P53 Target Research Articles

P53 Regulation upon Lipid Peroxidation and Ferroptosis for Intervention against Atherogenesis

Abstract: Tumor protein 53 (P53), as an intracellular regulator of antioxidant responses, participates in the expression of antioxidant defense and lipid metabolism as well as the synthesis of genes in cells. The balance of oxidation and reduction can be disrupted by many pathological conditions, and the role of the antioxidant system in protecting the equilibrium state from pathological effects, such as reactive lipids, is crucial. In particular, the excessive accumulation of lipid peroxidation products is a key factor driving the occurrence and development of various diseases. Ferroptosis is an iron-dependent, lipid peroxidation-driven cell death cascade reaction, which has become a key research area in cardiovascular diseases. Atherosclerosis (AS) is a pathological change caused by lipid metabolic disorder, inflammatory response, and endothelial cell injury, and is the most common cause of cardiovascular disease. This review briefly outlines lipid peroxidation and key components involving ferroptosis cascade reactions, summarizes and emphasizes the role of P53-related signaling pathways in mediating lipid peroxidation and ferroptosis, and focuses on the known P53 target genes that regulate these pathways, as well as explores the possibility of P53 intervention in the treatment of AS by regulating lipid peroxidation and ferroptosis processes.

MiR-17-5p-engineered sEVs Encapsulated in GelMA Hydrogel Facilitated Diabetic Wound Healing by Targeting PTEN and p21.

Delayed wound healing is a major complication of diabetes, and is associated with impaired cellular functions. Current treatments are unsatisfactory. Based on the previous reports on microRNA expression in small extracellular vesicles (sEVs), miR-17-5p-engineered sEVs (sEVs17-OE) and encapsulated them in gelatin methacryloyl (GelMA) hydrogel for diabetic wounds treatment are fabricated. SEVs17-OE are successfully fabricated with a 16-fold increase in miR-17-5p expression. SEVs17-OE inhibited senescence and promoted the proliferation, migration, and tube formation of high glucose-induced human umbilical vein endothelial cells (HG-HUVECs). Additionally, sEVs17-OE also performs a promotive effect on high glucose-induced human dermal fibroblasts (HG-HDFs). Mechanism analysis showed the expressions of p21 and phosphatase and tensin homolog (PTEN), as the target genes of miR-17-5p, are downregulated significantly by sEVs17-OE. Accordingly, the downstream genes and pathways of p21 and PTEN, are activated. Next, sEVs17-OE are loaded in GelMA hydrogel to fabricate a novel bioactive wound dressing and to evaluate their effects on diabetic wound healing. Gel-sEVs17-OE effectively accelerated wound healing by promoting angiogenesis and collagen deposition. The cellular mechanism may be associated with local cell proliferation. Therefore, a novel bioactive wound dressing by loading sEVs17-OE in GelMA hydrogel, offering an option for chronic wound management is successfully fabricated.

Acacetin inhibited non-small-cell lung cancer (NSCLC) cell growth via upregulating miR-34a in vitro and in vivo

Acacetin, one of the flavonoid compounds, is a natural product found in various plants, including Silver birch, and Damiana. Previous studies showed that acacetin has anti-cancer effects on many kinds of cancer cells, however, the role of and the mechanisms of actions of acacetin on non-small cell lung cancer (NSCLC) cells is still not fully understood. Herein, we found that, in vitro, acacetin inhibited the proliferation, invasion, and migration of NSCLC cells, A549 and H460, in a dose-dependent manner. Meanwhile, flow cytometry assay results showed that acacetin induced G2/M phase cell cycle arrest, and apoptosis of NSCLC cells. In vivo, acacetin suppressed tumor formation of A549-xenografted nude mice model with no obvious toxicities. Western blotting results showed that the protein levels of cell cycle-related proteins cyclin B1, cyclin D, and anti-apoptotic protein Bcl-2 had decreased, while the apoptosis-related protein Bak had increased both in NSCLC cells and in A549-xenografted tumor tissues. For investigating the molecular mechanism behind the biological effects of acacetin on NSCLC, we found that acacetin induced the expression levels of tumor suppressor p53 both in vitro and in vivo. MicroRNA, miR-34a, the direct target of p53, has been shown anti-NSCLC proliferation effects by suppressing the expression of its target gene programmed death ligand 1 (PD-L1). We found that acacetin upregulated the expression levels of miR-34a, and downregulated the expression levels of PD-L1 of NSCLC cells in vitro and of tumors in vivo. In vitro, knockdown p53 expression by siRNAs reversed the induction effects of acacetin on miR34a expression and abolished the inhibitory activity of acacetin on NSCLC cell proliferation. Furthermore, using agomir and antagomir to overexpress and suppress the expression miR-34a in NSCLC cells was also examined. We found that miR-34a agomir showed similar effects as acacetin on A549 cells, while miR-34a antagomir could partially or completely reverse acacetin’s effects on A549 cells. In vivo, intratumor injection of miR-34a antagomir could drastically suppress the anti-tumor formation effects of acacetin in A549-xenografted nude mice. Overall, our results showed that acacetin inhibits cell proliferation and induces cell apoptosis of NSCLC cells by regulating miR-34a.

Development and Nanoparticle-Mediated Delivery of Novel MDM2/MDM4 Heterodimer Peptide Inhibitors to Enhance 5-Fluorouracil Nucleolar Stress in Colorectal Cancer Cells.

Colorectal cancer (CRC) often involves wild-type p53 inactivation by MDM2 and MDM4 overexpression, promoting tumor progression and resistance to 5-fluoruracil (5-FU). Disrupting the MDM2/4 heterodimer can proficiently reactivate p53, sensitizing cancer cells to 5-FU. Herein, we developed 16 peptides based on Pep3 (1), the only known peptide acting through this mechanism. The new peptides, notably 3 and 9, showed lower IC50 values than 1. When incorporated into tumor-targeted biodegradable nanoparticles, these exhibited cytotoxicity against three different CRC cell lines. Notably, NPs/9 caused a significant increase in p53 levels associated with a strong increment of its main downstream target p21 inducing apoptosis. Also, the combined treatment of 9 with 5-FU caused the activation of nucleolar stress and a synergic apoptotic effect. Hence, the co-delivery of MDM2/4 heterodimer disruptors with 5-FU through nanoparticles might be a promising strategy to overcome drug resistance in CRC.

Abstract C089: A novel role of p53 in pancreatic acinar cell identity

Abstract Pancreatitis is an inflammatory disease that affects acinar cells in the exocrine pancreas, and can be triggered by several factors, such as alcohol abuse, smoking and familial genetic alterations. Pancreatic injury associated with pancreatitis is characterized by inflammation, acinar cell death, and acinar-to-ductal metaplasia (ADM), a regenerative process in which metaplastic cells proliferate and re-differentiate into acinar cells. Recurrent pancreatitis can cause persistent ADM, impairing exocrine function and causing precancerous lesions known as pancreatic intraepithelial neoplasia (PanIN) that can initiate pancreatic ductal adenocarcinoma (PDAC), a nearly always fatal disease. Importantly, the lack of treatment options for pancreatitis patients reinforces the need for strategies that could resolve pancreatic damage and stop disease progression. We have recently shown that pancreatic cells harboring a hyperactive variant of p53 display increased resistance to developing acute pancreatitis induced by cerulein (a secretagogue which mimics cholecystokinin). Here, we show that p53 activation using the drug Nutlin-3a can repair the damage caused by cerulein-induced pancreatitis, and reduce the formation of PanIN lesions. This repair is achieved exclusively at low doses of Nutlin-3a, which cause a mild p53 activation, and is entirely dependent on the presence of the p53 gene. We have also identified novel p53 target genes relevant to acinar identity from ChIP-seq and RNA-seq data, and validated their dependence on p53 in mouse embryonic fibroblasts and in pancreatic precancerous lesions. Lastly, we have observed expression of p53 in the developing pancreas at embryonic day 15.5, indicating a potential function of p53 in pancreatic development. Our findings suggest a novel role of p53 in rescuing acinar cells from damage, and that p53 activation may be used as a treatment for pancreatitis and pancreatic cancer prevention. Citation Format: Jennifer J. Twardowski, Stephano S. Mello, Thomas I. Heist. A novel role of p53 in pancreatic acinar cell identity [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr C089.

Club cell-specific telomere protection protein 1 (TPP1) protects against tobacco smoke-induced lung inflammation, xenobiotic metabolic dysregulation, and injurious responses.

Inhaling xenobiotics, such as tobacco smoke is a major risk factor for pulmonary diseases, e.g., COPD/emphysema, interstitial lung disease, and pre-invasive diseases. Shelterin complex or telosome provides telomeric end protection during replication. Telomere protection protein 1 (TPP1) is one of the main six subunits of the shelterin complex supporting the telomere stability and genomic integrity. Dysfunctional telomeres and shelterin complex are associated as a disease mechanism of tobacco smoke-induced pulmonary damage and disease processes. The airway epithelium is critical to maintaining respiratory homeostasis and is implicated in lung diseases. Club cells (also known as clara cells) play an essential role in the immune response, surfactant production, and metabolism. Disrupted shelterin complex may lead to dysregulated cellular function, DNA damage, and disease progression. However, it is unknown if the conditional removal of TPP1 from Club cells can induce lung disease pathogenesis caused by tobacco smoke exposure. In this study, conditional knockout of Club-cell specific TPP1 demonstrated the instability of other shelterin protein subunits, such as TRF1, dysregulation of cell cycle checkpoint proteins, p53 and downstream targets, and dysregulation of telomeric genes. This was associated with age-dependent senescence-associated genes, increased DNA damage, and upregulated RANTES/IL13/IL33 mediated lung inflammation and injury network by cigarette smoke (CS). These phenomena are also associated with alterations in cytochrome P450 and glutathione transferases, upregulated molecular pathways promoting lung lesions, bronchial neoplasms, and adenocarcinomas. These findings suggest a pivotal role of TPP1 in maintaining lung homeostasis and injurious responses in response to CS. Thus, these data TPP1 may have therapeutic value in alleviating telomere-related chronic lung diseases.

Pien Tze Huang Inhibits Proliferation of Colorectal Cancer Cells through Suppressing PNO1 Expression and Activating p53/p21 Signaling Pathway.

To explore the regulatory effect of Pien Tze Huang (PZH) on targeting partner of NOB1 (PNO1) and it's down-stream mediators in colorectal cancer (CRC) cells. Quantitative polymerase chain reaction was performed to determine mRNA levels of PNO1, TP53, and CDKN1A. Western blotting was performed to determine protein levels of PNO1, p53, and p21. HCT-8 cells were transduced with a lentivirus over-expressing PNO1. Colony formation assay was used to detect cell survival in PNO1 overexpression of HCT-8 cells after PZH treatment. Cell-cycle distribution, cell viability and cell apoptosis were performed to identify the effect of PNO1 overexpression on cell proliferation and apoptosis of HCT-8 cells after PZH treatment. Xenograft BALB/c nude mice bearing HCT116 cells transduced with sh-PNO1 or sh-Ctrl lentivirus were evaluated. Western blot assay was performed to detect PNO1, p53, p21 and PCNA expression in tumor sections. Terminal deoxynucleotidyl transferase dUTP nick end labling (TUNEL) assay was used to determine the apoptotic cells in tissues. PZH treatment decreased cell viability, down-regulated PNO1 expression, and up-regulated p53 and p21 expressions in HCT-8 cells (P<0.05). PNO1 overexpression attenuated the effects of PZH treatment, including the expression of p53 and p21, cell growth, cell viability, cell cycle arrest and cell apoptosis in vitro (P<0.05). PNO1 knockdown eliminated the effects of PZH treatment on tumor growth, inhibiting cell proliferation inhibition and apoptosis induction in vivo (P<0.05). Similarly, PNO1 knockdown attenuated the effects of PZH treatment on the down-regulation of PNO1 and up-regulation of p53 and p21 in vivo (P<0.05). The mechanism by which PZH induces its CRC anti-proliferative effect is at least in part by regulating the expression of PNO1 and its downstream targets p53 and p21.

Ninjurin 2, a Cell Adhesion Molecule and a Target of p53, Modulates Wild-Type p53 in Growth Suppression and Mutant p53 in Growth Promotion.

The nerve injury-induced protein 1 (NINJ1) and NINJ2 constitute a family of homophilic adhesion molecules and are involved in nerve regeneration. Previously, we showed that NINJ1 and p53 are mutually regulated and the NINJ1-p53 loop plays a critical role in p53-dependent tumor suppression. However, the biology of NINJ2 has not been well-explored. By using multiple in vitro cell lines and genetically engineered mouse embryo fibroblasts (MEFs), we showed that NINJ2 is induced by DNA damage in a p53-dependent manner. Moreover, we found that the loss of NINJ2 promotes p53 expression via mRNA translation and leads to growth suppression in wild-type p53-expressing MCF7 and Molt4 cells and premature senescence in MEFs in a wild-type p53-dependent manner. Interestingly, NINJ2 also regulates mutant p53 expression, and the loss of NINJ2 promotes cell growth and migration in mutant p53-expressing MIA-PaCa2 cells. Together, these data indicate that the mutual regulation between NINJ2 and p53 represents a negative feedback loop, and the NINJ2-p53 loop has opposing functions in wild-type p53-dependent growth suppression and mutant p53-dependent growth promotion.

C-71980262, a novel small molecule against human papilloma virus-16 E6 (HPV-16 E6) with anticancer potency against cervical cancer: A computational guided in vitro approach.

Human papillomavirus-16 E6 (HPV-16 E6) forms a heterodimer complex to up-regulate the degradation of tumor suppressor protein p53 to promote cervical cancer. This study aims to identify a novel small molecule against E6 with anticancer efficacy against HPV-16, a prime high-risk serotype inducer for cervical cancer. Autodock-vina-based high-throughput virtual screening and atomistic molecular dynamic simulations were used for identification of targeted lead molecules. HPV-16 infected SiHa and CaSki cell lines were used to validate the lead compound in vitro. Proliferation of cancer cells was analyzed by MTT assay and flow cytometry was used to analyze target inhibition, apoptosis, and p53. High throughput virtual screening and molecular dynamic simulation identified C-71980262 as a lead candidate that could bind HPV-E6. Atomistic molecular dynamic simulation of E6 bound C-71980262 for 200 ns showed that the predicted ligand binding was stable with minimal energy expenditure, proposing the viability and veracity of the assessed molecule. C-71980262 inhibited the proliferation of SiHa and CaSki cells with GI50 values of 355.70 nM and 505.90 nM, respectively. The compound reduced HPV-16 E6 while inducing early and late-phase apoptosis in these cells. Treatment with C-71980262 increased the p53-positive populations in SiHa and CaSki cells. C-71980262 was identified as a novel lead molecule that could inhibit the HPV-16 E6 and increase p53 in cervical cancer cells. Further in vitro and in vivo validation is warranted to consolidate and corroborate this lead compound against HPV-induced cancer progression.

Cancer-associated MDM2 W329G mutant attenuates ribosomal stress-mediated p53 responses to promote cell survival and glycolysis.

Although amplification/overexpression is the predominant mechanism for the oncogenic properties of MDM2, an increasing number of MDM2 somatic missense mutations were identified in cancer patients with the recent advances in sequencing technology. Here, we characterized an MDM2 cancer-associated mutant variant W329G identified from a patient sample that contains a wild-type p53 gene. Trp329 is one of residues that were reported to be critical to MDM2's binding to ribosomal protein L11 (RPL11). We found that the MDM2 W329G mutant was resistant to the inhibitory effect of RPL11 on MDM2-mediated p53 ubiquitination and degradation, in line with its defect on RPL11 binding. Using isogenic U2OS cells with or without endogenous MDM2 W329G mutation, we demonstrated that the expression of classic p53 targets induced by ribosomal stress signals was reduced in mutant cells. RNA-seq analysis revealed that upon 5-FU treatment, the p53 response was significantly impaired. Also, the 5-FU-mediated repression of genes in cell cycle progression and DNA replication was diminished in W329G mutant-containing cells. Physiologically, U2OS W329G cells were more resistant to cell growth inhibition induced by ribosomal stress and exhibited higher glycolytic rates upon 5-FU treatment. Together, our data indicated that cancer-associated MDM2 W329G mutant attenuates ribosomal stress-mediated p53 responses to promote cell survival and glycolysis.

The prognostic impact of EpCAM and p53 expressions in infiltrating duct carcinoma of the breast and their association with the clinicopathological prognostic parameters

Background Breast cancer is the most common cause of cancer death among women worldwide. Adhesion molecule EpCAM is an important player in carcinogenesis; however, its exact biological role is not clear. Tumor suppressor gene p53 maintains genomic stability. In malignant cells, its function can be compromised by various mechanisms such as mutations, alteration of p53 regulators, and alteration of p53 target genes. This study aimed to find the relationship between epithelial cell adhesion molecule (EpCAM) and p53 expressions on one hand and clinicopathological factors of prognostic importance in breast cancer on the other hand and find any correlations between EpCAM and p53 markers. Materials and methods Immunohistochemical staining with EpCAM and p53 was studied on 42 cases of infiltrating duct carcinoma. Results A significant association was found between EpCAM and tumor size (P=0.049), tumor grade (P=0.005), lymph node status (P=0.043), pathological tumor stage; pathological tumor stage (P=0.027), and lymphovascular invasion (P=0.048). However, EpCAM was negatively associated with estrogen receptor (P=0.007), progesterone receptor (P=0.031), and human epidermal growth factor receptor 2/neu (P=0.025) expressions. Expression of p53 was positively associated with tumor size (P=0.025), tumor grade (P=0.002), lymph node status (P=0.05), pathological tumor stage (P=0.041), and lymphovascular invasion (P=0.043), while negatively associated with estrogen receptor (P=0.029), progesterone receptor (P=0.043), and human epidermal growth factor receptor 2/neu (P=0.039) expressions. A positive association was found between EpCAM and p53 expressions and triple-negative breast cancer (P=0.007 and 0.029, respectively). There was a positive association between EpCAM and p53 (P=0.007). Conclusion EpCAM and p53 expressions are good markers of predicting poorer outcomes in breast cancer patients. There is a positive association suggesting a combined prognostic value in breast cancer and it may confirm the binding of p53 with the EpCAM gene to regulate its function.

Oleanane triterpenoids with C-14 carboxyl group from Astilbe grandis inhibited LPS-induced macrophages activation by suppressing the NF-κB signaling pathway.

Excessive inflammation poses significant risks to human physical and mental health. Astilbe grandis, a traditional Miao medicine, is renowned for its anti-inflammatory properties. However, the specific anti-inflammatory effects and mechanisms of many compounds within this plant remain unclear. This study aims to investigate the anti-inflammatory effects and mechanisms of two characteristic oleanane triterpenoids, 3α-acetoxyolean-12-en-27-oic acid (1) and 3β-acetoxyolean-12-en-27-oic acid (2), isolated from Astilbe grandis, using lipopolysaccharide (LPS)-induced Macrophages. The anti-inflammatory effects and mechanisms of compounds 1 and 2 were investigated by establishing an LPS-induced inflammation model in RAW 264.7 cells and THP-1 cells. Nitric oxide (NO) levels were assessed using the Griess method. The concentrations of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and interleukin-1beta (IL-1β) were measured via enzyme-linked immunosorbent assay (ELISA). The expression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) was determined using western blotting and quantitative real-time PCR (qRT-PCR). Additionally, the phosphorylation level of p65 in nuclear factor-kappa B (NF-κB) was assessed through western blotting. The nuclear translocation of NF-κB p65 was assessed through immunofluorescence staining. Finally, the binding affinity of the compounds to NF-κB p65 target was validated through molecular docking. Compounds 1 and 2 significantly inhibited the expression of NO, TNF-α, IL-6, IL-1β, COX-2, and iNOS in LPS-induced Macrophages. Mechanistically, they attenuated the activation of the NF-κB signaling pathway by downregulating the phosphorylation level and nuclear translocation of p65. This study elucidates the anti-inflammatory activities and potential mechanism of the characteristic oleanane triterpenoids with C-14 carboxyl group, compounds 1 and 2, in LPS-induced Macrophages by inhibiting the NF-κB signaling pathway for the first time. These findings suggest that these two compounds hold promise as potential candidates for anti-inflammatory interventions in the future.

Analyzing the Expression of MicroRNA-375 and its Target Gene p53 in Oral Squamous Cell Carcinoma and its Implication in Oral Carcinogenesis

Objective: Oral mucosal cancers are the 11th most common human malignancies worldwide with a five-year survival rate of ≤50%. The lacunae of reliable diagnostic and prognostic markers pose an enormous challenge to the timely identification and prediction of disease progression in oral cancer. MicroRNAs (miRNAs) are emerging molecular markers associated with cancer initiation, progression, and therapy. The present study evaluated the microRNA -375(miR-375) expression and its target p53 gene in Oral squamous cell carcinoma (OSCC) to validate its utility as a diagnostic marker of the disease. Patients and Methods: This case-control study targeted histopathologically diagnosed cases of OSCC. miR-375 was quantified from 22 cases of OSCC and corresponding control tissues using qRT-PCR. Mutant p53 expression in cases and controls was determined by subjecting the tissues to immunohistochemical Results: Significant downregulation of miR-375 was noted in OSCC tissues (68.1%) compared to the control tissues with a mean fold change of 83.9 (p&lt;0.05). Significant downregulation of miR-375 was noted in Paan and tobacco chewing patients (77.8%). Men exhibited considerable downregulation compared to women (p&lt;0.05). The miR-375 expression levels did not correlate with the patient’s age, location, size, nodal status, and histopathological grade of the tumor. About 63.6 % of OSCC tissues showed mutant p53 positivity. Mutant p53 expression was noted in 73.3% of miR-375 downregulated tumors. Smokers exhibited higher expression of mutant p53 contrary to non-smokers(p&lt;0.00). P53 immunopositivity showed a correlation with tumor size, histopathological grade, and nodal metastasis. Conclusion: The findings of the study indicate that miR-375 downregulation may have a crucial effect on oral carcinogenesis by targeting p53. miR-375 should be further evaluated as a potential marker for oral cancer diagnosis.

CPEB2 inhibit cell proliferation through upregulating p21 mRNA stability in glioma

Glioma is the most common primary malignant brain tumor in adults and remains an incurable disease at present. Thus, there is an urgent need for progress in finding novel molecular mechanisms that control the progression of glioma which could be used as therapeutic targets for glioma patients. The RNA binding protein cytoplasmic polyadenylate element-binding protein 2 (CPEB2) is involved in the pathogenesis of several tumors. However, the role of CPEB2 in glioma progression is unknown. In this study, the functional characterization of the role and molecular mechanism of CPEB2 in glioma were examined using a series of biological and cellular approaches in vitro and in vivo. Our work shows CPEB2 is significantly downregulated in various glioma patient cohorts. Functional characterization of CPEB2 by overexpression and knockdown revealed that it inhibits glioma cell proliferation and promotes apoptosis. CPEB2 exerts an anti-tumor effect by increasing p21 mRNA stability and inducing G1 cell cycle arrest in glioma. Overall, this work stands as the first report of CPEB2 downregulation and involvement in glioma pathogenesis, and identifies CPEB2 as an important tumor suppressor gene through targeting p21 in glioma, which revealed that CPEB2 may become a promising predictive biomarker for prognosis in glioma patients.

NNMT/1-MNA Promote Cell-Cycle Progression of Breast Cancer by Targeting UBC12/Cullin-1-Mediated Degradation of P27 Proteins.

Cell cycle dysregulation is a defining feature of breast cancer. Here, 1-methyl-nicotinamide (1-MNA), metabolite of nicotinamide N-methyltransferase(NNMT) is identified, as a novel driver of cell-cycle progression in breast cancer. NNMT, highly expressed in breast cancer tissues, positively correlates with tumor grade, TNM stage, Ki-67 index, and tumor size. Ablation of NNMT expression dramatically suppresses cell proliferation and causes cell-cycle arrest in G0/G1 phase. This phenomenon predominantly stems from the targeted action of 1-MNA, resulting in a specific down-regulation of p27 protein expression. Mechanistically, 1-MNA expedites the degradation of p27 proteins by enhancing cullin-1 neddylation, crucial for the activation of Cullin-1-RING E3 ubiquitin ligase(CRL1)-an E3 ubiquitin ligase targeting p27 proteins. NNMT/1-MNA specifically up-regulates the expression of UBC12, an E2 NEDD8-conjugating enzyme required for cullin-1 neddylation. 1-MNA showes high binding affinity to UBC12, extending the half-life of UBC12 proteins via preventing their localization to lysosome for degradation. Therefore, 1-MNAis a bioactive metabolite that promotes breast cancer progression by reinforcing neddylation pathway-mediated p27 degradation. The study unveils the link between NNMT enzymatic activity with cell-cycle progression, indicating that 1-MNA may be involved in the remodeling of tumor microenvironment.

Combined absence of TRP53 target genes ZMAT3, PUMA and p21 cause a high incidence of cancer in mice

Transcriptional activation of target genes is essential for TP53-mediated tumour suppression, though the roles of the diverse TP53-activated target genes in tumour suppression remains poorly understood. Knockdown of ZMAT3, an RNA-binding zinc-finger protein involved in regulating alternative splicing, in haematopoietic cells by shRNA caused leukaemia only with the concomitant absence of the PUMA and p21, the critical effectors of TRP53-mediated apoptosis and cell cycle arrest respectively. We were interested to further investigate the role of ZMAT3 in tumour suppression beyond the haematopoietic system. Therefore, we generated Zmat3 knockout and compound gene knockout mice, lacking Zmat3 and p21, Zmat3 and Puma or all three genes. Puma−/−p21−/−Zmat3−/− triple knockout mice developed tumours at a significantly higher frequency compared to wild-type, Puma−/−Zmat3−/− or p21−/−Zmat3−/−deficient mice. Interestingly, we observed that the triple knockout and Puma−/−Zmat3−/− double deficient animals succumbed to lymphoma, while p21−/−Zmat3−/− animals developed mainly solid cancers. This analysis suggests that in addition to ZMAT3 loss, additional TRP53-regulated processes must be disabled simultaneously for TRP53-mediated tumour suppression to fail. Our findings reveal that the absence of different TRP53 regulated tumour suppressive processes changes the tumour spectrum, indicating that different TRP53 tumour suppressive pathways are more critical in different tissues.

Capturing Protein-Protein Interactions with Acidic Amino Acids Reactive Cross-Linkers.

Acidic residues (Asp and Glu) have a high prevalence on protein surfaces, but cross-linking reactions targeting these residues are limited. Existing methods either require high-concentration coupling reagents or have low structural compatibility. Here a previously reported "plant-and-cast" strategy is extended to develop heterobifunctional cross-linkers. These cross-linkers first react rapidly with Lys sidechains and then react with Asp and Glu sidechains, in a proximity-enhanced fashion. The cross-linking reaction proceeds at neutral pH and room temperature without coupling reagents. The efficiency and robustness of cross-linking using model proteins, ranging from small monomeric proteins to large protein complexes are demonstrated. Importantly, it is shown that this type of cross-linkers are efficient at identifying protein-protein interactions involving acidic domains. The Cross-linking mass spectrometry (XL-MS) study with p53 identified 87 putative binders of the C-terminal domain of p53. Among them, SARNP, ZRAB2, and WBP11 are shown to regulate the expression and alternative splicing of p53 target genes. Thus, these carboxylate-reactive cross-linkers will further expand the power of XL-MS in the analysis of protein structures and protein-protein interactions.

Epigenetic priming of an epithelial enhancer by p63 and CTCF controls expression of a skin-restricted gene XP33

The transcription factor p63 is a renowned master regulator of gene expression of stratified epithelia. While multiple proteins have been identified as p63 bona fide targets, little is known about non-coding RNAs (ncRNAs) whose transcription is controlled by p63. Here, we describe a skin-specific non-coding RNA XP33 as a novel target of p63. XP33 levels are increased during keratinocyte differentiation in vitro, while its depletion results in decreased expression of late cornified gene LCE2D. By using publicly available multi-omics data, we show that CTCF and p63 establish an epithelial enhancer to prime XP33 transcription in a tissue-restricted manner. XP33 promoter and enhancer form a chromatin loop exclusively in keratinocytes but not in other cell types. Moreover, the XP33 enhancer is occupied by differentiation-specific factors that control XP33 transcription. Altogether, we identify a tissue-specific non-coding RNA whose expression is epigenetically regulated by p63 and CTCF.

Abstract C096: Targeting the p53 pathway to treat pediatric Malignant Rhabdoid and Atypical Teratoid Rhabdoid Tumors

Abstract Background: Pediatric rhabdoid tumors, namely Malignant Rhabdoid Tumors (MRTs) and Atypical Teratoid Rhabdoid Tumors (ATRTs) in the central nervous system (CNS), are aggressive pediatric malignancies characterized by the loss of functional INI1 protein due to SMARCB1 gene mutations. Current treatment options for these tumors are limited and ineffective, necessitating the exploration of novel therapeutic strategies. Rhabdoid cells retain an intact p53 pathway, a critical tumor suppressor pathway involved in regulating cell cycle and apoptosis. Previous studies have shown that the MDM2 inhibitor, Idasanutlin, effectively eliminates flanked rhabdoid tumors, suggesting that targeting the p53 pathway holds promise for developing effective therapies against MRTs and ATRTs. Methods: In this study, we employed a combination approach using the MDM2 inhibitor, Idasanutlin, and the XPO1 inhibitor, Selinexor, to activate the p53 pathway. The impact of this combination treatment on tumor cell viability, proliferation, and apoptosis was assessed both in vitro and in vivo using MRT and ATRT models. Additionally, CRISPR screening and proteomic studies were conducted to identify specific dependencies in refractory models and investigate their influence on treatment response. Results: Treatment with the combination of Idasanutlin and Selinexor activated the p53 signaling pathway, leading to increased levels of MDM2 and p21 proteins, two direct targets of p53, and resulting in apoptosis in MRT and ATRT models. In vitro experiments demonstrated a significant reduction in cell viability and proliferation upon treatment. In vivo studies using MRT and ATRT xenograft models showed a remarkable decrease in tumor growth following the combination treatment. However, variable responses were observed among different models, indicating the presence of dependency patterns influencing treatment sensitivity. Proteomic studies and genetic manipulation provided further insights into the potential dependencies Conclusions: Our findings highlight the potential of the combination of Idasanutlin and Selinexor to activate the p53 pathway and induce apoptosis in MRT and ATRT models. Although the treatment strategy effectively activated p53, we identified dependencies that may contribute to incomplete treatment sensitivity. Further investigation into these dependency patterns is necessary to optimize the therapeutic approach. Overall, targeting the p53 pathway using combination therapies shows promise for the development of effective treatments for pediatric MRTs and ATRTs, warranting further preclinical and clinical investigations. Citation Format: Alaa Refaat, Hyekyung Cho, Jennifer Stripay, Charles Roberts, Christopher Tinkle, Anang Shelat, Martine Roussel. Targeting the p53 pathway to treat pediatric Malignant Rhabdoid and Atypical Teratoid Rhabdoid Tumors [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C096.

Abstract B143: HRO761, a first-in-class, clinical stage WRN inhibitor with potent preclinical anti-tumor activity in MSIhigh models

Abstract Colorectal carcinoma (CRC) as well as other indications that have lost competence in mismatch repair and have a phenotype known as microsatellite instability (MSI), remain a significant unmet medical need. Large-scale functional genomics screens across cell line panels have identified the Werner Syndrome RecQ helicase (WRN) as being synthetic lethal with MSIhigh cancers. Thus, WRN inhibitors may offer a new therapeutic avenue in MSIhigh cancers. We report the preclinical characteristics of HRO761, a first-in-class, highly potent and selective inhibitor of WRN helicase, with optimized drug-like properties. We evaluated the pharmacokinetics and pharmacodynamics of HRO761 when administered orally once daily in MSIhigh and also assessed the efficacy as single agent across cell (CDX) and patient-derived (PDX) xenografts as well as in combination with irinotecan, a prodrug derivative of camptothecin which acts as topoisomerase I inhibitor. Daily oral administration of HRO761 was highly efficacious across the CDX and PDX models evaluated with a disease control rate of 70% across all indications. In the SW48 CDX model, tumor regression was sustained for 2 months at the highest dose followed by slow relapse. HRO761 also induced WRN degradation, activated the DNA damage response and induced p53 target genes in a dose dependent manner. In vitro combination with irinotecan deepened sensitivity to HRO761 with a more sustained response in MSIhigh CRC cell lines. Combining administration of HRO761 daily with irinotecan weekly was highly efficacious and beneficial over single agent in CDX and PDX models. In CDX models, the combination showed a robust benefit, translating into homogeneous, sustained regression leading to a dose-dependent tumor growth delay even after treatment discontinuation. Overall, we demonstrate that the novel, selective, first-in-class WRN inhibitor HRO761 is a promising therapeutic approach for the treatment of MSIhigh cancer patients either as single agent or in combination with irinotecan. Clinical development is currently ongoing to assess the safety, tolerability and preliminary anti-tumor activity in patients with MSIhigh colorectal cancer and other MSIhigh solid tumors [clinicaltrials.gov NCT05838768]. Citation Format: Stephane Ferretti, Isabel Jaco, Andrea Decker, Christelle Hemmerlin, Clemens Scheufler, Cornelia Quadt, Dario Sterker, Elena Gavioli, Eloisa Jimenez Nunez, Ernesta Dammassa, Fanny Schaeffer, Genevieve Albrecht, Giorgia Clementi, Hansjoerg Martus, Jacques Hamon, Juergen Hinrichs, Laurent Laborde, Marion Dourdoigne, Michele Moschetta, Ramona Stump, Rita Andraos-Rey, Sarah Welly, Stephanie Barbe, Vincent Romanet, Markus Reschke, Ruben De Kanter, Michael Jensen, Henrik Moebitz, Marta Cortes Cros. HRO761, a first-in-class, clinical stage WRN inhibitor with potent preclinical anti-tumor activity in MSIhigh models [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B143.