Alternate exon insertion controls selective ubiquitination and degradation of different AUF1 protein isoforms

Laroia, Gaurav; Schneider, Robert J.

doi:10.1093/nar/gkf444

Cited by 63 publications

(57 citation statements)

References 59 publications

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“…This domain structure is shared by many other hnRNP proteins (18,21). It has four isoforms, p37, p40, p42, and p45, that are the result of alternative splicing of exon 2 and exon 7 (20,22). AUF1 has also been described to participate in other regulatory mechanisms.…”

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confidence: 99%

AUF1 Is Expressed in the Developing Brain, Binds to AT-rich Double-stranded DNA, and Regulates Enkephalin Gene Expression

Dobi

Szemes

Lee

et al. 2006

Journal of Biological Chemistry

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During our search for transcriptional regulators that control the developmentally regulated expression of the enkephalin (ENK) gene, we identified AUF1. ENK, a peptide neurotransmitter, displays precise cell-specific expression in the adult brain. AUF1 (also known as heterogeneous nuclear ribonucleoprotein D) has been known to regulate gene expression through altering the stability of AU-rich mRNAs. We show here that in the developing brain AUF1 proteins are expressed in a spatiotemporally defined manner, and p37 and p40/42 isoforms bind to an AT-rich double-stranded (ds) DNA element of the rat ENK (rENK) gene. This AT-rich dsDNA sequence acts as a cis-regulatory DNA element and is involved in regulating the cell-specific expression of the ENK gene in primary neuronal cultures. The AT-rich dsDNA elements are present at ϳ2.5 kb 5 upstream of the rat, human, and mouse ENK genes. AUF1 proteins are shown here to provide direct interaction between these upstream AT-rich DNA sequences and the TATA region of the rENK gene. Double immunohistochemistry demonstrated that in the developing brain AUF1 proteins are expressed by proliferating neural progenitors and by differentiating neurons populating brain regions, which will not express the ENK gene in the adult, suggesting a repressor role for AUF1 proteins during enkephalinergic differentiation. Their subnuclear distribution and interactions with AT-rich DNA suggest that in the developing brain they can be involved in complex nuclear regulatory mechanisms controlling the development-and cell-specific expression of the ENK gene.The expression of the ENK 3 gene in the adult brain is highly cell-specific and spatially restricted. Many enkephalinergic neurons (i.e. express the ENK gene and use enkephalin peptides as neurotransmitters) are in the striatum (caudate putamen), and most of the other brain structures, such as cerebral cortex, are devoid of enkephalinergic neurons (1). This contrasting distribution is the result of the developmental process.ENK is a single copy gene encoding for preproenkephalin polypeptide, which is proteolytically cleaved, yielding four copies of Met-enkephalin and one copy of Leu-enkephalin peptides, which are endogenous ligands of opiate receptors (2). Enkephalins in the basal forebrain mediate social behavior, aggression, and reward and are implicated in mediating euphoric properties of drugs.The identity of neurons is established during neurodevelopment when multipotent progenitors differentiate into their various neurotransmitter phenotypes (3). Enkephalinergic differentiation, the cell-specific expression of the ENK gene, i.e. in spiny projection neurons in the striatum, takes place between embryonic day 14 (E14) and postnatal day 2 (P2) in the rat (4). It is during this period when transcription factors that directly regulate the developmental expression of neurotransmitter genes, such as ENK, are specifically expressed. They bind to cis-regulatory DNA elements and regulate the expression of their target genes, such as ENK (5), by restrict...

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confidence: 99%

AUF1 Is Expressed in the Developing Brain, Binds to AT-rich Double-stranded DNA, and Regulates Enkephalin Gene Expression

Dobi

Szemes

Lee

et al. 2006

Journal of Biological Chemistry

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“…The significance of these alternatively spliced forms has been elucidated for members of the hnRNP families A/B, D, and I. For example, the stabilities of human hnRNP D isoforms are differentially controlled by the insertion of an alternate exon that regulates their ubiquitin targeting activities (12). Different isoforms of hrp40, a Drosophila hnRNP A/B homolog, play distinct roles in Gurken localization during oogenesis (13).…”

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confidence: 99%

The Drosophila Heterogeneous Nuclear Ribonucleoprotein M Protein, HRP59, Regulates Alternative Splicing and Controls the Production of Its Own mRNA

Hase

Yalamanchili

Visa

2006

Journal of Biological Chemistry

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The Drosophila heterogeneous nuclear ribonucleoprotein M, HRP59, is a nuclear protein that associates co-transcriptionally with pre-mRNA and is necessary for the correct expression of a subset of mRNAs. We show here that the hrp59 pre-mRNA is alternatively spliced to generate two different mRNAs that differ in the presence of exon 3. Exon 3-containing transcripts make up the majority of hrp59 transcripts and encode for the functional protein, HRP59-1. Transcripts that lack exon 3 contain a premature translation termination codon and are targeted to the nonsense mediated decay pathway. We show that exon 3 inclusion is itself inhibited by HRP59 and that changes in the HRP59 protein levels affect the splicing activity of the cell. We propose that the ability of HRP59 to regulate the alternative splicing of its own pre-mRNA serves in a negative feedback loop that controls the levels of the HRP59 protein and maintains the homeostasis of the splicing environment.Pre-mRNAs associate co-transcriptionally with a variety of RNA-binding proteins known as hnRNP 2 proteins or mRNP proteins (reviewed in Refs. 1 and 2). hnRNP proteins exist in all eukaryotes and are evolutionarily conserved. More than 20 hnRNP proteins have been identified in human cells, and these have been designated from A1 to U (reviewed in Ref. 2). Although the degree of homology at the amino acid level is not very high, hnRNP proteins from different organisms share the same types of domain and the same domain organization. In Drosophila melanogaster, more than 10 hnRNP proteins have been identified (3-6).hnRNP proteins are abundant nuclear proteins and they play a general role in the packaging of nascent transcripts into ribonucleoprotein complexes (pre-mRNP). Many hnRNP proteins also have specific functions in gene expression. For instance, in the cell nucleus the mammalian hnRNP K interacts with the transcription machinery and stimulates transcription (7), while in the cytoplasm hnRNP K controls translation initiation of specific mRNAs (8). hnRNP I, also known as polypyrimidine tract-binding protein, plays a role in mRNA stability and mRNA localization (9, 10).hnRNP proteins are modular and characterized by the presence of one or more RNA-binding motifs and auxiliary domains of different types (reviewed in Ref. 11). Several hnRNP genes generate multiple isoforms through alternative splicing. The significance of these alternatively spliced forms has been elucidated for members of the hnRNP families A/B, D, and I. For example, the stabilities of human hnRNP D isoforms are differentially controlled by the insertion of an alternate exon that regulates their ubiquitin targeting activities (12). Different isoforms of hrp40, a Drosophila hnRNP A/B homolog, play distinct roles in Gurken localization during oogenesis (13). Alternative skipping of exon 11 in the human hnRNP I transcript leads to the production of a mRNA that is degraded by the nonsense-mediated decay (NMD) pathway (14). Exon 11 skipping is promoted by hnRNP I itself, and thus it has been propose...

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“…The localisation of AUF1 can be influenced by a variety of factors including: the presence or absence of exons containing nuclear localisation signals [33,34]; interaction with transporters [35] or chaperones [36,37]; protein ubiquitination [13]; and phosphorylation of specific residues [7,38]. At steady-state, most AUF1 isoforms accumulate in the nucleus but are partially relocalised upon exposure of insulin-secreting cells to proinflammatory cytokines.…”

Section: Discussionmentioning

confidence: 99%

“…The production of these isoforms varies between cell types and developmental stages and can be modified in response to different stimuli [12]. Moreover, AUF1 isoforms are subjected to post-translational modifications that affect the activation state of the RNA-binding protein in a cell-type and treatment-dependent manner [13,14].…”

Section: Introductionmentioning

confidence: 99%

Involvement of the RNA-binding protein ARE/poly(U)-binding factor 1 (AUF1) in the cytotoxic effects of proinflammatory cytokines on pancreatic beta cells

et al. 2011

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Aims/hypothesis Chronic exposure of pancreatic beta cells to proinflammatory cytokines leads to impaired insulin secretion and apoptosis. ARE/poly(U)-binding factor 1 (AUF1) belongs to a protein family that controls mRNA stability and translation by associating with adenosine-and uridine-rich regions of target messengers. We investigated the involvement of AUF1 in cytokine-induced beta cell dysfunction. Methods Production and subcellular distribution of AUF1 isoforms were analysed by western blotting. To test for their role in the control of beta cell functions, each isoform was overproduced individually in insulin-secreting cells. The contribution to cytokine-mediated beta cell dysfunction was evaluated by preventing the production of AUF1 isoforms by RNA interference. The effect of AUF1 on the production of potential targets was assessed by western blotting. Results MIN6 cells and human pancreatic islets were found to produce four AUF1 isoforms (p42>p45>p37>p40). AUF1 isoforms were mainly localised in the nucleus but were partially translocated to the cytoplasm upon exposure of beta cells to cytokines and activation of the ERK pathway. Overproduction of AUF1 did not affect glucose-induced insulin secretion but promoted apoptosis. This effect was associated with a decrease in the production of the antiapoptotic proteins, B cell leukaemia/lymphoma 2 (BCL2) and myeloid cell leukaemia sequence 1 (MCL1). Silencing of AUF1 isoforms restored the levels of the anti-apoptotic proteins, attenuated the activation of the nuclear factor-κB (NFκB) pathway, and protected the beta cells from cytokineinduced apoptosis. Conclusions/interpretation Our findings point to a contribution of AUF1 to the deleterious effects of cytokines on beta cell functions and suggest a role for this RNA-binding protein in the early phases of type 1 diabetes.

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Alternate exon insertion controls selective ubiquitination and degradation of different AUF1 protein isoforms

Cited by 63 publications

References 59 publications

AUF1 Is Expressed in the Developing Brain, Binds to AT-rich Double-stranded DNA, and Regulates Enkephalin Gene Expression

AUF1 Is Expressed in the Developing Brain, Binds to AT-rich Double-stranded DNA, and Regulates Enkephalin Gene Expression

The Drosophila Heterogeneous Nuclear Ribonucleoprotein M Protein, HRP59, Regulates Alternative Splicing and Controls the Production of Its Own mRNA

Involvement of the RNA-binding protein ARE/poly(U)-binding factor 1 (AUF1) in the cytotoxic effects of proinflammatory cytokines on pancreatic beta cells

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