Structural characterization and subcellular localization of Drosophila organic solute carrier partner 1

CiliaCarta: An integrated and validated compendium of ciliary genes

The cilium is an essential organelle at the surface of mammalian cells whose dysfunction causes a wide range of genetic diseases collectively called ciliopathies. The current rate at which new ciliopathy genes are identified suggests that many ciliary components remain undiscovered. We generated and rigorously analyzed genomic, proteomic, transcriptomic and evolutionary data and systematically integrated these using Bayesian statistics into a predictive score for ciliary function. This resulted in 285 candidate ciliary genes. We generated independent experimental evidence of ciliary associations for 24 out of 36 analyzed candidate proteins using multiple cell and animal model systems (mouse, zebrafish and nematode) and techniques. For example, we show that OSCP1, which has previously been implicated in two distinct non-ciliary processes, causes ciliogenic and ciliopathy-associated tissue phenotypes when depleted in zebrafish. The candidate list forms the basis of CiliaCarta, a comprehensive ciliary compendium covering 956 genes. The resource can be used to objectively prioritize candidate genes in whole exome or genome sequencing of ciliopathy patients and can be accessed at http://bioinformatics.bio.uu.nl/john/syscilia/ciliacarta/.

Novel Drosophila model for mitochondrial diseases by targeting of a solute carrier protein SLC25A46

Mutations in SLC25A46 gene have been identified in mitochondrial diseases that are sometimes classified as Charcot-Marie-Tooth disease type 2, optic atrophy and Leigh syndrome. Human SLC25A46 functions as a transporter across the outer mitochondrial membrane. However, it is still unknown how the neurodegeneration occurring in these diseases relates to the loss of SLC25A46 function. Drosophila has CG5755 (dSLC25A46) as a single human SLC25A46 homolog. Here we established pan-neuron specific dSLC25A46 knockdown flies, and examined their phenotypes. Neuron specific knockdown of dSLC25A46 resulted in an impaired motility in both larvae and adults. Defects at neuromuscular junctions (NMJs), such as reduced synaptic branch length, decreased number and size of bouton, reduced density and size of active zone were also observed with the dSLC25A46 knockdown flies. Mitochondrial hyperfusion in synapse at NMJ, accumulation of reactive oxygen species and reduction of ATP were also observed in the dSLC25A46 knockdown flies. These results indicate that depletion of SLC25A46 induces mitochondrial defects accompanied with aberrant morphology of motoneuron and reduction of active zone that results in defect in locomotive ability. In addition, it is known that SLC25A46 mutations in human cause optic atrophy and knockdown of dSLC25A46 induces aberrant morphology of optic stalk of photoreceptor neurons in third instar larvae. Morphology and development of optic stalk of photoreceptor neurons in Drosophila are precisely regulated via cell proliferation and migration. Immunocytochemical analyses of subcellular localization of dSLC25A46 revealed that dSLC25A46 localizes not only in mitochondria, but also in plasma membrane. These observations suggest that in addition to the role in mitochondrial function, plasma membrane-localized dSLC25A46 plays a role in cell proliferation and/or migration to control optic stalk formation. The dSLC25A46 knockdown fly thus recapitulates most of the phenotypes in mitochondrial disease patients, providing a useful tool to study these diseases.

The NOR1/OSCP1 proteins in cancer: from epigenetic silencing to functional characterization of a novel tumor suppressor

NOR1 (Oxidored-nitro domain-containing protein 1), also known as OSCP1, was first identified in nasopharyngeal carcinoma (NPC) cells in 2003. NOR1 is evolutionarily conserved among species with its expression is restricted to brain, testis and respiratory epithelial cells. NOR1 was downregulated in NPC and the downregulation associates with poor prognosis. Previous study demonstrated that hypermethylation of NOR1 promoter was observed in NPC and hematological malignancies, which has been believed to be the main epigenetic cause for NOR1 silencing in these cancers. Recently, the NOR1 tumor suppressor status has been fully established. NOR1 inhibited cancer cell growth by disturbing tumor cell energe metabolism. NOR1 also promote tumor cells apoptosis in oxidative stress and hypoxia by inhibition of stress induced autophagy. Moreover, NOR1 suppressed cancer cell epithelial-mesenchymal transition, invasion and metastasis via activation of FOXA1/HDAC2-slug regulatory network. Deciphering the molecular mechanisms underlying NOR1 mediated tumor suppressive role would be helpful to a deeper understanding of carcinogenesis and, furthermore, to the development of new therapeutic approaches. Here we summarize the current knowledge on NOR1 focusing on its expression pattern, epigenetic and genetic association with human cancers and its biological functions. This review will also elucidate the potential application of NOR1/OSCP1 for some human malignancies.

Tumor suppressor gene OSCP1/NOR1 regulates apoptosis, proliferation, differentiation, and ROS generation during eye development of Drosophila melanogaster

OSCP1/NOR1 (organic solute carrier partner 1/oxidored nitrodomain-containing protein 1) is a known tumor suppressor protein. OSCP1 has been reported to mediate transport of various organic solutes into cells; however, its role during development has not yet been addressed. Here we report the results of studies on dOSCP1 (the Drosophila ortholog of hOSCP1) to elucidate the role of OSCP1/NOR1 during development. Knockdown of dOSCP1 in the eye imaginal discs induced a rough-eye phenotype in adult flies. This phenotype resulted from induction of caspase-dependent apoptosis followed by a compensatory cell proliferation and generation of reactive oxygen species in eye imaginal discs. The induction of apoptosis appears to be associated with down-regulation of the anti-apoptotic Buffy gene and up-regulation of the pro-apoptotic Debcl gene. These effects of knockdown of dOSCP1 lead to mitochondrial fragmentation, degradation, and a shortfall in ATP production. We also found that knockdown of dOSCP1 causes a defect in cone cell and pigment cell differentiation in pupal retinae. Moreover, mutations in epidermal growth factor receptor pathway-related genes, such as Spitz and Drk, enhanced the rough-eye phenotype induced by dOSCP1 knockdown. These results suggest that dOSCP1 positively regulates the epidermal growth factor receptor signaling pathway. Overall, our findings indicate that dOSCP1 plays multiple roles during eye development in Drosophila.

Overexpression of tumor suppressor protein OSCP1/NOR1 induces ER stress and apoptosis during development of Drosophila melanogaster

OSCP1/NOR1 (organic solute carrier partner 1/oxidored-nitro domain-containing protein 1) is known as a transporter of various organic solutes into cells and also is reported to act as a tumor suppressor protein. Although overexpression of OSCP1 has been shown to play multiple roles in mammalian cell lines, its biological significance in living organisms is not fully understood. To explore the effects of OSCP1/NOR1 on development, we performed genetic studies in flies featuring overexpression of its Drosophila orthologue, dOSCP1. Overexpression of dOSCP1 in eye imaginal discs induced a rough eye phenotype in adult flies, likely resulting from a delay in S phase progression and induction of caspase-dependent apoptosis followed by compensatory proliferation. However, it did not appear to be involved in differentiation of R7 photoreceptor cells. We also found that overexpression of dOSCP1 caused endoplasmic reticulum stress in salivary gland cells. These results indicate that overexpression of dOSCP1 exerts effects on various biological processes during Drosophila development.