FAD Regulates CRYPTOCHROME Protein Stability and Circadian Clock in Mice

Cell Rep. 2017 Apr 11;19(2):255-266. doi: 10.1016/j.celrep.2017.03.041.


The circadian clock generates biological rhythms of metabolic and physiological processes, including the sleep-wake cycle. We previously identified a missense mutation in the flavin adenine dinucleotide (FAD) binding pocket of CRYPTOCHROME2 (CRY2), a clock protein that causes human advanced sleep phase. This prompted us to examine the role of FAD as a mediator of the clock and metabolism. FAD stabilized CRY proteins, leading to increased protein levels. In contrast, knockdown of Riboflavin kinase (Rfk), an FAD biosynthetic enzyme, enhanced CRY degradation. RFK protein levels and FAD concentrations oscillate in the nucleus, suggesting that they are subject to circadian control. Knockdown of Rfk combined with a riboflavin-deficient diet altered the CRY levels in mouse liver and the expression profiles of clock and clock-controlled genes (especially those related to metabolism including glucose homeostasis). We conclude that light-independent mechanisms of FAD regulate CRY and contribute to proper circadian oscillation of metabolic genes in mammals.

Keywords: CRY; CRYPTOCHROME; FAD; FBXL3; Riboflavin kinase; circadian clock; circadian rhythms; metabolism; protein degradation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Circadian Clocks / genetics*
  • Circadian Rhythm / genetics
  • Cryptochromes / biosynthesis*
  • Cryptochromes / genetics*
  • F-Box Proteins / genetics
  • Flavin-Adenine Dinucleotide / biosynthesis
  • Gene Expression Regulation, Developmental
  • Gene Knockdown Techniques
  • Humans
  • Liver / metabolism
  • Male
  • Mice
  • Mutation, Missense
  • Period Circadian Proteins / biosynthesis*
  • Period Circadian Proteins / genetics
  • Phosphotransferases (Alcohol Group Acceptor) / genetics*
  • Protein Stability
  • Proteolysis
  • Riboflavin / genetics
  • Riboflavin / metabolism


  • Cry1 protein, mouse
  • Cry2 protein, mouse
  • Cryptochromes
  • F-Box Proteins
  • Fbxl3 protein, mouse
  • Per1 protein, mouse
  • Period Circadian Proteins
  • Flavin-Adenine Dinucleotide
  • Phosphotransferases (Alcohol Group Acceptor)
  • riboflavin kinase
  • Riboflavin