HP1 Promotes the Centromeric Localization of ATRX and Protects Cohesion by Interfering Wapl Activity in Mitosis.

Background: α thalassemia/mental retardation syndrome X-linked (ATRX) serves as a part of the sucrose nonfermenting 2 (SNF2) chromatin-remodeling complex. In interphase, ATRX localizes to pericentromeric heterochromatin, contributing to DNA double-strand break repair, DNA replication, and telomere maintenance. During mitosis, most ATRX proteins are removed from chromosomal arms, leaving a pool near the centromere region in mammalian cells, which is critical for accurate chromosome congression and sister chromatid cohesion protection. However, the function and localization mechanisms of ATRX at mitotic centromeres remain largely unresolved.

Methods: The clustered regularly interspaced short palindromic repeats with CRISPR-associated protein 9 (CRISPR-Cas9) system and overexpression approaches were employed alongside immunofluorescence to investigate the mechanism of ATRX localization at the centromere. To study the binding mechanism between ATRX and heterochromatin protein 1 (HP1), both full-length and truncated mutants of hemagglutinin (HA)-ATRX were generated for co-immunoprecipitation and glutathione S-transferase (GST)-pull assays. Wild-type ATRX and HP1 binding-deficient mutants were created to investigate the role of ATRX binding to HP1 during mitosis, with the Z-Leu-Leu-Leu-al (MG132) maintenance assay, cohesion function assay, and kinetochore distance measurement.

Results and conclusions: Our research demonstrated that HP1α, HP1β, and HP1γ facilitate the positioning of ATRX within the mitotic centromere area through their interaction with the first two [P/L]-X-V-X-[M/L/V] (PxVxL)motifs at the N-terminus of ATRX. ATRX deficiency causes aberrant mitosis and decreased centromeric cohesion. Furthermore, reducing Wapl activity can bypass the need for ATRX to protect centromeric cohesion. These results provide insights into the mechanism of ATRX's centromeric localization and its critical function in preserving centromeric cohesion by reducing Wapl activity in human cells.