Biology subjects

Chan, K.-L.

Publications and source records attributed to Chan, K.-L..

5 recordsLinked to original sources

bioRxiv2026

Mechanistic basis for the spatiotemporal assembly of the Bloom Syndrome complex on ultrafine DNA bridges

The BTRR (BLM/TOP3A/RMI1/RMI2) complex resolves DNA replication and recombination intermediates, as well as mitotic DNA intertwinements, yet how its diverse activities are regulated remains unclear. Here, we identify key determinants of stable assembly of the BTRR complex on ultrafine DNA bridges (UFBs). We reveal that the RMI1-RMI2 subcomplex acts as a molecular reader of hydrophobic-rich short linear motifs (SLiMs) embedded within PICH and FANCM, thereby providing a conserved mechanism for engaging distinct Superfamily2 DNA translocases during chromosome segregation and DNA repair. During UFB resolution, SLiM binding stabilises the PICH-BTRR complex assembly and supports essential interactions among BLM, PICH, and DNA. Persistent PICH-BTRR complex association post-mitosis would compromise interphase DNA damage responses and is prevented by active PICH nuclear exclusion. Our findings define the molecular basis of UFB-binding complex assembly and highlight its spatiotemporal control required to specialise BTRR complex functions.

cell biology↗

bioRxiv2024

Centromere protection requires strict mitotic inactivation of the Bloom syndrome helicase complex

The BTRR (BLM/TOP3A/RMI1/RMI2) complex resolves various DNA replication and recombination intermediates to suppress genome instability. Alongside PICH, they target mitotic DNA intertwinements, known as ultrafine DNA bridges, facilitating chromosome segregation. Both BLM and PICH undergo transient mitotic hyper-phosphorylation, but the biological significance of this remains elusive. Here, we uncover that during early mitosis, multiple protein kinases act together to strictly constrain the BTRR complex for the protection of centromeres. Mechanistically, CDK1 destabilises the complex and suppresses its association with PICH at the chromatin underneath kinetochores. Inactivating the BLM and TOP3A interaction compromises the UFB-binding complex mitotic functions and can prevent centromere destruction. We further unravel how different clusters of mitotic phosphorylation on BLM affect its interaction with the TOP3A/RMI1/RMI2 subcomplex and illegitimate centromere unwinding. Furthermore, we identify specific phosphorylation sites targeted by the MPS1-PLK1 axis functioning to prevent BLM hyper-activation at centromeres. Notably, unleashing such activity after sister-chromatid cohesion loss facilitates separation of entangled chromosomes. Together, our study defines a centromere protection pathway in human mitotic cells, heavily reliant on a tight spatiotemporal control of the BTRR complex.

cell biology↗

bioRxiv2022

The FIGNL1-interacting protein C1orf112 is synthetic lethal with PICH and mediates RAD51 retention on chromatin.

Joint DNA molecules are natural by-products of DNA replication and repair. Persistent joint molecules give rise to ultrafine DNA bridges (UFBs) in mitosis, which compromise sister chromatid separation. The DNA translocase PICH (ERCC6L) plays a central role in UFB resolution. A genome-wide loss-of-function screen was performed to identify the genetic contexts in which cells become dependent on PICH. In addition to genes involved in DNA condensation, centromere stability and DNA damage repair, we identified the uncharacterized protein C1orf112. We find that C1orf112 interacts with and stabilizes the AAA+ ATPase FIGNL1. Inactivation of either C1orf112 or FIGNL1 resulted in UFB formation, prolonged retention of RAD51 on chromatin, impaired replication fork dynamics, and consequently impaired genome maintenance. Combined, our data reveal that inactivation of C1orf112 and FIGNL1 dysregulates RAD51 dynamics at replication forks, resulting in DNA replication defects, and a dependency on PICH to preserve cell viability.

cancer biology↗

bioRxiv2018

PLK1 protects centromeres from BLM-mediated disintegration to promote chromosome biorientation

Faithful chromosome segregation cannot be achieved without proper chromosome biorientation (so-called metaphase alignment). Disabling PLK1, a key mitotic kinase, impairs multiple aspects of mitosis, particularly chromosome alignment. This is believed primarily due to unstable bipolar spindle-kinetochore attachments. Contrary to this belief, PLK1 inactivation does not necessarily abolish metaphase establishment, instead impairing its maintenance. Here, we demonstrate that the failure of chromosome biorientation maintenance is driven by a hitherto undescribed mechanism named centromere dislocation. Without an active PLK1 during mitosis, BLM helicase is illegitimately recruited to and unwinds a specific centromere domain underneath kinetochores in a PICH-dependent manner, impairing centromere configuration and rigidity. Acting with bipolar spindle pulling forces, the distorted centromeric chromatin is promptly converted into an ultra-thin DNA structure, termed pre-anaphase interchromatin DNA threads(PITs) and fails to withstand spindle tension, resulting in whole-chromosome arms splitting. This devastating dechromatinisation action severely damages the centromere integrity and destroys normal metaphase maintenance. Therefore, our study unveils that in order to facilitate chromosome biorientation, PLK1 serves as a chromosome guardian to protect centromeres from disintegration, driven by a BLM-mediated chromatin decompaction activity.

cell biology↗

bioRxiv2017

The cohesin ring uses its hinge to organize DNA using non-topological as well as topological mechanisms

As predicted by the notion that sister chromatid cohesion is mediated by entrapment of sister DNAs inside cohesin rings, there is a perfect correlation between co-entrapment of circular minichromosomes and sister chromatid cohesion in a large variety of mutants. In most cells where cohesin loads onto chromosomes but fails to form cohesion, loading is accompanied by entrapment of individual DNAs. However, cohesin with a hinge domain whose positively charged lumen has been neutralized not only loads onto and translocates along chromatin but also organizes it into chromatid-like threads, despite largely failing to entrap DNAs inside its ring. Thus, cohesin engages chromatin in a non-topological as well as a topological manner. Our finding that hinge mutations, but not fusions between Smc and kleisin subunits, abolish entrapment suggests that DNAs may enter cohesin rings through hinge opening. Lastly, mutation of three highly conserved lysine residues inside the Smc1 moiety of Smc1/3 hinges abolishes all loading without affecting cohesins initial recruitment to CEN loading sites or its ability to hydrolyze ATP. We suggest that loading and translocation are mediated by conformational changes in cohesins hinge driven by cycles of ATP hydrolysis.

molecular biology↗