Biology subjects

Parico, G. C. G.

Publications and source records attributed to Parico, G. C. G..

4 recordsLinked to original sources

bioRxiv2022

CHRONO participates in multi-modal repression of circadian transcriptional complexes

The mammalian protein CHRONO is a rhythmically expressed repressor of the circadian transcriptional activator complex CLOCK:BMAL1, and was proposed to be a novel component of the circadian clock. However, lack of specific mechanistic understanding of the activity and function of CHRONO meant that its role within the circadian machinery was opaque. Here we fill this knowledge gap, confirming an evolutionarily conserved minimal repressive domain (MRD) of CHRONO that interacts with specific regions in the BMAL1 C-terminal transactivation domain (TAD) to repress CLOCK:BMAL1 activity. Notably, this binding region overlaps with the binding site for the repressor CRY and coactivators CBP/p300, with CHRONO capable of competing with both of these classical regulators of BMAL1 for TAD binding, highlighting CHRONO as a direct regulator of BMAL1 function. Additionally, we investigate the interaction between CHRONO and the major circadian repressor, PERIOD2 (PER2). We show that CHRONO reduces PER2 stability through interaction between the CHRONO C-terminus and the Casein Kinase 1 (CK1)-binding domain of PER2. This results in competition between CHRONO and CK1 for binding at this site on PER2, with CHRONO binding inhibiting CK1 phosphorylation of PER2 at the stabilising S662 residue. Taken together, these data show a more substantive and complex role for CHRONO in molecular circadian timekeeping than previously posited, suggesting that CHRONO acts to fine-tune cellular timekeeping by modulating multiple protein-protein interactions that are critical for maintenance of circadian rhythmicity.

biochemistry↗

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↗