van der Horst GT, etal., Nature 1999 Apr 15;398(6728):627-30.
Many biochemical, physiological and behavioural processes show circadian rhythms which are generated by an internal time-keeping mechanism referred to as the biological clock. According to rapidly developing models, the core oscillator driving this clock is composed of an autoregulatory transcriptio
n-(post) translation-based feedback loop involving a set of 'dock' genes. Molecular clocks do not oscillate with an exact 24-hour rhythmicity but are entrained to solar day/night rhythms by light. The mammalian proteins Cryl and Cry2, which are members of the family of plant blue-light receptors (cryptochromes) and photolyases, have been proposed as candidate light receptors for photoentrainment of the biological clock. Here we show that mice lacking the Cryl or Cry2 protein display accelerated and delayed free-running periodicity of locomotor activity, respectively. Strikingly, in the absence of both proteins, an instantaneous and complete loss of free-running rhythmicity is observed. This suggests that, in addition to a possible photoreceptor and antagonistic clock-adjusting function, both proteins are essential for the maintenance of circadian rhythmicity.
Papp SJ, etal., Elife. 2015 Mar 10;4. doi: 10.7554/eLife.04883.
The circadian transcriptional repressors cryptochrome 1 (Cry1) and 2 (Cry2) evolved from photolyases, bacterial light-activated DNA repair enzymes. In this study, we report that while they have lost DNA repair activity, Cry1
/2 adapted to protect genomic integrity by responding to DNA damage through posttranslational modification and coordinating the downstream transcriptional response. We demonstrate that genotoxic stress stimulates Cry1 phosphorylation and its deubiquitination by Herpes virus associated ubiquitin-specific protease (Hausp, a.k.a Usp7), stabilizing Cry1 and shifting circadian clock time. DNA damage also increases Cry2 interaction with Fbxl3, destabilizing Cry2. Thus, genotoxic stress increases the Cry1/Cry2 ratio, suggesting distinct functions for Cry1 and Cry2 following DNA damage. Indeed, the transcriptional response to genotoxic stress is enhanced in Cry1-/- and blunted in Cry2-/- cells. Furthermore, Cry2-/- cells accumulate damaged DNA. These results suggest that Cry1 and Cry2, which evolved from DNA repair enzymes, protect genomic integrity via coordinated transcriptional regulation.
Patke A, etal., Cell. 2017 Apr 6;169(2):203-215.e13. doi: 10.1016/j.cell.2017.03.027.
Patterns of daily human activity are controlled by an intrinsic circadian clock that promotes ∼24 hr rhythms in many behavioral and physiological processes. This system is altered in delayed sleep phase disorder (DSPD), a common form of insomnia in which sleep episodes are shifted to later times mis
aligned with the societal norm. Here, we report a hereditary form of DSPD associated with a dominant coding variation in the core circadian clock gene CRY1, which creates a transcriptional inhibitor with enhanced affinity for circadian activator proteins Clock and Bmal1. This gain-of-function CRY1 variant causes reduced expression of key transcriptional targets and lengthens the period of circadian molecular rhythms, providing a mechanistic link to DSPD symptoms. The allele has a frequency of up to 0.6%, and reverse phenotyping of unrelated families corroborates late and/or fragmented sleep patterns in carriers, suggesting that it affects sleep behavior in a sizeable portion of the human population.
The CUL4-DDB1 E3 ligase complex serves as a critical regulator in various cellular processes, including cell proliferation, DNA damage repair, and cell cycle progression. However, whether this E3 ligase complex regulates clock protein turnover and the molecular clock activity in mammalian cells is u
nknown. Here we show that CUL4-DDB1-CDT2 E3 ligase ubiquitinates CRY1 and promotes its degradation both in vitro and in vivo. Depletion of the major components of this E3 ligase complex, including Ddb1, Cdt2, and Cdt2-cofactor Pcna, leads to CRY1 stabilization in cultured cells or in the mouse liver. CUL4A-DDB1-CDT2 E3 ligase targets lysine 585 within the C-terminal region of CRY1 protein, shown by the CRY1 585KA mutant's resistance to ubiquitination and degradation mediated by the CUL4A-DDB1 complex. Surprisingly, both depletion of Ddb1 and over-expression of Cry1-585KA mutant enhance the oscillatory amplitude of the Bmal1 promoter activity without altering its period length, suggesting that CUL4A-DDB1-CDT2 E3 targets CRY1 for degradation and reduces the circadian amplitude. All together, we uncovered a novel biological role for CUL4A-DDB1-CDT2 E3 ligase that regulates molecular circadian behaviors via promoting ubiquitination-dependent degradation of CRY1.
Yang L, etal., Int Immunopharmacol. 2015 Sep;28(1):525-30. doi: 10.1016/j.intimp.2015.07.001. Epub 2015 Jul 25.
It has been demonstrated that the circadian clock system could be a potential factor involved in inflammation and the progression of atherosclerosis. A previous study has reported that cryptochrome 1 (CRY1), which is a core clock component, is associated with re
gulating proinflammation. However, whether CRY1 is involved in atherosclerosis is currently unknown. In the present study, we aimed to explore the role of CRY1 in regulating atherosclerosis in apolipoprotein E (ApoE)-deficient mice and the underlying molecular mechanism. We found that CRY1 mRNA expression was significantly decreased in atherosclerotic patients compared to the healthy subjects. Overexpression of CRY1 in the mouse model of atherosclerosis by adenovirus-mediated gene transfer significantly decreased the expression of proinflammatory factors including tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1, IL-6, and macrophage inflammatory protein-1alpha (MIP-1alpha). In addition, the adhesion molecules including vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), and E-selectin, were also downregulated by CRY1 overexpression. Furthermore, the plaque area of the aortic sinus and the concentrations of total cholesterol (TC), triglyceride (TG), and low density lipoprotein cholesterol (LDL-C) were also decreased in the atherosclerotic mice by CRY1 overexpression. Moreover, overexpression of CRY1 significantly decreased the protein levels of toll-like receptor (TLR) 2, TLR4 and phosphorylated p65 (p-p65). Additionally, the results of luciferase reporter assay exhibited that CRY1 overexpression was capable of inhibiting the activation of nuclear factor-kappa B (NF-kappaB). Taken together, our results suggest that overexpression of CYR1 relieves the development of atherosclerosis that may be associated with regulating the TLR/NF-kappaB pathway.
