Biology subjects

Diernfellner, A.

Publications and source records attributed to Diernfellner, A..

4 recordsLinked to original sources

bioRxiv2026

Cell cycle-coupled CK1δ turnover, autoinhibition, and activity

Casein kinase 1{delta} (CK1{delta}) is a ubiquitously expressed kinase involved in diverse cellular processes, including cell cycle regulation. CK1{delta} activity is attenuated by (auto)phosphorylation. However, inhibitory phosphorylation is efficiently opposed by cellular phosphatases as CK1{delta} accumulates in its hypophosphorylated, active state. CK1{delta} is a target of the nuclear ubiquitin ligase APC/C-CDH1, yet the kinase is apparently stable. Thus, the physiological relevance of CK1{delta} (auto)phosphorylation, autoinhibition, and regulated turnover has remained unclear. Here we show that CK1{delta} activity and abundance are coordinated in a cell cycle-dependent manner. During G1, assembled CK1{delta} kinase is stable while free active kinase is degraded. In S phase, unassembled CK1{delta} is no longer degraded, likely to support functions in DNA damage signaling. Upon mitotic entry, the downregulation of phosphatases promotes CK1{delta} (auto)phosphorylation and consequent autoinhibition, thereby preserving a pool of kinase to rapidly reestablish the post-mitotic steady state.

biochemistry↗

bioRxiv2025

Nuclear CK1δ as a Critical Determinant of PER:CRY Complex Dynamics and Circadian Period

The mammalian circadian clock is governed by a feedback loop in which the transcription activator CLOCK:BMAL1 induces expression of its inhibitors, PERs and CRYs, which form a complex with CK1{delta}, the main circadian kinase. However, the spatiotemporal dynamics of this feedback loop and the precise role of CK1{delta} remain incompletely understood. Using an inducible overexpression system, we show that nuclear availability of CK1{delta} is limited by both rapid nuclear degradation and active export of unassembled kinase, while cytoplasmic kinase is readily available for association with PERs. We demonstrate that CK1{delta}-mediated phosphorylation may disrupt PER2-CRY1 interaction thereby resulting in cytoplasmic PER2 dimers containing substoichiometric amounts of CRY1. Analysis of endogenous PER2 localization in the context of an intact circadian clock reveals that PER2 accumulates in the cytoplasm late in the circadian cycle. Based on these findings, we propose that cytoplasmic accumulation of PER:CRY:CK1{delta} complexes contributes to the clearance of nuclear PER2, while the CK1{delta}-dependent release of CRY1 into the nucleus may sustain CLOCK:BMAL1 repression on DNA supporting the transition from the early to the late repressive phase.

biochemistry↗

bioRxiv2020

Multiple random phosphorylations provide long delays and switches in circadian clocks

Theory predicts that self-sustained oscillations require robust delays and nonlinearities (ultrasensitivity). Delayed negative feedback loops with switch-like inhibition of transcription constitute the core of eukaryotic circadian clock. The kinetics of core clock proteins such as PER2 in mammals and FRQ in Neurospora crassa is governed by multiple phosphorylations. We investigate how multiple, slow and random phosphorylations control delay and molecular switches. We model phosphorylations of intrinsically disordered clock proteins (IDPs) using conceptual models of sequential and distributive phosphorylations. Our models help to understand the underlying mechanisms leading to delays and ultrasensitivity. The model shows temporal and steady state switches for the free kinase and the phosphoprotein. We show that random phosphorylations and sequestration mechanisms allow high Hill coefficients required for self-sustained oscillations.

systems biology↗

bioRxiv2019

MXD/MIZ1 complexes activate transcription of MYC-repressed genes

MXD proteins are transcription repressors that antagonize the E-box dependent activation of genes by MYC. MYC together with MIZ1 acts also as a repressor of a subset of genes, including cell cycle inhibitor genes such as p15 and p21. A role of MXDs in regulation of MYC-repressed genes is not known. Here we report that MXDs are functionally expressed in U2OS cells and activate transcription of p15 and p21, and other MYC-repressed genes. Activation of transcription was dependent on the interaction of MXDs with MIZ1, and on an intact DNA binding domain. MIZ1-binding deficient MXD mutants interacted with MAX and were active as repressors of MYC-activated genes but failed to activate MYC-repressed genes. Mutant MXDs with reduced DNA binding affinity interacted with MAX and MIZ1 but neither repressed nor activated transcription. Overexpression of MXDs attenuated proliferation of U2OS cells predominantly via MIZ1-dependent induction of p21. Our data show that MXDs and MYC have a reciprocally antagonistic potential to regulate transcription of mutual target genes.

molecular biology↗