The p53 orchestra: Mdm2 and Mdmx set the tone

A highly selective and orally bioavailable casein kinase 1 alpha degrader through p53 signaling pathway targets B-cell lymphoma cells

The modest reduction in casein kinase 1 alpha (CK1α) by lenalidomide contributes to its clinical effectiveness in treating del(5q) myelodysplastic syndrome. However, the mechanism by which CK1α impacts lymphoma survival remains inadequately defined. We developed INNO-220, a CRBN-dependent CK1α degrader, by leveraging cytokine expression profiling in T cells. Unlike lenalidomide, INNO-220 is a highly selective and potent degrader of CK1α without affecting IKZF1/3. Screening across lymphoma cell lines revealed that cells harboring wild-type p53 and exhibiting constitutive NF-κB signaling were particularly sensitive to CK1α degradation yet resistant to Bruton tyrosine kinase inhibitors. Moreover, INNO-220 suppresses NF-κB signaling and activates p53 pathway, leading to complete inhibition of lymphoma tumor growth in vivo. Mechanistically, INNO-220 disrupts the assembly and function of the CARD11/BCL10/MALT1 complex, thereby inhibiting NF-κB signaling in stimulated T cells and lymphoma cells that harbor an activating mutation in CARD11. Moreover, we observed that activation of wild-type p53 upon INNO-220 treatment was sufficient to induce potent cancer cell death even in the absence of constitutive NF-κB activity. In summary, our findings introduce a selective CK1α degrader as a novel therapeutic approach for lymphoma, providing both mechanistic insights and a potential patient selection strategy in treating lymphoma and possibly other cancers.

MDMX enhances radiosensitivity in lung adenocarcinoma and squamous cell carcinoma by inhibiting P53-mediated autophagy

OBJECTIVE

Radioresistance is a common cause of poor radiation therapy effectiveness for non-small cell lung cancer. Finding molecular targets or methods to enhance radiosensitivity or overcome radioresistance is crucial. This study aimed to investigate the effects of MDMX on modulating radiosensitivity in lung adenocarcinoma (LUAD) and squamous cell carcinoma (LUSC).

METHODS

The expression of MDMX and its correlation with radiotherapy response were analyzed in 101 LUAD and LUSC patient samples. LUAD and LUSC cell lines (A549, SK-MES-1) and their radioresistant counterparts (A549R, SK-MES-1R) were used to assess the effects of MDMX and P53 on radiosensitivity through autophagy by using molecular assays and animal models.

RESULTS

The expression of MDMX was decreased, but the autophagy was enhanced in radioresistant LUAD and LUSC cells. Overexpression of MDMX inhibited P53 activity, leading to autophagy suppression and increasing radiosensitivity. In contrast, P53 upregulation counteracted the effects of MDMX, resulting in increasing autophagy and radioresistance. The higher MDMX expression was associated with improved radiotherapy response and prolonged overall survival in LUAD and LUSC cells. The 5-year survival rate was 93.62% in the low MDMX expression group and 98.11% in the high MDMX expression group (P < 0.01).

CONCLUSION

MDMX enhances LUAD and LUSC radiosensitivity by downregulating P53-mediated autophagy. High MDMX expression correlated with better clinical outcomes, suggesting that MDMX could be a potential biomarker for predicting radiotherapy response and prognosis in LUAD and LUSC patients.

FLT4 activation promotes acute lymphoid leukemia survival through stabilization of MDM2/MDMX and inactivation of p53

Aberrant Receptor Tyrosine Kinase (RTK) signaling allows cancer cells to modulate survival, proliferation, and death, leading to tumorigenesis and chemoresistance. In leukemia, the RTK FMS-Related Tyrosine Kinase 4 (FLT4) (also known as VEGFR3, Vascular Endothelial Growth Factor Receptor- 3) is deregulated and correlates with cancer progression. However, the underlying consequences of its deregulation remain to be determined. Moreover, chemotherapy treatment requires that cancer cells retain a wild-type p53 to respond to DNA damage by tumor-suppressing activities, i.e. apoptosis. p53 activity is predominantly limited by its two major negative regulators, MDM2 and MDMX, which inactivate p53 by promoting its degradation and/or cytoplasmic localization. In this study, we have shown that activation of FLT4 by either overexpression or binding of its ligand, VEGFC, increases MDM2/MDMX stability, inactivates p53, and leads to resistance to DNA-damaging therapies. Moreover, we found that MDMX Ser-314 phosphorylation, a consensus sequence of CDK4/6, increases MDMX stability, which subsequently affects MDM2 and p53 degradation and could be reversed by the CDK4/6 inhibitor Palbociclib. More importantly, leukemic cells treated with Palbociclib were more susceptible to DNA-damaging induction of apoptosis and had reduced cell proliferation. Leukemic cells overexpressing FLT4 displayed accelerated proliferation when injected into NOD-SCID mice as compared to wild-type cells. Altogether, our research proposes an innovative way to reactivate p53 in leukemia through the pharmacological inhibition of FLT4 signaling, which could serve as a potential treatment option. Schematic representation of FLT4-mediated MDM2/MDMX complex stabilization and suppression of p53 activity. VEGFC triggers FLT4 activation, leading to CDK4/6 activation, which phosphorylates MDMX on Ser-314. As a result, MDMX levels increase and bind to MDM2, stabilizing the MDM2/MDMX complex. This complex binds to p53, facilitating its suppression by reducing its transcriptional activity or enhancing its export to the cytoplasm for proteasomal degradation. Consequently, p53 inactivation promotes their survival, proliferation, and resistance to chemotherapy-induced apoptosis. The figure was created in BioRender.com.

eIF4A1 exacerbates myocardial ischemia-reperfusion injury in mice by promoting nuclear translocation of transgelin/p53

Eukaryotic translation initiation factor 4A1 (eIF4A1) is an ATP-dependent RNA helicase that participates in a variety of biological and pathological processes such as cell proliferation and apoptosis, and cancer. In this study we investigated the role of eIF4A1 in ischemic heart disease. The myocardial ischemia/reperfusion (I/R) model was established in mice by ligation of the left anterior descending artery for 45 min with the subsequent reperfusion for 24 h; cultured neonatal mouse ventricular cardiomyocytes (NMVCs) treated with H2O2 (200 μM) or H/R (12 h hypoxia and 12 h reoxygenation) were used for in vitro study. We showed that the expression levels of eIF4A1 were significantly increased in I/R-treated myocardium and in H2O2- or H/R-treated NMVCs. In NMVCs, eIF4A1 overexpression drastically enhanced LDH level, caspase 3 activity, and cell apoptosis. eIF4A1 overexpression also significantly reduced anti-apoptotic protein Bcl2 and elevated pro-apoptotic protein Bax expression, whereas eIF4A1 deficiency produced the opposite responses. Importantly, cardiomyocyte-specific eIF4A1 knockout attenuated cardiomyocyte apoptosis, reduced infarct area, and improved cardiac function in myocardial I/R mice. We demonstrated that eIF4A1 directly bound to transgelin (Tagln) to prevent its ubiquitination degradation and subsequent up-regulation of p53, and then promoted nuclear translocation of Tagln and p53. Nuclear localization of Tagln and p53 was increased in H2O2-treated NMVCs. Silencing Tagln reversed the pro-apoptotic effects of eIF4A1. Noticeably, eIF4A1 exerted the similar effects in AC16 human cardiomyocytes. In conclusion, eIF4A1 is a detrimental factor in myocardial I/R injury via promoting expression and nuclear translocation of Tagln and p53 and might be a potential target for myocardial I/R injury. This study highlights a novel biological role of eIF4A1 by interacting with non-translational-related factor Tagln in myocardial I/R injury.

Regulation of PEST-containing nuclear proteins in cancer cells: implications for cancer biology and therapy

The PEST-containing nuclear protein (PCNP) is a nuclear protein involved in the regulation of cell cycle progression, protein degradation, and tumorigenesis. PCNP contains a PEST sequence, a polypeptide structural motif rich in proline (P), glutamic acid (E), serine (S), and threonine (T), which serves as a proteolytic recognition signal. The degradation of specific proteins via the PEST sequence plays a crucial role in modulating signaling pathways that control cell growth, differentiation, apoptosis, and stress responses. PCNP is primarily degraded through the ubiquitin-proteasome system (UPS) and the calpain pathway, with phosphorylation of threonine and serine residues further accelerating its degradation. The ubiquitination of PCNP by the ring finger protein NIRF in an E3 ligase-dependent manner is well documented, along with its involvement in the MAPK and PI3K/AKT/mTOR signaling pathways. Additionally, PCNP is implicated in p53-mediated cell cycle arrest and apoptosis, which are essential for inhibiting tumor growth. To explore the role of PCNP in cancer, this review examines its effects on cell growth, differentiation, proliferation, and apoptosis in lung adenocarcinoma, thyroid cancer, ovarian cancer, and other malignancies derived from glandular epithelial cells. By focusing on PCNP and its regulatory mechanisms, this study provides a scientific basis for further research on the biological functions of the PEST sequence in tumor development and cancer progression.

Computational identification of potential natural terpenoid inhibitors of MDM2 for breast cancer therapy: molecular docking, molecular dynamics simulation, and ADMET analysis

Background

Breast cancer (BC) remains a leading cause of cancer-related mortality in women. The oncoprotein MDM2 negatively regulates the tumor suppressor p53, and its overexpression in BC promotes tumor progression and resistance to therapy. Targeting the MDM2-p53 interaction represents a promising therapeutic approach. However, many existing MDM2 inhibitors suffer from poor pharmacokinetics and off-target toxicity, necessitating the discovery of novel, more selective alternatives. This study aims to identify natural terpenoid compounds with potent MDM2 inhibitory potential through computational approaches.

Methods

A library of 398 natural terpenoids was sourced from the NPACT database and filtered based on Lipinski's Rule of Five. A two-stage docking strategy was applied: 1) rigid protein-flexible ligand docking to screen for high-affinity binders, followed by 2) ensemble docking using multiple MDM2 conformations derived from molecular dynamics (MD) simulations. The top candidates were further evaluated for their pharmacokinetic and toxicity profiles using ADMET analysis. Finally, 150 ns MD simulations and binding free energy (MM-PBSA) calculations were performed to assess the stability and strength of protein-ligand interactions.

Results

Three terpenoid compounds, olean-12-en-3-beta-ol, cabralealactone, and 27-deoxyactein demonstrated strong binding affinities toward MDM2 in ensemble docking studies. ADMET analysis confirmed their favorable pharmacokinetic properties. Further MD simulations indicated that these compounds formed highly stable complexes with MDM2. Notably, 27-deoxyactein exhibited the lowest binding free energy (-154.514 kJ/mol), outperforming the reference inhibitor Nutlin-3a (-133.531 kJ/mol), suggesting superior binding stability and interaction strength.

Conclusion

Our findings highlight 27-deoxyactein as a promising MDM2 inhibitor with strong binding affinity, stability, and a favorable pharmacokinetic profile. This study provides a computational foundation for further experimental validation, supporting the potential of terpenoid-based MDM2 inhibitors in BC therapy.

Strategies for p53 Activation and Targeted Inhibitors of the p53-Mdm2/MdmX Interaction

p53 is a tumor suppressor gene and is regarded as one of the most crucial genes in protecting humans against cancer. The protein Mdm2 and its homolog MdmX serve as negative regulators of p53. In nearly half of cancer cells, there is an overexpression of Mdm2 and MdmX, which inhibit p53 activity. Furthermore, Mdm2's E3 ubiquitin ligase activity promotes the ubiquitination and degradation of p53. Therefore, blocking the interaction between p53 and Mdm2/MdmX to prevent the degradation of wild-type p53 is an effective strategy for inhibiting tumor growth. This paper primarily discusses the regulatory relationship between p53, MdmX and Mdm2, and provides a review of the current status of p53-Mdm2/MdmX inhibitors. It aims to offer a theoretical foundation and research direction for the future discovery and design of targeted inhibitors against the p53-Mdm2/MdmX interaction.

Construction of ubiquitination-related risk model for predicting prognosis in lung adenocarcinoma

Lung adenocarcinoma is the most prevalent lung cancer type. Ubiquitination, a critical post-translational modification process that regulates protein degradation and signaling pathways, has been implicated in various cancers, including LUAD. We aimed to explore the associations between ubiquitination and lung adenocarcinoma. TCGA-LUAD cohort served as the training set. Unsupervised clustering, univariate Cox regression, Random Survival Forests, and least absolute shrinkage and selection operator (LASSO) Cox regression were applied to identify ubiquitination-related genes (URGs), then ubiquitination-related risk scores (URRS) were calculated using gene expression and the univariate Cox's coefficient. Comparisons between the high and the low URRS group regarding chemotherapy drug response, immune infiltration level, tumor mutation burden (TMB), tumor neoantigen load (TNB), PD1/L1 expression, and enriched pathways were performed. URRS was calculated based on the expression of DTL, UBE2S, CISH, and STC1. Patients with higher URRS had a worse prognosis (Hazard Ratio [HR] = 0.54, 95% Confidence Interval [CI]: 0.39-0.73, p < 0.001), and the prognosis of the URRS was further confirmed in 6 external validation cohorts (Hazard Ratio [HR] = 0.58, 95% Confidence Interval [CI]: 0.36-0.93, pmax = 0.023). The high URRS group had higher PD1/L1 expression level (p < 0.05), TMB (p < 0.001), TNB (p < 0.001), and TME scores (p < 0.001). The IC50 values of various chemotherapy drugs were lower in the high URRS group. In addition, we found that upregulation of STC1, UBE2S, and DTL was associated with worse, while upregulation of CISH was associated with better prognosis. We also performed a reverse transcription-quantitative polymerase chain reaction (RT-qPCR) for validation. In conclusion, the ubiquitination-based signature might serve as a biomarker to help evaluate the prognosis, biological features, and appropriate treatment for patients with lung adenocarcinoma.

A structure-based virtual screening identifies a novel MDM2 antagonist in the activation of the p53 signaling and inhibition of tumor growth

p53, a tumor suppressor protein, has a vital role in the regulation of the cell cycle, apoptosis, and DNA damage repair. The degradation of p53 is predominantly controlled by the murine double minute 2 (MDM2) protein, a ubiquitin E3 ligase. The overexpression or amplification of MDM2 is commonly observed in various human cancers bearing wild-type p53 alleles, leading to the rapid degradation of the p53 protein and the attenuation of p53 tumor suppression functions. Thus, a major effort in p53-based cancer therapy has been to research MDM2 antagonists that specifically stabilize and activate p53, leading to the suppression of tumor growth. However, despite numerous efforts to develop MDM2 antagonists, to date they have failed to reach clinical use, largely because of the cytotoxicity associated with these small molecules. This study used our newly designed structure-based virtual screening approach on a commercial compound library to identify a novel compound, CGMA-Q18, which directly binds to MDM2, leading to the activation of p53, the induction of apoptosis, and cell cycle arrest in cancer cells. Notably, CGMA-Q18 significantly inhibited tumor xenograft growth in nude mice without observable toxicity. These findings highlight our useful virtual screening protocol and CGMA-Q18 as a putative MDM2 antagonist.

JMJD4 promotes tumor progression via inhibition of the PDCD5-TP53 pathway

Programmed cell death 5 (PDCD5) regulates cell death and suppresses tumor progression. Since the stability and nuclear translocation of PDCD5 are regulated by TP53-dependent cell death stimuli, knowledge of the regulatory mechanism of PDCD5 function is required to better understand the TP53-signaling pathway. We identified Jumonji domain-containing protein 4 (JMJD4) to be a PDCD5-interacting protein using liquid chromatography- mass spectrometry (LC-MS). Interestingly, JMJD4 upregulates cell proliferation and chemo-resistance under genotoxic stress conditions by colony-formation assay and decreases TP53-related apoptotic genes (BAX, PUMA) by suppressing protein levels of PDCD5. Additionally, using the Cancer Genome Atlas and the Gene Expression Omnibus database to confirm the clinical correlation between JMJD4 and cancer patients, we verified that JMJD4 is associated with a poor prognosis in colon cancer and lung cancer patients. Therefore, this study demonstrates that JMJD4 directly interacts with PDCD5, regulates cancer cell death negatively, and could be a potential therapeutic target for cancer development. [BMB Reports 2025; 58(2): 64-69].

Engineered MSC-sEVs as a Versatile Nanoplatform for Enhanced Osteoarthritis Treatment via Targeted Elimination of Senescent Chondrocytes and Maintenance of Cartilage Matrix Metabolic Homeostasis

Chondrocyte senescence is an important pathogenic factor causing osteoarthritis (OA) progression through persistently producing pro-inflammatory factors. Mesenchymal stem cells-derived small extracellular vesicles (MSC-sEVs) have shown anti-inflammatory effects in OA models, while persistent existence of senescent chondrocytes still promotes cartilage destruction. Therefore, improving the targeted elimination ability on senescent chondrocytes is required to facilitate the translation of MSC-sEVs in OA treatment. In this study, versatile engineered MSC-sEVs are developed to targetedly clear senescent chondrocytes and maintain cartilage metabolic homeostasis. Specifically, MSC-sEVs are loaded with siRNA mouse double minute 2 homologue (siMDM2) and modified with cartilage-targeting peptide WYRGRL-PEG2K-DSPE (WPD), named WPD-sEVssiMDM2. The results demonstrate versatile modification improves the cellular uptake of MSC-sEVs in chondrocytes, and thus improves the antiaging effects. Importantly, multifunctional modification enhances cartilage penetration ability and extends joint retention time of MSC-sEVs. In both post-traumatic OA mice and naturally aged mice, WPD-sEVssiMDM2 more effectively eliminates senescent chondrocytes and maintained matrix metabolic homeostasis. By using the P53 phosphorylation inhibitor, the essential role MDM2-P53 pathway in the antiaging function of WPD-sEVssiMDM2 on chondrocytes is verified. In ex vivo cultured human OA cartilage explants, it is confirmed that WPD-sEVssiMDM2 alleviates senescent phenotype. Altogether, the findings suggest that WPD-sEVssiMDM2 have promising translational potential for OA treatment.

Chemoresistance in Pancreatic Cancer: The Role of Adipose-Derived Mesenchymal Stem Cells and Key Resistance Genes

Drug resistance is a significant challenge in pancreatic ductal adenocarcinoma (PDAC), where stromal elements such as adipose-derived mesenchymal stem cells (ASCs) contribute to a chemoresistant tumor microenvironment (TME). This study explored the effects of oxaliplatin (OXP) and 5-fluorouracil (5-FU) on PDAC cells (Capan-1) and ASCs to investigate the mechanisms of chemoresistance. While OXP and 5-FU reduced Capan-1 viability in a dose- and time-dependent manner, ASCs demonstrated high resistance, maintaining > 90% viability even at cytotoxic doses. Transcriptomic analyses revealed OXP-induced transcriptional reprogramming in ASCs, with over 7000 differentially expressed genes, highlighting the pathways related to DNA damage response, cell cycle regulation, and stress-related signaling. In contrast, 5-FU elicited limited transcriptional changes, affecting only 192 genes. Cytokine proteome profiling revealed that OXP-treated ASCs significantly influenced the tumor microenvironment by promoting immune evasion (via IL-4, GM-CSF, IP-10, and GROα) and driving extracellular matrix remodeling (through EMMPRIN and DPPIV). In contrast, 5-FU induced comparatively weaker effects, primarily limited to hypoxia-related pathways. Although OXP reduced angiogenic factors, it paradoxically activated pro-survival pathways, thereby enhancing ASC-mediated tumor support. These findings underscore ASCs as modulators of chemoresistance via secretome alterations and stress adaptation. Therefore, future strategies should prioritize the precise targeting of tumor cells while also focusing on the development of personalized treatments to achieve durable therapeutic responses in PDAC.

Prostate cancer and the cell cycle: Focusing on the role of microRNAs

Prostate cancer is the most frequent solid tumor in terms of incidence and ranks second only to lung cancer in terms of cancer mortality among men. It has a considerably high mortality rate; around 375,000 deaths occurred worldwide in 2020. In 2024, the American Cancer Society estimated that the number of new prostate cancer cases will be around 299,010 cases, and the estimated deaths will be around 32,250 deaths only in the USA. Cell cycle dysregulation is inevitable in cancer etiology and is targeted by various therapies in cancer treatment. MicroRNAs (miRNAs) are small, endogenous, non-coding regulatory molecules involved in both normal and abnormal cellular events. One of the cellular processes regulated by miRNAs is the cell cycle. Although there are some exceptions, tumor suppressor miRNAs could potentially arrest the cell cycle by downregulating several molecular machineries involved in catalyzing the cell cycle progression. In contrast, oncogenic miRNAs (oncomirs) help the cell cycle to progress by targeting various regulatory proteins such as retinoblastoma (Rb) or cell cycle inhibitors such as p21 or p27, and hence may contribute to prostate cancer progression; however, this is not always the case. In this review, we emphasize how a dysregulated miRNA expression profile is linked to an abnormal cell cycle progression in prostate cancer, which subsequently paves the way to a new therapeutic option for prostate cancer.

Research progress of the Otubains subfamily in hepatocellular carcinoma

In cancer research, oncogenesis can be affected by modulating the deubiquitination pathway. Ubiquitination regulates proteins post-translationally in variety of physiological processes. The Otubain Subfamily includes OTUB1 (ovarian tumor-associated proteinase B1) and OTUB2(ovarian tumor-associated proteinase B2). They are deubiquitinating enzymes, which are research hotspots in tumor immunotherapy, with their implications extending across the spectrum of tumor development. Understanding their important role in tumorigenesis, includ-ing hepatocellular carcinoma (HCC) is crucial. HCC has alarming global incidence rates and mortality statistics, ranking among the top five prevalent cancers in Malaysia1. Numerous studies have consistently indicated significant expression of OTUB1 and OTUB2 in HCC cells. In addition, OTUB1 has important biological functions in cancer, suggesting its important role in tumorigenesis. However, the mechanism underlying the action of OTUB1 and OTUB2 in liver cancer remains inadequately explored. Therefore, Otubain Subfamily, as potential molecular target, holds promise for advancing HCC treatments. However, further clinical studies are required to verify its efficacy and application prospects.

Targeted therapies in advanced biliary malignancies: a clinical review

INTRODUCTION

Despite several therapeutic advancements, the proportion of patients with advanced biliary tract cancers (BTC) surviving 5 years from diagnosis remains dismal. The increasing recognition of targetable genetic alterations in BTCs has ushered in a new era in the treatment of these patients. Newer therapeutic agents targeting mutations such as isocitrate dehydrogenase (IDH), fibroblastic growth factor receptor (FGFR), human epidermal growth factor receptor (HER), and so on have established a new standard of care for treatment upon progression on frontline therapy in patients with disease harboring these mutations.

AREAS COVERED

The current review aims to concisely summarize progress with various targeted therapy options for BTC. We also briefly discuss future directions in clinical and translational research for the adoption of a personalized approach for the treatment of unresectable or advanced BTC.

EXPERT OPINION

Several new agents continue to emerge as feasible treatment options for patients with advanced BTC harboring targetable mutations. There is a growing need to identify mechanisms to conquer primary and acquired resistance to these agents. The identification of potential biomarkers that predict response to targeted therapy may be helpful in adopting a more tailored approach. All patients receiving treatment for advanced BTC should undergo tissue genomic profiling at diagnosis.

Cucurbitacin B Inhibits the Proliferation of WPMY-1 Cells and HPRF Cells via the p53/MDM2 Axis

Modern research has shown that Cucurbitacin B (Cu B) possesses various biological activities such as liver protection, anti-inflammatory, and anti-tumor effects. However, the majority of research has primarily concentrated on its hepatoprotective effects, with limited attention devoted to exploring its potential impact on the prostate. Our research indicates that Cu B effectively inhibits the proliferation of human prostate stromal cells (WPMY-1) and fibroblasts (HPRF), while triggering apoptosis in prostate cells. When treated with 100 nM Cu B, the apoptosis rates of WPMY-1 and HPRF cells reached 51.73 ± 5.38% and 26.83 ± 0.40%, respectively. In addition, the cell cycle assay showed that Cu B had a G2/M phase cycle arrest effect on WPMY-1 cells. Based on RNA-sequencing analysis, Cu B might inhibit prostate cell proliferation via the p53 signaling pathway. Subsequently, the related gene and protein expression levels were measured using quantitative real-time PCR (RT-qPCR), immunocytochemistry (ICC), and enzyme-linked immunosorbent assays (ELISA). Our results mirrored the regulation of tumor protein p53 (TP53), mouse double minute-2 (MDM2), cyclin D1 (CCND1), and thrombospondin 1 (THBS1) in Cu B-induced prostate cell apoptosis. Altogether, Cu B may inhibit prostate cell proliferation and correlate to the modulation of the p53/MDM2 signaling cascade.

Hdm2 disrupts HdmX-mediated nuclear export of p53 by sequestering it in nucleus

Dysfunction of the tumor suppressor p53 occurs in most human cancers, Hdm2 and HdmX play critical roles in p53 inactivation and degradation. Under unstressed conditions, HdmX binds to p53 like Hdm2, but HdmX cannot directly induce p53 degradation. Moreover, HdmX has been reported to stimulate Hdm2-mediated ubiquitination and degradation of p53. Here we reported that HdmX promoted the nuclear export of p53 independent of Hdm2 in living cells using FRET technology. Whereas, Hdm2 impeded HdmX-mediated nuclear export of p53 by sequestering it in nucleus. Interestingly, the C-terminal RING domain mutant Hdm2C464A formed heterooligomers with p53 in nucleus, which was inhibited by HdmX. The heterooligomers were located near PML-NBs. This study indicate that the nuclear Hdm2-HdmX interaction aborts the HdmX-mediated nuclear export of p53.

USP19 Negatively Regulates p53 and Promotes Cervical Cancer Progression

p53 is a tumor suppressor gene activated in response to cellular stressors that inhibits cell cycle progression and induces pro-apoptotic signaling. The protein level of p53 is well balanced by the action of several E3 ligases and deubiquitinating enzymes (DUBs). Several DUBs have been reported to negatively regulate and promote p53 degradation in tumors. In this study, we identified USP19 as a negative regulator of p53 protein level. We demonstrate a direct interaction between USP19 and p53 by pull down assay. The overexpression of USP19 promoted ubiquitination of p53 and reduced its protein half-life. We also demonstrate that CRISPR/Cas9-mediated knockout of USP19 in cervical cancer cells elevates p53 protein levels, resulting in reduced colony formation, cell migration, and cell invasion. Overall, our results indicate that USP19 negatively regulates p53 protein levels in cervical cancer progression.

Discovery of a Highly Potent, Selective and Efficacious USP7 Degrader for the Treatment of Acute Lymphoblastic Leukemia

USP7 is an attractive therapeutic target for cancers, especially for acute lymphoblastic leukemia (ALL) with wild-type p53. Herein, we report the discovery of XM-U-14 as a highly potent, selective and efficacious USP7 proteolysis-targeting chimera degrader. XM-U-14 achieves DC50 values of 0.74 nM and Dmax of 93% in inducing USP7 degradation in RS4;11 cell lines, and also significantly inhibits ALL cell growth. XM-U-14 even at 5 mg/kg dosed daily effectively inhibits RS4;11 tumor growth with 64.7% tumor regressions and causes no signs of toxicity in mice. XM-U-14 is a promising USP7 degrader for further optimization for ALL treatment.

Treatment options for biliary tract cancer: unmet needs, new targets and opportunities from both physicians' and patients' perspectives

Biliary tract cancer (BTC) is a rare cancer with poor prognosis, characterized by considerable pathophysiological and molecular heterogeneity. While this makes it difficult to treat, it also provides targeted therapy opportunities. Current standard-of-care is chemotherapy ± immunotherapy, but several targeted agents have recently been approved. The current investigational landscape in BTC emphasizes the importance of biomarker testing at diagnosis. MDM2/MDMX are important negative regulators of the tumor suppressor p53 and provide an additional target in BTC (∼5-8% of tumors are MDM2-amplified). Brigimadlin (BI 907828) is a highly potent MDM2-p53 antagonist that has shown antitumor activity in preclinical studies and promising results in early clinical trials; enrollment is ongoing in a potential registrational trial for patients with BTC.

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.

Efficacy and Safety of the MDM2-p53 Antagonist Brigimadlin (BI 907828) in Patients with Advanced Biliary Tract Cancer: A Case Series

Background

In patients with advanced biliary tract cancer (BTC), first-line chemotherapy plus immunotherapy has improved outcomes; however, second-line options that reflect the disease's molecular heterogeneity are still needed. One emerging target is MDM2, amplified in ~5-8% of BTC cases.

Methods

This is a subset analysis of two ongoing Phase Ia/Ib trials assessing patients treated with brigimadlin (BI 907828; a highly potent, oral MDM2-p53 antagonist) ± ezabenlimab (PD-1 inhibitor) ± BI 754111 (anti-LAG-3; n = 1).

Results

Results from 12 patients with BTC are shown (monotherapy: n = 6/combination: n = 6). Six patients achieved partial response (monotherapy: n = 2/combination: n = 4), four had stable disease; responses were durable. Brigimadlin had a manageable safety profile. Seven patients had dose reductions due to adverse events, but no treatment-related adverse events led to treatment discontinuation.

Conclusion

Brigimadlin demonstrated anti-tumor activity in patients with advanced MDM2-amplified BTC, and warrants further investigation.

Murine double minute 2-mediated estrogen receptor 1 degradation activates macrophage migration inhibitory factor to promote vascular smooth muscle cell dedifferentiation and oxidative stress during thoracic aortic aneurysm progression

Estrogen receptor 1 (ESR1) has been recently demonstrated as a potential diagnostic biomarker for thoracic aortic aneurysm (TAA). However, its precise role in the progression of TAA remains unclear. In this study, TAA models were established in ApoE-knockout mice and primary mouse vascular smooth muscle cells (VSMCs) through treatment with angiotensin (Ang) II. Our findings revealed a downregulation of ESR1 in Ang II-induced TAA mice and VSMCs. Upregulation of ESR1 mitigated expansion and cell apoptosis in the mouse aorta, reduced pathogenetic transformation of VSMCs, and reduced inflammatory infiltration and oxidative stress both in vitro and in vivo. Furthermore, we identified macrophage migration inhibitory factor (MIF) as a biological target of ESR1. ESR1 bound to the MIF promoter to suppress its transcription. Artificial MIF restoration negated the mitigating effects of ESR1 on TAA. Additionally, we discovered that murine double minute 2 (MDM2) was highly expressed in TAA models and mediated protein degradation of ESR1 through ubiquitination modification. Silencing of MDM2 reduced VSMC dedifferentiation and suppressed oxidative stress. However, these effects were reversed upon further silencing of ESR1. In conclusion, this study demonstrates that MDM2 activates MIF by mediating ESR1 degradation, thus promoting VSMC dedifferentiation and oxidative stress during TAA progression.

Staufen1 Represses the FOXA1-Regulated Transcriptome by Destabilizing FOXA1 mRNA in Colorectal Cancer Cells

Transcription factors play key roles in development and disease by controlling gene expression. Forkhead box A1 (FOXA1), is a pioneer transcription factor essential for mouse development and functions as an oncogene in prostate and breast cancer. In colorectal cancer (CRC), FOXA1 is significantly downregulated and high FOXA1 expression is associated with better prognosis, suggesting potential tumor suppressive functions. We therefore investigated the regulation of FOXA1 expression in CRC, focusing on well-differentiated CRC cells, where FOXA1 is robustly expressed. Genome-wide RNA stability assays identified FOXA1 as an unstable mRNA in CRC cells. We validated FOXA1 mRNA instability in multiple CRC cell lines and in patient-derived CRC organoids, and found that the FOXA1 3'UTR confers instability to the FOXA1 transcript. RNA pulldowns and mass spectrometry identified Staufen1 (STAU1) as a potential regulator of FOXA1 mRNA. Indeed, STAU1 knockdown resulted in increased FOXA1 mRNA and protein expression due to increased FOXA1 mRNA stability. Consistent with these data, RNA-seq following STAU1 knockdown in CRC cells revealed that FOXA1 targets were upregulated upon STAU1 knockdown. Collectively, this study uncovers a molecular mechanism by which FOXA1 is regulated in CRC cells and provides insights into our understanding of the complex mechanisms of gene regulation in cancer.

LncRNA NRON promotes tumorigenesis by enhancing MDM2 activity toward tumor suppressor substrates

The E3 ligase MDM2 promotes tumor growth and progression by inducing ubiquitin-mediated degradation of P53 and other tumor-suppressing proteins. Here, we identified an MDM2-interacting lncRNA NRON, which promotes tumor formation by suppressing both P53-dependent and independent pathways. NRON binds to MDM2 and MDMX (MDM4) via two different stem-loops, respectively, and induces their heterogenous dimerization, thereby enhancing the E3 ligase activity of MDM2 toward its tumor-suppressing substrates, including P53, RB1, and NFAT1. NRON knockdown dramatically inhibits tumor cell growth in vitro and in vivo. More importantly, NRON overexpression promotes oncogenic transformation by inducing anchorage-independent growth in vitro and facilitating tumor formation in immunocompromised mice. Clinically, NRON expression is significantly associated with poor clinical outcome in breast cancer patients. Together, our data uncover a pivotal role of lncRNA that induces malignant transformation of epithelial cells by inhibiting multiple tumor suppressor proteins.

A chemotherapy response prediction model derived from tumor-promoting B and Tregs and proinflammatory macrophages in HGSOC

Background

Most patients with high-grade serous ovarian cancer (HGSOC) experienced disease recurrence with cumulative chemoresistance, leading to treatment failure. However, few biomarkers are currently available in clinical practice that can accurately predict chemotherapy response. The tumor immune microenvironment is critical for cancer development, and its transcriptomic profile may be associated with treatment response and differential outcomes. The aim of this study was to develop a new predictive signature for chemotherapy in patients with HGSOC.

Methods

Two HGSOC single-cell RNA sequencing datasets from patients receiving chemotherapy were reinvestigated. The subtypes of endoplasmic reticulum stress-related XBP1+ B cells, invasive metastasis-related ACTB+ Tregs, and proinflammatory-related macrophage subtypes with good predictive power and associated with chemotherapy response were identified. These results were verified in an independent HGSOC bulk RNA-seq dataset for chemotherapy. Further validation in clinical cohorts used quantitative real-time PCR (qRT-PCR).

Results

By combining cluster-specific genes for the aforementioned cell subtypes, we constructed a chemotherapy response prediction model containing 43 signature genes that achieved an area under the receiver operator curve (AUC) of 0.97 (p = 2.1e-07) for the GSE156699 cohort (88 samples). A huge improvement was achieved compared to existing prediction models with a maximum AUC of 0.74. In addition, its predictive capability was validated in multiple independent bulk RNA-seq datasets. The qRT-PCR results demonstrate that the expression of the six genes has the highest diagnostic value, consistent with the trend observed in the analysis of public data.

Conclusions

The developed chemotherapy response prediction model can be used as a valuable clinical decision tool to guide chemotherapy in HGSOC patients.

RPS27a and RPL40, Which Are Produced as Ubiquitin Fusion Proteins, Are Not Essential for p53 Signalling

Two of the four human ubiquitin-encoding genes express ubiquitin as an N-terminal fusion precursor polypeptide, with either ribosomal protein (RP) RPS27a or RPL40 at the C-terminus. RPS27a and RPL40 have been proposed to be important for the induction of the tumour suppressor p53 in response to defects in ribosome biogenesis, suggesting that they may play a role in the coordination of ribosome production, ubiquitin levels and p53 signalling. Here, we report that RPS27a is cleaved from the ubiquitin-RP precursor in a process that appears independent of ribosome biogenesis. In contrast to other RPs, the knockdown of either RPS27a or RPL40 did not stabilise the tumour suppressor p53 in U2OS cells. Knockdown of neither protein blocked p53 stabilisation following inhibition of ribosome biogenesis by actinomycin D, indicating that they are not needed for p53 signalling in these cells. However, the knockdown of both RPS27a and RPL40 in MCF7 and LNCaP cells robustly induced p53, consistent with observations made with the majority of other RPs. Importantly, RPS27a and RPL40 are needed for rRNA production in all cell lines tested. Our data suggest that the role of RPS27a and RPL40 in p53 signalling, but not their importance in ribosome biogenesis, differs between cell types.

KLF5 and p53 comprise an incoherent feed-forward loop directing cell-fate decisions following stress

In response to stress, cells make a critical decision to arrest or undergo apoptosis, mediated in large part by the tumor suppressor p53. Yet the mechanisms of these cell fate decisions remain largely unknown, particularly in normal cells. Here, we define an incoherent feed-forward loop in non-transformed human squamous epithelial cells involving p53 and the zinc-finger transcription factor KLF5 that dictates responses to differing levels of cellular stress from UV irradiation or oxidative stress. In normal unstressed human squamous epithelial cells, KLF5 complexes with SIN3A and HDAC2 repress TP53, allowing cells to proliferate. With moderate stress, this complex is disrupted, and TP53 is induced; KLF5 then acts as a molecular switch for p53 function by transactivating AKT1 and AKT3, which direct cells toward survival. By contrast, severe stress results in KLF5 loss, such that AKT1 and AKT3 are not induced, and cells preferentially undergo apoptosis. Thus, in human squamous epithelial cells, KLF5 gates the response to UV or oxidative stress to determine the p53 output of growth arrest or apoptosis.

Biomarkers of aging

Aging biomarkers are a combination of biological parameters to (i) assess age-related changes, (ii) track the physiological aging process, and (iii) predict the transition into a pathological status. Although a broad spectrum of aging biomarkers has been developed, their potential uses and limitations remain poorly characterized. An immediate goal of biomarkers is to help us answer the following three fundamental questions in aging research: How old are we? Why do we get old? And how can we age slower? This review aims to address this need. Here, we summarize our current knowledge of biomarkers developed for cellular, organ, and organismal levels of aging, comprising six pillars: physiological characteristics, medical imaging, histological features, cellular alterations, molecular changes, and secretory factors. To fulfill all these requisites, we propose that aging biomarkers should qualify for being specific, systemic, and clinically relevant.

Attenuation of indoxyl sulfate-induced cell damage by cinchonidine-a Cinchona alkaloid-through the downregulation of p53 signaling pathway by promoting MDM2 cytoplasmic-nuclear shuttling in endothelial cells

Renocardiac syndromes are a critical concern among patients with chronic kidney disease (CKD). High level of indoxyl sulfate (IS), a protein-bound uremic toxin, in plasma is known to promote the pathogenesis of cardiovascular diseases by impairing endothelial function. However, the therapeutic effects of the adsorbent of indole, a precursor of IS, on renocardiac syndromes is still debated. Therefore, novel therapeutic approaches should be developed to treat IS-associated endothelial dysfunction. In the present study, we have found that cinchonidine, a major Cinchona alkaloid, exhibited superior cell-protective effects among the 131 test compounds in IS-stimulated human umbilical vein endothelial cells (HUVECs). IS-induced cell death, cellular senescence, and impairment of tube formation in HUVECs were substantially reversed after treatment with cinchonidine. Despite the cinchonidine did not alter reactive oxygen species formation, cellular uptake of IS and OAT3 activity, RNA-Seq analysis showed that the cinchonidine treatment downregulated p53-modulated gene expression and substantially reversed IS-caused G0/G1 cell cycle arrest. Although the mRNA levels of p53 were not considerably downregulated by cinchonidine in IS-treated HUVECs, the treatment of cinchonidine promoted the degradation of p53 and the cytoplasmic-nuclear shuttling of MDM2. Cinchonidine exhibited cell-protective effects against the IS-induced cell death, cellular senescence, and impairment of vasculogenic activity in HUVECs through the downregulation of p53 signaling pathway. Collectively, cinchonidine may be a potential cell-protective agent to rescue IS-induced endothelial cell damage.

Targeting p53 pathways: mechanisms, structures, and advances in therapy

The TP53 tumor suppressor is the most frequently altered gene in human cancers, and has been a major focus of oncology research. The p53 protein is a transcription factor that can activate the expression of multiple target genes and plays critical roles in regulating cell cycle, apoptosis, and genomic stability, and is widely regarded as the "guardian of the genome". Accumulating evidence has shown that p53 also regulates cell metabolism, ferroptosis, tumor microenvironment, autophagy and so on, all of which contribute to tumor suppression. Mutations in TP53 not only impair its tumor suppressor function, but also confer oncogenic properties to p53 mutants. Since p53 is mutated and inactivated in most malignant tumors, it has been a very attractive target for developing new anti-cancer drugs. However, until recently, p53 was considered an "undruggable" target and little progress has been made with p53-targeted therapies. Here, we provide a systematic review of the diverse molecular mechanisms of the p53 signaling pathway and how TP53 mutations impact tumor progression. We also discuss key structural features of the p53 protein and its inactivation by oncogenic mutations. In addition, we review the efforts that have been made in p53-targeted therapies, and discuss the challenges that have been encountered in clinical development.

The profiles of miR-4510 expression level in breast cancer

MicroRNA that is abnormally produced in breast cells can disrupt biological processes, which can lead to cancer. This study aims to screen differentially expressed genes (DEGs) and ncRNAs (DEncRNAs) in the formalin-fixed paraffin-embedded (FFPE) tissues of breast cancer (BC) as compared with the normal adjacent tissues (NAT), and identify miR-4510 as a novel biomarker of BC. This study looked at differentially expressed genes (DEGs) using MACE-Seq and differentially expressed ncRNAs (DEncRNAs) using the small RNA-Seq. Real-time qPCR was used to determine the level of expression of miR-4510. In this study, MACE-Seq results showed that 26,795 genes, with a p-value < 0.05, were differentially expressed in BC paraffin tissues as compared with NAT. Small RNA-Seq results revealed that 1326 ncRNAs, with a p-value < 0.05, were differentially expressed. We confirmed that miR-4510 was significantly down-expressed (p-value = 0.001) by qRT-PCR in the paraffin tissue of 120 BC patients. Based on eleven computational prediction programs, TP53, TP53INP1, MMP11, and COL1A1 for the miR-4510 were identified as miR-4510 targets. The MACE-seq result showed that the gene of TP53 (p-value = 0.001) and TP53INP1 (p-value = 0.02) was significantly down-regulated, but the gene of MMP11 (p-value = 0.004) and COL1A1 (p-value = 0.0001) was significantly over-expressed in 20 paired specimens of the BC and NAT. We discovered that a single SNP inside the miR-4510 binding site occurred only in BC, in which Guanine (G) changed into Adenine (A). Two SNPs outside the miR-4510 binding site occurred, and Guanine (G) in both BC and NAT was changed into Thymine (T), as compared to the reference sequence (RefSeq). Overall, our results suggested that miR-4510 functions as a tumor suppressor in the BC. Mir-4510 may act as a tumor suppressor, however additional experimental data is needed to corroborate these assumptions and can be exploited as a biomarker for BC.

Benzimidazole and its derivatives as cancer therapeutics: The potential role from traditional to precision medicine

Cancer is the second leading cause of mortality globally which remains a continuing threat to human health today. Drug insensitivity and resistance are critical hurdles in cancer treatment; therefore, the development of new entities targeting malignant cells is considered a high priority. Targeted therapy is the cornerstone of precision medicine. The synthesis of benzimidazole has garnered the attention of medicinal chemists and biologists due to its remarkable medicinal and pharmacological properties. Benzimidazole has a heterocyclic pharmacophore, which is an essential scaffold in drug and pharmaceutical development. Multiple studies have demonstrated the bioactivities of benzimidazole and its derivatives as potential anticancer therapeutics, either through targeting specific molecules or non-gene-specific strategies. This review provides an update on the mechanism of actions of various benzimidazole derivatives and the structure‒activity relationship from conventional anticancer to precision healthcare and from bench to clinics.

Unmasking the biological function and regulatory mechanism of NOC2L: a novel inhibitor of histone acetyltransferase

NOC2 like nucleolar associated transcriptional repressor (NOC2L) was recently identified as a novel inhibitor of histone acetyltransferase (INHAT). NOC2L is found to have two INHAT function domains and regulates histone acetylation in a histone deacetylases (HDAC) independent manner, which is distinct from other INHATs. In this review, we summarize the biological function of NOC2L in histone acetylation regulation, P53-mediated transcription, ribosome RNA processing, certain development events and carcinogenesis. We propose that NOC2L may be explored as a potential biomarker and a therapeutic target in clinical practice.

Cellular functions and molecular mechanisms of ubiquitination in osteosarcoma

Although some advances have been made in the treatment of osteosarcoma in recent years, surgical resection remains the mainstream treatment. Initial and early diagnosis of osteosarcoma could be very difficult to achieve due to the insufficient sensitivity for the means of examination. The distal metastasis of osteosarcoma also predicts the poor prognosis of osteosarcoma. In order to solve this series of problems, people begin to discover a new method of diagnosing and treating osteosarcoma. Ubiquitination, as an emerging posttranslational modification, has been shown to be closely related to osteosarcoma in studies over the past decades. In general, this review describes the cellular functions and molecular mechanisms of ubiquitination during the development of osteosarcoma.

In vitro and in vivo study of GSK2830371 and RG7388 combination in liver adenocarcinoma

Intrahepatic cholangiocarcinoma (iCCA) is an adenocarcinoma arising from the intrahepatic bile duct and accounts for the second highest incidence of primary liver cancers after hepatocellular carcinoma. The lack of effective treatment leads to a poor prognosis for advanced iCCA, so new targeted therapy is needed. The impairment of wild-type (WT) p53 tumor suppressor function by its negative regulators frequently occurs in iCCA. Therefore, restoration of WT p53 function by inhibiting its negative regulators is a therapeutic strategy being explored for cancer treatment. Combining an MDM2 inhibitor (MDM2i, RG7388) to stabilize p53 and a WIP1 inhibitor (WIP1i, GSK2830371) to increase p53 phosphorylation enhances p53 function. The combination of MDM2 and WIP1 inhibitors has been reported in several cancer types but in vivo studies are lacking. In the current study, liver adenocarcinoma cell lines, RBE and SK-Hep-1, were treated with RG7388 alone and in combination with GSK2830371. Cell proliferation, clonogenicity, protein and mRNA expressions, and cell cycle distribution were performed to investigate the effect and mechanism of growth suppression. To evaluate the antitumor efficacy of RG7388 and GSK2830371 in vivo, SK-Hep-1 xenografts in NOD-SCID mice were treated with combination therapy for two weeks. The combination of MDM2i and WIP1i significantly increased the growth inhibition, cytotoxicty, p53 protein expression, and phosphorylation (Ser15), leading to transactivation of downstream targets (p21^WAF1 and MDM2). The in vivo results demonstrated that the combination treatment can significantly inhibit tumor growth. In this study, the liver adenocarcinoma cell lines responded to combination treatment via reactivation of p53 function evidenced by increased p53 expression, phosphorylation and expression of its downstream targets. This efficacy was also demonstrated in vivo. The current research provides a novel strategy for targeting the p53 pathway in liver adenocarcinoma that warrants further investigation.

Cellular senescence and abdominal aortic aneurysm: From pathogenesis to therapeutics

As China’s population enters the aging stage, the threat of abdominal aortic aneurysm (AAA) mainly in elderly patients is becoming more and more serious. It is of great clinical significance to study the pathogenesis of AAA and explore potential therapeutic targets. The purpose of this paper is to analyze the pathogenesis of AAA from the perspective of cellular senescence: on the basis of clear evidence of cellular senescence in aneurysm wall, we actively elucidate specific molecular and regulatory pathways, and to explore the targeted drugs related to senescence and senescent cells eliminate measures, eventually improve the health of patients with AAA and prolong the life of human beings.

Phase separation in immune regulation and immune-related diseases

Phase separation is an emerging paradigm for understanding the biochemical interactions between proteins, DNA, and RNA. Research over the past decade has provided mounting evidence that phase separation modulates a great variety of cellular activities. Particularly, phase separation is directly relevant to immune signaling, immune cells, and immune-related diseases like cancer, neurodegenerative diseases, and even SARS-CoV-2. In this review, we summarized current knowledge of phase separation in immunology and emerging findings related to immune responses as they enable possible treatment approaches.

Transcriptional regulation of INK4/ARF locus by cis and trans mechanisms

9p21 locus is one of the most reproducible regions in genome-wide association studies (GWAS). The region harbors CDKN2A/B genes that code for p16INK4a, p15INK4b, and p14ARF proteins, and it also harbors a long gene desert adjacent to these genes. The polymorphisms that are associated with several diseases and cancers are present in these genes and the gene desert region. These proteins are critical cell cycle regulators whose transcriptional dysregulation is strongly linked with cellular regeneration, stemness, aging, and cancers. Given the importance of this locus, intense scientific efforts on understanding the regulation of these genes via promoter-driven mechanisms and recently, via the distal regulatory mechanism have provided major insights. In this review, we describe these mechanisms and propose the ways by which this locus can be targeted in pathologies and aging.

Understanding the interaction of 14-3-3 proteins with hDMX and hDM2: a structural and biophysical study

p53 plays a critical role in regulating diverse biological processes: DNA repair, cell cycle arrest, apoptosis and senescence. The p53 pathway has therefore served as the focus of multiple drug-discovery efforts. p53 is negatively regulated by hDMX and hDM2; prior studies have identified 14-3-3 proteins as hDMX and hDM2 client proteins. 14-3-3 proteins are adaptor proteins that modulate localization, degradation and interactions of their targets in response to phosphorylation. Thus, 14-3-3 proteins may indirectly modulate the interaction between hDMX or hDM2 and p53 and represent potential targets for modulation of the p53 pathway. In this manuscript, we report on the biophysical and structural characterization of peptide/protein interactions that are representative of the interaction between 14-3-3 and hDMX or hDM2. The data establish that proximal phosphosites spaced ~20-25 residues apart in both hDMX and hDM2 co-operate to facilitate high-affinity 14-3-3 binding and provide structural insight that can be utilized in future stabilizer/inhibitor discovery efforts.

Targeting the deubiquitinase USP7 for degradation with PROTACs

Targeting deubiquitinating enzymes (DUBs) has emerged as a promising therapeutic approach in several human cancers and other diseases. DUB inhibitors are exciting pharmacological tools but often exhibit limited cellular potency. Here we report PROTACs based on a ubiquitin-specific protease 7 (USP7) inhibitor scaffold to degrade USP7. By investigating several linker and E3 ligand types, including novel cereblon recruiters, we discovered a highly selective USP7 degrader tool compound that induced apoptosis of USP7-dependent cancer cells. This work represents one of the first DUB degraders and unlocks a new drug target class for protein degradation.

Tumor suppressor LHPP suppresses cell proliferation and epithelial-mesenchymal transition in hepatocellular carcinoma cell lines

Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer in the world with high mortality due to its high potential of metastasis. Epithelial-mesenchymal transition (EMT) plays a key role in the pathogenesis of HCC occurrence and metastasis. Phospholysine phosphohistidine inorganic pyrophosphate phosphatase (LHPP) is a novel tumor suppressor. There is little study about LHPP in human HCC development. In the present study, we aimed to investigate the role of LHPP in human HCC cell metastasis. We analyzed the LHPP expression level in human HCC tissues compared with normal tissues in the public database. We detected the mRNA level and protein level of LHPP in transformed liver cell line (LO2) and human HCC cell lines (MHCC-97 H, MHCC-97L, and HepG2). We performed genetic gain and loss of function experiments with LHPP using small interfering RNA (siRNA) and lentivirus infection. Then, we detected that LHPP suppressed proliferation and promoted apoptosis in hepatocellular carcinoma cell lines. Also, we investigated the role of LHPP in the EMT process. Finally, we examined the effect of LHPP on TGF-β-induced EMT. Interestingly, we also found that LHPP expression is positively regulated tumor suppressor p53. Our data showed that LHPP is significantly decreased in the human HCC tissues and human HCC cell lines compared with normal liver tissues and transformed liver cells. Knockdown of LHPP promotes HCC cell proliferation and metastasis, and LHPP expression levels negatively correlate with EMT-related genes. Furthermore, LHPP inhibits TGF-β-induced EMT in HCC cell lines. These studies validate LHPP as a tumor suppressor in liver cancer and provide a new genetic target for HCC diagnosis and treatment.

LIN28B inhibition sensitizes cells to p53-restoring PPI therapy through unleashed translational suppression

p53 is the most highly mutated tumor suppressor across multiple types of human cancers. The level and function of p53 are fine-tuned through multifaced mechanisms in which the protein–protein interaction between p53 and MDM2 is considered as a major circuit. Recent studies suggest therapeutic strategy attempts to restore p53 function by small molecule inhibitors targeting p53–MDM2 interaction can be a promising direction in treating cancers with wild-type or functional p53. Currently, clinical tests of the p53–MDM2 protein–protein interaction inhibitors (PPIs) are underway. However, it remains elusive about the biomarkers that may predict the therapeutic responses to those inhibitors. Here we report that RNA-binding protein LIN28B directly regulates p53 through binding to the 5′΄ untranslated region of p53 mRNA and blocks its translation by competing with a translation enhancer protein, ribosomal protein L26 (RPL26). This regulatory mechanism of LIN28B does not involve let-7 maturation or the canonical protein turnover pathway of p53. Furthermore, we show that inhibition of LIN28B unleashes the translational suppression of p53 through RPL26, and leads to enhanced sensitivities of cancer cells to inhibitors of p53–MDM2 interaction. Together, we demonstrate a competitive regulatory mechanism of p53 by LIN28B, which has important implications in developing biomarkers to the therapies aiming to reinstate p53 function.

Complementary omics strategies to dissect p53 signaling networks under nutrient stress

Signaling trough p53is a major cellular stress response mechanism and increases upon nutrient stresses such as starvation. Here, we show in a human hepatoma cell line that starvation leads to robust nuclear p53 stabilization. Using BioID, we determine the cytoplasmic p53 interaction network within the immediate-early starvation response and show that p53 is dissociated from several metabolic enzymes and the kinase PAK2 for which direct binding with the p53 DNA-binding domain was confirmed with NMR studies. Furthermore, proteomics after p53 immunoprecipitation (RIME) uncovered the nuclear interactome under prolonged starvation, where we confirmed the novel p53 interactors SORBS1 (insulin receptor signaling) and UGP2 (glycogen synthesis). Finally, transcriptomics after p53 re-expression revealed a distinct starvation-specific transcriptome response and suggested previously unknown nutrient-dependent p53 target genes. Together, our complementary approaches delineate several nodes of the p53 signaling cascade upon starvation, shedding new light on the mechanisms of p53 as nutrient stress sensor. Given the central role of p53 in cancer biology and the beneficial effects of fasting in cancer treatment, the identified interaction partners and networks could pinpoint novel pharmacologic targets to fine-tune p53 activity.

Enhanced Expression of p21 Promotes Sensitivity of Melanoma Cells Towards Targeted Therapies

Metastatic melanoma patients benefit from the approved targeted BRAF inhibitor (BRAFi) therapy. Despite the great progress in the therapeutic approach to combat metastatic melanoma, fast emerging drug resistance in patients limits its long-term efficacy. In this study we aimed to unravel the role of the p53 target gene CDKN1A/p21 in the response of melanoma cells towards BRAFi. We show that p53 activation increases BRAFi sensitivity in a synergistic manner exclusively in cells with a high expression of CDKN1A/p21. In a similar way high expression of p21 was associated with a better response towards the mouse double minute 2 inhibitor (MDM2i) compared to those with low p21 expression. Indeed, p21 knockdown decreased the sensitivity towards both targeted therapies. The results indicate that the sensitivity of melanoma cells towards targeted therapies (BRAFi and MDM2i) is dependent on the p21 protein level in the cells. In addition to that, we found that p53 negatively regulates p73 expression, however, p73 seems not to have an influence on p53 expression. These findings offer new potential strategies for the treatment improvement of melanoma patients with high basal p21 levels with BRAFi by increasing treatment efficacy using combination therapies with p53 activating substances, which are able to further increase p21 expression levels. Furthermore, the data suggest that the expression and induction level of p21 could be used as a predictive biomarker in melanoma patients to forecast the outcome of a treatment with p53 activating substances and BRAFi. All in all, this manuscript shows the distinct roles and of the p53 family members and its impact on melanoma therapy. In the future, individualized treatment regimens based on p21 basal and induction levels could benefit melanoma patients with limited treatment options.

Synonymous Variants: Necessary Nuance in our Understanding of Cancer Drivers and Treatment Outcomes

Once called "silent mutations" and assumed to have no effect on protein structure and function, synonymous variants are now recognized to be drivers for some cancers. There have been significant advances in our understanding of the numerous mechanisms by which synonymous single nucleotide variants (sSNVs) can affect protein structure and function by affecting pre-mRNA splicing, mRNA expression, stability, folding, miRNA binding, translation kinetics, and co-translational folding. This review highlights the need for considering sSNVs in cancer biology to gain a better understanding of the genetic determinants of human cancers and to improve their diagnosis and treatment. We surveyed the literature for reports of sSNVs in cancer and found numerous studies on the consequences of sSNVs on gene function with supporting in vitro evidence. We also found reports of sSNVs that have statistically significant associations with specific cancer types but for which in vitro studies are lacking to support the reported associations. Additionally, we found reports of germline and somatic sSNVs that were observed in numerous clinical studies and for which in silico analysis predicts possible effects on gene function. We provide a review of these investigations and discuss necessary future studies to elucidate the mechanisms by which sSNVs disrupt protein function and are play a role in tumorigeneses, cancer progression, and treatment efficacy. As splicing dysregulation is one of the most well recognized mechanisms by which sSNVs impact protein function, we also include our own in silico analysis for predicting which sSNVs may disrupt pre-mRNA splicing.

Evolutionary history of the p53 family DNA-binding domain: insights from an Alvinella pompejana homolog

The extremophile Alvinella pompejana, an annelid worm living on the edge of hydrothermal vents in the Pacific Ocean, is an excellent model system for studying factors that govern protein stability. Low intrinsic stability is a crucial factor for the susceptibility of the transcription factor p53 to inactivating mutations in human cancer. Understanding its molecular basis may facilitate the design of novel therapeutic strategies targeting mutant p53. By analyzing expressed sequence tag (EST) data, we discovered a p53 family gene in A. pompejana. Protein crystallography and biophysical studies showed that it has a p53/p63-like DNA-binding domain (DBD) that is more thermostable than all vertebrate p53 DBDs tested so far, but not as stable as that of human p63. We also identified features associated with its increased thermostability. In addition, the A. pompejana homolog shares DNA-binding properties with human p53 family DBDs, despite its evolutionary distance, consistent with a potential role in maintaining genome integrity. Through extensive structural and phylogenetic analyses, we could further trace key evolutionary events that shaped the structure, stability, and function of the p53 family DBD over time, leading to a potent but vulnerable tumor suppressor in humans.

Molecular glues modulate protein functions by inducing protein aggregation: A promising therapeutic strategy of small molecules for disease treatment

Molecular glues can specifically induce aggregation between two or more proteins to modulate biological functions. In recent years, molecular glues have been widely used as protein degraders. In addition, however, molecular glues play a variety of vital roles, such as complex stabilization, interactome modulation and transporter inhibition, enabling challenging therapeutic targets to be druggable and offering an exciting novel approach for drug discovery. Since most molecular glues are identified serendipitously, exploration of their systematic discovery and rational design are important. In this review, representative examples of molecular glues with various physiological functions are divided into those mediating homo-dimerization, homo-polymerization and hetero-dimerization according to their aggregation modes, and we attempt to elucidate their mechanisms of action. In particular, we aim to highlight some biochemical techniques typically exploited within these representative studies and classify them in terms of three stages of molecular glue development: starting point, optimization and identification.

A small-molecule inhibitor of MDMX suppresses cervical cancer cells via the inhibition of E6-E6AP-p53 axis

Dysfunction of p53 is observed in many malignant tumors, which is related to cancer susceptibility. In cervical cancer, p53 is primarily degradated through the complex of high-risk human papillomaviruses (HPV) oncoprotein E6 and E6-associated protein (E6AP) ubiquitin ligase. What is less clear is the mechanism and role of murine double minute X (MDMX) in cervical carcinogenesis due to the inactive status of murine double minute 2 (MDM2). In the current study, XI-011 (NSC146109), a small-molecule inhibitor of MDMX, showed robust anti-proliferation activity against several cervical cancer cell lines. XI-011 promoted apoptosis of cervical cancer cells via stabilizing p53 and activating its transcription activity. Moreover, XI-011 inhibited the growth of xenograft tumor in HeLa tumor-bearing mice, as well as enhanced the cytotoxic activity of cisplatin both in vitro and in vivo. Interestingly, MDMX co-locolized with E6AP and seems to be a novel binding partner of E6AP to promote p53 ubiquitination. In conclusion, this work revealed a novel mechanism of ubiquitin-dependent p53 degredation via MDMX-E6AP axis in cervical carcinogenesis, and offered the first evidence that MDMX could be a viable drug target for the treatment of cervical cancer.

p53 ubiquitination co-mediated by HUWE1 and TRAF6 contributes to WSSV infection in crustacean

p53, the guardian of the genome, is a short-lived protein that is tightly controlled at low levels by constant ubiquitination and proteasomal degradation in higher organisms. p53 stabilization and activation are early crucial events to cope with external stimuli in cells. However, the role of p53 ubiquitination and its relevant molecular mechanisms have not been addressed in invertebrates. In this study, our findings revealed that both HUWE1 (HECT, UBA, and WWE domain-containing E3 ubiquitin-protein ligase 1) and TRAF6 (tumor necrosis factor receptor-associated factor 6) could serve as E3 ubiquitin ligases for p53 in mud crabs (Scylla paramamosain). Moreover, the expression of HUWE1 and TRAF6 was significantly downregulated during white spot syndrome virus (WSSV) infection, and therefore the ubiquitination of p53 was interrupted, leading to the activation of apoptosis and reactive oxygen species (ROS) signals through p53 accumulation, which eventually suppressed viral invasion in the mud crabs. To the best of our knowledge, this is the first study to reveal the p53 ubiquitination simultaneously induced by two E3 ligases in arthropods, which provides a novel molecular mechanism of invertebrates for resistance to viral infection.

IMPORTANCE p53, which is a well-known tumor suppressor that has been widely studied in higher animals, has been reported to be tightly controlled at low levels by ubiquitin-dependent proteasomal degradation. However, recent p53 ubiquitination-relevant research mainly involved an individual E3 ubiquitin ligase, but not whether there exist other mechanisms that need to be explored. The results of this study show that HUWE1 and TRAF6 could serve as p53 E3 ubiquitin ligases and synchronously mediate p53 ubiquitination in mud crabs (Scylla paramamosain), which confirmed the diversity of the p53 ubiquitination regulatory pathway. In addition, the effects of p53 ubiquitination are mainly focused on tumorigenesis, but a few are focused on the host immune defense in invertebrates. Our findings reveal that p53 ubiquitination could affect ROS and apoptosis signals to cope with WSSV infection in mud crabs, which is the first clarification of the immunologic functions and mechanisms of p53 ubiquitination in invertebrates.