Neuroprotection resulting from insufficiency of RANBP2 is associated with the modulation of protein and lipid homeostasis of functionally diverse but linked pathways in response to oxidative stress

Abstract

SUMMARYOxidative stress is a deleterious stressor associated with a plethora of disease and aging manifestations, including neurodegenerative disorders, yet very few factors and mechanisms promoting the neuroprotection of photoreceptor and other neurons against oxidative stress are known. Insufficiency of RAN-binding protein-2 (RANBP2), a large, mosaic protein with pleiotropic functions, suppresses apoptosis of photoreceptor neurons upon aging and light-elicited oxidative stress, and promotes age-dependent tumorigenesis by mechanisms that are not well understood. Here we show that, by downregulating selective partners of RANBP2, such as RAN GTPase, UBC9 and ErbB-2 (HER2; Neu), and blunting the upregulation of a set of orphan nuclear receptors and the light-dependent accumulation of ubiquitylated substrates, light-elicited oxidative stress and Ranbp2 haploinsufficiency have a selective effect on protein homeostasis in the retina. Among the nuclear orphan receptors affected by insufficiency of RANBP2, we identified an isoform of COUP-TFI (Nr2f1) as the only receptor stably co-associating in vivo with RANBP2 and distinct isoforms of UBC9. Strikingly, most changes in proteostasis caused by insufficiency of RANBP2 in the retina are not observed in the supporting tissue, the retinal pigment epithelium (RPE). Instead, insufficiency of RANBP2 in the RPE prominently suppresses the light-dependent accumulation of lipophilic deposits, and it has divergent effects on the accumulation of free cholesterol and free fatty acids despite the genotype-independent increase of light-elicited oxidative stress in this tissue. Thus, the data indicate that insufficiency of RANBP2 results in the cell-type-dependent downregulation of protein and lipid homeostasis, acting on functionally interconnected pathways in response to oxidative stress. These results provide a rationale for the neuroprotection from light damage of photosensory neurons by RANBP2 insufficiency and for the identification of novel therapeutic targets and approaches promoting neuroprotection.Neuroprotection resulting from insufficiency of RANBP2 is associated with the modulation of protein and lipid homeostasis of functionally diverse but linked pathways in response to oxidative stress

Differential Loss of Prolyl Isomerase or Chaperone Activity of Ran-binding Protein 2 (Ranbp2) Unveils Distinct Physiological Roles of Its Cyclophilin Domain in Proteostasis

“…Hence, we took an unbiased proteomic approach to screen and identify proteins with proteostatic changes between wild-type and Tg-Ranbp2 R2944A-HA ::Ranbp2 Ϫ/Ϫ mice. This survey also included another transgenic line with a mutation in the cyclophilin-like domain (CLD) of Ranbp2 (58) Ϫ/Ϫ were highly selective, because no changes were observed in the levels of other partners of Ranbp2, such as SUMO-1-RanGAP, Nr2e3, and COUP-TFI (data not shown) (89).…”

Selective Impairment of a Subset of Ran-GTP-binding Domains of Ran-binding Protein 2 (Ranbp2) Suffices to Recapitulate the Degeneration of the Retinal Pigment Epithelium (RPE) Triggered by Ranbp2 Ablation

“…Ranbp2 modulates the nucleocytoplasmic shuttling of a set of partners that are functionally diverse, due to the direct association of distinct domains of Ranbp2 with nuclear import and export receptors, such as importin-␤ and exportin-1/Crm1, respectively, and other shuttling substrates (22,48,64,79). Hence, we examined changes in the subcellular distribution of some Ranbp2 partners in the RPE between RPE-cre::Ranbp2 ϩ/ϩ and RPE-cre::Ranbp2 Ϫ/Ϫ mice (Fig.…”

Dynamics and diverse functions of nuclear pore complex proteins

“…71 Insufficiency in Nup358 furthermore causes upregulation of the orphan transmembrane tyrosine kinase receptor ErbB2 and suppression of ubiquitylation in response to light stress, which may also contribute to apoptosis suppression in central retina regions of Nup358 +/− mice. 70 Together these studies have revealed a determinant role for Nup358 in glucose, energy and lipid homeostasis in neurons of the CNS and the retina, and implicate Nup358 (and its binding partners) as key player in neuropathic and neurodegenerative diseases. 96 Hypomorphic mutant alleles of Nup154 affect female and male fertility in Drosophila (see above).…”

“…2 and Table 1), that range from more general functions in nucleocytoplasmic transport, [56][57][58][59] mitosis, [60][61][62] and cellular signaling due to its E3 SUMO ligase activity [63][64][65][66] to tissue-specific functions particularly in neurons and muscle cells. [67][68][69][70][71][72] Moreover, Nup358 interacts with interphase microtubules (MTs) through its N-terminal, leucine-rich domain and overexpression of this MT-targeting domain in CHO cells increased MT bundling and stability, whereas depletion of Nup358 led to a decrease in polarized cell migration and stable MTs. 73 Endogenous Nup358 and a GFP-fusion of Nup358's N-terminal domain were found in the cytoplasm and to colocalize with MTs at cell extensions.…”

“…97 In aged mice, haploinsufficiency of Nup358 protects neurons against light-induced oxidative stress. 70,71 Prolonged light exposure is a determinant factor in inducing neurodegeneration of photoreceptors by apoptosis. Upon light-elicited stress, aged Nup358 +/− mice have suppressed apoptosis and reduced membrane dysgenesis in central retina regions as compared with wild type mice.…”