Notch is Deltex, a cytoplasmic, zinc finger domain protein, which binds to the intracellular domain of Notch. Phenotypes resulting from mutations in deltex resemble loss-of-function Notch phenotypes and are suppressed by the mutation Suppressor of deltex [Su(dx)]. Homozygous Su(dx) mutations result in wing-vein phenotypes and interact genetically with Notch pathway genes. We have previously defined Su(dx) genetically as a negative regulator of Notch signaling. Here we present the molecular identification of the Su(dx) gene product. Su(dx) belongs to a family of E3 ubiquitin ligase proteins containing membrane-targeting C2 domains and WW domains that mediate protein-protein interactions through recognition of proline-rich peptide sequences. We have identified a seven-codon deletion in a Su(dx) mutant allele and we show that expression of Su(dx) cDNA rescues Su(dx) mutant phenotypes. Overexpression of Su(dx) also results in ectopic vein differentiation, wing margin loss, and wing growth phenotypes and enhances the phenotypes of loss-of-function mutations in Notch, evidence that supports the conclusion that Su(dx) has a role in the downregulation of Notch signaling.

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Exon 3 of the NUMB Gene Emerged in the Chordate Lineage Coopting the NUMB Protein to the Regulation of MDM2

G3 Genes|Genome|Genetics ◽

10.1534/g3.119.400494 ◽

2019 ◽

Vol 9 (10) ◽

pp. 3359-3367

Author(s):

Stefano Confalonieri ◽

Ivan Nicola Colaluca ◽

Andrea Basile ◽

Salvatore Pece ◽

Pier Paolo Di Fiore

Keyword(s):

Cell Fate ◽

Ubiquitin Ligase ◽

Common Ancestor ◽

Stem Cell Fate ◽

Major Function ◽

Cellular Processes ◽

Cell Fate Determinant ◽

The Common ◽

Evolutionary Aspects ◽

Ptb Domain

MDM2 regulates a variety of cellular processes through its dual protein:protein interaction and ubiquitin ligase activities. One major function of MDM2 is to bind and ubiquitinate P53, thereby regulating its proteasomal degradation. This function is in turn controlled by the cell fate determinant NUMB, which binds to and inhibits MDM2 via a short stretch of 11 amino acids, contained in its phosphotyrosine-binding (PTB) domain, encoded by exon 3 of the NUMB gene. The NUMB-MDM2-P53 circuitry is relevant to the specification of the stem cell fate and its subversion has been shown to be causal in breast cancer leading to the emergence of cancer stem cells. While extensive work on the evolutionary aspects of the MDM2/P53 circuitry has provided hints as to how these two proteins have evolved together to maintain conserved and linked functions, little is known about the evolution of the NUMB gene and, in particular, how it developed the ability to regulate MDM2 function. Here, we show that NUMB is a metazoan gene, which acquired exon 3 in the common ancestor of the Chordate lineage, first being present in the Cephalochordate and Tunicate subphyla, but absent in invertebrates. We provide experimental evidence showing that since its emergence, exon 3 conferred to the PTB domain of NUMB the ability to bind and to regulate MDM2 functions.

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