Abstract
Midnolin (MIDN) was first discovered in embryonic stem cells, but its physiological and pathological roles are, to date, poorly understood. In the present study, we therefore examined the role of MIDN in detail. We found that in PC12 cells, a model of neuronal cells, MIDN localized primarily to the nucleus and intracellular membranes. Nerve growth factor promoted MIDN gene expression, which was attenuated by specific inhibitors of extracellular signal-regulated kinases 1/2 and 5. MIDN-deficient PC12 cells created using CRISPR/Cas9 technology displayed significantly impaired neurite outgrowth. Interestingly, a genetic approach revealed that 10.5% of patients with sporadic Parkinson’s disease (PD) had a lower MIDN gene copy number whereas no copy number variation was observed in healthy people, suggesting that MIDN is involved in PD pathogenesis. Furthermore, the expression of parkin, a major causative gene in PD, was significantly reduced by CRISPR/Cas9 knockout and siRNA knockdown of MIDN. Activating transcription factor 4 (ATF4) was also down-regulated, which binds to the cAMP response element (CRE) in the parkin core promoter region. The activity of CRE was reduced following MIDN loss. Overall, our data suggests that MIDN promotes the expression of parkin E3 ubiquitin ligase, and that MIDN loss can trigger PD-related pathogenic mechanisms.
Highlights
Midbrain nucleolar protein was first discovered by Tsukahara et al using a gene trap approach in embryonic stem cells[1]
We demonstrate for the first time that MIDN expression occurs primarily in the nucleus and intracellular vesicle membranes of PC12 cells, and is induced by both nerve growth factor (NGF) and cAMP signaling
MIDN deletion resulted in a loss of expression of parkin, suggesting that MIDN loss participates in the accumulation of misfolded proteins in neurons, where they exert toxic effects
Summary
Midbrain nucleolar protein (midnolin, MIDN) was first discovered by Tsukahara et al using a gene trap approach in embryonic stem cells[1]. They reported that MIDN was strongly expressed in the midbrain of day E12.5 mice, and experiments with green fluorescent protein (GFP) tagged-MIDN showed that the protein localized primarily to the nucleus and nucleolus via a nucleolar localizing signal located in its C-terminal region. In approximately 10% of PD patients, the disease is familial, and many causative genes have been identified including α-synuclein, parkin, PTEN-induced putative kinase 1, DJ-1, and the leucine repeat-rich kinases[4, 5]. We examined the physiological and pathological roles of MIDN in neuronal cells, as well as the pathological mechanisms of MIDN depletion in PD
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