Conformational changes in inhibitory PAS domain protein associated with binding of HIF-1α and Bcl-xL in living cells

Direct protein-protein interaction between Npas4 and IPAS mutually inhibits their critical roles in neuronal cell survival and death

Inhibitory PAS domain protein (IPAS) is a bifunctional protein that acts as a transcriptional repressor in hypoxia and as a pro-apoptotic protein involved in neuronal cell death. Npas4 (NXF or LE-PAS) is a transcriptional factor that protects nerve cells from endogenous and foreign neurotoxins. Here we show that IPAS and Npas4 antagonize each other through their direct interaction. Coimmunoprecipitation experiments revealed that multiple binding sites on each protein were involved in the interaction. CoCl₂ treatment of PC12 cells that induces IPAS repressed the transactivation activity of Npas4, and IPAS siRNA treatment reduced the CoCl₂-induced repression. CoCl₂-induced apoptosis was suppressed by the addition of KCl that induces Npas4. The protective effect of KCl was attenuated by siRNA-mediated gene silencing of Npas4. Npas4 and IPAS proteins were induced and localized in the cytoplasm of the dopaminergic neurons in the substantia nigra pars compacta after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment. Npas4^−/− mice exhibited greater sensitivity to MPTP in nigral dopaminergic neurons. Together, these results strongly suggest that neuroprotective activity of Npas4 was, at least partly, exerted by inhibiting the pro-apoptotic activity of IPAS through direct interaction.

A Guide to Fluorescence Lifetime Microscopy and Förster's Resonance Energy Transfer in Neuroscience

Fluorescence lifetime microscopy (FLIM) and Förster's resonance energy transfer (FRET) are advanced optical tools that neuroscientists can employ to interrogate the structure and function of complex biological systems in vitro and in vivo using light. In neurobiology they are primarily used to study protein-protein interactions, to study conformational changes in protein complexes, and to monitor genetically encoded FRET-based biosensors. These methods are ideally suited to optically monitor changes in neurons that are triggered optogenetically. Utilization of this technique by neuroscientists has been limited, since a broad understanding of FLIM and FRET requires familiarity with the interactions of light and matter on a quantum mechanical level, and because the ultra-fast instrumentation used to measure fluorescent lifetimes and resonance energy transfer are more at home in a physics lab than in a biology lab. In this overview, we aim to help neuroscientists overcome these obstacles and thus feel more comfortable with the FLIM-FRET method. Our goal is to aid researchers in the neuroscience community to achieve a better understanding of the fundamentals of FLIM-FRET and encourage them to fully leverage its powerful ability as a research tool. Published 2020. U.S. Government.

Mitochondrial E3 Ubiquitin Ligase Parkin: Relationships with Other Causal Proteins in Familial Parkinson's Disease and Its Substrate-Involved Mouse Experimental Models

Parkinson’s disease (PD) is a common neurodegenerative disorder. Recent identification of genes linked to familial forms of PD has revealed that post-translational modifications, such as phosphorylation and ubiquitination of proteins, are key factors in disease pathogenesis. In PD, E3 ubiquitin ligase Parkin and the serine/threonine-protein kinase PTEN-induced kinase 1 (PINK1) mediate the mitophagy pathway for mitochondrial quality control via phosphorylation and ubiquitination of their substrates. In this review, we first focus on well-characterized PINK1 phosphorylation motifs. Second, we describe our findings concerning relationships between Parkin and HtrA2/Omi, a protein involved in familial PD. Third, we describe our findings regarding inhibitory PAS (Per/Arnt/Sim) domain protein (IPAS), a member of PINK1 and Parkin substrates, involved in neurodegeneration during PD. IPAS is a dual-function protein involved in transcriptional repression of hypoxic responses and the pro-apoptotic activities.