Nuclear import carrier Hikeshi cooperates with HSP70 to promote murine oligodendrocyte differentiation and CNS myelination

Bisphenol AF induces lipid metabolism disorders, oxidative stress and upregulation of heat shock protein 70 in zebrafish

Bisphenol AF (BPAF) is a widespread endocrine disruptor in the environment, and the use of BPAF has been strongly associated with the development of several diseases. In this study, we investigated the effects of BPAF on growth, development, oxidative stress and lipid metabolism in zebrafish. We chose the concentrations based on the measured LC50 at 96 h post-fertilization (96 hpf), and the zebrafish embryos were exposed to three different concentrations (0.125, 0.5 and 2 μmol/L). The findings indicated that BPAF exposure in zebrafish leaded to alterations in heart rate, body length and hatching rate, as well as an accumulation of red blood cells in the heart. Additionally, BPAF exposure resulted in increased levels of neutrophils, reactive oxygen species (ROS) and malondialdehyde (MDA), and decreased activity of antioxidant enzymes (superoxide dismutase (SOD) and catalase (CAT)), thus disturbing the balance between oxidative and antioxidative systems. BPAF promoted fatty acid catabolism and inhibited fatty acid synthesis, ultimately leading to a reduction in fatty acid content. Mechanistically, RNA-seq analysis and RT-qPCR revealed a significant upregulation of heat shock protein 70 (hsp70) after BPAF exposure. Inhibition of hsp70 with VER-155008 ameliorated BPAF-induced oxidative stress. These data provided a novel approach to investigate BPAF-induced oxidative stress and suggested that regulation of hsp70 is a crucial target for alleviating this process.

Functional analysis of Hikeshi reveals physiological significance of nuclear Hsp70

Nucleocytoplasmic transport is a basic cellular reaction that plays an important role in regulating cell physiology in eukaryotic cells. Here we show that the identification of one nucleocytoplasmic transport pathway led to the notification of intracellular reaction that has not been acknowledged. Hikeshi was originally identified as a nuclear import carrier of heat stress-induced nuclear import of molecular chaperone Hsp70. We now know that Hikeshi mediates nuclear import of Hsp70 at a variety of different cellular conditions, such as at normal conditions, at proteotoxic conditions, during differentiation, and probably more. Recent studies gradually revealed the physiological significances of Hikeshi-mediated nuclear import of Hsp70.

The interaction between the import carrier Hikeshi and HSP70 is modulated by heat, facilitating the nuclear import of HSP70 under heat stress conditions

Heat stress strongly triggers the nuclear localization of the molecular chaperone HSP70. Hikeshi functions as a unique nuclear import carrier of HSP70. However, how the nuclear import of HSP70 is activated in response to heat stress remains unclear. Here, we investigated the effects of heat on the nuclear import of HSP70. In vitro transport assays revealed that pretreatment of the test samples with heat facilitated the nuclear import of HSP70. Furthermore, binding of Hikeshi to HSP70 increased when temperatures rose. These results indicated that heat is one of the factors that activates the nuclear import of HSP70. Previous studies showed that the F97A mutation in Hikeshi in an extended loop induced an opening in the hydrophobic pocket and facilitated the translocation of Hikeshi through the nuclear pore complex. We found that nuclear accumulation of HSP70 occurred at a lower temperature in cells expressing the Hikeshi-F97A mutant than in cells expressing wild-type Hikeshi. Collectively, our results show that the movement of the extended loop may play an important role in the interaction of Hikeshi with both FG (phenylalanine-glycine)-nucleoporins and HSP70 in a temperature-dependent manner, resulting in the activation of nuclear import of HSP70 in response to heat stress.

Nucleoporin Seh1 controls murine neocortical development via transcriptional repression of p21 in neural stem cells

Mutations or dysregulation of nucleoporins (Nups) are strongly associated with neural developmental diseases, yet the underlying mechanisms remain poorly understood. Here, we show that depletion of Nup Seh1 in radial glial progenitors results in defective neural progenitor proliferation and differentiation that ultimately manifests in impaired neurogenesis and microcephaly. This loss of stem cell proliferation is not associated with defects in the nucleocytoplasmic transport. Rather, transcriptome analysis showed that ablation of Seh1 in neural stem cells derepresses the expression of p21, and knockdown of p21 partially restored self-renewal capacity. Mechanistically, Seh1 cooperates with the NuRD transcription repressor complex at the nuclear periphery to regulate p21 expression. Together, these findings identified that Nups regulate brain development by exerting a chromatin-associated role and affecting neural stem cell proliferation.