Human synapsin I mediates the function of nuclear respiratory factor 1 in neurite outgrowth in neuroblastoma IMR-32 cells.

Nuclear respiratory factor (NRF)-1 is a transcription factor with a novel function in neurite outgrowth. Synapsin I protein is a well-known phosphoprotein in neuronal terminals and has been implicated in neuronal differentiation. Human synapsin I gene promoter has a putative NRF-1 responsive element (NRE), but it is not known whether this NRE is functional. We hypothesized that synapsin I is downstream of NRF-1 and mediates its function in neurite outgrowth. Gel electrophoretic mobility shift assays, chromatin immunoprecipitation, site-directed mutagenesis, and promoter studies indicated that NRF-1 is a positive regulator of synapsin I promoter. Exogenous NRF-1 overexpression increased synapsin I protein levels in IMR-32 and HEK293T cells. Serum deprivation, which induces neurite outgrowth in IMR-32 cells, increased the binding activity of NRF-1 to synapsin I NRE and induced alternating synapsin I protein expression. Down-regulating synapsin I expression markedly decreased the percentage of neurite-bearing cells and the length of the longest neurite in IMR-32 cells that stably or transiently overexpressed NRF-1. We conclude that the human synapsin I gene is positively regulated by NRF-1 and mediates the function of NRF-1 in neurite outgrowth.

CCM-AMI, a Polyethylene Glycol Micelle with Amifostine, as an Acute Radiation Syndrome Protectant in C57BL/6 Mice.

Acute radiation syndrome results from radiation exposure, such as in accidental nuclear disasters. Safe and effective radioprotectants, mitigators, and treatment drugs must be developed as medical countermeasures against radiation exposure. Here, the authors evaluated CCM-Ami, a novel polyethylene glycol micelle encapsulated with amifostine, for its radioprotective properties after total-body irradiation from a 60Co source. Male C57BL/6 mice (6-8 wk old) were intravenously injected with 45 mg kg(-1) of CCM-Ami 90 min before exposure to 7.2 and 8.5 Gy irradiation at a dose rate of 0.04 Gy min(-1). Both survival benefit and hematopoietic protection were observed after prophylactic CCM-Ami administration when compared with the effects measured in excipient control and amifostine groups. Pharmacokinetic results showed that after the intravenous injection, the plasma concentration of WR-1065, the active form of amifostine, was higher in CCM-Ami-treated mice than in amifostine-treated mice. These findings suggest that CCM-Ami-mediated hematopoietic protection plays a key role in enhancing survival of mice exposed to radiation toxicity and thus indicate that CCM-Ami is a radioprotectant that can be used safely and effectively in nuclear disasters.

Novel genes FAM134C, C3orf10 and ENOX1 are regulated by NRF-1 and differentially regulate neurite outgrowth in neuroblastoma cells and hippocampal neurons.

Nuclear respiratory factor-1 (NRF-1) is a major transcription factor in the human genome and functions in neurite outgrowth in neuroblastoma cells. Whether genes downstream from NRF-1 differentially regulate axonal and dendritic outgrowth in neurons remains largely unknown. Three hypothetical genes, C3orf10, FAM134C, and ENOX1, were investigated because their NRF-1 response elements are 100% conserved in humans and mice. We found that NRF-1 positively regulates FAM134C and ENOX1, but negatively regulates C3orf10 in human neuroblastoma IMR-32 cells and primary rat cortical neurons. In IMR-32 cells, FAM134C positively regulates and C3orf10 negatively regulates neurite outgrowth, but ENOX1 plays no role in neurite outgrowth regulation. FAM134C but not C3orf10 mediates NRF-1-enhanced neurite outgrowth. In primary rat hippocampal neurons, Fam134c is predominantly expressed in the axon hillock and C3orf10 is ubiquitously expressed in all neurites and cell bodies at different developmental stages, suggesting their roles in axonal and dendritic outgrowth. Knockdown of Fam134c decreased both axonal length and the number of axonal collaterals and dendrites, however, knockdown of C3orf10 only increased the number of axonal collaterals and dendrites. Overall, we annotated FAM134C, C3orf10, and ENOX1 as NRF-1-regulated genes, which have differential effects on neurite outgrowth in neuroblastoma cells as well as neurons. This study provided an effective platform for annotating hypothetical genes in the human genome and increasing our knowledge in the molecular network underlying neuronal differentiation.

Novel genes that mediate nuclear respiratory factor 1-regualted neurite outgrowth in neuroblastoma IMR-32 cells.

Nuclear respiratory factor-1 (NRF-1) is a transcription factor that functions in neurite outgrowth; however, the genes downstream from NRF-1 that mediate this function remain largely unknown. This study employs a genome-wide analysis approach to identify NRF-1-targeted genes in human neuroblastoma IMR-32 cells. A total of 916 human genes containing the putative NRF-1 response element (NRE) in their promoter regions were identified using a cutoff score determined by results from electrophoretic mobility shift assays (EMSA). Seventy-four NRF-1 target genes were listed according to the typical locations and high conservation of NREs. Fifteen genes, MAPRE3, NPDC1, RAB3IP, TRAPPC3, SMAD5, PIP5K1A, USP10, SPRY4, GTF2F2, NR1D1, SUV39H2, SKA3, RHOA, RAPGEF6, and SMAP1 were selected for biological confirmation. EMSA and chromatin immunoprecipitation confirmed that all NREs of these fifteen genes are critical for NRF-1 binding. Quantitative RT-PCR demonstrated that mRNA levels of 12 of these genes are regulated by NRF-1. Overexpression or knockdown of candidate genes demonstrated that MAPRE3, NPDC1, SMAD5, USP10, SPRY4, GTF2F2, SKA3, SMAP1 positively regulated, and RHOA and RAPGEF6 negatively regulated neurite outgrowth. Overall, our data showed that the combination of genome-wide bioinformatic analysis and biological experiments helps to identify the novel NRF-1-regulated genes, which play roles in differentiation of neuroblastoma cells.