Biology subjects

Hochegger, H.

Publications and source records attributed to Hochegger, H..

7 recordsLinked to original sources

bioRxiv2026

The Greatwall/PP2A-B55α axis remodels the G2/M boundary and shapes cellular dependence on PKMYT1

The switch-like G2/M transition and mitotic exit depend on a feedback loop comprising CDK1, Greatwall kinase, and the PP2A-B55 phosphatase. Monogenic disruptions of these regulators impair cellular functions, drive genomic instability, and promote cancer-associated characteristics. Yet how perturbations of this feedback loop interact, and whether their effects depend on cellular context, remain unclear. Here, we assess how combinatorial perturbations of CDK1, Greatwall, and PP2A-B55 affect cell-cycle control in non-transformed RPE-1 and tumour-derived HeLa cells. We identify PP2A-B55 as a context-dependent G2/M repressor with a critical role in cancer cells, where it cooperates with PKMYT1 and, to a lesser extent, WEE1 to prevent premature mitosis. In cancer cells, but not in non-transformed cells, reduced PP2A-B55 activity and Greatwall overexpression produce marked sensitisation to the PKMYT1-selective RP-6306 and modest sensitisation to the WEE1-selective adavosertib. This asymmetric sensitisation reflects a functional separation between WEE1 and PKMYT1 in S- and G2-phase control. Our work outlines fundamental and cell-type-specific contributions of CDK1, Greatwall and PP2A-B55 to cell-cycle regulation and proposes G2/M plasticity as a vulnerability with utility in PKMYT1-targeted therapy.

cell biology↗

bioRxiv2026

Greatwall Kinase regulates Acute Myeloid Leukaemia Cell Division through a Non-Canonical Mechanism

Greatwall kinase regulates mitotic progression by phosphorylating ENSA and ARPP19, thereby inhibiting PP2A-B55. Moreover, Greatwall has been implicated in oncogenesis, particularly in solid tumours, but the mechanisms by which Greatwall regulates the cell cycle in other malignancies remain unclear. Here, we show that Greatwall regulates cytokinesis and cell cycle progression in acute myeloid leukaemia (AML) cells through a pathway distinct from ENSA-PP2A-B55. AML cells require Greatwall expression and activity to proliferate, as revealed by pharmacological and systematic genetic perturbation experiments. Mechanistically, Greatwall inactivation or genetic depletion does not measurably affect the ENSA-PP2A-B55 pathway. Instead, loss of Greatwall function alters cytokinesis, and the phosphorylation of proteins involved in cytoskeletal organisation and cytokinesis, including MARK3, which we identify as a direct Greatwall substrate in AML cells. Together, these findings reveal that the Greatwall kinase signalling network is wired differently in leukemic cells, thus uncovering a novel of cell cycle regulation.

cell biology↗

bioRxiv2025

The Balance between B55α and Greatwall expression levels predicts sensitivity to Greatwall inhibition in cancer cells

The Greatwall kinase inhibits PP2A-B55 phosphatase activity during mitosis to stabilise critical Cdk1-driven mitotic phosphorylation. Although Greatwall represents a potential oncogene and prospective therapeutic target, our understanding of cellular and molecular consequences of chemical Greatwall inactivation remains limited. To address this, we introduce C-604, a highly selective Greatwall inhibitor, and characterise both immediate and long-term cellular responses to the chemical attenuation of Greatwall activity. We demonstrate that Greatwall inhibition causes systemic destabilisation of the mitotic phosphoproteome, premature mitotic exit and pleiotropic cellular pathologies. Importantly, we demonstrate that the cellular and molecular abnormalities linked to reduced Greatwall activity are specifically dependent on the B55 isoform rather than other B55 variants, underscoring PP2A-B55 phosphatases as key mediators of cytotoxic effects of Greatwall-targeting agents in human cells. Additionally, we show that sensitivity to Greatwall inhibition varies in different cell line models and that dependency on Greatwall activity reflects the balance between Greatwall and B55 expression levels. Our findings highlight Greatwall dependency as a cell-specific vulnerability and propose the B55-to-Greatwall expression ratio as a predictive biomarker of cellular responses to Greatwall-targeted therapeutics.

cell biology↗

bioRxiv2021

Mechanisms of genetic instability in a single S-phase following whole genome doubling

Diploid and stable karyotypes are associated with health and fitness in animals. In contrast, whole genome duplications (WGDs) - doubling full chromosome content - are linked to genetic instability (GIN) and frequently found in human cancers 1-3. It has been established that WGDs fuel chromosome instability through abnormal mitosis 4-8, however, the immediate consequences of tetraploidy in the first interphase are not known. This is an essential question because single WGD events such as cytokinesis failure can promote tumorigenesis 9. Here, we found that newly born tetraploid human cells undergo high rates of DNA damage during DNA replication in the first S-phase. Using DNA combing and single cell sequencing, we show that DNA replication dynamics is perturbed, generating under- and over-replicated regions. Mechanistically, we found that these defects result from the lack of protein mass scaling up at the G1/S transition, which impairs the fidelity of DNA replication. This work shows that within a single interphase, unscheduled tetraploid cells can acquire highly abnormal karyotypes. These findings provide an explanation for the GIN landscape that favors tumorigenesis after tetraploidization.

cell biology↗

bioRxiv2018

Cyclin A triggers Mitosis either via Greatwall or Cyclin B

Two mitotic Cyclins, A and B, exist in higher eukaryotes, but their specialised functions in mitosis are poorly understood. Using degron tags we analyse how acute depletion of these proteins affects mitosis. Loss of Cyclin A in G2-phase prevents the initial activation of Cdk1. Cells lacking Cyclin B can enter mitosis and phosphorylate most mitotic proteins, because of parallel PP2A:B55 phos-phatase inactivation by Greatwall kinase. The final barrier to mitotic establishment corresponds to nuclear envelope breakdown that requires a decisive shift in the balance of Cdk1 and PP2A:B55 activity. Beyond this point Cyclin B/Cdk1 is essential to phosphorylate a distinct subset mitotic Cdk1 substrates that are essential to complete cell division. Our results identify how Cyclin A, B and Greatwall coordinate mitotic progression by increasing levels of Cdk1-dependent substrate phos-phorylation.

cell biology↗

bioRxiv2018

Contractile actomyosin network on nuclear envelope remnants positions chromosomes for mitosis

To ensure proper segregation during mitosis, chromosomes must be efficiently captured by kinetochore microtubules and subsequently aligned on the mitotic spindle. The efficacy of chromosome capture by the mitotic spindle can be influenced by how widely chromosomes are scattered in space. Here, we quantify chromosome-scattering volume (CSV) and find that it is reduced immediately after nuclear envelope breakdown (NEBD) in human cells. The reduction of CSV occurs independently of microtubules and is therefore not an outcome of interactions between chromosomes and the spindle. We find that, prior to NEBD, an acto-myosin network is assembled in a LINC complex-dependent manner on the cytoplasmic surface of the nuclear envelope. This acto-myosin network remains around chromosomes soon after NEBD, and its myosin-II-mediated contraction reduces CSV and facilitates chromosome interaction with spindle microtubules.

cell biology↗

bioRxiv2018

Live-cell imaging of marked chromosome regions reveals dynamics of mitotic chromosome resolution and compaction

When human cells enter mitosis, chromosomes undergo substantial changes in their organisation to resolve sister chromatids and compact chromosomes. Despite the fundamental importance of this phenomenon to genome stability, we still do not fully comprehend the timing and coordination of these events. To address these questions, we need to evaluate the progression of both sister chromatid resolution and chromosome compaction in one assay. We achieved this by analysing changes in configuration of marked chromosome regions over time, with high spatial and temporal resolution. This assay showed that sister chromatid resolution is an iterative process that begins in late G2 phase and completes in prophase. Cohesins and WAPL antagonistically regulate sister chromatid resolution in late G2 and prophase whilst local enrichment of cohesin on chromosomes prevents precocious sister chromatid resolution. Moreover, our assay allowed quantitative evaluation of the timing and efficiency of condensin II and I activities in promoting sister chromatid resolution and chromosome compaction, respectively. Thus, our real-time assay sheds new light on the dynamics of mitotic chromosome resolution and compaction.

cell biology↗