An Iron-responsive Element Type II in the 5′-Untranslated Region of the Alzheimer's Amyloid Precursor Protein Transcript

Abstract

Iron-responsive elements (IREs) are the RNA stem loops that control cellular iron homeostasis by regulating ferritin translation and transferrin receptor mRNA stability. We mapped a novel iron-responsive element (IRE-Type II) within the 5-untranslated region (5-UTR) of the Alzheimer's amyloid precursor protein (APP) transcript (؉51 to ؉94 from the 5-cap site). The APP mRNA IRE is located immediately upstream of an interleukin-1 responsive acute box domain (؉101 to ؉146). APP 5-UTR conferred translation was selectively downregulated in response to intracellular iron chelation using three separate reporter assays (chloramphenicol acetyltransferase, luciferase, and red fluorescent protein reflecting an inhibition of APP holoprotein translation in response to iron chelation. Iron influx reversed this inhibition. As an internal control to ensure specificity, a viral internal ribosome entry sequence was unresponsive to intracellular iron chelation with desferrioxamine. Using RNA mobility shift assays, the APP 5-UTRs, encompassing the IRE, bind specifically to recombinant iron-regulatory proteins (IRP) and to IRP from neuroblastoma cell lysates. IRP binding to the APP 5-UTR is reduced after treatment of cells with desferrioxamine and increased after interleukin-1 stimulation. IRP binding is abrogated when APP cRNA probe is mutated in the core IRE domain (⌬4 bases:⌬83AGAG86). Iron regulation of APP mRNA through the APP 5-UTR points to a role for iron in the metabolism of APP and confirms that this RNA structure can be a target for the selection of small molecule drugs, such as desferrioxamine (Fe chelator) and clioquinol (Fe, Cu, and Zn chelator), which reduce A␤ peptide burden during Alzheimer's disease. The amyloid precursor protein (APP)1 is cleaved into the 40 -42-amino acid A␤ peptides that constitute the main component of the neurotoxic amyloid plaques formed during the progression of Alzheimer's disease (AD) and Down's syndrome (1, 2). In healthy individuals, APP holoprotein is expressed ubiquitously as a protein resembling a type I transmembrane receptor and metal-binding protein (3-6). Secreted APP (APP(s)) is neurotrophic (7).There are now several reports supporting an important role for translational regulatory mechanisms to control APP synthesis and probably A␤ peptide secretion in biologically relevant circumstances (8). First, interleukin-1 (IL-1), the first cytokine released during the acute phase response, significantly increases APP protein synthesis in astrocytes without altering APP mRNA levels (9). IL-1 acts by regulating APP and ferritin genes at the level of message translation (9). Second, reversible ischemic assault significantly increases APP levels without any alteration in the steady-state levels of APP mRNA in rabbit spinal cord neurons (10). Third, APP mRNA 3Ј-UTR sequences located between alternative poly(A) selection sites maintain efficient translation of microinjected APP in Xenopus oocytes and in Chinese hamster ovary transfectants (11).Iron-responsive elements (IREs) are RNA stem loops...

Biology of ferritin in mammals: an update on iron storage, oxidative damage and neurodegeneration

“…A direct relationship between iron level and A production has been recently observed also in a transgenic mouse model of AD, together with perturbation of the glutamatergic neurotransmission (Becerril-Ortega et al 2014). If one considers that iron levels regulates APP expression through an IRE in its mRNA (Rogers et al 2002) and that APP itself may participate in the ferroportin-dependent iron efflux from the cells acting as a ferroxidase (Duce et al 2010), it is then possible that the capacity of ferritin to control iron homeostasis in neural cells may be central in the pathogenesis of AD.…”

The 5′-untranslated region of Parkinson's disease α-synuclein messengerRNA contains a predicted iron responsive element

“…Iron homeostasis is achieved in part by post-transcriptional regulation through highly conserved messenger RNA (mRNA) stem loops called iron regulatory elements (IREs), which are present in the untranslated regions (UTRs) of a number of transcripts essential to iron metabolism. 7,8 Here we provide the first report of a putative IRE in the 5 0 -UTR of mRNA encoding the 140-residue a-synuclein and predict that this RNA structure posttranscriptionally regulates a-synuclein protein production in response to cellular iron and redox events.…”

“…Furthermore, it would provide an explanation for the well-characterized neuropathologic association of a-synuclein and the Alzheimer b-amyloid protein 3 since the Alzheimer bamyloid precursor protein mRNA also contains an IRE in its 5 0 -UTR. 8 If and how the IRE-like structure in asynuclein mRNA functions as a post-transcriptional regulator now awaits experimental clarification. Cocaine-amphetamine-regulated transcript (CART) gene was identified in 1995 in a search for mRNAs in the striatum acutely upregulated by psychostimulants.…”

“…7 Furthermore, CART knockout mice displayed increased body weight, and marked reduction of the expression of some important genes, such as pancreatic duodenal homeobox 1 (PDX-1) and glucose transporter-2 (GLUT-2) in pancreatic islets. 8 Thus, we tested the hypothesis that CART may have transcription function by a putative approach 9 in mammalian cells.…”

Biometals and Their Therapeutic Implications in Alzheimer's Disease

“…APP has a 5′ untranslated region ironresponsive element [140]; in conditions of high iron (e.g., AD) restricted translation of APP by iron-responsive proteins is disinhibited, leading to increased translation of the transcript. High iron conditions also leads to increased processing of APP [141], which leads to accelerated degeneration in a mouse model of AD [142].…”