Biology subjects

Karki, M.

Publications and source records attributed to Karki, M..

4 recordsLinked to original sources

bioRxiv2026

CDK/mTOR-dependent phosphorylation of UBE2H restrains its charging with ubiquitin and regulates CTLH-dependent degradation

The C-terminal to LisH (CTLH) complex is a modular multi-subunit E3 ligase with diverse biological functions, yet how its overall ubiquitylation activity is tuned remains unclear. Here, we identify CDK- and mTOR-dependent phosphorylation of the cognate E2 enzyme UBE2H as a key regulator of CTLH E3 catalytic capacity. Phosphorylation of two N-terminal serine residues (S3/S5) reduces UBE2H charging with ubiquitin, thereby limiting the pool of active E2 available to CTLH. Mitotic CDK activity inactivates UBE2H during mitosis, whereas mTOR restrains UBE2H charging in interphase to couple CTLH-dependent ubiquitylation to nutrient status. Preventing this phosphorylation maintains UBE2H charging, enhances CTLH-mediated substrate degradation, promotes CTLH subunit turnover, and causes proliferation and mitotic defects. Using hyperactive UBE2H, we identify two additional CTLH substrates, the mitotic kinase NEK9 and Angio-associated migratory cell protein (AAMP) and define a DR-like C-degron recognized by the CTLH subunit MKLN1. These findings reveal how regulation of an E2 enzyme by cell cycle and nutrient signaling pathways dynamically shape CTLH activity.

cell biology↗

bioRxiv2026

Lysine Demethylase 4A (KDM4A) Maintains Basal Body Architecture and Protects Against Ciliary Destabilization

Primary cilia are sensory organelles essential for signaling and defects in formation, maintenance or structure underlie diverse ciliopathies. Here, we identify lysine demethylase 4A (KDM4A) as a previously unrecognized mediator of ciliogenesis. Using genetic depletion and pharmacologic inhibition, we show that KDM4A is required for cilia assembly and maintenance. Super-resolution imaging reveals KDM4A localization at the basal body, where it distinctively wraps around the centrioles. We uncover a direct interaction between KDM4A and Rootletin (CROCC), a structural protein mediating centriole cohesion, and demonstrate that KDM4A loss increases inter-centriolar distances, implicating basal body architecture in ciliary failure. Together, these findings define a demethylase-centrosome axis that integrates KDM4A activity with organelle biology, revealing new mechanisms underlying ciliogenesis.

cell biology↗

bioRxiv2020

A Cytoskeletal Function for PBRM1 Reading Methylated Microtubules

The chromatin modifier SETD2 was recently shown to be a dual-function methyltransferase that "writes" methyl marks on both chromatin and the mitotic spindle, revealing -tubulin methylation as a new posttranslational modification of microtubules. Here, we report the first cytoskeletal "reader" for this SETD2 methyl mark: the polybromo protein PBRM1. We found PBRM1 directly binds the -Tub-K40me3 mark on tubulin, and localizes to the mitotic spindle and spindle pole during cell division. PBRM1 can assemble a PBAF complex in the absence of chromatin as revealed by mass spectrometry, and can recruit other PBAF complex components including SMARCA4 and ARID2 to -tubulin. In addition to PBRM1, other PBAF components were also localized to the mitotic spindle and spindle pole. This PBAF localization was dependent on recruitment to microtubules by PBRM1, and loss of spindle-associated PBRM1/PBAF led to genomic instability as assessed by increased formation of micronuclei. These data reveal a previously unknown function for PBRM1 beyond its role remodeling chromatin, and expand the repertoire of chromatin remodelers involved in writing and reading methyl marks on the cytoskeleton. The results of this study lay the foundation for a new paradigm for the epigenetic machinery as chromatocytoskeletal modifiers, with coordinated nuclear and cytoskeletal functions.

cell biology↗

bioRxiv2020

SETD2 is an actin lysine methyltransferase

SET-domain-containing-2 (SETD2) was identified as the methyltransferase responsible for the histone 3 lysine 36 trimethyl (H3K36me3) mark of the histone code. Most recently, SETD2 has been shown to be a dual-function remodeler that regulates genome stability via methylation of dynamic microtubules during mitosis and cytokinesis. Here we show that actin is a bona fide target for methylation by SETD2 in vitro and in cells. Antibodies against the SETD2 trimethyl lysine epitope recognize methylated actin, with this methyl mark localizing to areas of active actin cytoskeleton reorganization in migrating cells. Disruption of this methylation activity causes defects in actin polymerization and impairs collective cell migration. Together, these data identify SETD2 as a multifunctional cytoskeletal remodeler regulating methylation and polymerization of actin filaments, and provide new avenues for understanding how defects in SETD2 drive disease via aberrant cytoskeletal methylation.

cell biology↗