Stability Determinants Are Localized to the 3′-Untranslated Region and 3′-Coding Region of the Neurofilament Light Subunit mRNA Using a Tetracycline-inducible Promoter

Abstract

The tetracycline-responsive expression system of Bujard was used to compare rates of decay of wild-type and mutant neurofilament (NF) light subunit (NF-L) mRNAs. Optimal conditions for activation and inactivation of the target transgene were determined using a luciferase reporter gene. Analyses of mRNA stability were thereupon conducted on cells that were doubly transfected with transactivator and inducible target genes and derived from pooled clones of transfected cells. Rates of mRNA decay were compared upon inactivation of the transgenes after high levels of mRNA had been induced. Altering mRNA stability is a universal post-transcriptional mechanism for modulating gene expression during growth, development and differentiation. Post-transcriptional regulation may be particularly important in cells, such as neurons, that undergo extensive differentiation and change after cessation of cell division. Alterations in mRNA stability are known to affect the levels of several key proteins in post-mitotic neurons (2-5). Increases in mRNA stability accompany the postnatal up-regulation in neurofilament (NF) 1 expression and are, therefore, instrumental in determining the size and shape of neuronal processes (6, 7). Moreover, levels of NF expression have been implicated in motoneuron disease by virtue of the selective motoneuron degeneration that occurs when a light (NF-L) or heavy (NF-H) subunit transgene is overexpressed in transgenic mice (8, 9). A transient up-regulation of endogenous NF mRNA also precedes the spontaneous motoneuron degeneration in the Wobbler mice (10).Functional assays for mapping stability determinants use a variety of methods to compare stabilities of mutant versus wild-type mRNAs (11). Most of these methods are limited by their disruptive or pleiotrophic effects on the host cells and are, therefore, especially problematic for assessing stabilities of long-lived mRNAs. An alternative method is provided by the development of the tetracycline-responsive promoter system whereby target gene expression is stringently controlled by a non-toxic antibiotic ligand (12-19). Here, we have adapted this system to assess mRNA stability in neuronal and non-neuronal cell lines and to map stability determinants in the NF-L transcript. The method has enabled the identification of stability determinants in the 3Ј-CR and 3Ј-UTR of the NF-L mRNA and have localized a key determinant to a 68-nt sequence at the junction of the 3Ј-CR and 3Ј-UTR. EXPERIMENTAL PROCEDURESPlasmids-pUHD15.1, pUHD10.3, and pUHD13.3 were a generous gift of Dr. H. Bujard. pUHD15.1M is a modified expression vector that was rendered autoinducible (see Ref. 16) by placing an EcoRI site and consensus translation start sequence immediately upstream of the tTA open reading frame and subcloning the EcoRI/BamHI PCR fragment from pUHD15.1 into the polylinker of pUHD10.3. Fig. 1) were constructed by splicing together three PCR fragments. Fragment 1 extended from ϩ1 to a BglII site at ϩ829 in exon 1, fragment 2 extended from ϩ829 to a KpnI site at ϩ1208, a...

Mutant Copper-Zinc Superoxide Dismutase Binds to and Destabilizes Human Low Molecular Weight Neurofilament mRNA

“…Murine NFL mRNA cis-acting elements are present in the 3Ј-coding region (3Ј-CR) and 3Ј-UTR of the NFL mRNA (18,19). Deletion of the 3Ј-UTR or 527 nt of the 3Ј-CR increased the stability of murine NFL mRNA compared with the full-length transcript in cell lines.…”

“…Cloning and Expression of hNFL Genes-Because of the limitations in the length of an RNA probe for RNA-protein binding assays, the last 1000 nt of hNFL mRNA, including the 3Ј-untranslated region (hNFL-1000), which contains the putative major stability regulatory elements (18), was RT-PCR amplified from an ALS patient RNA sample and cloned into pcDNA3.1(ϩ) as the representative for the full-length hNFL (16). hNFL cDNA devoid of the 3Ј-untranslated region (hNFL-CDS) was also amplified and cloned.…”

“…It is possible that the binding sites for hNFL mRNA on the SOD1 protein may have been blocked by antibody, thus entirely eliminating the probe binding. The major ribonucleoprotein binding and regulatory sequence on murine NFL mRNA is located in the 3Ј-UTR of the mRNA (18,19), suggesting that possible binding sites for mutant SOD1 on hNFL could also fall into that region. We assessed this possibility with North-Western blotting (Fig.…”

Aldolases A and C Are Ribonucleolytic Components of a Neuronal Complex That Regulates the Stability of the Light-Neurofilament mRNA

“…It was shown that a 68 nucleotide (nt) segment of the NF-L mRNA was essential for NF-L mRNA stabilization in neuronal cells (Cañete-Soler et al, 1998a) (Fig. 1 A).…”

Fending off decay: A combinatorial approach in intact cells for identifying mRNA stability elements

“…Messenger RNA is a key molecule in cell biology and the control of transcription plays a critical role in gene expression+ It is not, however, simply the rate of production but the rate of mRNA decay that controls gene expression within cells+ In most instances, mRNA stability and expression are effected by interplay of cisacting elements in the nucleic acid with RNA-binding proteins acting in trans+ Control of these RNA-protein interactions is not just fundamentally important to our understanding of cell biology, but is important in the pathogenesis of disease+ Changes in mRNA stability, for example, have been implicated in the etiology of several neurological disorders (Amara et al+, 1999;Canete-Soler et al+, 1999), rheumatoid arthritis (Jeddi et al+, 1994), and systemic scleroderma (Eckes et al+, 1996)+ Differences in stability can vary over several orders of magnitude, with half-lives ranging from several minutes for human lymphokine and cytokine mRNAs (Ross, 1995), to many hours for transcripts encoding members of the globin family (Weiss & Liebhaber, 1995) or respiratory chain components (ChrzanowskaLightowlers et al+, 1994)+ Stabilities of numerous mRNA species are known to be regulated in response to many forms of external stimuli, during development or at certain stages of the cell cycle+ In most instances, it is the 39 UTR that harbors the cis-acting sequences that are important in stability (Chkheidze et al+, 1999;Jacobs Anderson & Parker, 2000;Mitchell & Tollervey, 2000), although examples outside this region have been identified (Canete-Soler et al+, 1998)+ Since the observation that an AU-rich element introduced into the 39 UTR of transcripts could mediate selective mRNA degradation (Shaw & Kamen, 1986), research has focused on characterizing this element (Chen & Shyu, 1995;Rajagopalan & Malter, 1996;Di Noia et al+, 2000), the trans-acting proteins (SelaBrown et al+, 2000), and their importance in regulating mRNA decay+ Although the factors defining rapid degradation began to be identified a decade ago (Shaw & Kamen, 1986), less has been achieved in identifying determinants that increase transcript stability+ Polypyrimidine elements have been found in the 39 UTRs of several long-lived mRNA species (Czyzyk-Krzeska & Beresh, 1996)+ Additionally, a family of poly-C binding proteins with homology to the hnRNP K polypeptides were shown to bind to the 39 UTR stability element in b-globin mRNA (Chkheidze et al+, 1999)+ Originally found in erythroid cells, this family of poly-C bindin...…”