Accumulation of the amyloid ␤ (A␤) peptide derived from the proteolytic processing of amyloid precursor protein (APP) is the defining pathological hallmark of Alzheimer disease. We previously demonstrated that the C-terminal 37 amino acids of lipoprotein receptor-related protein (LRP) robustly promoted A␤ generation independent of FE65 and specifically interacted with Ran-binding protein 9 (RanBP9). In this study we found that RanBP9 strongly increased BACE1 cleavage of APP and A␤ generation. This pro-amyloidogenic activity of RanBP9 did not depend on the KPI domain or the Swedish APP mutation. In cells expressing wild type APP, RanBP9 reduced cell surface APP and accelerated APP internalization, consistent with enhanced ␤-secretase processing in the endocytic pathway. The N-terminal half of RanBP9 containing SPRY-LisH domains not only interacted with LRP but also with APP and BACE1. Overexpression of RanBP9 resulted in the enhancement of APP interactions with LRP and BACE1 and increased lipid raft association of APP. Importantly, knockdown of endogenous RanBP9 significantly reduced A␤ generation in Chinese hamster ovary cells and in primary neurons, demonstrating its physiological role in BACE1 cleavage of APP. These findings not only implicate RanBP9 as a novel and potent regulator of APP processing but also as a potential therapeutic target for Alzheimer disease. The major defining pathological hallmark of Alzheimer disease (AD)2 is the accumulation of amyloid ␤ protein (A␤), a neurotoxic peptide derived from ␤-and ␥-secretase cleavages of the amyloid precursor protein (APP). The vast majority of APP is constitutively cleaved in the middle of the A␤ sequence by ␣-secretase (ADAM10/TACE/ADAM17) in the non-amyloidogenic pathway, thereby abrogating the generation of an intact A␤ peptide. Alternatively, a small proportion of APP is cleaved in the amyloidogenic pathway, leading to the secretion of A␤ peptides (37-42 amino acids) via two proteolytic enzymes, ␤-and ␥-secretase, known as BACE1 and presenilin, respectively (1).The proteolytic processing of APP to generate A␤ requires the trafficking of APP such that APP and BACE1 are brought together in close proximity for ␤-secretase cleavage to occur. We and others have shown that the low density lipoprotein receptor-related protein (LRP), a multifunctional endocytosis receptor (2), binds to APP and alters its trafficking to promote A␤ generation. The loss of LRP substantially reduces A␤ release, a phenotype that is reversed when full-length (LRP-FL) or truncated LRP is transfected in LRP-deficient cells (3, 4). Specifically, LRP-CT lacking the extracellular ligand binding regions but containing the transmembrane domain and the cytoplasmic tail is capable of rescuing amyloidogenic processing of APP and A␤ release in LRP deficient cells (3). Moreover, the LRP soluble tail (LRP-ST) lacking the transmembrane domain and only containing the cytoplasmic tail of LRP is sufficient to enhance A␤ secretion (5). This activity of LRP-ST is achieved by promoting APP/BACE1 intera...

The brains of fetal alcohol syndrome patients exhibit impaired neuronal migration, but little is known about the mechanisms underlying this abnormality. Here we show that Ca 2ϩ signaling and cyclic nucleotide signaling are the central targets of alcohol action in neuronal cell migration. Acute administration of ethanol reduced the frequency of transient Ca 2ϩ elevations in migrating neurons and cGMP levels and increased cAMP levels. Experimental manipulations of these second-messenger pathways, through stimulating Ca 2ϩ and cGMP signaling or inhibiting cAMP signaling, completely reversed the action of ethanol on neuronal migration in vitro as well as in vivo. Each second messenger has multiple but distinct downstream targets, including Ca 2ϩ /calmodulin-dependent protein kinase II, calcineurin, protein phosphatase 1, Rho GTPase, mitogen-activated protein kinase, and phosphoinositide 3-kinase. These results demonstrate that the aberrant migration of immature neurons in the fetal brain caused by maternal alcohol consumption may be corrected by controlling the activity of these second-messenger pathways.

Neurodegeneration associated with amyloid b (Ab) peptide accumulation, synaptic loss, neuroinflammation, tauopathy, and memory impairments encompass the pathophysiological features of Alzheimer's disease (AD). We previously reported that the scaffolding protein RanBP9, which is overall increased in brains of AD patients, simultaneously promotes Ab generation and focal adhesion disruption by accelerating the endocytosis of amyloid precursor protein (APP) and b1-integrin, respectively. Here, we show that RanBP9 protein levels are increased by fourfold in FAD mutant APP transgenic mice. Accordingly, RanBP9 transgenic mice demonstrate significantly increased synapse loss, neurodegeneration, gliosis, and spatial memory deficits. RanBP9 overexpression promotes apoptosis and potentiates Ab-induced neurotoxicity independent of its capacity to promote Ab generation. Conversely, RanBP9 reduction by siRNA or gene dosage mitigates Ab-induced neurotoxicity. Importantly, RanBP9 activates/dephosphorylates cofilin, a key regulator of actin dynamics and mitochondria-mediated apoptosis, and siRNA knockdown of cofilin abolishes both Ab and RanBP9-induced apoptosis. These findings implicate the RanBP9-cofilin pathway as critical therapeutic targets not only for stemming Ab generation but also antagonizing Ab-induced neurotoxicity. Cell Death and Differentiation (2012) 19, 1413-1423; doi:10.1038/cdd.2012.14; published online 24 February 2012Alzheimer's disease (AD) is a neurodegenerative disorder characterized by accumulations of the amyloid b (Ab) -peptide and hyperphosphorylated tau in senile plaques and neurofibrillary tangles, respectively. Ab is a neurotoxic peptide derived from b-and g-secretase cleavages of the amyloid precursor protein (APP) and is thought to be a critical early player in AD pathogenesis. 1 In addition to the accumulation of Ab and tau, abnormalities in the actin cytoskeleton are detected earlier during the course of AD and other neurodegenerative diseases. 2 Indeed, it has been demonstrated that Ab can induce actin/cofilin pathology associated with hyperphosphorylated tau in primary neurons and in vivo. [3][4][5] We recently demonstrated that the scaffolding protein RanBP9 interacts with the cytoplasmic tails of LRP, APP, and BACE1, and functions as a scaffold upon which APP is brought together with BACE1 and LRP. Such interactions of RanBP9 promote the endocytosis of APP and strongly increase BACE1 cleavage of APP to generate Ab in vitro and in vivo. 6,7 Conversely, siRNA knockdown of RanBP9 reduces BACE1 cleavage of APP and Ab generation, indicating that endogenous RanBP9 normally functions in this capacity. 6 In addition, a 60-kD proteolytic fragment of RanBP9 is increased by more than sixfold in brains of AD patients, and this fragment potentiates Ab generation via BACE1 processing of APP. 8 In addition to promoting Ab generation by accelerating APP endocytosis, RanBP9 also potently disrupts integrin-dependent focal adhesion signaling and assembly by accelerating b1-integrin and LRP endocytosis. 9 In th...

Growing evidence indicates that cell cycle arrest and neurogenesis are highly coordinated and interactive processes, governed by cell cycle genes and neural transcription factors. The gene PC3 (Tis21/BTG2) is expressed in the neuroblast throughout the neural tube and inhibits cell cycle progression at the G 1 checkpoint by repressing cyclin D1 transcription. We generated inducible mouse models in which the expression of PC3 was upregulated in neuronal precursors of the neural tube and of the cerebellum. These mice exhibited a marked increase in the production of postmitotic neurons and impairment of cerebellar development. Cerebellar granule precursors of PC3 transgenic mice displayed inhibition of cyclin D1 expression and a strong increase in the expression of Math1, a transcription factor required for their differentiation. Furthermore, PC3, encoded by a recombinant adenovirus, also induced Math1 in postmitotic granule cells in vitro and stimulated the Math1 promoter activity. In contrast, PC3 expression was unaffected in the cerebellar primordium of Math1 null mice, suggesting that PC3 acts upstream to Math1. As a whole, our data suggest that cell cycle exit of cerebellar granule cell precursors and the onset of cerebellar neurogenesis are coordinated by PC3 through transcriptional control of cyclin D1 and Math1, respectively.

The phagocytosis of apoptotic cells (ACs), or efferocytosis, by DCs is critical for self-tolerance and host defense. Although many efferocytosis-associated receptors have been described in vitro, the functionality of these receptors in vivo has not been explored in depth. Using a spleen efferocytosis assay and targeted genetic deletion in mice, we identified a multiprotein complex -composed of the receptor tyrosine kinase AXL, LDL receptorrelated protein-1 (LRP-1), and RAN-binding protein 9 (RANBP9) -that mediates DC efferocytosis and antigen cross-presentation. We found that AXL bound ACs, but required LRP-1 to trigger internalization, in murine CD8α + DCs and human-derived DCs. AXL and LRP-1 did not interact directly, but relied on RANBP9, which bound both AXL and LRP-1, to form the complex. In a coculture model of antigen presentation, the AXL/ LRP-1/RANBP9 complex was used by DCs to cross-present AC-associated antigens to T cells. Furthermore, in a murine model of herpes simplex virus-1 infection, mice lacking DC-specific LRP-1, AXL, or RANBP9 had increased AC accumulation, defective viral antigen-specific CD8 + T cell activation, enhanced viral load, and decreased survival. The discovery of this multiprotein complex that mediates functionally important DC efferocytosis in vivo may have implications for future studies related to host defense and DC-based vaccines.