Extensive proteomic screening identifies the obesity-related NYGGF4 protein as a novel LRP1-interactor, showing reduced expression in early Alzheimer's disease

<p>Abstract</p> <p>Background</p> <p>The low-density lipoprotein receptor related protein 1 (LRP1) has been implicated in Alzheimer's disease (AD) but its signalling has not been fully evaluated. There is good evidence that the cytoplasmic domain of LRP1 is involved in protein-protein interactions, important in the cell biology of LRP1.</p> <p>Results</p> <p>We carried out three yeast two-hybrid screens to identify proteins that interact with the cytoplasmic domain of LRP1. The screens included both conventional screens as well as a novel, split-ubiquitin-based screen in which an LRP1 construct was expressed and screened as a transmembrane protein. The split-ubiquitin screen was validated in a screen using full-length amyloid protein precursor (APP), which successfully identified FE65 and FE65L2, as well as novel interactors (Rab3a, Napg, and ubiquitin b). Using both a conventional screen as well as the split-ubiquitin screen, we identified NYGGF4 as a novel LRP1 interactor. The interaction between LRP1 and NYGGF4 was validated using two-hybrid assays, coprecipitation and colocalization in mammalian cells. Mutation analysis demonstrated a specific interaction of NYGGF4 with an NPXY motif that required an intact tyrosine residue. Interestingly, while we confirmed that other LRP1 interactors we identified, including JIP1B and EB-1, were also able to bind to APP, NYGGF4 was unique in that it showed specific binding with LRP1. Expression of NYGGF4 decreased significantly in patients with AD as compared to age-matched controls, and showed decreasing expression with AD disease progression. Examination of Nyggf4 expression in mice with different alleles of the human <it>APOE4 </it>gene showed significant differences in Nyggf4 expression.</p> <p>Conclusions</p> <p>These results implicate NYGGF4 as a novel and specific interactor of LRP1. Decreased expression of LRP1 and NYGGF4 over disease, evident with the presence of even moderate numbers of neuritic plaques, suggests that LRP1-NYGGF4 is a system altered early in disease. Genetic and functional studies have implicated both LRP1 and NYGGF4 in obesity and cardiovascular disease and the physical association of these proteins may reflect a common mechanism. This is particularly interesting in light of the dual role of ApoE in both cardiovascular risk and AD. The results support further studies on the functional relationship between NYGGF4 and LRP1.</p

Alcohol and gene expression in nerve cells with emphasis on transcription factor AP-1

Alcohol induces profound effects on the function of the nerve cells in the nervous system. Alterations in gene expression is an important way by which these effects could be induced and sustained. Activating Protein-1 (AP-1) is a dimeric transcription factor constituted of proteins from the fos and jun immediate-early gene families. AP-1 induces gene expression of genes having a functional AP-1 binding site in their promoter. Alcohol has previously been demonstrated to modulate the expression of individual fos and jun genes and to alter the AP-1 binding activity in neuronal cells. The present study investigated the effects of alcohol on jun gene expression and AP-1 transcriptional activity and the signalling pathways involved in these processes in a human neuroblastoma SH-SY5Y cell line. Furthermore, experiments were conducted to screen for ethanol sensitive genes. The main findings of this study were that acute ethanol attenuated basal and TPA-induced junD mRNA expression without affecting the expression of the other jun genes, c-jun and junB. Acute ethanol exposure also attenuated muscarinic receptor-induced activation of the MAP kinases, p38 and JNK. The p38 MAPK was shown to be involved in muscarinic receptor-induced activation of junB and junD mRNA expression. Long-term ethanol exposure enhanced AP-1 transcriptional activity. This enhancement was blocked by inhibitors of PKC and MAPKs. Cellular retinoic acid-binding protein-I (CRABP-I) was identified as an ethanol sensitive gene. The CRABP-I gene expression was up-regulated by ethanol in a time- and dose-dependent manner. This findings support the idea that immediate-early genes and AP-1 are involved in the alcohol-induced changes in the function of nerve cells and that alcohol alters the expression of particular genes

Chronic ethanol exposure enhances activating protein-1 transcriptional activity in human neuroblastoma cells

This study demonstrates a method for studying the effects of ethanol on transcription mediated by activating protein-1 (AP-1). The effects of ethanol on AP-1 activity and on the signaling cascades in this process were investigated by using a reporter gene technique with secreted alkaline phosphatase as the reporter gene coupled to nine DNA AP-1-binding elements. Long-term ethanol exposure (48-72 h) dose dependently enhanced AP-1 transcriptional activity in SH-SY5Y cells. Shorter exposure periods with ethanol did not influence AP-1 transcriptional activity compared with findings for control cells. Inhibition of protein kinase C (PKC) dramatically decreased AP-1 activity in both control and ethanol-exposed cells and abolished the ethanol enhancement. This finding suggests a pivotal role for PKC-coupled signaling in AP-1 transcriptional activity. Phorbol ester stimulation of AP-1 transcriptional activity was not influenced by long-term ethanol exposure. This finding indicates that signaling events upstream of PKC are the targets for ethanol. Mitogen-activated protein kinases ERK and p38 may play a role in ethanol-enhanced AP-1 activity because inhibitors of both enzymes partly reduced the enhancement. The inhibitors also partly blocked phorbol ester-induced AP-1 activation, which demonstrates a function of these mitogen-activated protein kinases downstream of PKC

Acute ethanol exposure attenuates expression of junD in human neuroblastoma cells

This study describes the effects of acute ethanol exposure on the mRNA levels of c-jun,junB and junD in the human neuroblastoma SH-SY5Y cell line. An acute exposure to 100 mM ethanol did not influence the basal and phorbol ester-induced expression of c-jun and junB, whereas the basal mRNA level of junD was attenuated by 30%. This effect was dose- and time-dependent with maximal inhibition being detected 2 h after 100 mM ethanol treatment and the mRNA levels gradually returned towards normal afterwards. Ethanol also inhibited phorbol ester-induced expression of junD. The fact that ethanol did not influence degradation of the junD mRNA suggests that acute ethanol suppresses the transcription of the gene. These results indicate that acute ethanol exerts different effects on expression of Jun transcription factors, suggesting that as compared to c-jun and junB, the junD gene may be more sensitive to acute ethanol treatment in neuronal cells

Ethanol exposure potentiates fosB and junB expression induced by muscarinic receptor stimulation in neuroblastoma SH-SY5Y cells

Muscarinic receptor stimulation and activation of protein kinase C cause an increase in fosB and junB transcripts in human neuroblastoma SH-SY5Y cells. In this study, the effect of long-term ethanol exposure on these events was investigated. Carbachol-stimulated fosB and junB expression was elevated in ethanol-exposed cells compared with control cells. The potentiation was time- and dose-dependent on ethanol. Preincubation with muscarinic antagonists or protein kinase C inhibitor demonstrated that the carbachol-stimulated increase in fosB and junB mRNA levels was primarily mediated via M1 receptors and dependent on the activity of protein kinase C in both control and ethanol-exposed cells. Long-term ethanol exposure did not influence the expression of fosB and junB induced by activation of protein kinase C with phorbol ester. These results demonstrate that the muscarinic receptor-stimulated fosB and junB expression is sensitive to ethanol exposure in SH-SY5Y cells, suggesting that these genes participate in the regulation of neuronal function in response to chronic ethanol treatment