br Conclusion br Author contributions br Ethics approval
Introduction VHL is a well-known tumor suppressor and works as a target recruitment subunit of an E3 ubiquitin ligase complex that recruits hydroxylated hypoxia inducible factor α (HIF-α) for proteasomal degradation under normoxia [1,2]. While under hypoxia or when VHL gene is mutated, VHL protein cannot bind to HIF-α and trigger its degradation. This allows HIF-α to associate with HIF-β and activate many genes transcription . In addition to HIF-α, VHL can interact with many other proteins and is implicated in several biological processes by its roles during cell proliferation, apoptosis, microtubule dynamics, extracellular matrix deposition, DNA damage response/repair and primary cilia maintenance . NEK1, the first mammalian ortholog of the NEK kinases, also plays an important role in cilia disassembly . NEK1 is a conserved serine/threonine (Ser/Thr) and tyrosine kinase of 774 amino acids, which includes an N-terminal kinase domain with most similar catalytic domain of NIMA (never in mitosis gene A-related kinase in A.nidulans) with critical role in promoting trk receptor progression, and a long basic C-terminal extension. In addition to cilia, the roles of NEK1 has been associated with DNA damage response . Mallikarjun Patil et al. . disclosed the molecular connection between NEK1 and VHL. They reported that NEK1 can phosphorylate VHL to stimulate its degradation and ciliary disassembly. On the other hand, our previous work show that VHL can down-regulate NEK8 via HIF pathway . Considering both NEK1 and NEK8 are members of NEK kinases family and involved in ciliary disassembly [9,10], we postulated NEK1 may also be a downstream target of VHL.
Materials and methods
Discussion NEK1 is a serine/threonine kinase in regard to cell cycle regulation and found firstly in a centrosome complex with fasciculation and elongation protein zeta 1 (FEZ1) [5,12]. Loss of NEK1 is associated with polycystic kidney disease (PKD) . Resent research showed that NEK1 also involves in cilia dynamics and DNA damage response [, , , ]. However, the underlying mechanism of NEK1 regulation is poorly understudied [18,19]. Here, we showed for the first that the VHL played an important role in NEK1 regulation. We showed there is a hypoxia reaction elements (HRE, 5′-RCGTG-3′, R = A/G) candidate in NEK1 promoter. Consequently, NEK1 supposed to be a new target of HIFs. This hypothesis was testified by related experiments of inducing NEK1 expression by hypoxia in vitro and in vivo. In addition, we also found the association of VHL with NEK1 using immunoprecipitation assay in Caki-1 cells. As VHL is a classic E3 ligase, the primary data proposed that VHL may directly promote NEK1 degradation. The fact that proteasome inhibitor could attenuate VHL-induced NEK1 degradation and VHL could promote NEK1 ubiquitination verified that VHL mediated NEK1 degradation via the ubiquitin-proteasomal pathway. Since Mallikarjun Patil et al. . revealed that NEK1 can phosphorylate VHL to promote its proteasomal degradation, while our data conversely showed that VHL down-regulated NEK1, there should be a positive feedback between VHL and NEK1 to promote cancer developing.
Acknowledgments This work was supported by Zhejiang Provincial Natural Science Foundation of China (No. LY16H310006, LY15H310001, LY15H310002), National Natural Science Foundation of China (No. 81802657), Public Technology Research Projects of the Science Technology Department of Zhejiang Province (No.2016C33235 and 2018C37109), Grant from Zhejiang Medical association (No. 2013zyc-A138) and Technology Research Projects of the Science Technology Department of Jiaojiang District (No. 132055).
Introduction In the 1970s, a serious energy crisis triggered by oil crisis damaged the global economy. Accelerator scientists proposed several HIF projects to solve the energy problem, such as HIBALL , HIDIF ,  and HIBLIC  in USA, Germany and Japan respectively. The heavy-ion beams were used to irradiate the deuterium-tritium (D-T) target and to increase the plasma temperature and density to reach the Lawson criterion, and to initiate the D-T fusion reaction. In this case, the D-T fusion would be caused by the initially confined D-T plasma. All proposed HIF plans were large scale facilities. For example, there are 16 injectors in the design of HIBLIC , and the total length of the driver linac is more than 30 km. Compared with magnetic-field confined Tokomak facilities and the National Ignition Facility , the proposed linac-driven HIF injectors are too large to be built. Nevertheless, for linac-driven HIF facilities, the energy gain is about 3 times that of Tokomak facilities, and the linac-driven HIF is safer .