The non-classical nuclear import carrier Transportin 1 modulates circadian rhythms through its effect on PER1 nuclear localization

Abstract

Circadian clocks are molecular timekeeping mechanisms that allow organisms to anticipate daily changes in their environment. The fundamental cellular basis of these clocks is delayed negative feedback gene regulation with PERIOD and CRYPTOCHROME containing protein complexes as main inhibitory elements. For a correct circadian period, it is essential that such clock protein complexes accumulate in the nucleus in a precisely timed manner, a mechanism that is poorly understood. We performed a systematic RNAi-mediated screen in human cells and identified 15 genes associated with the nucleo-cytoplasmic translocation machinery, whose expression is important for circadian clock dynamics. Among them was Transportin 1 (TNPO1), a non-classical nuclear import carrier, whose knockdown and knockout led to short circadian periods. TNPO1 was found in endogenous clock protein complexes and particularly binds to PER1 regulating its (but not PER2’s) nuclear localization. While PER1 is also transported to the nucleus by the classical, Importin β-mediated pathway, TNPO1 depletion slowed down PER1 nuclear import rate as revealed by fluorescence recovery after photobleaching (FRAP) experiments. In addition, we found that TNPO1-mediated nuclear import may constitute a novel input pathway of how cellular redox state signals to the clock, since redox stress increases binding of TNPO1 to PER1 and decreases its nuclear localization. Together, our RNAi screen knocking down import carriers (but also export carriers) results in short and long circadian periods indicating that the regulatory pathways that control the timing of clock protein subcellular localization are far more complex than previously assumed. TNPO1 is one of the novel players essential for normal circadian periods and potentially for redox regulation of the clock.

The Circadian Gene Per1 Plays an Important Role in Radiation-Induced Apoptosis and DNA Damage in Glioma

“…DOI:10.31557/APJCP.2019.20.7.2195 Down-Regulation of PER1 Decreases Apoptosis of Glioma Cells after X-ray Irradiate the role of PER1 in glioma cells. Evidence from initial research implicated PER1 as a regulator of the circadian clock (Han et al, 2016;Korge et al, 2018;Repouskou et al, 2016;Reinhardt et al, 2012;Riley et al, 2008); however, recent evidence has expanded the function of PER1 to include the promotion of apoptosis in cancer cells (Han et al, 2016;Korge et al, 2007). We hypothesized that PER1 is also a tumor suppressor gene.…”

Transportin-1: A Nuclear Import Receptor with Moonlighting Functions

“…Here ROS enhances the binding of the DJ-1 PY-NLS to Trn1, but the effect is likely indirect and triggered by DJ-1 monomerization ( Björkblom et al, 2014 ). In a last example, it was also shown that ROS stimulates the interaction of Trn1 with the circadian clock protein PERIOD 1 (PER1) ( Korge et al, 2018 ). Here, H 2 O 2 treatment resulted in a dose-dependent increase of Trn1-PER1 interaction.…”

“…It is worth mentioning that Trn1-binding to PER1 is abolished under reducing conditions, which suggests that a disulfide bond might be formed between a cysteine residue of PER1 and a cysteine residue in Trn1, as reported for FOXO4 ( Putker et al, 2013 ). Unexpectedly, increased binding upon H 2 O 2 treatment did not lead to an increased nuclear import of PER1, but was rather associated with a specific slow-down of PER1 nuclear import ( Korge et al, 2018 ). This intriguing observation might be related to the fact that PER1 is translocated into the nucleus by several karyopherins, but would definitely deserve further examination.…”

The NRON complex controls circadian clock function through regulated PER and CRY nuclear translocation

“…These kinases also regulate phosphorylation-related proteolysis and nuclear entry of PER and CRY proteins 13,14,20,22 . Further, two other components of the NRON complex, nuclear importin beta (KPNB1) and nuclear import carrier Transportin 1 (TNPO1) were recently shown to play a key role in post-translational regulation of the PER/CRY complex 20,29 . Thus, the NFAT and circadian clock pathways share functional components.…”