This perspective brings together multiple observations concerning the regulatory architecture and functional interactions of the TP53 gene and its isoforms. The TP53 gene encompasses an internal enhancer-promoter region (P2) located between exons 2 and 5, which is transactivated by full-length TAp53α, to drive the expression of truncated TP53 isoforms ΔN133p53α, β or γ. ΔN133p53α homo-monomers or dimers very likely form hetero-tetramers with homo-dimers of full-length TAp53α. The TAp53α-ΔN133p53 tetramer then acts as a transcription factor augmenting mitochondrial efficiency, DNA repair, telomere restoration and reversing cellular senescence, thus opposing many outputs of tumor suppressive TAp53α homo-tetramers. Other transcription factors, such as estrogen receptor (ER), OCT1, and SOX9 also may bind the P2 promoter-enhancer to promote transcription of oncogenic TP53 isoforms. These transcription factors, together with full-length TAp53α, appear to cooperate to maintain an open chromatin state in the P2 region in a manner reminiscent of a neural "associative memory" network.

ER stress underlies numerous severe pathologies. We have metabolically perturbed normal fibroblasts to study the biological roles of microRNAs (miRs) under mild and extended ER stress. We now report that miR-4488 quenches inflammation-associated gene expression in such metabolically perturbed cells. Remarkably, generation of miR-4488 is Drosha-independent. Furthermore, we define miR-4488 as a noncanonical miRNA derived from the expansion segment ES7L of the 28S ribosomal RNA. Moreover, its generation involves the autophagy-lysosome route and is inhibited when this pathway is blocked, thus unveiling an anti-inflammatory role for ribosomal RNA and lysosomes, engaged at the onset of stress. Mechanistically, miR-4488 suppresses the expression of NFKB2 and RELB, whose mRNAs specifically associate with miR-4488 exclusively upon stress. This selectivity suggests that miR-4488 may bear promise for treating mild ER stress-associated diseases.

Estrogen receptor alpha (ERα)-positive luminal breast cancer is commonly treated with aromatase inhibitors (AI) to block estrogen signaling; however, resistance frequently develops, limiting therapy success. We observed that GLYATL1 (Glycine-N-Acyltransferase Like 1) expression is upregulated in AI-resistant breast cancer cell models and in patients undergoing AI therapy, correlating with poorer survival. Here we demonstrate that GLYATL1 promotes resistance to estrogen deprivation by elevating succinate levels and altering epigenetic histone marks associated with active transcription. Knockdown or knockout of GLYATL1 reverses these effects and reduces proliferation under estrogen-deprived conditions. Notably, GLYATL1 expression is positively regulated by estrogen receptor alpha signaling, however, independently of estrogen. These findings reveal GLYATL1 as a metabolic and epigenetic mediator of endocrine therapy resistance, suggesting it as a potential target to overcome AI resistance in luminal breast cancer.

Antigen processing and presentation (APP) is essential for adaptive immunosurveillance. We uncover a mechanism whereby activated T cell-derived extracellular vesicles (ATEVs) drive a positive feedback loop that enhances antigen presentation and immune responses in normal physiology and cancer. ATEV-induced immunogenicity relies on extracellular vesicular double-stranded DNA (EVDNA), which is notably abundant and primarily composed of genomic DNA enriched in immune-related genes, including those encoding APP machinery. Mechanistically, granzyme B (Gzmb) packaged by ATEVs disrupts the nuclear envelope of recipient cells, facilitating intranuclear transfer and subsequent transient expression of EVDNA encoding APP genes. DNase treatment removes most AT-EVDNA, abrogating APP upregulation and thus T cell activation and recruitment to tumors. Notably, ATEVs hold promise as an acellular immunotherapy, restoring APP and synergizing with checkpoint blockade in immunotherapy-refractory tumors. Collectively, our findings uncover a mechanism of transient, non-viral gene delivery by ATEVs that boosts APP and anti-tumor immunity while limiting autoimmunity.

High-grade serous ovarian cancer demonstrates limited responsiveness to immune checkpoint inhibitors, owing in part to immunosuppressive environments shaped by nearly universal p53 aberrations. Utilizing an immunocompetent mouse model and individual p53 mutations, we identified a dependence of the p53-R270H mutation (equivalent of human R273H) on regulatory T cells (Tregs) and the PD-1/PD-L1 axis. Analysis of patient datasets associated R273H with elevated levels of two p53 targets, PD-L1 and amphiregulin (AREG), a Tregs growth factor. In contrast to p53-R172H tumors, where there was limited activity, dual antibody therapy targeting AREG and PD-L1 selectively and effectively inhibited R270H tumors. This involved polarization toward M1 macrophages, infiltration of CD8+ T cells, diminished Ly6G+ neutrophils and downregulation of interleukin-4. In patient-derived R273C organoids, the combination treatment reduced the CD4/CD8 ratio. This study is the first to establish a mutation-tailored therapeutic approach that leverages the capacity of p53 to modulate immunosuppressive mechanisms.

Metastasis are responsible for over 90% of cancer related mortality and remain the major challenge for successful management of malignant diseases. The liver is a preferred site of metastatic disease and a major cause of death from various malignancies, including colon, gastric, and pancreatic carcinomas as well as melanoma, breast cancer, and sarcomas. Recent evidence has indicated the role of microRNAs in modulating the metastatic processes. MicroRNAs (miRs) constitute a class of short noncoding RNAs which regulate gene expression by targeting messenger RNA (mRNA), including translational repression and mRNA degradation. There are specific miRs that exhibit tumor-suppressive activity by targeting cancer driver genes. miR-34a is a well-known tumor suppressor and anti-metastatic miR. However, the administration, and particularly the delivery of miR-34a, constitutes a major challenge. To overcome this major hurdle of translating miR-34a into a therapeutic molecule, we hypothesize that induction of endogenous expression and secretion of the tumor-suppressive miR-34a, in the vicinity of metastasis, using small synthetic molecules, could be a new strategy for metastasis therapy. To identify small molecules which activate miR-34a expression and secretion, we generated a PmiR-34a-EGFP reporter system in vitro and performed high throughput screening of synthetic small molecule libraries, searching for compounds that induce the miR-34a promoter. Once compounds were identified by our high-through-put system that we established, validation experiments in vitro and in vivo followed. The readout of the first high-through-put screening helped us to identify 15, out of over 8000 compounds, which induce miR-34a promoter activity. However, when validating these compounds, only 6 (AT7519, A-674563, BBI503, PCM0240249, KRIBB and SB273005) out of 9 compounds that were tested -induced miR-34a promoter activation and only 2 (AT7519 and A-674563) out of the 6, also caused miR-34a secretion from HepG2, a human hepatoblastoma cell line. As both AT7519 and A-674563 are known as multi-Cyclin Dependent Kinase (CDK) inhibitors, we searched for more potent CDK inhibitors, and we identified two compounds: Dinaciclib and A51. Both compounds induced miR-34a expression and secretion in vitro. Dinaciclib exhibited a better miR-34a dependent anti-tumoral effect in vitro whereas, A51 exhibited a better anti-metastatic effect in the forced colorectal cancer (CRC) liver metastasis model in vivo. Induction of miR-34a using small synthetic molecules is a novel therapeutic approach to eradicate CRC liver metastasis. Dayana Yaish, Auerlia Markezana, Alexander Plotnikov, Nofar Rosenberg, Shanny Barnoy, Emma Klahr, Moshe Oren, Yinon Ben-Neriah, Haim Barr, Hilla Giladi, Eithan Galun. Suppressing liver metastasis growth by inducing the endogenous expression of the tumor suppressor miR-34a by small synthetic molecules [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB457.

Breast cancer is the leading cause of death in women under 50. The majority of breast cancers are estrogen receptor α-positive (ER+) and are commonly treated with hormonal therapies such as tamoxifen that inhibit ER activity. The TP53 tumor suppressor gene, encoding the p53 protein, is the most frequently mutated gene in breast cancer, and TP53 mutations are associated with diminished tamoxifen response and worse prognosis for breast cancer patients. Here, we report that in breast cancer cells p53 and ER cooperate to regulate the transcription of a set of genes encoding chromatin modifiers. The net result is a global increase in H3K4me3 and decrease in H3K9me3 chromatin marks. The resultant "open" chromatin is associated with increased transcription of luminal cell identity genes and enhanced tamoxifen sensitivity. Conversely, diminished p53 control of these chromatin modulators is associated with the evolution of tamoxifen resistance and cancer stem cell properties.

High-grade serous ovarian cancer (HGSOC) represents the most common and lethal subtype of ovarian cancer. Despite initial response to platinum-based standard therapy, patients commonly suffer from relapse that likely originates from drug-tolerant persister (DTP) cells. We generated isogenic clones of treatment-naïve and cisplatin-tolerant persister HGSOC cells. In addition, single-cell RNA sequencing of barcoded cells was performed in a xenograft model with HGSOC cell lines after platinum-based therapy. Published single-cell RNA-sequencing data from neo-adjuvant and non-treated HGSOC patients and patient data from TCGA were analyzed. DTP-derived cells exhibited morphological alterations and upregulation of epithelial-mesenchymal transition (EMT) markers. An aggressive subpopulation of DTP-derived cells showed high expression of the stress marker ATF3. Knockdown of ATF3 enhanced the sensitivity of aggressive DTP-derived cells to cisplatin-induced cell death, implying a role for ATF3 stress response in promoting a drug tolerant persister cell state. Furthermore, single cell lineage tracing to detect transcriptional changes in a HGSOC cell line-derived xenograft relapse model showed that cells derived from relapsed solid tumors express increased levels of EMT and multiple endoplasmic reticulum (ER) stress markers, including ATF3. Single cell RNA sequencing of epithelial cells from four HGSOC patients also identified a small cell population resembling DTP cells in all samples. Moreover, analysis of TCGA data from 259 HGSOC patients revealed a significant progression-free survival advantage for patients with low expression of the ATF3-associated partial EMT genes. These findings suggest that increased ATF3 expression together with partial EMT promote the development of aggressive DTP, and thereby relapse in HGSOC patients.

The story of p53 is illuminating. Despite widespread attention, the tumor-suppressive functions of wild-type p53 or the oncogenic activities of its cancer-associated mutants are still not fully understood, and our discoveries have not yet led to major therapeutic breakthroughs. There is still much to learn about this fascinating protein.

Mutations resulting in decreased activity of p53 tumor suppressor protein promote tumorigenesis. P53 protein levels are tightly regulated through the Ubiquitin Proteasome System (UPS). Several E3 ligases were shown to regulate p53 stability, including MDM2. Here we report that the ubiquitin E3 ligase XIAP (X-linked Inhibitors of Apoptosis) is a direct ligase for p53 and describe a novel approach for modulating the levels of p53 by targeting the XIAP pathway. Using in vivo (live-cell) and in vitro (cell-free reconstituted system) ubiquitylation assays, we show that the XIAP-antagonist ARTS regulates the levels of p53 by promoting the degradation of XIAP. XIAP directly binds and ubiquitylates p53. In apoptotic cells, ARTS inhibits the ubiquitylation of p53 by antagonizing XIAP. XIAP knockout MEFs express higher p53 protein levels compared to wild-type MEFs. Computational screen for small molecules with high affinity to the ARTS-binding site within XIAP identified a small-molecule ARTS-mimetic, B3. This compound stimulates apoptosis in a wide range of cancer cells but not normal PBMC (Peripheral Blood Mononuclear Cells). Like ARTS, the B3 compound binds to XIAP and promotes its degradation via the UPS. B3 binding to XIAP stabilizes p53 by disrupting its interaction with XIAP. These results reveal a novel mechanism by which ARTS and p53 regulate each other through an amplification loop to promote apoptosis. Finally, these data suggest that targeting the ARTS binding pocket in XIAP can be used to increase p53 levels as a new strategy for developing anti-cancer therapeutics.

Metastasis occurs frequently after resection of pancreatic cancer (PaC). In this study, we hypothesized that multi-parametric analysis of pre-metastatic liver biopsies would classify patients according to their metastatic risk, timing and organ site. Liver biopsies obtained during pancreatectomy from 49 patients with localized PaC and 19 control patients with non-cancerous pancreatic lesions were analyzed, combining metabolomic, tissue and single-cell transcriptomics and multiplex imaging approaches. Patients were followed prospectively (median 3 years) and classified into four recurrence groups; early (<6 months after resection) or late (>6 months after resection) liver metastasis (LiM); extrahepatic metastasis (EHM); and disease-free survivors (no evidence of disease (NED)). Overall, PaC livers exhibited signs of augmented inflammation compared to controls. Enrichment of neutrophil extracellular traps (NETs), Ki-67 upregulation and decreased liver creatine significantly distinguished those with future metastasis from NED. Patients with future LiM were characterized by scant T cell lobular infiltration, less steatosis and higher levels of citrullinated H3 compared to patients who developed EHM, who had overexpression of interferon target genes (MX1 and NR1D1) and an increase of CD11B(+) natural killer (NK) cells. Upregulation of sortilin-1 and prominent NETs, together with the lack of T cells and a reduction in CD11B(+) NK cells, differentiated patients with early-onset LiM from those with late-onset LiM. Liver profiles of NED closely resembled those of controls. Using the above parameters, a machine-learning-based model was developed that successfully predicted the metastatic outcome at the time of surgery with 78% accuracy. Therefore, multi-parametric profiling of liver biopsies at the time of PaC diagnosis may determine metastatic risk and organotropism and guide clinical stratification for optimal treatment selection.

Downregulation of the urea cycle enzyme argininosuccinate synthase (ASS1) in multiple tumors is associated with a poor prognosis partly because of the metabolic diversion of cytosolic aspartate for pyrimidine synthesis, supporting proliferation and mutagenesis owing to nucleotide imbalance. Here, we find that prolonged loss of ASS1 promotes DNA damage in colon cancer cells and fibroblasts from subjects with citrullinemia type I. Following acute induction of DNA damage with doxorubicin, ASS1 expression is elevated in the cytosol and the nucleus with at least a partial dependency on p53; ASS1 metabolically restrains cell cycle progression in the cytosol by restricting nucleotide synthesis. In the nucleus, ASS1 and ASL generate fumarate for the succination of SMARCC1, destabilizing the chromatin-remodeling complex SMARCC1–SNF5 to decrease gene transcription, specifically in a subset of the p53-regulated cell cycle genes. Thus, following DNA damage, ASS1 is part of the p53 network that pauses cell cycle progression, enabling genome maintenance and survival. Loss of ASS1 contributes to DNA damage and promotes cell cycle progression, likely contributing to cancer mutagenesis and, hence, adaptability potential.

Tumor suppressor p53 (TP53) is frequently mutated in cancer, often resulting not only in loss of its tumor-suppressive function but also acquisition of dominant-negative and even oncogenic gain-of-function traits. While wild-type p53 levels are tightly regulated, mutants are typically stabilized in tumors, which is crucial for their oncogenic properties. Here, we systematically profiled the factors that regulate protein stability of wild-type and mutant p53 using marker-based genome-wide CRISPR screens. Most regulators of wild-type p53 also regulate p53 mutants, except for p53 R337H regulators, which are largely private to this mutant. Mechanistically, FBXO42 emerged as a positive regulator for a subset of p53 mutants, working with CCDC6 to control USP28-mediated mutant p53 stabilization. Additionally, C16orf72/HAPSTR1 negatively regulates both wild-type p53 and all tested mutants. C16orf72/HAPSTR1 is commonly amplified in breast cancer, and its overexpression reduces p53 levels in mouse mammary epithelium leading to accelerated breast cancer. This study offers a network perspective on p53 stability regulation, potentially guiding strategies to reinforce wild-type p53 or target mutant p53 in cancer.

PDF file - 86K, Patient characteristics and treatment regimens

AbstractLung cancer is the leading cause of cancer-related deaths worldwide. The paralogous transcriptional cofactors Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ, also called WWTR1), the main downstream effectors of the Hippo signal transduction pathway, are emerging as pivotal determinants of malignancy in lung cancer. Traditionally, studies have tended to consider YAP and TAZ as functionally redundant transcriptional cofactors with similar biological impact. However, there is growing evidence that each of them also possesses distinct attributes. Here we sought to systematically characterize the division of labor between YAP and TAZ in non–small cell lung cancer (NSCLC), the most common histological subtype of lung cancer. Representative NSCLC cell lines as well as patient-derived data showed that the two paralogs orchestrated nonoverlapping transcriptional programs in this cancer type. YAP preferentially regulated gene sets associated with cell division and cell-cycle progression, whereas TAZ preferentially regulated genes associated with extracellular matrix organization. Depletion of YAP resulted in growth arrest, whereas its overexpression promoted cell proliferation. Likewise, depletion of TAZ compromised cell migration, whereas its overexpression enhanced migration. The differential effects of YAP and TAZ on key cellular processes were also associated with differential response to anticancer therapies. Uncovering the different activities and downstream effects of YAP and TAZ may thus facilitate better stratification of patients with lung cancer for anticancer therapies.Significance:Thease findings show that oncogenic paralogs YAP and TAZ have distinct roles in NSCLC and are associated with differential response to anticancer drugs, knowledge that may assist lung cancer therapy decisions.

PDF file - 39K, siGenome SMARTpool (Dharmacon) siRNA sequences