Biology subjects

Riemers, F. M.

Publications and source records attributed to Riemers, F. M..

6 recordsLinked to original sources

bioRxiv2026

Degenerated intervertebral disc environment impairs notochordal cell-derived extracellular vesicles release and their matrix anabolic effect

At the onset of intervertebral disc degeneration, within the disc core, the pH and osmolarity decrease, and the residing notochordal cells (NCs) gradually transition towards nucleus pulposus cells (NPCs). How these microenvironmental cues shape the NCs extracellular vesicles (EV)-enriched secretome, and thus EV-mediated communication with NPCs during this transition, remains poorly understood. To study this, we collected the secretome from pig NC-rich tissue cultured for 4 days in either healthy or degenerate disc media to mimic these changes. In both conditions, NC-rich tissues were largely comparable at the histological and biochemical levels. Despite, tissues released glycosaminoglycans (GAGs), depleting the extracellular matrix. Surprisingly, degenerative media did not differentially release inflammatory regulators, though it reduced PGE2 release. We asked whether this extended to EV-enriched secretome media (SM_EV+), and found that the degenerative media reduced the number of EVs without altering their morphology or size. We then determined NC-EV association of inflammatory and matrix regulators. NC-EV isolation enriched MMP1, IL6 and IL10 and depleted soluble GAGs. Conversely, EV-depletion (SM_EV-) removed most GAGs without affecting MMP1, IL6, and IL10, suggesting that they contribute to the NC-EV soft corona. Functionally, healthy SM_EV+ improved GAG production by NPCs, but attenuated TBXT expression. Degenerate SM_EV+ did not elicit detectable EV-specific effects. These findings suggest that, in health, secretome-mediated communication from NCs to NPCs is only partially EV-mediated. At the onset of IVD degeneration, low pH and osmolarity impair the release of NC-EVs and negate the EV-specific beneficial matrix-anabolic effects on NPCs, contributing to the NC-to-NPC transition.

cell biology↗

bioRxiv2025

E2F3 amplification primes bladder cancer cells for premature mitosis.

The E2F-RB pathway controls the G1/S checkpoint, and tumors often bypass it through RB1 or CDKN2A loss. Unlike these lesions, E2F3 amplification drives persistent excessive E2F-dependent transcription through S and G2 phases. This oncogene is frequently amplified in for example bladder cancer, but its impact on the cancer cell cycle remains unclear. Using isogenic bladder cancer models and patient data, we show that E2F3 amplification hyperactivates a mitotic gene expression program, including cyclin B1. This predisposes cells to unscheduled mitosis when the G2/M checkpoint is inhibited using the PKMYT1 inhibitor lunresertib, alone or in combination with low dosages of the WEE1 inhibitor zederosertib. E2F3-amplified cells acquired resistance to lunresertib by permanently reducing cyclin B1 expression, thereby preventing premature mitotic entry. Importantly, this resistance was reversed by co-treatment with a low dose of WEE1 inhibitor. These findings identify PKMYT1-dependent CDK1 inhibition as a critical safeguard against premature mitosis in E2F3-amplified bladder cancer. Thus, we uncover an opportunity for precision medicine strategies aimed at G2/M checkpoint inhibition to promote catastrophic mitosis in bladder cancer patients with E2F3 amplification and excessive cyclin B1 expression.

cancer biology↗

bioRxiv2024

Stochastic variation in the FOXM1 transcription program mediates replication stress tolerance.

Oncogene-induced replication stress (RS) is a vulnerability of cancer cells that forces reliance on the intra-S-phase checkpoint to ensure faithful genome duplication. Inhibitors of the crucial intra-S-phase checkpoint kinases ATR and CHK1 have been developed, but persistent proliferation and resistance to these drugs remain problematic. Understanding drug tolerance mechanisms is impeded by analysis of bulk samples, which neglect tumor heterogeneity and often fail to accurately interpret cell cycle-mediated resistance. Here, by combining intracellular immunostaining and RNA-sequencing of single cells, we characterized the transcriptomes of oncogenic RAS-expressing cells that exhibit variable levels of RS when challenged with a CHK1 inhibitor in combination with the chemotherapeutic drug gemcitabine. We identified 40 genes differentially expressed between tolerant and sensitive cells, including several FOXM1 target genes. While complete knockdown of FOXM1 impeded cell proliferation, a partial knockdown protected cells against DNA damage, and improved recovery from drug-induced RS. Our results suggest that low levels of FOXM1 expression protects subsets of oncogenic RAS-expressing cells against DNA damage during drug-induced replication stress.

cancer biology↗

bioRxiv2021

Circulating microRNAs as noninvasive biomarkers for canine Cushing's syndrome

Canine Cushings syndrome (hypercortisolism) can be caused by a pituitary tumor (pituitary-dependent hypercortisolism; PDH) or a cortisol-secreting adrenocortical tumor (csACT). For both cases, noninvasive biomarkers that could pre-operatively predict the risk of recurrence after surgery would greatly impact clinical decision making. The aim of this study was to determine whether circulating microRNAs (miRNAs) can be used as noninvasive biomarkers for canine Cushings syndrome. After a pilot study with 40 miRNAs in blood samples of healthy dogs (n = 3), dogs with PDH (n = 3) and dogs with a csACT (n = 4), we selected a total of 20 miRNAs for the definitive study. In the definitive study, these 20 miRNAs were analyzed in blood samples of healthy dogs (n = 6), dogs with PDH (n = 19, pre-and post-operative samples) and dogs with a csACT (n = 26, pre-operative samples). In dogs with PDH, six miRNAs (miR-122-5p, miR-126-5p, miR-141-3p, miR-222-3p, miR-375-3p and miR-483-3p) were differentially expressed compared to healthy dogs. Of one miRNA, miR-122-5p, the expression levels did not overlap between healthy dogs and dogs with PDH (p = 2.9x10-4), significantly decreased after hypophysectomy (p = 0.013), and were significantly higher (p = 0.017) in dogs with recurrence (n = 3) than in dogs without recurrence for at least one year after hypophysectomy (n = 7). In dogs with csACTs, two miRNAs (miR-483-3p and miR-223-3p) were differentially expressed compared to healthy dogs. Additionally, miR-141-3p was expressed significantly lower (p = 0.009) in dogs with csACTs that had a histopathological Utrecht score of [≥] 11 compared to those with a score of < 11. These results indicate that circulating miRNAs have the potential to be noninvasive biomarkers in dogs with Cushings syndrome that may contribute to clinical decision-making.

cancer biology↗

bioRxiv2021

Oncogenic RAS sensitizes cells to drug-induced replication stress via transcriptional silencing of P53

Cancer cells often experience high basal levels of DNA replication stress (RS), for example due to hyperactivation of oncoproteins like MYC or RAS. Therefore, cancer cells are considered to be sensitive to drugs that exacerbate the level of RS or block the intra S-phase checkpoint. Consequently, RS-inducing drugs including ATR and CHK1 inhibitors are used or evaluated as anti-cancer therapies. However, drug resistance and lack of biomarkers predicting therapeutic efficacy limit efficient use. This raises the question what determines sensitivity of individual cancer cells to RS. Here, we report that oncogenic RAS does not only enhance the sensitivity to ATR/CHK1 inhibitors by directly causing RS. Instead, we observed that HRASG12V dampens the activation of the P53-dependent transcriptional response to drug-induced RS, which in turn confers sensitivity to RS. We demonstrate that inducible expression of HRASG12V sensitized retina pigment epithelial (RPE-hTERT) as well as osteosarcoma (U2OS) cells to ATR and CHK1 inhibitors. Using RNA-sequencing of FACS-sorted cells we discovered that P53 signaling is the sole transcriptional response to RS. However, oncogenic RAS attenuates the transcription of P53 and its target genes. Accordingly, live cell imaging showed that HRASG12V exacerbates RS in S/G2-phase, which could be rescued by stabilization of P53. Thus, our results demonstrate that transcriptional control of P53 is a prime determinant in the response to ATR/CHK1 inhibitors and show that hyperactivation of the MAPK pathway impedes this response. Our findings suggest that the level of oncogenic MAPK signaling could predict sensitivity to intra-S-phase inhibition in cancers with intact P53.

cancer biology↗

bioRxiv2020

Excessive E2F transcription in single cancer cells precludes transient cell cycle exit after DNA damage.

E2F transcription factors control the expression of cell cycle genes. Cancers often demonstrate enhanced E2F target gene expression, which can be explained by increased percentages of replicating cells. However, we now demonstrate in human cancer biopsies that individual neoplastic cells display abnormally high levels of E2F-dependent transcription. To mimic this situation, we deleted the atypical E2F repressors (E2F7/8) in untransformed cells. Individual cells with elevated E2F-activity during S/G2-phase failed to exit the cell cycle after DNA damage and underwent mitosis. In contrast, wild type cells completed S-phase and then exit the cell cycle by activating the APC/CCdh1 via repression of the E2F-target Emi1. Strikingly, many arrested wildtype cells could eventually inactivate APC/CCdh1 to execute a second round of DNA replication and mitosis, thereby becoming tetraploid. Cells with elevated E2F-transcription fail to exit the cell cycle after DNA damage which potentially causes genomic instability, promotes malignant progression and reduces drug sensitivity.

cancer biology↗