Biology subjects

Keuper, K.

Publications and source records attributed to Keuper, K..

5 recordsLinked to original sources

bioRxiv2025

Ubiquitin-dependent degradation of p21Waf1/Cip1 is mediated by AMBRA1 to limit DNA replication stress

The cell cycle is a fundamental process that orchestrates the events that lead to cell replication and division. AMBRA1 is a scaffold factor that interacts with the E3 ubiquitin ligase CRL4-DDB1 complex to regulate the stability of cyclin D-type proteins, key regulators of the G1/S phase transition. However, how cells complete S-phase and coordinate the speed of DNA synthesis is still to be fully elucidated. Here we demonstrate that AMBRA1 affects the turnover of p21Waf1/Cip1 and p27Kip1, by coupling the CRL4-DDB1 complex directly to these proteins. In the absence of AMBRA1, the increased stability of p21Waf1/Cip1, rather than p27Kip1, resulted in the accumulation of replication stress by leaving under-replicated DNA during the S phase. We also found that AMBRA1-depleted cells with consequent high p21Waf1/Cip1 are sensitive to the inhibition of lagging-strand DNA synthesis. Of clinical relevance, low levels of AMBRA1 in Sonic-Hedgehog medulloblastoma correlate with a worse prognosis, suggesting that AMBRA1 expression levels could be an informative criterion for patient stratification and treatment.

molecular biology↗

bioRxiv2024

Proteogenomic analysis reveals adaptive strategies to alleviate the consequences of aneuploidy in cancer

Aneuploidy is prevalent in cancer and associates with fitness advantage and poor patient prognosis. Yet, experimentally induced aneuploidy initially leads to adverse effects and impaired proliferation, suggesting that cancer cells must adapt to aneuploidy. We performed in vitro evolution of cells with extra chromosomes and obtained cell lines with improved proliferation and gene expression changes congruent with changes in aneuploid cancers. Integrated analysis of cancer multi-omics data and model cells revealed increased expression of DNA replicative and repair factors, reduced genomic instability, and reduced lysosomal degradation. We identified E2F4 and FOXM1 as transcription factors required for adaptation to aneuploidy in vitro and in cancers and validated this finding. The adaptation to aneuploidy also coincided with specific copy number aberrations that correlate with poor patient prognosis. Chromosomal engineering mimicking these aberrations improved aneuploid cell proliferation, while loss of previously present extra chromosome impaired it. The identified common adaptation strategies suggest replication stress, genomic instability, and lysosomal stress as common liabilities of aneuploid cancers.

genetics↗

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↗

bioRxiv2021

Whole-genome duplication shapes the aneuploidy landscape of human cancers

Aneuploidy - a hallmark of cancer - has tissue-specific recurrence patterns suggesting it plays a driving role in cancer initiation and progression. However, the contribution of aneuploidy to tumorigenesis depends on the cellular and genomic context in which it arises. Whole-genome duplication (WGD) is a common macro-evolutionary event that occurs in >25% of human tumors during the early stages of tumorigenesis. Although tumors that have undergone WGD are reported to be more permissive to aneuploidy than tumors that have not, it remains unknown whether WGD affects aneuploidy recurrence patterns in human cancers. Here we analyzed clinical tumor samples from 449 WGD- tumors and 157 WGD+ tumors across 22 tumor types. We found distinct recurrence patterns of aneuploidy in WGD- and WGD+ tumors. The relative prevalence of recurrent aneuploidies decreased in WGD+ tumors, in line with increased aneuploidy tolerance. Moreover, the genetic interactions between chromosome arms differed between WGD- and WGD+ tumors, giving rise to distinct co-occurrence and mutual exclusivity aneuploidy patterns. The proportion of whole-chromosome aneuploidy vs. arm-level aneuploidy was significantly higher in WGD+ tumors, indicating distinct dominant mechanisms for aneuploidy formation in WGD- and WGD+ tumors. Human cancer cell lines successfully reproduced these WGD/aneuploidy interactions, confirming the relevance of studying this phenomenon in culture. Lastly, we induced WGD in human colon cancer cell lines, and followed aneuploidy formation in the isogenic WGD+/WGD-cells under standard or selective conditions. These experiments validated key findings from the clinical tumor analysis, and revealed a causal link between WGD and altered aneuploidy landscapes. We conclude that WGD shapes the aneuploidy landscape of human tumors, and propose that the interaction between WGD and aneuploidy is a major contributor to tumor evolution.

cancer biology↗

bioRxiv2020

USP28 and SPINT2 mediate cell cycle arrest after whole genome doubling

Tetraploidy is frequent in cancer and whole genome doubling shapes the evolution of cancer genomes, thereby driving the transformation, metastasis and drug resistance. Yet, human cells usually arrest when they become tetraploid due to p53 activation that leads to CDKN1A expression, cell cycle arrest, senescence or apoptosis. To uncover the barriers that block proliferation of tetraploids, we performed an RNAi mediated genome-wide screen in a human cancer cell line. We identified 140 genes whose depletion improved survival of tetraploids and characterized in depth two of them: SPINT2 and USP28. We show that SPINT2 is a general regulator of CDKN1A, regulating its transcription via histone acetylation. By mass spectrometry and immunoprecipitation, we show that USP28 interacts with NuMA1 and affects centrosome clustering. Moreover, tetraploid cells accumulate DNA damage and loss of USP28 reduces checkpoint activation. Our results indicate three aspects that contribute to survival of tetraploid cells: i) increased mitogenic signaling and reduced expression of cell cycle inhibitors, ii) the ability to establish functional bipolar spindle, and iii) reduced DNA damage signaling.

cell biology↗