Dysregulation of Hypoxia-Inducible Factor by Presenilin/ Gamma-Secretase Loss-of-Function Mutations

Presenilin (PSEN) 1 and 2 are the catalytic components of the Gamma-secretase complex, which cleaves a variety of proteins, including the amyloid precursor protein (APP). Proteolysis of APP leads to the formation of the APP intracellular domain (AICD) and amyloid Beta that is crucially involved in the pathogenesis of Alzheimer’s disease. Prolyl-4-hydroxylase-domain (PHD) proteins regulate the hypoxia inducible factors (HIFs), the master regulators of the hypoxic response.Wepreviously identified the FK506 binding protein 38 (FKBP38)as a negative regulator of PHD2. Genetic ablation of PSEN1/2 has been shown to increase FKBP38 protein levels. Therefore, we investigated the role of PSEN1/2 in the oxygen sensing pathway using a variety of genetically modified cell and mouse lines. Increased FKBP38 protein levels and decreased PHD2 protein levels were found in PSEN1/2-deficient mouse embryonic fibroblasts and in the cortex of forebrain-specific PSEN1/2 conditional double knock-out mice. Hypoxic HIF-1alpha protein accumulation and transcriptional activity were decreased, despite reduced PHD2 protein levels. Proteolytic gamma-secretase function ofPSEN1/2wasneeded for proper HIF activation. Intriguingly, PSEN1/2 mutations identified in Alzheimer patients differentially affected the hypoxicresponse, involving the generation of AICD. Together,our results suggest a direct role for PSEN in the regulation of the oxygen sensing pathway via the APP/AICD cleavage cascade

Delta1 Expression, Cell Cycle Exit, and Commitment to a Specific Secretory Fate Coincide within a Few Hours in the Mouse Intestinal Stem Cell System

The stem cells of the small intestine are multipotent: they give rise, via transit-amplifying cell divisions, to large numbers of columnar absorptive cells mixed with much smaller numbers of three different classes of secretory cells - mucus-secreting goblet cells, hormone-secreting enteroendocrine cells, and bactericide-secreting Paneth cells. Notch signaling is known to control commitment to a secretory fate, but why are the secretory cells such a small fraction of the population, and how does the diversity of secretory cell types arise? Using the mouse as our model organism, we find that secretory cells, and only secretory cells, pass through a phase of strong expression of the Notch ligand Delta1 (Dll1). Onset of this Dll1 expression coincides with a block to further cell division and is followed in much less than a cell cycle time by expression of Neurog3 – a marker of enteroendocrine fate – or Gfi1 – a marker of goblet or Paneth cell fate. By conditional knock-out of Dll1, we confirm that Delta-Notch signaling controls secretory commitment through lateral inhibition. We infer that cells stop dividing as they become committed to a secretory fate, while their neighbors continue dividing, explaining the final excess of absorptive over secretory cells. Our data rule out schemes in which cells first become committed to be secretory, and then diversify through subsequent cell divisions. A simple mathematical model shows how, instead, Notch signaling may simultaneously govern the commitment to be secretory and the choice between alternative modes of secretory differentiation

Do genetic factors protect for early onset lung cancer? A case control study before the age of 50 years

<p>Abstract</p> <p>Background</p> <p>Early onset lung cancer shows some familial aggregation, pointing to a genetic predisposition. This study was set up to investigate the role of candidate genes in the susceptibility to lung cancer patients younger than 51 years at diagnosis.</p> <p>Methods</p> <p>246 patients with a primary, histologically or cytologically confirmed neoplasm, recruited from 2000 to 2003 in major lung clinics across Germany, were matched to 223 unrelated healthy controls. 11 single nucleotide polymorphisms of genes with reported associations to lung cancer have been genotyped.</p> <p>Results</p> <p>Genetic associations or gene-smoking interactions was found for <it>GPX1(Pro200Leu) </it>and <it>EPHX1(His113Tyr)</it>. Carriers of the Leu-allele of <it>GPX1(Pro200Leu) </it>showed a significant risk reduction of OR = 0.6 (95% CI: 0.4–0.8, p = 0.002) in general and of OR = 0.3 (95% CI:0.1–0.8, p = 0.012) within heavy smokers. We could also find a risk decreasing genetic effect for His-carriers of <it>EPHX1(His113Tyr) </it>for moderate smokers (OR = 0.2, 95% CI:0.1–0.7, p = 0.012). Considered both variants together, a monotone decrease of the OR was found for smokers (OR of 0.20; 95% CI: 0.07–0.60) for each protective allele.</p> <p>Conclusion</p> <p>Smoking is the most important risk factor for young lung cancer patients. However, this study provides some support for the T-Allel of <it>GPX1(Pro200Leu) </it>and the C-Allele of <it>EPHX1(His113Tyr) </it>to play a protective role in early onset lung cancer susceptibility.</p

AICD nuclear signaling and its possible contribution to Alzheimer's disease

Altered proteolytic processing of the β-amyloid precursor protein (APP) is a central event in familial and sporadic Alzheimer's disease (AD). In a process termed regulated intramembrane proteolysis (RIP), APP first undergoes ectodomain shedding executed either by α- secretases at the plasma membrane or by β-secretase in the endosomal compartment. The remaining membrane-anchored stubs are cleaved within the membrane plane by the γ-secretase complex, releasing the APP intracellular domain (AICD) into the cytosol and leading to the generation of the Aβ peptide in the amyloidogenic pathway that is initiated by β-secretase. The Aβ peptides aggregate to form soluble oligomers and finally deposit into amyloid plaques that are a hallmark of AD. Recent evidence indicates a role for Aβ oligomers in regulating synaptic plasticity with excess amounts of oligomers disrupting synaptic function. The amyloid cascade hypothesis of AD is centered on the Aβ peptide, the APP fragment that has been most intensely studied, while other cleavage products have been largely neglected. The secreted ectodomain generated after α-cleavage in the non-amyloidogenic pathway has neurotrophic and neuroproliferative activities, thus opposing the neurotoxicity observed with high concentrations of Aβ. Further, in analogy to many other membrane proteins that are subject to RIP, AICD can translocate to the nucleus to regulate transcription. Many RIP substrates are localized to the synapse and thus could convey a direct signal from the synapse to the nucleus upon cleavage. Evidence indicates that only the amyloidogenic pathway generates AICD capable of nuclear signaling, due to the subcellular compartmentalization of APP processing. In aging and sporadic AD there is an increase in β-secretase levels and activity generating more Aβ peptides and concomitantly leading to an increase in AICD nuclear signaling. In this review, I summarize the current knowledge on AICD nuclear signaling and propose mechanisms to explain how this physiological function of APP might impact the pathology seen in AD

A subtractive hybridisation method for the enrichment of moderately induced sequences.

Moderately induced genes often escape detection in conventional subtraction hybridisation cloning. Here a modification of a phagemid subtraction protocol is described that overcomes this problem. The protocol uses low ratio hybridisation of driver to target sequences to allow enrichment of the sequences of interest, and back-hybridisation of the subtracted sequences with induced sequences to reduce the accumulation of false positive clones. The procedure takes advantage of the quantitative representation of cellular RNA populations in cDNA libraries, therefore, they may serve not only as renewable sources of driver and target sequences, but also as sources of population cRNAs used in northern blots and differential Southern blots

Abeta oligomer-mediated long-term potentiation impairment involves protein phosphatase 1-dependent mechanisms

Amyloid beta (Abeta) oligomers are derived from proteolytic cleavage of amyloid precursor protein (APP) and can impair memory and hippocampal long-term potentiation (LTP) in vivo and in vitro. They are recognized as the primary neurotoxic agents in Alzheimer's disease. The mechanisms underlying such toxicity on synaptic functions are complex and not fully understood. Here, we provide the first evidence that these mechanisms involve protein phosphatase 1 (PP1). Using a novel transgenic mouse model expressing human APP with the Swedish and Arctic mutations that render Abeta more prone to form oligomers (arcAbeta mice), we show that the LTP impairment induced by Abeta oligomers can be fully reversed by PP1 inhibition in vitro. We further demonstrate that the genetic inhibition of endogenous PP1 in vivo confers resistance to Abeta oligomer-mediated toxicity and preserves LTP. Overall, these results reveal that PP1 is a key player in the mechanisms of AD pathology

Nuclear signaling by the APP intracellular domain occurs predominantly through the amyloidogenic processing pathway

Proteolytic processing of the amyloid precursor protein (APP) occurs via two alternative pathways, localized to different subcellular compartments, which result in functionally distinct outcomes. Cleavage by a beta-gamma sequence generates the Abeta peptide that plays a central role in Alzheimer's disease. In the case of alpha-gamma cleavage, a secreted neurotrophic molecule is generated and the Abeta peptide cleaved and destroyed. In both cases, a cytosolic APP intracellular domain (AICD) is generated. We have previously shown that coexpression of APP with the APP-binding protein Fe65 and the histone acetyltransferase Tip60 results in the formation of nuclear complexes (termed AFT complexes), which localize to transcription sites. We now show that blocking endocytosis or the pharmacological or genetic inhibition of the endosomal beta-cleavage pathway reduces translocation of AICD to these nuclear AFT complexes. AICD signaling further depends on active transport along microtubules and can be modulated by interference with both anterograde and retrograde transport systems. Nuclear signaling by endogenous AICD in primary neurons could similarly be blocked by inhibiting beta-cleavage but not by alpha-cleavage inhibition. This suggests that amyloidogenic cleavage, despite representing the minor cleavage pathway of APP, is predominantly responsible for AICD-mediated nuclear signaling