The work, led by Jianzhao Liu and Xin-Hua Feng of Zhejiang University together with colleagues at Soochow University and other Chinese institutions, began with a simple but technically demanding question: is METTL14, the scaffold subunit of the m6A methyltransferase complex, itself chemically modified? Using immunoprecipitation followed by immunoblotting in HEK293T and HeLa cells, the team found that METTL14, but not its catalytic partner METTL3 nor the regulatory subunit WTAP, is robustly ubiquitinated. Ubiquitin is best known as a destruction tag: chains linked through its lysine-48 residues deliver proteins to the proteasome. But ubiquitin can be assembled into eight distinct chain types, and several of them, including K27-linked chains, are thought to modulate protein interactions and localization rather than stability. When the researchers restricted cellular ubiquitin to single-linkage variants, METTL14’s modification turned out to be dominated by exactly this noncanonical K27 linkage.

Mass spectrometry then mapped the modification to specific lysine residues on METTL14, including lysines 148 and 278, positions that sit near the interfaces through which METTL14 grips its partners. To find the enzyme responsible, the team pulled down METTL14 and searched its associated proteins for candidate E3 ubiquitin ligases. The screen converged on RLIM, also known as RNF12, a RING-domain ligase first characterized as a corepressor of LIM homeodomain transcription factors. RLIM’s catalytic activity proved essential: a ligase-dead H569A/C572A mutant or a construct lacking the RING domain entirely failed to promote METTL14 ubiquitination, whereas wild-type RLIM drove robust K27-linked tagging in cells and in reconstituted in vitro reactions with defined E1 and E2 enzymes.

What makes this finding conceptually striking is what the ubiquitin mark does not do. RLIM knockout did not alter METTL14 protein abundance, and immunofluorescence showed that METTL14 still entered the nucleus normally in cells lacking RLIM. Instead, the modification acted on function. In vitro methylation assays demonstrated that K27-ubiquitinated METTL3–METTL14 complexes were markedly impaired in their ability to methylate RNA substrates. Two mechanisms accounted for the deficit. First, structural modeling and biochemical assays indicated that ubiquitin conjugated at lysine 278 distorts the loop regions at the METTL3–METTL14 interface, weakening the heterodimer that constitutes the active writer. Second, electrophoretic mobility shift assays and microscale thermophoresis showed that ubiquitinated or ubiquitination-mimicking complexes bound RNA less tightly, reducing substrate engagement. A split Nano-Luciferase reporter confirmed in living cells that RLIM expression disrupts METTL3–METTL14 association. In other words, RLIM acts as a rheostat on the writer’s activity rather than a trigger for its disposal.

The physiological consequence was visible across the transcriptome. MeRIP-seq and RNA-seq comparisons of control and RLIM-knockout cells revealed widespread hypermethylation of mRNA m6A peaks when RLIM was absent, with the affected transcripts enriched for genes governing the G2/M transition of the cell cycle. Consistent with known links between m6A and mRNA stability, hypermethylated transcripts in RLIM-knockout cells showed shortened half-lives, and many overlapped with binding targets of the m6A reader YTHDF2, which routes methylated transcripts toward degradation. Representative loci such as E4F1 and RHOB, both implicated in cell-cycle control, gained m6A and lost stability when RLIM was removed, and MeRIP-qPCR validated these changes independently.

The cell-cycle connection then became explicit. When the researchers synchronized cells by double thymidine block and released them, they observed coordinated periodic oscillations in three quantities: transcriptome-wide m6A levels, the intensity of K27-linked ubiquitin on METTL14, and RLIM protein abundance. RLIM knockout arrested cells at the G2/M boundary, an effect that could be rescued by knocking down METTL14, placing RLIM upstream of the writer in a pathway that governs mitotic entry. Measurements of global m6A-to-A ratios by LC-MS/MS across G1/S, S, G2, M and G1 phases confirmed that the methylation landscape rises and falls with the cycle, and immunofluorescence for phospho-histone H3 showed RLIM levels dropping precisely in mitotic cells.

The mechanism behind RLIM’s own oscillation turned out to be a classic mitotic kinase. The CDK1–cyclin B1 complex, the master switch for mitotic entry, physically associated with RLIM and phosphorylated it. Phosphatase treatments and Ser/Thr-to-Ala mutant analysis identified the phosphorylation sites responsible, and these modifications triggered RLIM to ubiquitinate itself with K48-linked chains, condemning it to proteasomal degradation. Blocking CDK1 or cyclin B1 by RNA interference stabilized RLIM, while proteasome inhibition with MG132, but not lysosomal inhibition with chloroquine, rescued the protein. This arrangement creates an elegant feedback loop: as CDK1–cyclin B1 surges at G2/M, it destroys RLIM, which releases METTL14 from inhibitory ubiquitination, allowing the writer complex to reassemble and retune the m6A landscape for the next phase of the cycle.

To test whether this axis matters beyond cultured cells, the team turned to animal and clinical models. In mice with Rlim deleted specifically in the myeloid lineage, bone marrow cells showed elevated m6A methylation on cell-cycle and differentiation genes, and flow cytometry revealed perturbed hematopoietic populations, effects that intensified after vesicular stomatitis virus infection. Endogenous METTL14 in these marrow cells lost its K27-linked ubiquitination, confirming the pathway operates in primary tissue. The researchers also examined MOLM-13, an acute myeloid leukemia cell line, where RLIM knockdown altered cell-cycle distribution and myeloid differentiation markers and reduced colony formation. Most compellingly, samples from patients with acute monocytic leukemia, collected through collaborating hospitals in Suzhou, displayed dysregulation of the RLIM–METTL14 axis, linking the molecular circuit to human disease.

The study’s broader significance lies in expanding the vocabulary of epitranscriptomic regulation. For a decade, the m6A writer has been viewed largely as a stable assembly whose output is tuned by accessory proteins, substrate availability and chromatin state. This work adds a temporal dimension: a cell-cycle-programmed, noncanonical ubiquitin code that switches the writer’s activity on and off without touching its concentration. Because K27-linked chains are increasingly recognized as scaffolds for protein–protein interactions in cell-cycle and quality-control pathways, the finding suggests that other RNA-processing enzymes may carry similar non-degradative marks awaiting discovery. It also reframes ubiquitin ligases, traditionally studied in the context of protein turnover, as direct modulators of the epitranscriptome.

Therapeutically, the implications are tantalizing but preliminary. Acute myeloid leukemia has already emerged as a disease exquisitely sensitive to m6A dosage, with the writer METTL3, the erasers FTO and ALKBH5, and the reader YTHDF2 each implicated in leukemic self-renewal. The new axis adds RLIM, and the CDK1–cyclin B1 switch that controls it, to the list of potential intervention points. CDK1 inhibitors are already in clinical use for other indications, raising the possibility that modulating RLIM stability could tune m6A levels in leukemia cells. For now, the study stands as a demonstration that the cell’s division clock reaches deep into its RNA chemistry, and that a ubiquitin tag once dismissed as obscure may be one of the hands on that clock.

Subject of Research: Cell-cycle-regulated noncanonical K27-linked ubiquitination of METTL14 controlling mRNA m6A methylation

Article Title: Cell-cycle-driven noncanonical ubiquitination of METTL14 orchestrates RNA methylation

Article References: Cao, J., Ying, X., Zhou, L., Zhang, Q., Huang, C., Dai, T., Shu, X., Gao, M., Mi, Y., Wu, X., Wang, F., Zhang, L., Zhou, F., Feng, X.-H., & Liu, J. (2026). Cell-cycle-driven noncanonical ubiquitination of METTL14 orchestrates RNA methylation. Nature Chemical Biology. https://doi.org/10.1038/s41589-026-02328-5

Image Credits: AI Generated

DOI: 10.1038/s41589-026-02328-5

Keywords: m6A, METTL14, RLIM, ubiquitination, K27-linked ubiquitin, cell cycle, CDK1, cyclin B1, epitranscriptomics, RNA methylation, acute myeloid leukemia, post-translational modification

The researchers, led by investigators at Nanjing Medical University, began by building a single-cell transcriptomic atlas spanning the disease continuum. They collected tissue from five patients undergoing gastrectomy for intestinal-type gastric cancer, sampling not only the tumors themselves but also matched intestinal metaplasia lesions near the tumor margin and non-atrophic gastritis tissue farther away. After rigorous quality control, the dataset comprised 55,785 individual cells from 13 specimens, which the team sorted into nine major cell types, including epithelial cells, malignant cells, T cells, B cells, plasma cells, myeloid cells, mast cells, fibroblasts, and endothelial cells. The composition shifted tellingly across disease stages: as lesions progressed, the fractions of myeloid cells, endothelial cells, and fibroblasts expanded, while malignant epithelial cells came to dominate the tumor samples.

Within the epithelial compartment, the team re-clustered more than 34,000 cells into eight subtypes, ranging from chief and parietal cells, which dwindled as disease advanced, to tumor cells, which appeared only in cancerous tissue. The pivotal move came from pseudotime trajectory analysis, a computational technique that orders cells along an inferred developmental path based on their gene expression. The trajectory originated in neck cells and flowed toward enterocytes, the absorptive cells characteristic of intestinal metaplasia. One enterocyte population, which the researchers designated Enterocytes-S3, sat squarely between earlier epithelial states and the malignant cells along this trajectory, and tumor cells were heavily enriched in the same transcriptional state. To corroborate this intermediate identity, the team scored each cell against a published signature of incomplete intestinal metaplasia. The score climbed steadily from neck cells through successive enterocyte states, peaked in Enterocytes-S3, and then fell in cancer cells, exactly the pattern expected of a waystation on the road to malignancy.

What makes Enterocytes-S3 dangerous, the data suggest, is its cell-cycle program. Weighted gene co-expression network analysis identified 25 gene modules across the epithelial subtypes, and one of them, Module 4, was strongly upregulated in Enterocytes-S3 and enriched for genes governing mitotic nuclear division and mitotic cell-cycle phase transitions. The subpopulation also showed elevated activity of the G2/M checkpoint and E2F target gene sets, hallmarks of cells primed to proliferate. In short, this transitional population was not merely drifting toward a cancer-like identity; it was rewiring its division machinery, acquiring the proliferative momentum that tumors require.

To find the conductor of that rewiring, the researchers scored bulk transcriptomes from The Cancer Genome Atlas stomach adenocarcinoma cohort against the Enterocytes-S3 signature. PTTG1 emerged as the most significantly upregulated gene in tumors with high signature scores. The finding held up across multiple independent datasets, including the Asian Cancer Research Group cohort and the team’s own in-house transcriptomic data, with paired analyses confirming that PTTG1 expression was elevated in intestinal-type gastric cancer relative to matched normal mucosa. Pseudotime analysis showed the gene’s expression rising progressively from enterocytes toward malignant cells, and immunohistochemistry on a tissue microarray of 88 evaluable paired samples told the same story at the protein level: strong nuclear PTTG1 staining in tumors, weak or absent staining in adjacent normal tissue, and significantly higher levels in intestinal-type than in diffuse-type gastric cancer.

PTTG1 is no stranger to oncology. Originally discovered in rat pituitary tumor cells, the gene encodes securin, an inhibitor that prevents sister chromatids from separating until mitosis is properly timed, thereby safeguarding genomic integrity. It is barely expressed in most normal tissues apart from the testis, yet it is markedly overexpressed in hepatocellular, breast, lung, colon, testicular, and ovarian cancers, where it has been linked to proliferation, invasion, and metastasis through pathways ranging from PI3K/AKT to Wnt/beta-catenin and MAPK signaling. What the new study adds is a specific, mechanistic account of how PTTG1 reprograms the cell cycle in gastric epithelium, and evidence that its activity tracks the premalignant-to-malignant transition in a subtype-specific manner.

The functional experiments were decisive. When the team silenced PTTG1 in MKN1 and MKN7 gastric cancer cell lines using small interfering RNAs, proliferation measured by CCK-8 and EdU assays dropped significantly, and Transwell assays showed reduced migration and invasion. RNA sequencing of the knockdown cells revealed widespread downregulation of cell-cycle genes, with gene set enrichment analysis pinpointing the G2/M checkpoint pathway. Flow cytometry then delivered a subtle but important insight: PTTG1 depletion reduced the proportion of cells in G2 phase and increased the G1 fraction, indicating impaired progression through the G2/M transition rather than a classical arrest at the checkpoint. Western blotting confirmed the molecular signature of stalled mitotic entry, with Cyclin B1 and phosphorylated CDK1 both diminished, while levels of gamma-H2AX, a marker of DNA double-strand breaks, rose sharply, and immunofluorescence showed increased gamma-H2AX foci in the nuclei of PTTG1-deficient cells.

Digging deeper, the researchers traced a regulatory axis from PTTG1 to the machinery of mitosis. Knockdown reduced the expression of E2F1, a transcription factor known to bind directly the promoter of the CCNB1 gene, which encodes Cyclin B1. Using CUT&RUN-qPCR, a technique that maps where a protein sits on chromatin, the team showed that E2F1 occupied the CCNB1 promoter in control cells but that this occupancy fell markedly after PTTG1 silencing, accompanied by reduced CCNB1 messenger RNA. The model that emerges is one in which PTTG1 sustains E2F1-dependent transcription of Cyclin B1, thereby licensing the G2-to-M transition, while simultaneously helping to coordinate cell-cycle progression with DNA damage responses. The precise mechanism by which PTTG1 controls E2F1 remains an open question the authors acknowledge.

Two model systems extended the story beyond cell lines. In human paracancerous gastric organoids derived from intestinal-type gastric cancer patients, lentiviral overexpression of PTTG1 produced organoids that grew significantly larger than controls by days 6, 10, and 12 of culture, with more Ki67-positive proliferating cells and elevated Cyclin B1, much of it in the nucleus, a location associated with mitotic commitment. Strikingly, the overexpressing organoids also stained more intensely with Alcian blue and produced more MUC2, a goblet-cell mucin characteristic of intestinal metaplasia, suggesting that PTTG1 can push gastric epithelium toward an intestinal, mucin-producing identity. In the opposite direction, stable PTTG1 knockdown in MKN1 cells injected subcutaneously into nude mice markedly suppressed tumor growth, with smaller volumes and lower weights at the experimental endpoint, reduced Ki67 and Cyclin B1 staining, and altered AB-PAS mucin staining that, however, was not accompanied by a change in MUC2 expression, hinting that PTTG1’s effects on mucin phenotypes depend on the biological context.

The study is candid about its limits. Tissue dissociation erases the spatial geography of the gastric gland, the cross-sectional sampling of five patients cannot fully capture the temporal dynamics of a cascade that unfolds over years, and the cohort was too small to assess sex-associated differences. The tumor-initiating potential of Enterocytes-S3 remains to be proven, and more physiologically relevant culture systems will be needed to settle the mucin question. Notably, PTTG1 expression showed no significant association with overall survival in the TCGA or ACRG cohorts, suggesting the gene functions as an engine of tumor-intrinsic biology rather than an independent prognostic marker. Even so, by placing a chromosome-segregation guardian at the hinge between intestinal metaplasia and carcinoma, the work offers the clearest single-cell-resolved view yet of how the Correa cascade accelerates, and it flags PTTG1, and the G2/M checkpoint it commands, as a target worth pursuing in the fight against intestinal-type gastric cancer.

Subject of Research: The role of PTTG1 in G2/M checkpoint-mediated cell-cycle reprogramming during intestinal-type gastric cancer progression

Article Title: PTTG1 drives intestinal-type gastric cancer progression via G2/M checkpoint-mediated cell-cycle reprogramming

Article References: Hu, C., Bian, L., Luo, L., Zheng, Z., Chen, Y., Gao, X., Li, F., Yang, D., Liu, Y., Li, G., Xu, H., Yan, C., & Jin, G. (2026). PTTG1 drives intestinal-type gastric cancer progression via G2/M checkpoint-mediated cell-cycle reprogramming. iScience, 29(11), Article 117742. https://doi.org/10.1016/j.isci.2026.117742

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117742

Keywords: gastric cancer, PTTG1, securin, G2/M checkpoint, single-cell RNA sequencing, intestinal metaplasia, Correa cascade, Cyclin B1, E2F1, organoids, xenograft, cell cycle

The scale of the clinical problem gives the research its urgency. Ovarian cancer is the sixth leading cause of cancer-related death among women in the United States, with roughly 21,000 new diagnoses and nearly 13,000 deaths each year. Because early-stage disease is frequently silent, more than half of patients are discovered only after the tumor has spread across the peritoneal cavity, often accompanied by malignant ascites. Standard care combines cytoreductive surgery with platinum agents, a taxane, and bevacizumab, and many patients initially achieve complete or partial remission. Yet that benefit is typically short-lived: more than half relapse, and the disease ultimately proves fatal for most of them. New therapeutic angles are badly needed.

The Japanese research team, led by Takahiro Koyanagi and Yasushi Saga, focused on a protein family with a double identity. The vasohibins consist of vasohibin-1, an angiogenesis inhibitor produced by vascular endothelial cells, and vasohibin-2, a homolog that tumors themselves secrete to promote new blood vessel growth. The group had previously shown that forcing VASH1 expression suppresses tumor growth and peritoneal dissemination in ovarian cancer models, while VASH2 knockdown or antibody blockade similarly restrains tumor progression. Crucially, VASH2 is barely detectable in normal tissues, and mice engineered to lack it show no obvious abnormalities, making it an attractive drug target with a potentially wide therapeutic window.

What has transformed the field in recent years is the discovery that vasohibins are not merely signaling molecules. They function as tubulin carboxypeptidases, enzymes that clip the terminal tyrosine residue from alpha-tubulin, a chemical modification known as detyrosination that alters microtubule behavior. This matters enormously for oncology because paclitaxel works by binding beta-tubulin, stabilizing microtubules, and freezing their dynamic equilibrium so that dividing cells cannot complete mitosis. The researchers had already shown that ovarian cancer cells with VASH2 knocked out by CRISPR/Cas9 display reduced detyrosinated microtubules and dramatically heightened sensitivity to paclitaxel, hinting that anything which modulates VASH2 activity might tune the cell’s response to the drug.

Progesterone entered the picture through the team’s earlier work on non-genomic hormone signaling. Classically, progesterone diffuses into the nucleus and binds nuclear progesterone receptors, which regulate gene transcription. But a second family of receptors, the membrane progesterone receptors, sits on the cell surface and triggers rapid, non-genomic responses. The two ovarian cancer cell lines used in the study, TU-OS-4 and OVKATE, are progesterone receptor-negative but express membrane progesterone receptors, and the team had previously shown that progesterone can kill these cells quickly through mPR-mediated mechanisms and can enhance sensitivity to SN38, the active metabolite of irinotecan, by suppressing topoisomerase I and inducing ferroptosis.

In the new experiments, the researchers exposed both cell lines to a high concentration of progesterone, 400 micromolar, for just 30 minutes, then measured VASH2 messenger RNA by quantitative reverse transcription PCR. Expression rose significantly in both lines compared with untreated controls. Western blotting told a consistent story at the protein level: detyrosinated alpha-tubulin accumulated in progesterone-treated cells, and cyclin B1, a regulatory protein that rises from the G2 phase into early mitosis and partners with Cdk1 to drive cells through metaphase, appeared in treated cells while remaining nearly absent in controls. Together, the results sketch a picture of progesterone pushing cells toward a state of altered microtubule chemistry and perturbed mitotic progression.

The functional payoff came in the drug sensitivity assays. When cells were pretreated with 100 micromolar progesterone for 30 minutes and then challenged with paclitaxel for 48 hours, the paclitaxel IC50 fell from 35.3 to 19.8 nanomolar in TU-OS-4 cells, a 1.8-fold gain in sensitivity, and from 128.0 to 9.5 nanomolar in OVKATE cells, a striking 13.5-fold gain, with both differences statistically significant at p less than 0.01. Gemcitabine, an antimetabolite that attacks DNA rather than microtubules, showed no such shift in either line, its IC50 remaining essentially unchanged. That selectivity is the strongest clue that the progesterone effect operates specifically through the microtubule pathway that paclitaxel targets.

The authors are candid about what the study does and does not prove. Because the effects appeared within 30 minutes in progesterone receptor-negative cells, they most likely reflect non-genomic signaling through membrane progesterone receptors, but the team did not directly inhibit or knock down those receptors, so mPR dependence remains an inference rather than a demonstration. Likewise, the measurements captured VASH2 mRNA and detyrosinated tubulin, not VASH2 protein abundance or enzymatic activity, so the link between the hormone, the enzyme, and the drug response is an association consistent with causality rather than a proven causal chain. Direct assessment of spindle function and microtubule dynamics was also beyond the scope of the work.

There are other caveats that temper any temptation to celebrate. The progesterone concentrations used far exceed physiological circulating levels; they were chosen because comparable conditions reproducibly triggered early non-genomic responses in previous experiments without nonspecific cytotoxicity, not because they mirror the endocrine environment in a patient’s body. The authors also stress that progesterone biology is highly context-dependent, shaped by receptor expression profiles, tumor subtype, and the hormonal microenvironment, and recent evidence suggests the hormone can exert distinct or even opposing effects depending on cellular context rather than acting uniformly protectively in ovarian cancer. Generalizing these findings across the heterogeneity of real tumors would be premature.

Even so, the study adds an intriguing layer to a research program that has steadily built the case for VASH2 as a therapeutic target, from shRNA knockdowns that suppressed peritoneal dissemination in animal models, to atelocollagen-protected siRNA that inhibited tumor growth in vivo, to a neutralizing anti-VASH2 antibody with efficacy comparable to bevacizumab and no apparent adverse effects in mice. If progesterone can push ovarian cancer cells into a microtubule state that paclitaxel exploits more effectively, a hormonally guided priming strategy could one day widen the therapeutic index of an indispensable drug. Whether VASH2’s roles in angiogenesis and microtubule regulation are independent or interconnected remains an open question, and the authors call for lower concentrations, prolonged exposures, in vivo models, and mechanistic studies to determine whether the promise survives translation. For now, the message is one of cautious excitement: an old hormone, viewed through the lens of modern microtubule biology, may have more to offer ovarian cancer patients than anyone suspected.

Subject of Research: Progesterone effects on vasohibin-2 expression, tubulin detyrosination, and paclitaxel sensitivity in ovarian cancer cells

Article Title: Progesterone Is Associated With Increased Vasohibin‐2 Expression, Tubulin Detyrosination, and Paclitaxel Sensitivity in PR‐Negative Ovarian Cancer Cells

Article References: Koyanagi, T., Saga, Y., Takahashi, Y., Tamura, K., Suizu, E., Yamamoto, K., Taneichi, A., Takei, Y., Mizukami, H., & Fujiwara, H. (2026). Progesterone Is Associated With Increased Vasohibin‐2 Expression, Tubulin Detyrosination, and Paclitaxel Sensitivity in PR ‐Negative Ovarian Cancer Cells. Cancer Reports, 9(9), Article e70681. https://doi.org/10.1002/cnr2.70681

Image Credits: AI Generated

DOI: 10.1002/cnr2.70681

Keywords: ovarian cancer, progesterone, paclitaxel, vasohibin-2, tubulin detyrosination, membrane progesterone receptor, microtubules, chemosensitivity, cyclin B1, angiogenesis, gemcitabine, drug resistance