Biology subjects

Fribourgh, J. L.

Publications and source records attributed to Fribourgh, J. L..

4 recordsLinked to original sources

bioRxiv2021

Quantification of circadian interactions and protein abundance defines a mechanism for operational stability of the circadian clock

The mammalian circadian clock exerts substantial control of daily gene expression through cycles of DNA binding. Understanding of mechanisms driving the circadian clock is hampered by lack of quantitative data, without which predictive mathematical models cannot be developed. Here we develop a quantitative understanding of how a finite pool of BMAL1 protein can regulate thousands of target sites over daily time scales. We have used fluorescent correlation spectroscopy (FCS) to track dynamic changes in CRISPR-modified fluorophore-tagged proteins in time and space in single cells across SCN and peripheral tissues. We determine the contribution of multiple rhythmic processes in coordinating BMAL1 DNA binding, including the roles of cycling molecular abundance, binding affinities and two repressive modes of action. We find that nuclear BMAL1 protein numbers determine corresponding nuclear CLOCK concentrations through heterodimerization and define a DNA residence time of 2.6 seconds for this complex. Repression of CLOCK:BMAL1 is in part achieved through rhythmic changes to BMAL1:CRY1 affinity as well as a high affinity interaction between PER2:CRY1 which mediates CLOCK:BMAL1 displacement from DNA. Finally, stochastic modelling of these data reveals a dual role for PER:CRY complexes in which increasing concentrations of PER2:CRY1 promotes removal of BMAL1:CLOCK from genes consequently enhancing ability to move to new target sites.

systems biology↗

bioRxiv2021

CRY2 missense mutations suppress P53 and enhance cell growth

Disruption of circadian rhythms increases the risk of several types of cancer. Mammalian cryptochromes (CRY1 and CRY2) are circadian transcriptional repressors that are related to DNA repair enzymes. While CRYs lack DNA repair activity, they modulate the transcriptional response to DNA damage, and CRY2 can promote SCFFBXL3-mediated ubiquitination of c-MYC and other targets. Here, we characterize five mutations in CRY2 observed in human cancers in The Cancer Genome Atlas. We demonstrate that two orthologous mutations of mouse CRY2 (D325H and S510L) accelerate the growth of primary mouse fibroblasts expressing high levels of c-MYC. Neither mutant affects steady state levels of overexpressed c-MYC, and they have divergent impacts on circadian rhythms and on the ability of CRY2 to interact with SCFFBXL3. Unexpectedly, stable expression of either CRY2 D325H or of CRY2 S510L robustly suppresses P53 target gene expression, suggesting that this is the primary mechanism by which they influence cell growth.

cell biology↗

bioRxiv2019

The CRY1 tail controls circadian timing by regulating its association with CLOCK:BMAL1

Circadian rhythms are generated by a transcription-translation feedback loop that establishes cell-autonomous biological timing of ~24-hours. A prevalent human variation in the core clock gene cryptochrome 1, Cry1{Delta}11, lengthens circadian period to cause Delayed Sleep Phase Disorder (DSPD). CRY1 has a 55 kDa photolyase homology region (PHR) followed by a ~100 residue tail that is intrinsically disordered; the {Delta}11 variant lacks a short segment encoded by Exon 11 within its tail. We show here that the disordered tail of CRY1 interacts directly with its PHR, and that Exon 11 is necessary and sufficient to disrupt the interaction between CRY1 and CLOCK, a subunit of the primary circadian transcription factor. Competition between PER2 and the tail for the CRY1 PHR suggests a regulatory role for the tail in the early morning, when CRY1 binds to CLOCK:BMAL1 on DNA independently of PER2. Discovery of this autoregulatory role for mammalian CRY1 highlights functional conservation with plant and insect cryptochromes, which also utilize PHR-tail interactions to reversibly control their activity.\n\nOne Sentence SummaryThe disordered tail of the CRY1 protein regulates interactions between CRY1 and other core circadian rhythm proteins.

biochemistry↗

bioRxiv2019

Protein dynamics regulate distinct biochemical properties of cryptochromes in mammalian circadian rhythms

Circadian rhythms are generated by a transcription-based feedback loop where CLOCK:BMAL1 drive transcription of their repressors (PER1/2, CRY1/2), which bind to CLOCK:BMAL1 to close the feedback loop with ~24-hour periodicity. Here we identify a key biochemical and structural difference between CRY1 and CRY2 that underlies their differential strengths as transcriptional repressors. While both cryptochromes bind the BMAL1 transactivation domain with similar affinity to sequester it from coactivators, CRY1 is recruited with much higher affinity to the PAS domain core of CLOCK:BMAL1, allowing it to serve as a stronger repressor that lengthens circadian period. We identify a dynamic loop in the secondary pocket that regulates differential binding of cryptochromes to the PAS domain core. Notably, PER2 binding remodels this loop in CRY2 to enhance its affinity for CLOCK:BMAL1, explaining why CRY2 forms an obligate heterodimer with PER2, while CRY1 is capable of repressing CLOCK:BMAL1 both with and without PER2.

biochemistry↗