In Vivo Role of Phosphorylation of Cryptochrome 2 in the Mouse Circadian Clock

Abstract

The circadian clock is finely regulated by posttranslational modifications of clock components. Mouse CRY2, a critical player in the mammalian clock, is phosphorylated at Ser557 for proteasome-mediated degradation, but its in vivo role in circadian organization was not revealed. Here, we generated CRY2(S557A) mutant mice, in which Ser557 phosphorylation is specifically abolished. The mutation lengthened free-running periods of the behavioral rhythms and PER2::LUC bioluminescence rhythms of cultured liver. In livers from mutant mice, the nuclear CRY2 level was elevated, with enhanced PER2 nuclear occupancy and suppression of E-box-regulated genes. Thus, Ser557 phosphorylation-dependent regulation of CRY2 is essential for proper clock oscillation in vivo.T ranscription-and translation-based negative-feedback loops play an important role in circadian clock regulation (1, 2). In mammals, a heterodimer of positive factors, CLOCK and BMAL1, activates the transcription of genes encoding negative factors such as PERIOD (PER1 to -3) and cryptochrome (CRY1 and -2) through binding to E-box enhancer elements in their promoter regions (3). Translated PERs and CRYs associate with each other, enter into cell nuclei, and inhibit their own transcription by interacting with the CLOCK-BMAL1 heterodimer (4). In addition to transcriptional and translational regulation, posttranslational modifications of the clock proteins play critical roles in the clockwork (5-8).Among the negative factors, CRY1 and CRY2 play major roles for repression of E-box-dependent gene expression (9). They share highly conserved N-terminal and central regions while having unique C-terminal tails. Although the roles of the diverged C-terminal regions remain unclear, both CRY1 and CRY2 have strong repressor activities (9), and therefore, their accumulation and decline are the major period-determining steps for circadian molecular oscillation. Previous studies reported that FBXL3, an F-box-type E3 ubiquitin ligase, enhances proteasomal degradation of . Recently, we and other groups demonstrated that ubiquitination of CRY1 and CRY2 by FBXL21, the closest paralog of FBXL3, stabilizes CRYs (13,14). It has been reported that FBXL3-dependent CRY1 degradation is regulated by CRY1 phosphorylation (15, 16). In contrast, we previously demonstrated that priming phosphorylation of CRY2 at Ser557 in the C-terminal region by DYRK1A is required for secondary phosphorylation at Ser553 by glycogen synthase kinase 3␤ (GSK-3␤) (17, 18). The dually phosphorylated CRY2 is led to proteasomal degradation (18), which is independent of FBXL3 action (17, 18). So far, the functions of CRY regulators, such as protein kinases and ubiquitin ligases, have been examined by using their inhibitors and/or gene knockout/knockdown (17-19). On the other hand, site-directed mutagenesis in CRY proteins will be the most specific strategy because the upstream regulators would have multiple targets in the clockwork. In the present study, we generated knock-in mice carrying a mutation at the priming pho...

FAD Regulates CRYPTOCHROME Protein Stability and Circadian Clock in Mice

“…The stability of CRY1 and CRY2 significantly affects the circadian period at molecular and behavioral levels (Godinho et al, 2007; Hirano et al, 2014; 2016a; Ode et al, 2016; Siepka et al, 2007). Additionally, the FASP mouse model expressing A260T-CRY2 protein exhibits shorter circadian period of both behavioral rhythms and cellular rhythms in peripheral tissues (Hirano et al, 2016b).…”

USP7 and TDP-43: Pleiotropic Regulation of Cryptochrome Protein Stability Paces the Oscillation of the Mammalian Circadian Clock

“…Previous studies demonstrated that dysregulation of CRY stabilities caused abnormal periodicity in mouse behavioral rhythms and gene expression rhythms [ 12 , 14 , 15 , 17 , 31 , 32 ]. For example, knockdown or knockout of Fbxl3 lengthened the circadian period [ 15 , 16 ], whereas knockdown or mutation of Fbxl21 shortened the period [ 15 , 17 ].…”

The intricate dance of post-translational modifications in the rhythm of life

“…This sequential phosphorylation recruits an unknown E3 ligase, thereby leading to CRY2 degradation 70 . Mutation at the priming site (S557A) leads to decreased CRY2 turnover and a lengthened circadian period in mice 72 . However, phosphorylation at Ser588 in the C-terminal region of CRY1 prevents the FBXL3-CRY1 interaction and consequently increases CRY1 stability 73 .…”