Oncogene-induced Senescence Research Articles

Werner syndrome RECQ helicase participates in and directs maintenance of the protein complexes of constitutive heterochromatin in proliferating human cells.

Werner syndrome of premature aging is caused by mutations in the WRN RECQ helicase/exonuclease, which functions in DNA replication, repair, transcription, and telomere maintenance. How the loss of WRN accelerates aging is not understood in full. Here we show that WRN is necessary for optimal constitutive heterochromatin levels in proliferating human fibroblasts. Locally, WRN deficiency derepresses SATII pericentromeric satellite repeats but does not reduce replication fork progression on SATII repeats. Globally, WRN loss reduces a subset of protein-protein interactions responsible for the organization of constitutive heterochromatin in the nucleus, namely, the interactions involving Lamin B1 and Lamin B receptor, LBR. Both the mRNA level and subcellular distribution of LBR are affected by WRN deficiency, and unlike the former, the latter phenotype does not require WRN catalytic activities. The phenotypes of heterochromatin disruption seen in WRN-deficient proliferating fibroblasts are also observed in WRN-proficient fibroblasts undergoing replicative or oncogene-induced senescence. WRN interacts with histone deacetylase 2, HDAC2; WRN/HDAC2 association is mediated by heterochromatin protein alpha, HP1α, and WRN complexes with HP1α and HDAC2 are downregulated in senescing cells. The data suggest that the effect of WRN loss on heterochromatin is separable from senescence program, but mimics at least some of the heterochromatin changes associated with it.

The discovery of oncogene-induced senescence.

The discovery of oncogene-induced senescence.

Nuclear receptor TLX functions to promote cancer stemness and EMT in prostate cancer via its direct transactivation of CD44 and stem cell-regulatory transcription factors.

Prostate cancer stem cells (PCSCs) play crucial roles in therapy-resistance and metastasis in castration-resistant prostate cancer (CRPC). Certain functional link between cancer stemness and epithelial-mesenchymal transition (EMT) is involved in CRPC. However, up-stream regulators controlling these two processes in PCSCs are still poorly understood. Recently, we have shown that orphan nuclear receptor TLX can promote tumour initiation and progression in CRPC by repressing androgen receptor and oncogene-induced senescence. PCSCs were isolated from various prostate cancer cell lines and clinical tumour tissues using multiple methods for various in vitro and in vivo oncogenic growth analyses. Direct targets of TLX involved in stemness and EMT regulation were determined by specific reporter gene assays and ligand-driven modulation of TLX activity. PCSCs isolated from various sources exhibited increased expression of TLX. Functional and molecular characterisation showed that TLX could function to promote cancer stemness and EMT in prostate cancer cells via its direct transactivation of CD44, SOX2, POU5F1 and NANOG, which share certain functional crosstalk in these two cellular processes. TLX could act as a key up-stream regulator in transcriptional control of stemness and EMT in PCSCs, which contribute to their tumorigenicity, castration-resistance and metastasis potentials in advanced prostate cancer.

PPM1D activity promotes cellular transformation by preventing senescence and cell death

Cell cycle checkpoints, oncogene-induced senescence and programmed cell death represent intrinsic barriers to tumorigenesis. Protein phosphatase magnesium-dependent 1 (PPM1D) is a negative regulator of the tumour suppressor p53 and has been implicated in termination of the DNA damage response. Here, we addressed the consequences of increased PPM1D activity resulting from the gain-of-function truncating mutations in exon 6 of the PPM1D. We show that while control cells permanently exit the cell cycle and reside in senescence in the presence of DNA damage caused by ionising radiation or replication stress induced by the active RAS oncogene, RPE1-hTERT and BJ-hTERT cells carrying the truncated PPM1D continue proliferation in the presence of DNA damage, form micronuclei and accumulate genomic rearrangements revealed by karyotyping. Further, we show that increased PPM1D activity promotes cell growth in the soft agar and formation of tumours in xenograft models. Finally, expression profiling of the transformed clones revealed dysregulation of several oncogenic and tumour suppressor pathways. Our data support the oncogenic potential of PPM1D in the context of exposure to ionising radiation and oncogene-induced replication stress.

HMGA1 orchestrates chromatin compartmentalization and sequesters genes into 3D networks coordinating senescence heterogeneity

HMGA1 is an abundant non-histone chromatin protein that has been implicated in embryonic development, cancer, and cellular senescence, but its specific role remains elusive. Here, we combine functional genomics approaches with graph theory to investigate how HMGA1 genomic deposition controls high-order chromatin networks in an oncogene-induced senescence model. While the direct role of HMGA1 in gene activation has been described previously, we find little evidence to support this. Instead, we show that the heterogeneous linear distribution of HMGA1 drives a specific 3D chromatin organization. HMGA1-dense loci form highly interactive networks, similar to, but independent of, constitutive heterochromatic loci. This, coupled with the exclusion of HMGA1-poor chromatin regions, leads to coordinated gene regulation through the repositioning of genes. In the absence of HMGA1, the whole process is largely reversed, but many regulatory interactions also emerge, amplifying the inflammatory senescence-associated secretory phenotype. Such HMGA1-mediated fine-tuning of gene expression contributes to the heterogeneous nature of senescence at the single-cell level. A similar ‘buffer’ effect of HMGA1 on inflammatory signalling is also detected in lung cancer cells. Our study reveals a mechanism through which HMGA1 modulates chromatin compartmentalization and gene regulation in senescence and beyond.

Dissecting the Natural Patterns of Progression and Senescence in Pediatric Low-Grade Glioma: From Cellular Mechanisms to Clinical Implications.

Pediatric low-grade gliomas (PLGGs) comprise a heterogeneous set of low-grade glial and glioneuronal tumors, collectively representing the most frequent CNS tumors of childhood and adolescence. Despite excellent overall survival rates, the chronic nature of the disease bears a high risk of long-term disease- and therapy-related morbidity in affected patients. Recent in-depth molecular profiling and studies of the genetic landscape of PLGGs led to the discovery of the paramount role of frequent upregulation of RAS/MAPK and mTOR signaling in tumorigenesis and progression of these tumors. Beyond, the subsequent unveiling of RAS/MAPK-driven oncogene-induced senescence in these tumors may shape the understanding of the molecular mechanisms determining the versatile progression patterns of PLGGs, potentially providing a promising target for novel therapies. Recent in vitro and in vivo studies moreover indicate a strong dependence of PLGG formation and growth on the tumor microenvironment. In this work, we provide an overview of the current understanding of the multilayered cellular mechanisms and clinical factors determining the natural progression patterns and the characteristic biological behavior of these tumors, aiming to provide a foundation for advanced stratification for the management of these tumors within a multimodal treatment approach.

Transcription factor network dynamics during the commitment to oncogene-induced senescence

Aberrant oncogenic signaling causes cells to transition into oncogene-induced senescence (OIS) to limit uncontrolled proliferation. Despite being a potent tumor suppressor mechanism, OIS is an unstable cell state susceptible to reprogramming that can promote tumorigenesis. Therefore, elucidating the underlying gene regulatory mechanisms that commit cells to OIS is critical to identifying actionable targets to modulate the senescence state. We previously showed that timely execution of the OIS program is governed by hierarchical transcription factor (TF) networks. However, the gene regulatory mechanisms that prime cells to commit to the OIS fate early upon oncogene hyperactivation are currently not known. Here, we leveraged our time-resolved multi-omic profiling approach to generate TF networks during the first 24 h of oncogenic HRASG12V activation. Using this approach, we demonstrate that the commitment to OIS requires the rearrangement of the TF network on a pre-established epigenomic landscape, priming the cells for the substantial chromatin remodeling that underpins the transition to OIS. Our results provide a detailed map of the chromatin landscape before cells transition to OIS thus offering a platform for manipulation of senescence outcomes of potentially therapeutic value.

Single-cell total-RNA profiling unveils regulatory hubs of transcription factors

Recent development of RNA velocity uses master equations to establish the kinetics of the life cycle of RNAs from unspliced RNA to spliced RNA (i.e., mature RNA) to degradation. To feed this kinetic analysis, simultaneous measurement of unspliced RNA and spliced RNA in single cells is greatly desired. However, the majority of single-cell RNA-seq chemistry primarily captures mature RNA species to measure gene expressions. Here, we develop a one-step total-RNA chemistry-based single-cell RNA-seq method: snapTotal-seq. We benchmark this method with multiple single-cell RNA-seq assays in their performance in kinetic analysis of cell cycle by RNA velocity. Next, with LASSO regression between transcription factors, we identify the critical regulatory hubs mediating the cell cycle dynamics. We also apply snapTotal-seq to profile the oncogene-induced senescence and identify the key regulatory hubs governing the entry of senescence. Furthermore, from the comparative analysis of unspliced RNA and spliced RNA, we identify a significant portion of genes whose expression changes occur in spliced RNA but not to the same degree in unspliced RNA, indicating these gene expression changes are mainly controlled by post-transcriptional regulation. Overall, we demonstrate that snapTotal-seq can provide enriched information about gene regulation, especially during the transition between cell states.

MRE11 and TREX1 control senescence by coordinating replication stress and interferon signaling

Oncogene-induced senescence (OIS) arrests cell proliferation in response to replication stress (RS) induced by oncogenes. OIS depends on the DNA damage response (DDR), but also on the cGAS-STING pathway, which detects cytosolic DNA and induces type I interferons (IFNs). Whether and how RS and IFN responses cooperate to promote OIS remains unknown. Here, we show that the induction of OIS by the H-RASV12 oncogene in immortalized human fibroblasts depends on the MRE11 nuclease. Indeed, treatment with the MRE11 inhibitor Mirin prevented RS, micronuclei formation and IFN response induced by RASV12. Overexpression of the cytosolic nuclease TREX1 also prevented OIS. Conversely, overexpression of a dominant negative mutant of TREX1 or treatment with IFN-β was sufficient to induce RS and DNA damage, independent of RASV12 induction. These data suggest that the IFN response acts as a positive feedback loop to amplify DDR in OIS through a process regulated by MRE11 and TREX1.

LGG-14. INTEGRATED MULTI-OMICS EXPLORATION OF MAPK PATHWAY INHIBITION IN PEDIATRIC PILOCYTIC ASTROCYTOMA

Abstract Pilocytic astrocytomas (PA), the most common pediatric brain tumors, exhibit MAPK pathway alterations leading to its constitutive activation. They are also associated with low proliferation index due to the oncogene-induced senescence (OIS), sustained by senescence-associated secretory phenotype (SASP) factors. Little is known about the downstream consequences of MAPK activation leading to OIS-SASP, and of the molecular implications of MAPK pathway inhibition in senescent PA cells. Senescent DKFZ-BT66 cells derived from a primary KIAA::BRAF-fusion positive PA were used to generate RNA-sequencing and phospho-/proteomic datasets, before and after treatment with the MEK inhibitor (MEKi) trametinib for different time-spans. A multi-omics factor analysis tool (MEFISTO) and single sample gene set enrichment analysis (ssGSEA) were used to identify key OIS effectors and differentially regulated pathways upon MAPK inhibition. Trametinib treatment inhibited OIS and SASP signatures across all omics levels in the senescent DKFZ-BT66 cells, associated with reduced sensitivity towards senolytics drugs, indicating inhibition of senescence features upon MEKi. MEFISTO analysis identified key effectors involved in MAPK-induced OIS in the senescent PA cells. We built a pathway network using a prior knowledge network approach allowing to map the direct downstream effectors of MAPK leading to OIS-SASP. We identified several parallel pathways (JAK/STAT, p38, GSK3B) potentially involved in OIS and under the control of the MAPK pathway. In addition, ssGSEA showed that pathways related to upstream MAPK activators (SOS1, CK2, several RTKs) were predicted to be upregulated upon treatment, highlighting putative targets to be further investigated. Our data suggest that MAPKi reverses OIS signaling in senescent PA cells, while inducing the activation of MAPK upstream regulators, identifying putative co-targets for the treatment of PA. Further validation of the targetability of these pathways is pending. Furthermore, the identification of the MAPK-related OIS-SASP genes provides insight into the regulation of OIS-SASP by the MAPK pathway.

Characterization of senescence in human cardiac fibroblasts

Abstract Funding Acknowledgements None. Background Recent studies suggest that senescence of cardiac fibroblasts (cFib) plays a significant role in cardiac aging and disease. However, senescence of cultured cFib in response to classical pro-senescent stimuli has not been characterized yet. Purpose We thoroughly studied oncogene- and stress-induced senescence, as well as replicative senescence, in primary human cFib. Methods Human cFib were isolated from specimens of right atrial appendages, collected during cardiac surgery with extracorporeal circulation. These cells were subjected to oncogene-induced senescence by overexpression of HRasV12, were exposed to ionizing radiation (IR, 5 Gy) to recapitulate stress-induced senescence, and were passaged until replicative senescence was reached (P12-P14). Senescence was assessed by staining for senescence associated (SA) β-galactosidase and EdU and by RT-PCR for CDKN1A, CDKN2A, and LamB1. Results The main results are summarized in the graphical abstract. HRasV12 overexpression, IR, and prolonged culturing consistently caused senescence of cFib: in fact, all senescent models showed a significant increase in SA-β-gal activity and CDKN1A expression and a decrease in EdU uptake and LamB1 expression over control cells. Interestingly, cFib with HRasV12 overexpression exhibited a peculiar morphological phenotype with vacuoles and showed higher levels of the typical markers of senescence compared to control and to IR-treated or extensively passaged cFib. Moreover, only cFib with HRasV12 overexpression showed a strong downregulation of CDKN2A. Conclusions Cultured primary human cFib undergo senescence in response to established inducers of senescence. HRasV12 overexpression uniquely causes vacuolization of senescent cFib, which is currently being further characterized by transmission electron microscopy.

MOST wanted: navigating the MAPK-OIS-SASP-tumor microenvironment axis in primary pediatric low-grade glioma and preclinical models

Understanding the molecular and cellular mechanisms driving pediatric low-grade glioma (pLGG)—the most prevalent brain tumor in children—is essential for the identification and evaluation of novel effective treatments. This review explores the intricate relationship between the mitogen-activated protein kinase (MAPK) pathway, oncogene-induced senescence (OIS), the senescence-associated secretory phenotype (SASP), and the tumor microenvironment (TME), integrating these elements into a unified framework termed the MAPK/OIS/SASP/TME (MOST) axis. This integrated approach seeks to deepen our understanding of pLGG and improve therapeutic interventions by examining the MOST axis’ critical influence on tumor biology and response to treatment. In this review, we assess the axis’ capacity to integrate various biological processes, highlighting new targets for pLGG treatment, and the need for characterized in vitro and in vivo preclinical models recapitulating pLGG’s complexity to test targets. The review underscores the need for a comprehensive strategy in pLGG research, positioning the MOST axis as a pivotal approach in understanding pLGG. This comprehensive framework will open promising avenues for patient care and guide future research towards inventive treatment options.

NEMO/NF-κB signaling functions as a double-edged sword in PanIN formation versus progression to pancreatic cancer

BackgroundPancreatic ductal adenocarcinoma (PDAC) is marked by a dismal survival rate, lacking effective therapeutics due to its aggressive growth, late-stage diagnosis, and chemotherapy resistance. Despite debates on NF-κB targeting for PDAC treatment, no successful approach has emerged.MethodsTo elucidate the role of NF-κB, we ablated NF-κB essential modulator (NEMO), critical for conventional NF-κB signaling, in the pancreata of mice that develop precancerous lesions (KC mouse model). Secretagogue-induced pancreatitis by cerulein injections was utilized to promote inflammation and accelerate PDAC development.ResultsNEMO deletion reduced fibrosis and inflammation in young KC mice, resulting in fewer pancreatic intraepithelial neoplasias (PanINs) at later stages. Paradoxically, however, NEMO deletion accelerated the progression of these fewer PanINs to PDAC and reduced median lifespan. Further, analysis of tissue microarrays from human PDAC sections highlighted the correlation between reduced NEMO expression in neoplastic cells and poorer prognosis, supporting our observation in mice. Mechanistically, NEMO deletion impeded oncogene-induced senescence (OIS), which is normally active in low-grade PanINs. This blockage resulted in fewer senescence-associated secretory phenotype (SASP) factors, reducing inflammation. However, blocked OIS fostered replication stress and DNA damage accumulation which accelerated PanIN progression to PDAC. Finally, treatment with the DNA damage-inducing reagent etoposide resulted in elevated cell death in NEMO-ablated PDAC cells compared to their NEMO-competent counterparts, indicative of a synthetic lethality paradigm.ConclusionsNEMO exhibited both oncogenic and tumor-suppressive properties during PDAC development. Caution is suggested in therapeutic interventions targeting NF-κB, which may be detrimental during PanIN progression but beneficial post-PDAC development.Graphical

Abstract PO2-01-08: Differential HOXB13 gene expression and promoter methylation analysis in breast cancer

Abstract Background: The Breast Cancer Index (BCI) is a gene expression-based signature comprising two functional biomarker panels: the Molecular Grade Index (MGI) and BCI (H/I), which is a ratio of the HOXB13 and IL17BR gene expression. Several studies have shown that BCI (H/I) is a predictive biomarker for extended adjuvant endocrine therapy benefit in hormone receptor-positive (HR+) early-stage breast cancer. Molecular mechanisms underlying endocrine responsiveness remain to be fully explored. The objective of this analysis is to evaluate the correlation between gene expression and methylation in breast cancer patients displaying different HOXB13 mRNA expression levels from The Cancer Genome Atlas (TCGA) project. Methods: Data from methylation microarrays and mRNA sequencing were examined in combination with clinical metadata from 1,095 TCGA breast cancer patients. After removing outliers, HR+ samples were ordered based on their HOXB13 expression levels and the top 10% of samples (HOXB13-high; n=95) and bottom 10% (HOXB13-low; n=95) were selected for further analysis. Differentially expressed genes (DEGs) were determined by comparing all protein-coding genes between the HOXB13-high and HOXB13-low sets, based on an absolute log-fold change above 2 and a Benjamini-Hochberg adjusted p-value threshold of 0.01. Among the subset of samples with matching methylation data (n=60 for the HOXB13-high group and n=48 for the HOXB13-low group), hypo-methylated and hyper-methylated differentially methylated probes (DMPs) were identified based on at least 10% change of β (i.e., average promoter methylation) and a Benjamini-Hochberg adjusted p-value threshold of 0.01. Motif and transcription factor (TF) enrichment analyses were identified at a minimum incidence of 10 and a lower boundary of 1.5 for the 95% confidence interval of the odds ratio. Results: Our analysis identified a total of 613 DEGs between the HOXB13-high and HOXB13-low groups. Gene ontology analysis of DEGs revealed a statistically significant enrichment of genes associated with PTK6 regulated cell cycle, oncogene-induced cellular senescence, and regulation of T cell activation. Analysis of protein-protein interactions of differentially expressed genes revealed differences in key biological processes including changes in cell cycle regulation, p53 pathway, and IL-17 signaling. A total of 5,295 hyper-methylated and 580 hypo-methylated DMPs were discovered when comparing HOXB13-high and HOXB13-low samples. Changes in global methylation patterns enabled classification of breast cancer samples with high or low HOXB13 expression with an accuracy of 0.90. Reconstruction of gene regulatory networks from DNA methylation and transcriptome profiles elucidated significant pairs of DMPs and differentially expressed genes. Specifically, a total of 197 differentially expressed genes were attributed to hyper-methylated DMPs, including genes involved in response to estrogen, activation of HOX genes during differentiation, and drug-mediated inhibition of CDK4/6 activity. Additionally, 8 differentially expressed genes were attributed to hypo-methylated DMPs and were associated with proteasomal protein catabolic processes. Lastly, motif analysis of transcriptional factors for the hyper-methylated DMPs revealed enrichment of binding motifs attributed to FOXA1, ESR1, XBR1, and FOXP1. Conclusion: A comprehensive and comparative analysis of mRNA expression levels and methylation patterns between TCGA breast cancer samples with high and low expression of HOXB13 revealed key signaling pathways and biological processes that may provide insights on the molecular mechanism of HOXB13 in the regulation of response to endocrine therapy in HR+ breast cancer. Citation Format: Natalia Siuliukina, Yi Zhang, Kai Treuner, Mark Pegram. Differential HOXB13 gene expression and promoter methylation analysis in breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-01-08.

BRAFV600E promotes anchorage-independent growth but inhibits anchorage-dependent growth in hTERT/Cdk4-Immortalized normal human bronchial epithelial cells

Certain oncogenes, including mutant RAS and BRAF, induce a type of senescence known as oncogene-induced senescence (OIS) in normal cells in a cell-type-specific manner. OIS serves as a barrier to transformation by activated oncogenes. Our previous studies showed that mutant KRASV12 did not efficiently induce OIS in an hTERT/Cdk4-immortalized normal human bronchial epithelial cell line (HBEC3), but it did enhance both anchorage-dependent and anchorage-independent growth. In this study, we investigated whether mutant BRAF, a well-known inducer of OIS, could trigger OIS in HBEC3 cells. We also assessed the impact of mutant BRAF on the growth of HBEC3 cells, as no previous studies have examined this using a normal bronchial epithelial cell line model. We established an HBEC3 cell line, designated as HBEC3-BIN, that expresses mutant BRAFV600E in a doxycycline-regulated manner. Unlike our previous finding that KRASV12 upregulated both pERK and pAKT, mutant BRAFV600E upregulated pERK but not pAKT in HBEC3-BIN cells. Similar to KRASV12, BRAFV600E did not efficiently induce OIS. Interestingly, while BRAFV600E inhibited colony formation in anchorage-dependent conditions, it dramatically enhanced colony formation in anchorage-independent conditions in HBEC3-BIN. In HBEC3 cells without BRAFV600E or KRASV12 expression, p21 was only detected in the cytoplasm, and its localization was not altered by the expression of BRAFV600E or KRASV12. Next-generation sequencing analysis revealed an enrichment of gene sets known to be involved in carcinogenesis, including IL3/JAK/STAT3, IL2, STAT5, and the EMT pathway. Our results indicate that, unlike KRASV12, which promoted both, BRAFV600E enhances anchorage-independent growth but inhibits anchorage-dependent growth of HBEC3. This contrast may result from differences in activation signaling in the downstream pathways. Furthermore, HBEC3 cells appear to be inherently resistant to OIS, which may be partly due to the fact that p21 remains localized in the cytoplasm upon expression of BRAFV600E or KRASV12.

Abstract 2967: The mammalian 8-oxo-dGTPase, MTH1, as a novel targetable vulnerability in pancreatic ductal adenocarcinoma

Abstract Pancreatic ductal adenocarcinoma (PDAC) is an aggressive KRAS-driven cancer that remains one of the most lethal of all human malignancies. Oncogenic KRAS relies on elevated reactive oxygen species (ROS) to support pro-tumorigenic signaling. However, these elevated ROS levels can also evoke tumor suppressive oxidative stress; thus KRAS-driven cancers must evolve protective redox adaptations to mitigate ROS-induced anti-tumor consequences. Here we report a unique adaptation centered on redox maintenance of nucleotide pool integrity, that supports aggressive PDAC tumorigenesis. MTH1 is the main mammalian 8-oxodGTPase that is known to be elevated in various RAS-driven cancers including PDAC. We have previously shown MTH1 is critical for ROS-mediated oncogenic signaling, and promotes escape from oncogene-induced senescence. We therefore hypothesized that MTH1 provides important redox support for aggressive PDAC tumor growth. Consistent with this, we found that elevated MTH1 expression was strongly correlated with poor disease-free survival in PDAC patients. These findings extended to KRAS-driven PDAC cell lines: highly proliferative human PDAC cells strongly expressed MTH1 (MTH1high), and MTH1 deletion was selectively anti-tumorigenic against MTH1high cells. Furthermore, introduction of MTH1-null backgrounds into gold standard genetically engineered PDAC mouse models selectively decreased 8-oxodGTPase activity levels and slowed PDAC growth in aggressive, short latency Ptf1acre/+;LSL-KrasG12D/+;Tgfbr2flox/flox (PKT) mice, but with no effect in longer latency Pdx1Cre; LSL- KrasG12D/+; LSL-Trp53R172H/+ (KPC) mice. These selective anti-tumorigenic effects were accompanied by a reduction in circulating immunosuppressive cytokines in PKT mice, further suggesting that MTH1 potentially supports aggressive tumorigenesis through induction of systemic immunosuppression. Consistent with this, pancreatic-restricted MTH1 conditional deletion fully rescued PDAC growth in PKT mice. Our findings here thus suggest that MTH1-dependent redox protection of the nucleotide pool represents a unique TME adaptation that supports aggressive PDAC tumorigenesis. Further studies will investigate whether this adaptation is maintained through symbiotic tumor/stroma or tumor/immune cell crosstalk, as observed for other KRAS-driven traits. Ultimately, interventions designed to target MTH1-dependent protection of the nucleotide pool could hold promise as novel therapeutic strategies for this untreatable disease. Citation Format: Beatriz Mateo-Victoriano, Ling Zhang, Jaya Samaranayake, Z McGaughey, Cassie Due, Clara Troccoli, Michael G. Mohsen, Nagaraj Nagathihalli, Oliver G. McDonald, Michael VanSaun, Eric T. Kool, Priyamvada Rai. The mammalian 8-oxo-dGTPase, MTH1, as a novel targetable vulnerability in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2967.

Abstract 2968: TWIST1-induced suppression of oncogene-induced senescence in non-small cell lung cancer requires the transactivation domain of TWIST1

Abstract Non-small cell lung carcinoma (NSCLC) is a major cause of cancer mortality. High expression of the epithelial-to-mesenchymal transition transcription factor TWIST1 is strongly associated with metastatic cancers and treatment resistance. Additionally, TWIST1 can upregulate O-GlcNAcylation which (1) is required to suppress fail-safe programs such as oncogene (KRasG12D)-induced senescence (OIS) to accelerate tumorigenesis in primary NSCLC tumors, and (2) is a potential modulator of DNA repair/radiation response. To decipher the domains and transcriptional targets required for tumorigenicity and radioresistance, we created a novel genetically engineered mouse model (GEMM) allowing tetracycline-inducible expression in the lung epithelium (via lung specific CCSP-reverse tetracycline transactivator (C)) of KRasG12D (R) with Twist1wt (T) or with Twist1F191G transactivation-null mutant (F). CRT mice had shorter tumor-free survival and more aggressive tumors compared to CR/CRF mice indicating that the Twist1 transactivation domain is required for Twist1-dependent tumorigenesis acceleration. Also, Twist1wt expression promoted radioresistance in cell lines and GEMMs. Contrary to CRT, CRF showed a progressive loss of Twist1F191G expression over time suggesting no functionality/no selective advantage. CRT lung tumors had higher proliferation (Ki67) and lower cell-cycle arrest (p16) compared to CR/CRF suggesting that the transactivation domain of Twist1 is important for the suppression of OIS. Supporting these data, we observed in non-cancer Human Bronchial Epithelial Cell (HBEC) that the co-expression of human TWIST1wt (HBEC-TWIST1wt) could suppress HRasG12V-induced senescence while the transactivation-null TWIST1F187G mutant (HBEC-TWIST1F187G) could not. Additionally, HBEC expressing HRasG12V-TWIST1wt had enhanced tumorigenic/invasive programs. Interestingly, we observed that the inhibition of O-GlcNAcylation rescued OIS in HBEC-HRasG12V-TWIST1wt while the stimulation of O-GlcNAcylation in HBEC-HRasG12V-TWIST1F187G suppressed OIS. Furthermore, TWIST1wt expression with HRasG12V modulated MYC downstream targets and the inhibition of MYC activity using the novel MYC inhibitor MYCi975 in HBEC-HRasG12V-TWIST1wt also rescued OIS induction. Altogether, these results suggest that TWIST1 may suppress OIS via MYC signaling and nominate MYCi975 as a means to activate latent OIS programs. In this context, MYC inhibiting strategies could serve as a therapeutic sensitizer for TWIST1-positive NSCLC. This work and our future studies on TWIST1 toward the control of OIS, O-GlcNAcylation and of mechanisms of radioresistance may help to identify new potential NSCLC therapeutic strategies. Citation Format: Audrey M. Lafargue, Hailun Wang, Sivarajan T. Chettiar, Rajendra P. Gajula, Amol C. Shetty, Yang Song, Brian W. Simons, Triet Nguyen, Christine Lam, Francesca A. Carrieri, Caleb Smack, Nick Connis, Dipanwita Dutta Chowdhury, Jinhee Chang, Danielle Council, Katriana Nugent, Ismaeel Siddiqui, Kekoa Taparra, Mohammad Rezaee, Natasha Zachara, Zachary S. Morris, Christopher McFarland, Sarki Abba Abdulkadir, Christine L. Hann, Phuoc T. Tran. TWIST1-induced suppression of oncogene-induced senescence in non-small cell lung cancer requires the transactivation domain of TWIST1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2968.

Alternative Wnt-signaling axis leads to a break of oncogene-induced senescence

Oncogene-induced senescence (OIS) is an important process that suppresses tumor development, but the molecular mechanisms of OIS are still under investigation. It is known that BRAFV600E-mutated melanocytes can overcome OIS and develop melanoma, but the underlying mechanism is largely unknown. Using an established OIS model of primary melanocytes transduced with BRAFV600E, YAP activity was shown to be induced in OIS as well as in melanoma cells compared to that in normal epidermal melanocytes. This led to the assumption that YAP activation itself is not a factor involved in the disruption of OIS. However, its role and interaction partners potentially change. As Wnt molecules are known to be important in melanoma progression, these molecules were the focus of subsequent studies. Interestingly, activation of Wnt signaling using AMBMP resulted in a disruption of OIS in BRAFV600E-transduced melanocytes. Furthermore, depletion of Wnt6, Wnt10b or β-catenin expression in melanoma cells resulted in the induction of senescence. Given that melanoma cells do not exhibit canonical Wnt/β-catenin activity, alternative β-catenin signaling pathways may disrupt OIS. Here, we discovered that β-catenin is an interaction partner of YAP on DNA in melanoma cells. Furthermore, the β-catenin–YAP interaction changed the gene expression pattern from senescence-stabilizing genes to tumor-supportive genes. This switch is caused by transcriptional coactivation via the LEF1/TEAD interaction. The target genes with binding sites for LEF1 and TEAD are involved in rRNA processing and are associated with poor prognosis in melanoma patients. This study revealed that an alternative YAP-Wnt signaling axis is an essential molecular mechanism leading to OIS disruption in melanocytes.

Transcription of endogenous retroviruses in senescent cells contributes to the accumulation of double-stranded RNAs that trigger an anti-viral response that reinforces senescence

An important epigenetic switch marks the onset and maintenance of senescence. This allows transcription of the genetic programs that arrest the cell cycle and alter the microenvironment. Transcription of endogenous retroviruses (ERVs) is also a consequence of this epigenetic switch. In this manuscript, we have identified a group of ERVs that are epigenetically silenced in proliferating cells but are upregulated during replicative senescence or during various forms of oncogene-induced senescence, by RAS and Akt, or after HDAC4 depletion. In a HDAC4 model of senescence, removal of the repressive histone mark H3K27me3 is the plausible mechanism that allows the transcription of intergenic ERVs during senescence. We have shown that ERVs contribute to the accumulation of dsRNAs in senescence, which can initiate the antiviral response via the IFIH1-MAVS signaling pathway and thus contribute to the maintenance of senescence. This pathway, and MAVS in particular, plays an active role in shaping the microenvironment and maintaining growth arrest, two essential features of the senescence program.

Cooperative pro-tumorigenic adaptation to oncogenic RAS through epithelial-to-mesenchymal plasticity.

In breast cancers, aberrant activation of the RAS/MAPK pathway is strongly associated with mesenchymal features and stemness traits, suggesting an interplay between this mitogenic signaling pathway and epithelial-to-mesenchymal plasticity (EMP). By using inducible models of human mammary epithelial cells, we demonstrate herein that the oncogenic activation of RAS promotes ZEB1-dependent EMP, which is necessary for malignant transformation. Notably, EMP is triggered by the secretion of pro-inflammatory cytokines from neighboring RAS-activated senescent cells, with a prominent role for IL-6 and IL-1α. Our data contrast with the common view of cellular senescence as a tumor-suppressive mechanism and EMP as a process promoting late stages of tumor progression in response to signals from the tumor microenvironment. We highlighted here a pro-tumorigenic cooperation of RAS-activated mammary epithelial cells, which leverages on oncogene-induced senescence and EMP to trigger cellular reprogramming and malignant transformation.