Review articleNEDDylation in liver cancer: The regulation of the RNA binding protein Hu antigen R
Section snippets
The RNA-binding protein HuR: regulation, functions and implications in liver cancer
The mammalian Hu/elav family of RNA-binding proteins (RBPs) includes the neuronal members HuB, HuC and HuD, and the more ubiquitous member HuR. Whereas the neuronal Hu has been related with neuronal development, neuronal plasticity and memory [1], [2], HuR (also known as ELAVL1) was first described to stabilize ARE-containing mRNAs [3]. After this, it has been also shown to modulate the translation, both enhancing and inhibiting it [4], [5].
HuR protein contains three RNA recognition motifs
Stabilization of target mRNAs
Some of the HuR-stabilized target mRNAs include p21, c-fos, VEGF, the MAPK phosphatase (MKP)-1, iNOS, granulocyte/macrophage colony-stimulating factor (GMCSF), sirtuin 1 (SIRT1), TNFα, B-cell lymphoma-2 (Bcl2), myeloid cell leukemia-1 (Mcl1), cyclooxygenase-2 (COX-2), γ-glutamylcysteine synthetase heavy subunit (γ-GCSh), urokinase-type plasminogen activator (uPA) and its receptor (uPAR), p53, interleukin (IL)-3, and cyclins A2, B1, E1, and D1 [11], [12].
The exact mechanisms by which HuR is able
Regulation of HuR function
According with the involvement of HuR in many important biological processes, its function is tightly regulated at many levels: abundance and integrity of the protein, subcellular localization and post-translational modification. The levels of HuR protein are regulated in many ways. Among them, we can find:
Regulation of HuR localization
Although HuR is predominantly nuclear, the best characterized HuR functions take place in the cytoplasm. Together with the HuR HNS domain, several transport machinery components are also necessary, including transportin 1, transportin 2 and CRM1 (chromosome region maintenance 1) [35], [36]. The phosphorylation of HuR by Cdk1, AMPK, PKC and p38 also influences HuR transport.
Together with the ubiquitination, HuR is also posttranslationally modified by several kinases and by methylation. These
HuR and cancer traits
Hu/elav family has been involved in most malignancies: breast, colon, stomach, kidney, pancreas, esophagus, prostate, skin, lung, etc. [44]. Indeed, numerous HuR-regulated mRNAs have been identified to directly contribute to the acquisition of the cancer traits, including enhanced ability to proliferate, enhanced cell survival, elevation of local angiogenesis, evasion of immune recognition, and invasion and metastasis (Fig. 2) [12].
Implication of HuR in specific cancer types
Taking into account the regulation of the cancer traits targeted by HuR, numerous studies have examined the levels of this RBP in individual cancer types.
HuR was found misregulated in breast, pancreatic, ovarian, oral, lung, gastric, pharyngeal and nervous system cancers.
HuR was identified as an important prognostic factor in breast, pancreatic and ovarian cancers. In colon cancer tissues, the expression and localization of HuR was associated with advanced tumor stage [11], [12].
The role of HuR
NEDDylation: protein stabilization and post-translational modification
The ubiquitin-like (UBL) molecule NEDD8 (neural precursor cell-expressed developmentally downregulated-8) is the protein involved in the NEDDylation, a post-translational modification of the proteins involved in several processes such as cell growth, viability and development. NEDD8 was identified in 1992 and the analysis of the sequence found a 60% amino acid identity with Ub [47], [48]. NEDD8 appears as mainly nuclear, and is highly conserved in most eukaryotes and expressed in most tissues,
NEDD8 conjugating cascade
Similar to Ub, NEDD8 attaches covalently to a lysine in the target protein. The NEDD8 conjugation cascade involves E1, E2, E3 and deNEDDylating enzymes. NEDD8 is first synthesized as a precursor processed at the Gly76 residue by NEDP1 (NEDD8 protease 1) and UCH-L3 (Ubiquitin carboxyl-terminal hydrolase L3) deNEDDylases. After this, the C-terminal glycine of NEDD8 is activated by the E1 NEDD8-activating enzyme (NAE), composed of APP-BP1 (APP binding protein 1) and Uba3 (ubiquitin-like modifier
NEDD8 substrates
Until recently, the only known substrates for the NEDDylation were the members of the cullin family of proteins [49]. Cullins interact with RING finger proteins to enable the recruitment of E2 enzymes [58]. These cullin-RING ligase complexes (CRLs) target numerous substrates for ubiquitination, which is increased by NEDDylation, and thus have an impact on cellular processes such as cell growth, development, signal transduction, transcriptional control, genomic integrity and tumor suppression
NEDD8 relation with cancer
As commented above, the NEDDylation of many substrates (cullins, p53, Mdm2, p73, BCA3, L11 ribosomal protein, EGFR) is related with tumorigenesis [51]. Many of the substrates of the CRL have been involved in cancer; the misregulation of the CRLs NEDDylation modifies the ubiquitination of their substrates, thus producing impairment in DNA replication, cell cycle progression, stress responses, etc.
Recently, it was generated an inhibitor of the NAE, MLN4924, that blocks substrate NEDDylation. This
NEDDylation in liver cancer
Taking in consideration the role of HuR in liver tumorigenesis and its tightly regulated levels, we provided new mechanisms involving the post-translational modification NEDD8 that explains the overexpression of HuR in HCC and colon cancer. There is a strong and positive correlation between the levels of HuR and Mdm2 in a cohort of human HCC and metastatic colon cancer to the liver. This correlation was corroborated by the findings that, according with the transformation status of the cells,
Financial support
This work is supported ETORTEK-2012 (to M.L.M.-C), Sanidad del Gobierno Vasco 2013 (to M.L.M.-C), FIS PI11/01588 (to M.L.M.-C), CIBERehd is funded by the Instituto de Salud Carlos III.
Author contribution
David Fernández-Ramos. Acquisition of data; analysis and interpretation of data. Critical revision of the manuscript.
María L Martínez-Chantar. Study concept and design; analysis and interpretation of data; study supervision; drafting of the manuscript; obtained funding.
References (67)
- et al.
Cloning and characterization of HuR, a ubiquitously expressed elav-like protein
J Biol Chem
(1996) - et al.
Integrative regulatory mapping indicates that the RNA-binding protein HuR (ELAVL1) couples pre-mRNA processing and mRNA stability
Mol Cell
(2011) - et al.
UneCLIPsing HuR nuclear function
Mol Cell
(2011) The yin and yang of the exosome
Trends Cell Biol
(2002)- et al.
A KH domain RNA binding protein, KSRP, promotes ARE-directed mRNA turnover by recruiting the degradation machinery
Mol Cell
(2004) - et al.
Relief of microRNA-mediated translational repression in human cells subjected to stress
Cell
(2006) - et al.
Phosphorylation of HuR by Chk2 regulates SIRT1 expression
Mol Cell
(2007) - et al.
Lipopolysaccharide-induced methylation of HuR, an mRNA-stabilizing Protein, by CARM1
J Biol Chem
(2002) - et al.
Characterization of NEDD8, a developmentally down-regulated ubiquitin-like protein
J Biol Chem
(1997) - et al.
Identification of a set of genes with developmentally down-regulated expression in the mouse brain
Biochem Biophys Res Commun
(1992)
NEDD8 pathways in cancer, sine quibus non
Cancer Cell
FBXO11 promotes the neddylation of p53 and inhibits its transcriptional activity
J Biol Chem
Conjugation to Nedd8 instigates ubiquitylation and down-regulation of activated receptor tyrosine kinases
J Biol Chem
Mdm2-Mediated NEDD8 conjugation of p53 inhibits its transcriptional activity
Cell
NEDP1, a highly conserved cysteine protease that deNEDDylates cullins
J Biol Chem
A general approach for investigating enzymatic pathways and substrates for ubiquitin-like modifiers
Arch Biochem Biophys
Mdm2-mediated NEDD8 modification of TAp73 regulates its transactivation function
J Biol Chem
YB-1 as a cell cycle-regulated transcription factor facilitating cyclin a and cyclin B1 gene expression
J Biol Chem
The RNA-binding protein HuD: a regulator of neuronal differentiation, maintenance and plasticity
BioEssays News Rev Mol Cell Dev Biol
Defining a neuron: neuronal ELAV proteins
Cell Mol Life Sci CMLS
HuR and mRNA stability
Cell Mol Life Sci
Posttranscriptional gene regulation by RNA-binding proteins during oxidative stress: implications for cellular senescence
Biol Chem
Diverse molecular functions of Hu proteins
Cell Mol Life Sci CMLS
A conserved family of elav-like genes in vertebrates
Proc Natl Acad Sci U S A
HNS, a nuclear-cytoplasmic shuttling sequence in HuR
Proc Natl Acad Sci U S A
HuR function in disease
Front Biosci
Posttranscriptional regulation of cancer traits by HuR
Wiley Interdiscip Rev RNA
The mammalian exosome mediates the efficient degradation of mRNAs that contain AU-rich elements
EMBO J
The GW182 protein colocalizes with mRNA degradation associated proteins hDcp1 and hLSm4 in cytoplasmic GW bodies
RNA
Stress granules and processing bodies are dynamically linked sites of mRNP remodeling
J Cell Biol
RNA-binding protein HuR mediates cytoprotection through stimulation of XIAP translation
Oncogene
RNA-binding protein HuR enhances p53 translation in response to ultraviolet light irradiation
Proc Natl Acad Sci U S A
Translational control of cytochrome c by RNA-binding proteins TIA-1 and HuR
Mol Cell Biol
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