Age-stratified comorbid and pharmacologic analysis of patients with glioblastoma.

Background: Increased age is a strong and unfavorable prognostic factor for patients with glioblastoma (GBM). However, the relationships between stratified patient age, comorbidities, and medications have yet to be explored in GBM patient survival analyses. Objective: To evaluate co-morbid conditions, tumor-related symptoms, medication prescriptions, and subject age for patients with GBM and to establish potential targets for prospective studies. Methods: Electronic health records for 565 patients with IDHwt GBM were evaluated at a single center between January 1, 2000 and August 9, 2021 were retrospectively assessed. Data were stratified by MGMT promoter methylation status when available and were used to construct multivariable time-dependent cox models and intra-cohort hazards. Results: Younger (<65 years of age) but not older (≥65 years) GBM patients demonstrated a worse prognosis with movement related disabilities (P < 0.0001), gait/balance difficulty (P = 0.04) and weakness (P = 0.007), as well as psychiatric conditions, mental health disorders (P = 0.002) and anxiety (P = 0.001). In contrast, older but not younger GBM patients demonstrated a worse prognosis with epilepsy (P = 0.039). Both groups had worse survival with confusion/altered mental status (P = 0.023 vs < 0.000) and an improved survival with a Temozolomide prescription. Older but not younger GBM patients experienced an improved hazard with a prescription of ace-inhibitor medications (P = 0.048). Conclusion: Age-dependent novel associations between clinical symptoms and medications prescribed for co-morbid conditions were demonstrated in patients with GBM. The results of the current work support future mechanistic studies that investigate the negative relationship(s) between increased age, comorbidities, and drug therapies for differential clinical decision-making across the lifespan of patients with GBM.

Advanced Age in Humans and Mouse Models of Glioblastoma Show Decreased Survival from Extratumoral Influence.

PURPOSE: Glioblastoma (GBM) is the most common aggressive primary malignant brain tumor in adults with a median age of onset of 68 to 70 years old. Although advanced age is often associated with poorer GBM patient survival, the predominant source(s) of maladaptive aging effects remains to be established. Here, we studied intratumoral and extratumoral relationships between adult patients with GBM and mice with brain tumors across the lifespan. EXPERIMENTAL DESIGN: Electronic health records at Northwestern Medicine and the NCI SEER databases were evaluated for GBM patient age and overall survival. The commercial Tempus and Caris databases, as well as The Cancer Genome Atlas were profiled for gene expression, DNA methylation, and mutational changes with varying GBM patient age. In addition, gene expression analysis was performed on the extratumoral brain of younger and older adult mice with or without a brain tumor. The survival of young and old wild-type or transgenic (INK-ATTAC) mice with a brain tumor was evaluated after treatment with or without senolytics and/or immunotherapy. RESULTS: Human patients with GBM ≥65 years of age had a significantly decreased survival compared with their younger counterparts. While the intra-GBM molecular profiles were similar between younger and older patients with GBM, non-tumor brain tissue had a significantly different gene expression profile between young and old mice with a brain tumor and the eradication of senescent cells improved immunotherapy-dependent survival of old but not young mice. CONCLUSIONS: This work suggests a potential benefit for combining senolytics with immunotherapy in older patients with GBM.

Identification and Characterization of a Novel Indoleamine 2,3-Dioxygenase 1 Protein Degrader for Glioblastoma.

Indoleamine 2,3-dioxygenase 1 (IDO1) is a potent immunosuppressive enzyme that inhibits the antitumor immune response through both tryptophan metabolism and non-enzymatic functions. To date, most IDO1-targeted approaches have focused on inhibiting tryptophan metabolism. However, this class of drugs has failed to improve the overall survival of patients with cancer. Here, we developed and characterized proteolysis targeting chimeras (PROTACs) that degrade the IDO1 protein. IDO1-PROTACs were tested for their effects on IDO1 enzyme and non-enzyme activities. After screening a library of IDO1-PROTAC derivatives, a compound was identified that potently degraded the IDO1 protein through cereblon-mediated proteasomal degradation. The IDO1-PROTAC: (i) inhibited IDO1 enzyme activity and IDO1-mediated NF-κB phosphorylation in cultured human glioblastoma (GBM) cells, (ii) degraded the IDO1 protein within intracranial brain tumors in vivo, and (iii) mediated a survival benefit in mice with well-established brain tumors. This study identified and characterized a new IDO1 protein degrader with therapeutic potential for patients with glioblastoma.

Chemical inhibition of oxygen-sensing prolyl hydroxylases impairs angiogenic competence of human vascular endothelium through metabolic reprogramming.

Endothelial cell (EC) metabolism has emerged as a driver of angiogenesis. While hypoxia inactivates the oxygen sensors prolyl-4 hydroxylase domain-containing proteins 1-3 (PHD1-3) and stimulates angiogenesis, the effects of PHDs on EC functions remain poorly defined. Here, we investigated the impact of chemical PHD inhibition by dimethyloxalylglycine (DMOG) on angiogenic competence and metabolism of human vascular ECs. DMOG reduced EC proliferation, migration, and tube formation capacities, responses that were associated with an unfavorable metabolic reprogramming. While glycolytic genes were induced, multiple genes encoding sub-units of mitochondrial complex I were suppressed with concurrent decline in nicotinamide adenine dinucleotide (NAD+) levels. Importantly, the DMOG-induced defects in EC migration could be partially rescued by augmenting NAD+ levels through nicotinamide riboside or citrate supplementation. In summary, by integrating functional assays, transcriptomics, and metabolomics, we provide insights into the effects of PHD inhibition on angiogenic competence and metabolism of human vascular ECs.

A systematic review of pharmacologic treatment efficacy for depression in older patients with cancer.

Background: Older adults ≥65 years of age represent the majority of new cancer diagnoses and are vulnerable to developing depression-like symptoms. Evaluation and management of depression in older cancer patients is underappreciated despite its high prevalence and impact on health-related quality of life. Although antidepressants are the primary pharmacologics used to treat depressive-like symptoms, the efficacy and overall benefit(s) are not well-characterized in older adult patients with cancer. The objective of this investigation was to review what is known about the efficacy of pharmacologic treatment for older adults with depression and cancer. Methods: PubMed (Medline) and EMBASE (Elsevier) databases were analyzed for relevant literature in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Results: 1,919 unique studies were identified for title and abstract screening. Forty-eight publications were retrieved for full review. None of the identified studies evaluated the potential for benefit after pharmacological treatment among older adults with cancer and depression. Twenty-seven publications met all study criteria except for an analysis focused on older patients. Conclusion: We discovered a universal absence of literature with a relevance to pharmacologic antidepressant treatment effects in older adult patients with cancer. This included a lack of evaluation in patients with brain tumors who have an unusually high predilection for developing depression. Our findings suggest that new research is critically needed for understanding optimal clinical management strategies in older adults with cancer and depression who are treated with antidepressants.

Hypoxic preconditioning protects against ischemic kidney injury through the IDO1/kynurenine pathway.

Prolonged cellular hypoxia leads to energetic failure and death. However, sublethal hypoxia can trigger an adaptive response called hypoxic preconditioning. While prolyl-hydroxylase (PHD) enzymes and hypoxia-inducible factors (HIFs) have been identified as key elements of oxygen-sensing machinery, the mechanisms by which hypoxic preconditioning protects against insults remain unclear. Here, we perform serum metabolomic profiling to assess alterations induced by two potent cytoprotective approaches, hypoxic preconditioning and pharmacologic PHD inhibition. We discover that both approaches increase serum kynurenine levels and enhance kynurenine biotransformation, leading to preservation of NAD+ in the post-ischemic kidney. Furthermore, we show that indoleamine 2,3-dioxygenase 1 (Ido1) deficiency abolishes the systemic increase of kynurenine and the subsequent renoprotection generated by hypoxic preconditioning and PHD inhibition. Importantly, exogenous administration of kynurenine restores the hypoxic preconditioning in the context of Ido1 deficiency. Collectively, our findings demonstrate a critical role of the IDO1-kynurenine axis in mediating hypoxic preconditioning.

Combination of Sulindac and Bexarotene for Prevention of Intestinal Carcinogenesis in Familial Adenomatous Polyposis.

Familial adenomatous polyposis (FAP) is a hereditary colorectal cancer syndrome, which results in the development of hundreds of adenomatous polyps carpeting the gastrointestinal tract. NSAIDs have reduced polyp burden in patients with FAP and synthetic rexinoids have demonstrated the ability to modulate cytokine-mediated inflammation and WNT signaling. This study examined the use of the combination of an NSAID (sulindac) and a rexinoid (bexarotene) as a durable approach for reducing FAP colonic polyposis to prevent colorectal cancer development. Whole transcriptomic analysis of colorectal polyps and matched normal mucosa in a cohort of patients with FAP to identify potential targets for prevention in FAP was performed. Drug-dose synergism of sulindac and bexarotene in cell lines and patient-derived organoids was assessed, and the drug combination was tested in two different mouse models. This work explored mRNA as a potential predictive serum biomarker for this combination in FAP. Overall, transcriptomic analysis revealed significant activation of inflammatory and cell proliferation pathways. A synergistic effect of sulindac (300 µmol/L) and bexarotene (40 µmol/L) was observed in FAP colonic organoids with primary targeting of polyp tissue compared with normal mucosa. This combination translated into a significant reduction in polyp development in ApcMin/+ and ApcLoxP/+-Cdx2 mice. Finally, the reported data suggest miRNA-21 could serve as a predictive serum biomarker for polyposis burden in patients with FAP. These findings support the clinical development of the combination of sulindac and bexarotene as a treatment modality for patients with FAP. PREVENTION RELEVANCE: This study identified a novel chemopreventive regimen combining sulindac and bexarotene to reduce polyposis in patients with FAP using in silico tools, ex vivo, and in vivo models. This investigation provides the essential groundwork for moving this drug combination forward into a clinical trial.

The Transcriptomic Landscape of Mismatch Repair-Deficient Intestinal Stem Cells.

Lynch syndrome is the most common cause of hereditary colorectal cancer and is secondary to germline alterations in one of four DNA mismatch repair (MMR) genes. Here we aimed to provide novel insights into the initiation of MMR-deficient (MMRd) colorectal carcinogenesis by characterizing the expression profile of MMRd intestinal stem cells (ISC). A tissue-specific MMRd mouse model (Villin-Cre;Msh2 LoxP/LoxP ) was crossed with a reporter mouse (Lgr5-EGFP-IRES-creERT2) to trace and isolate ISCs (Lgr5+) using flow cytometry. Three different ISC genotypes (Msh2-KO, Msh2-HET, and Msh2-WT) were isolated and processed for mRNA-seq and mass spectrometry, followed by bioinformatic analyses to identify expression signatures of complete MMRd and haplo-insufficiency. These findings were validated using qRT-PCR, IHC, and whole transcriptomic sequencing in mouse tissues, organoids, and a cohort of human samples, including normal colorectal mucosa, premalignant lesions, and early-stage colorectal cancers from patients with Lynch syndrome and patients with familial adenomatous polyposis (FAP) as controls. Msh2-KO ISCs clustered together with differentiated intestinal epithelial cells from all genotypes. Gene-set enrichment analysis indicated inhibition of replication, cell-cycle progression, and the Wnt pathway and activation of epithelial signaling and immune reaction. An expression signature derived from MMRd ISCs successfully distinguished MMRd neoplastic lesions of patients with Lynch syndrome from FAP controls. SPP1 was specifically upregulated in MMRd ISCs and colocalized with LGR5 in Lynch syndrome colorectal premalignant lesions and tumors. These results show that expression signatures of MMRd ISC recapitulate the initial steps of Lynch syndrome carcinogenesis and have the potential to unveil novel biomarkers of early cancer initiation. SIGNIFICANCE: The transcriptomic and proteomic profile of MMR-deficient intestinal stem cells displays a unique set of genes with potential roles as biomarkers of cancer initiation and early progression.

Naproxen chemoprevention promotes immune activation in Lynch syndrome colorectal mucosa.

OBJECTIVE: Patients with Lynch syndrome (LS) are at markedly increased risk for colorectal cancer. It is being increasingly recognised that the immune system plays an essential role in LS tumour development, thus making an ideal target for cancer prevention. Our objective was to evaluate the safety, assess the activity and discover novel molecular pathways involved in the activity of naproxen as primary and secondary chemoprevention in patients with LS. DESIGN: We conducted a Phase Ib, placebo-controlled, randomised clinical trial of two dose levels of naproxen sodium (440 and 220 mg) administered daily for 6 months to 80 participants with LS, and a co-clinical trial using a genetically engineered mouse model of LS and patient-derived organoids (PDOs). RESULTS: Overall, the total number of adverse events was not different across treatment arms with excellent tolerance of the intervention. The level of prostaglandin E2 in the colorectal mucosa was significantly decreased after treatment with naproxen when compared with placebo. Naproxen activated different resident immune cell types without any increase in lymphoid cellularity, and changed the expression patterns of the intestinal crypt towards epithelial differentiation and stem cell regulation. Naproxen demonstrated robust chemopreventive activity in a mouse co-clinical trial and gene expression profiles induced by naproxen in humans showed perfect discrimination of mice specimens with LS and PDOs treated with naproxen and control. CONCLUSIONS: Naproxen is a promising strategy for immune interception in LS. We have discovered naproxen-induced gene expression profiles for their potential use as predictive biomarkers of drug activity. TRIAL REGISTRATION NUMBER: gov Identifier: NCT02052908.

NER-factor DDB2 regulates HIF1α and hypoxia-response genes in HNSCC.

Cancers in the oral/head & neck region (HNSCC) are aggressive due to high incidence of recurrence and distant metastasis. One prominent feature of aggressive HNSCC is the presence of severely hypoxic regions in tumors and activation of hypoxia-inducible factors (HIFs). In this study, we report that the XPE gene product DDB2 (damaged DNA binding protein 2), a nucleotide excision repair protein, is upregulated by hypoxia. Moreover, DDB2 inhibits HIF1α in HNSCC cells. It inhibits HIF1α in both normoxia and hypoxia by reducing mRNA expression. Knockdown of DDB2 enhances the expression of angiogenic markers and promotes tumor growth in a xenograft model. We show that DDB2 binds to an upstream promoter element in the HIF1Α gene and promotes histone H3K9 trimethylation around the binding site by recruiting Suv39h1. Also, we provide evidence that DDB2 has a significant suppressive effect on expression of the endogenous markers of hypoxia that are also prognostic indicators in HNSCC. Together, these results describe a new mechanism of hypoxia regulation that opposes expression of HIF1Α mRNA and the hypoxia-response genes.

DDB2 regulates Epithelial-to-Mesenchymal Transition (EMT) in Oral/Head and Neck Squamous Cell Carcinoma.

DDB2 is a sensor of DNA damage and it plays an important role in Global Genomic Repair (GG-NER). Our previous studies show that DDB2 is involved in the regulation of metastasis in colon adenocarcinoma. Squamous Cell Carcinomas in the Oral/Head & Neck region (HNSCC) are particularly aggressive due to high incidence of recurrence and distant metastasis. In this study, we show that DDB2 expression is downregulated in advanced HNSCCs and loss of DDB2 expression coincides with reduced survival. Recent meta-analysis of gene expression data characterized the mesenchymal-type (EMT-type) as one most aggressive cancer cluster in HNSCC. Here, we report that DDB2 constitutively represses mRNA expression of the EMT- regulatory transcription factors SNAIL, ZEB1, and angiogenic factor VEGF in HNSCC cells. As a result, re-expression of DDB2 in metastatic cells reversed EMT with transcriptional upregulation of epithelial marker E-cadherin, and downregulation of mesenchymal markers N-cadherin, Vimentin, and Fibronectin. Interestingly, in a reverse assay, depletion of DDB2 in non-metastatic cells induced expression of the same EMT-regulatory transcription factors. TGFßs are major regulators of Snail and Zeb1, and we observed that DDB2 transcriptionally regulates expression of TGFB2 in HNSCC cells. Re-expression of DDB2 in mouse embryonic fibroblasts (MEFs) isolated from Ddb2 (-/-) knockout-mice resulted in repression of EMT-regulatory factors Zeb1, Snail and Tgfb2. Taken together, these results support the active role of DDB2 as a candidate suppressor of the EMT-process in HNSCC. Early detection leads to significantly higher survival in HNSCC and DDB2 expression in tumors can be a predictor of EMT progression.

DDB2 suppresses epithelial-to-mesenchymal transition in colon cancer.

Colon cancer is one of the deadliest cancers worldwide because of its metastasis to other essential organs. Metastasis of colon cancer involves a complex set of events, including epithelial-to-mesenchymal transition (EMT) that increases invasiveness of the tumor cells. Here, we show that the xeroderma pigmentosum group E (XPE) gene product, damaged DNA-binding protein (DDB)-2, is downregulated in high-grade colon cancers, and it plays a dominant role in the suppression of EMT of the colon cancer cells. Depletion of DDB2 promotes mesenchymal phenotype, whereas expression of DDB2 promotes epithelial phenotype. DDB2 constitutively represses genes that are the key activators of EMT, indicating that DDB2 is a master regulator of EMT of the colon cancer cells. Moreover, we observed evidence that DDB2 functions as a barrier for EMT induced by hypoxia and TGF-ß. Also, we provide evidence that DDB2 inhibits metastasis of colon cancer. The results presented here identify a transcriptional regulatory pathway of DDB2 that is directly linked to the mechanisms that suppress metastasis of colon cancer.

ßTrCP regulates BMI1 protein turnover via ubiquitination and degradation.

The polycomb group protein BMI1 has been linked to proliferation, senescence, cancer progression and stem cell phenotype. At present, very little is known about its regulation. Here, we report that BMI1 contains a functional recognition motif for the F box protein ßTrCP, which regulates ubiquitination and proteasome-mediated degradation of various proteins. We show that overexpression of wild-type ßTrCP but not the ΔF mutant of it promotes BMI1 ubiquitination and degradation, and knockdown of ßTrCP results in increased expression of BMI1. Furthermore, a mutant of BMI1 with an altered ßTrCP recognition motif is much more stable than wild-type BMI1. We also show that wild-type BMI1 but not the mutant BMI1 interacts with ßTrCP. Accordingly, compared to wild-type BMI1, mutant protein exhibited increased pro-oncogenic activity. In summary, our findings suggest that ßTrCP regulates turnover of BMI1 and its function relevant to oncogenesis, cellular senescence and aging.

Deletion analysis of BMI1 oncoprotein identifies its negative regulatory domain.

BACKGROUND: The polycomb group (PcG) protein BMI1 is an important regulator of development. Additionally, aberrant expression of BMI1 has been linked to cancer stem cell phenotype and oncogenesis. In particular, its overexpression has been found in several human malignancies including breast cancer. Despite its established role in stem cell maintenance, cancer and development, at present not much is known about the functional domains of BMI1 oncoprotein. In the present study, we carried out a deletion analysis of BMI1 to identify its negative regulatory domain. RESULTS: We report that deletion of the C-terminal domain of BMI1, which is rich in proline-serine (PS) residues and previously described as PEST-like domain, increased the stability of BMI1, and promoted its pro-oncogenic activities in human mammary epithelial cells (HMECs). Specifically, overexpression of a PS region deleted mutant of BMI1 increased proliferation of HMECs and promoted an epithelial-mesenchymal transition (EMT) phenotype in the HMECs. Furthermore, when compared to the wild type BMI1, exogenous expression of the mutant BMI1 led to a significant downregulation of p16INK4a and an efficient bypass of cellular senescence in human diploid fibroblasts. CONCLUSIONS: In summary, our data suggest that the PS domain of BMI1 is involved in its stability and that it negatively regulates function of BMI1 oncoprotein. Our results also suggest that the PS domain of BMI1 could be targeted for the treatment of proliferative disorders such as cancer and aging.

The polycomb group protein BMI1 is a transcriptional target of HDAC inhibitors.

Polycomb group (PcG) proteins are overexpressed in several human malignancies including breast cancer. In particular, aberrant expression of BMI1 and EZH2 has been linked to metastasis and poor prognosis in cancer patients. At present, very little is known about the pharmacological inhibitors of PcG proteins. Here we show that histone deacetylase inhibitors (HDACi) downregulate expression of BMI1. Treatment of MCF10A cells, which are immortal non-transformed breast epithelial cells, and breast cancer cells with HDACi led to decreased expression of BMI1. We further show that downregulation of BMI1 by HDACi results due to the transcriptional downregulation of BMI1 gene. Specifically, we show that primary transcription and promoter activity of BMI1 is suppressed upon treatment with HDACi. Furthermore, downregulation of BMI1 was accompanied by a decrease in histone 2A lysine 119 ubiquitination (H2AK119Ub), which is catalyzed by BMI1 containing polycomb repressive complex 1. HDACi treatment also led to derepression of growth inhibitory genes and putative tumor suppressors, which are known to be silenced by PcG proteins and polycomb repressive complexes (PRCs). In summary, our findings suggest that BMI1 is an important therapy target of HDACi, and that HDACi can be used alone or in combination with other therapies to inhibit growth of tumors that overexpress PcG proteins such as BMI1.

Dietary omega-3 polyunsaturated fatty acids suppress expression of EZH2 in breast cancer cells.

The polycomb group (PcG) protein, enhancer of zeste homologue 2 (EZH2), is overexpressed in several human malignancies including breast cancer. Aberrant expression of EZH2 has been associated with metastasis and poor prognosis in cancer patients. Despite the clear role of EZH2 in oncogenesis and therapy failure, not much is known about chemotherapeutics and chemopreventive agents that can suppress its expression and activity. Here, we show that dietary omega-3 (omega-3) polyunsaturated fatty acids (PUFAs) can regulate the expression of EZH2 in breast cancer cells. The treatment of breast cancer cells with omega-3 PUFAs, but not omega-6 PUFAs, led to downregulation of EZH2. Studies using proteosome inhibitor MG132 suggested that omega-3 PUFAs induce degradation of the PcG protein EZH2 through posttranslational mechanisms. Furthermore, downregulation of EZH2 by omega-3 PUFAs was accompanied by a decrease in histone 3 lysine 27 trimethylation (H3K27me3) activity of EZH2 and upregulation of E-cadherin and insulin-like growth factor binding protein 3, which are known targets of EZH2. Treatment with omega-3 PUFAs also led to decrease in invasion of breast cancer cells, an oncogenic phenotype that is known to be associated with EZH2. Thus, our studies suggest that the PcG protein EZH2 is an important target of omega-3 PUFAs and that downregulation of EZH2 may be involved in the mediation of anti-oncogenic and chemopreventive effects of omega-3 PUFAs.

Bmi1 functions as an oncogene independent of Ink4A/Arf repression in hepatic carcinogenesis.

Bmi1 is a polycomb group proto-oncogene that has been implicated in multiple tumor types. However, its role in hepatocellular carcinoma (HCC) development has not been well studied. In this article, we report that Bmi1 is overexpressed in human HCC samples. When Bmi1 expression is knocked down in human HCC cell lines, it significantly inhibits cell proliferation and perturbs cell cycle regulation. To investigate the role of Bmi1 in promoting liver cancer development in vivo, we stably expressed Bmi1 and/or an activated form of Ras (RasV12) in mouse liver. We found that while Bmi1 or RasV12 alone is not sufficient to promote liver cancer development, coexpression of Bmi1 and RasV12 promotes HCC formation in mice. Tumors induced by Bmi1/RasV12 resemble human HCC by deregulation of genes involved in cell proliferation, apoptosis, and angiogenesis. Intriguingly, we found no evidence that Bmi1 regulates Ink4A/Arf expression in both in vitro and in vivo systems of liver tumor development. In summary, our study shows that Bmi1 can cooperate with other oncogenic signals to promote hepatic carcinogenesis in vivo. Yet Bmi1 functions independent of Ink4A/Arf repression in liver cancer development.

Bmi-1 cooperates with H-Ras to transform human mammary epithelial cells via dysregulation of multiple growth-regulatory pathways.

Elevated expression of Bmi-1 is associated with many cancers, including breast cancer. Here, we examined the oncogenic potential of Bmi-1 in MCF10A cells, a spontaneously immortalized, nontransformed strain of human mammary epithelial cells (HMEC). Bmi-1 overexpression alone in MCF10A cells did not result in oncogenic transformation. However, Bmi-1 co-overexpression with activated H-Ras (RasG12V) resulted in efficient transformation of MCF10A cells in vitro. Although early-passage H-Ras-expressing MCF10A cells were not transformed, late-passage H-Ras-expressing cells exhibited features of transformation in vitro. Early- and late-passage H-Ras-expressing cells also differed in levels of expression of H-Ras and Ki-67, a marker of proliferation. Subsets of early-passage H-Ras-expressing cells exhibited high Ras expression and were negative for Ki-67, whereas most late-passage H-Ras-expressing cells expressed low levels of Ras and were Ki-67 positive. Injection of late-passage H-Ras-expressing cells in severe combined immunodeficient mice formed carcinomas with leiomatous, hemangiomatous, and mast cell components; these tumors were quite distinct from those induced by late-passage cells co-overexpressing Bmi-1 and H-Ras, which formed poorly differentiated carcinomas with spindle cell features. Bmi-1 and H-Ras co-overexpression in MCF10A cells also induced features of epithelial-to-mesenchymal transition. Importantly, Bmi-1 inhibited senescence and permitted proliferation of cells expressing high levels of Ras. Examination of various growth-regulatory pathways suggested that Bmi-1 overexpression together with H-Ras promotes HMEC transformation and breast oncogenesis by deregulation of multiple growth-regulatory pathways by p16(INK4a)-independent mechanisms.