Genome structure and chromosomal mapping of the gene for Fe65L2 interacting with Alzheimer's beta-amyloid precursor protein

Fe65: A Scaffolding Protein of Actin Regulators

The scaffolding protein family Fe65, composed of Fe65, Fe65L1, and Fe65L2, was identified as an interaction partner of the amyloid precursor protein (APP), which plays a key function in Alzheimer’s disease. All three Fe65 family members possess three highly conserved interaction domains, forming complexes with diverse binding partners that can be assigned to different cellular functions, such as transactivation of genes in the nucleus, modulation of calcium homeostasis and lipid metabolism, and regulation of the actin cytoskeleton. In this article, we rule out putative new intracellular signaling mechanisms of the APP-interacting protein Fe65 in the regulation of actin cytoskeleton dynamics in the context of various neuronal functions, such as cell migration, neurite outgrowth, and synaptic plasticity.

Extracellular Vesicles: A Possible Link between HIV and Alzheimer's Disease-Like Pathology in HIV Subjects?

The longevity of people with HIV/AIDS has been prolonged with the use of antiretroviral therapy (ART). The age-related complications, especially cognitive deficits, rise as HIV patients live longer. Deposition of beta-amyloid (Aβ), a hallmark of Alzheimer's disease (AD), has been observed in subjects with HIV-associated neurocognitive disorders (HAND). Various mechanisms such as neuroinflammation induced by HIV proteins (e.g., Tat, gp120, Nef), excitotoxicity, oxidative stress, and the use of ART contribute to the deposition of Aβ, leading to dementia. However, progressive dementia in older subjects with HIV might be due to HAND, AD, or both. Recently, extracellular vesicles (EVs)/exosomes, have gained recognition for their importance in understanding the pathology of both HAND and AD. EVs can serve as a possible link between HIV and AD, due to their ability to package and transport the toxic proteins implicated in both AD and HIV (Aβ/tau and gp120/tat, respectively). Given that Aß is also elevated in neuron-derived exosomes isolated from the plasma of HIV patients, it is reasonable to suggest that neuron-to-neuron exosomal transport of Aβ and tau also contributes to AD-like pathology in HIV-infected subjects. Therefore, exploring exosomal contents is likely to help distinguish HAND from AD. However, future prospective clinical studies need to be conducted to compare the exosomal contents in the plasma of HIV subjects with and without HAND as well as those with and without AD. This would help to find new markers and develop new treatment strategies to treat AD in HIV-positive subjects. This review presents comprehensive literatures on the mechanisms contributing to Aβ deposition in HIV-infected cells, the role of EVs in the propagation of Aβ in AD, the possible role of EVs in HIV-induced AD-like pathology, and finally, possible therapeutic targets or molecules to treat HIV subjects with AD.

The FE65 proteins and Alzheimer's disease

The FE65s (FE65, FE65L1, and FE65L2) are a family of multidomain adaptor proteins that form multiprotein complexes with a range of functions. FE65 is brain-enriched, whereas FE65L1 and FE65L2 are more widely expressed. All three members contain a WW domain and two PTB domains. Through the PTB2 domain, they all interact with the Alzheimer's disease amyloid precursor protein (APP) intracellular domain (AICD) and can alter APP processing. After sequential proteolytic processing of membrane-bound APP and release of AICD to the cytoplasm, FE65 can translocate to the nucleus to participate in gene transcription events. This role is further mediated by interactions of FE65 PTB1 with the transcription factors CP2/LSF/LBP1 and Tip60 and the WW domain with the nucleosome assembly factor SET. However, FE65 target genes have not yet been confirmed. The FE65 PTB1 domain also interacts with two cell surface lipoproteins receptors, the low-density lipoprotein receptor-related protein (LRP) and ApoEr2, forming trimeric complexes with APP. The FE55 WW domain also binds to mena, through which it functions in regulation of the actin cytoskeleton, cell motility, and neuronal growth cone formation. While single knockout mice appear normal, double FE65(-/-)/FE65L1(-/-) mice have substantial neurodevelopmental defects. These include heterotopic neurons and axonal pathfinding defects, findings similar to findings in both Mena and triple APP:APLP1:APLP2 knockout mice and also lissencephalopathies in humans. Thus APPs, FE65s, and mena may act together in a developmental signalling pathway. This article reviews the known functions of the FE65 family and their role in APP function and Alzheimer's disease.

Regulated proteolysis of APP and ApoE receptors

The beta-amyloid precursor protein (APP) shares intracellular and extracellular-binding partners with the family of receptors for apolipoprotein E (apoE). Binding of APP and apoE receptors to specific extracellular matrix proteins (F-spondin and Reelin) promotes their presence on the cell surface and influences whether they will interact with specific cytoplasmic adaptor proteins. Cleavage of APP and apoE receptors at the cell surface occurs by alpha-secretase activities; thus, the processing of these proteins can be regulated by their trafficking either to or from the cell surface. Their cleavages can also be regulated by tissue inhibitor of metalloproteinase-3 (TIMP-3), a metalloprotease inhibitor in the extracellular matrix. ApoE receptors have functions in neuronal migration during development and in proper synaptic function in the adult. Thus, the functions of apoE receptors and by analogy of APP will be modified by the various extracellular and intracellular interactions reviewed in this paper.

Sequences from the low density lipoprotein receptor-related protein (LRP) cytoplasmic domain enhance amyloid beta protein production via the beta-secretase pathway without altering amyloid precursor protein/LRP nuclear signaling

Increasing evidence suggests that the low density lipoprotein receptor-related protein (LRP) affects the processing of amyloid precursor protein (APP) and amyloid beta (Abeta) protein production as well as mediates the clearance of Abeta from the brain. Recent studies indicate that the cytoplasmic domain of LRP is critical for this modulation of APP processing requiring perhaps a complex between APP, the adaptor protein FE65, and LRP. In this study, we expressed a small LRP domain consisting of the C-terminal 97 amino acids of the cytoplasmic domain, or LRP-soluble tail (LRP-ST), in CHO cells to test the hypothesis that the APP.LRP complex can be disrupted. We anticipated that LRP-ST would inhibit the normal interaction between LRP and APP and therefore perturb APP processing to resemble a LRP-deficient state. Surprisingly, CHO cells expressing LRP-ST demonstrated an increase in both sAPP secretion and Abeta production compared with control CHO cells in a manner reminiscent of the cellular effects of the APP "Swedish mutation." The increase in sAPP secretion consisted mainly of sAPPbeta, consistent with the increase in Abeta release. Further, this effect is LRP-independent, as the same alterations remained when LRP-ST was expressed in LRP-deficient cells but not when the construct was membrane-anchored. Finally, deletion experiments suggested that the last 50 amino acid residues of LRP-ST contain the important domain for altering APP processing and Abeta production. These observations indicate that there are cellular pathways that may suppress Abeta generation but that can be altered to facilitate Abeta production.

Common mechanism of ligand recognition by group II/III WW domains: redefining their functional classification

WW domain is a well known protein module that mediates protein to protein interactions by binding to proline-containing ligands. Based on the ligand predilections, the WW domains have been classified into four major groups. Group II and III WW domains have been reported to bind the proline-leucine and proline-arginine motifs, respectively. In the present study, using surface plasmon resonance technique we have shown that these WW domains have almost indistinguishable ligand preferences and kinetic properties. Hence, we propose that Group II and III WW domains should be joined together as one group (Group II/III). Unlike Group I and IV WW domains, Group II/III WW domains can bind simple polyprolines as well as the proline-leucine and proline-arginine motifs, and they possess two Xaa-proline (where Xaa is any amino acid) binding grooves similar to SH3 domains. Our work assigns Group II and III WW domains to a larger family of polyproline-binding modules and proteins, which includes SH3 domains and profilin. Because polyprolines belong to the most frequently found peptide motifs in several genomes, our study implies the versatile importance of Group II/III WW domains in signaling.

Characterization of an amyloid precursor protein-binding protein Fe65L2 and its novel isoforms lacking phosphotyrosine-interaction domains

Human Fe65L2 is a member of the Fe65 protein family, which interacts with amyloid precursor protein (APP). Fe65L2 contains an N-terminal WW (Trp-Trp) domain followed by two phosphotyrosine-interaction domains, and consists of 486 amino acids. In the present study, we cloned and characterized two novel isoforms of Fe65L2, designated I-214 and I-245, which are produced by alternative splicing of the RNA. The splicing events disrupt the ability to bind with APP and low-density-lipoprotein-receptor-related protein. Fe65L2 was highly expressed in the brain, whereas I-214 and I-245 were expressed in various tissues. In HEK-293 cells, Fe65L2 was expressed in the nucleus and cytosol, whereas I-245 and I-214 were localized exclusively to the nucleus. The ratio of I-214 to Fe65L2 mRNA was increased by apoptotic stimuli. Although the overexpression of either Fe65L2 or I-214 did not significantly affect the half-life and maturation of APP, or the secretion of secreted APP, the secretion of beta-amyloid peptide (Abeta)40 and Abeta42 was increased by overexpression of Fe65L2, but not by that of I-214. These results suggest that Fe65L2 affects Abeta production and a possible regulation of Fe65L2 function by alternative splicing.