The epithelial-mesenchymal transition (EMT) has been associated with the acquisition of motility, invasiveness, and self-renewal traits. During both normal development and tumor pathogenesis, this ...change in cell phenotype is induced by contextual signals that epithelial cells receive from their microenvironment. The signals that are responsible for inducing an EMT and maintaining the resulting cellular state have been unclear. We describe three signaling pathways, involving transforming growth factor (TGF)-β and canonical and noncanonical Wnt signaling, that collaborate to induce activation of the EMT program and thereafter function in an autocrine fashion to maintain the resulting mesenchymal state. Downregulation of endogenously synthesized inhibitors of autocrine signals in epithelial cells enables the induction of the EMT program. Conversely, disruption of autocrine signaling by added inhibitors of these pathways inhibits migration and self-renewal in primary mammary epithelial cells and reduces tumorigenicity and metastasis by their transformed derivatives.
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► Induction of EMT in mammary epithelial cells depends on collaborating pathways ► Pathways that induce EMT also maintain the resultant cellular state ► Autocrine signaling maintains the mesenchymal and stem-cell traits induced by EMT ► Similar signals maintain both normal and neoplastic mammary stem cells
The HIF transcription factor promotes adaptation to hypoxia and stimulates the growth of certain cancers, including triple-negative breast cancer (TNBC). The HIFα subunit is usually ...prolyl-hydroxylated by EglN family members under normoxic conditions, causing its rapid degradation. We confirmed that TNBC cells secrete glutamate, which we found is both necessary and sufficient for the paracrine induction of HIF1α in such cells under normoxic conditions. Glutamate inhibits the xCT glutamate-cystine antiporter, leading to intracellular cysteine depletion. EglN1, the main HIFα prolyl-hydroxylase, undergoes oxidative self-inactivation in the absence of cysteine both in biochemical assays and in cells, resulting in HIF1α accumulation. Therefore, EglN1 senses both oxygen and cysteine.
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•HIF1 promotes triple-negative breast carcinogenesis•Triple-negative breast cancers secrete large amounts of glutamate•Extracellular glutamate inhibits cystine uptake by the xCT antiporter•Intracellular cysteine depletion directly inhibits the HIF prolyl-hydroxylases
Increased glutamate secretion by triple-negative breast cancer cells affects cellular cysteine levels and drives activation of HIF through disabling EglN1 under normoxic conditions. Thus, EglN1, which is known to sense oxygen, also senses cysteine.
Tumor cells metastasize to distant organs through genetic and epigenetic alterations, including changes in microRNA (miR) expression. Here we find miR-22 triggers epithelial-mesenchymal transition ...(EMT), enhances invasiveness and promotes metastasis in mouse xenografts. In a conditional mammary gland-specific transgenic (TG) mouse model, we show that miR-22 enhances mammary gland side-branching, expands the stem cell compartment, and promotes tumor development. Critically, miR-22 promotes aggressive metastatic disease in MMTV-miR-22 TG mice, as well as compound MMTV-neu or -PyVT-miR-22 TG mice. We demonstrate that miR-22 exerts its metastatic potential by silencing antimetastatic miR-200 through direct targeting of the TET (Ten eleven translocation) family of methylcytosine dioxygenases, thereby inhibiting demethylation of the mir-200 promoter. Finally, we show that miR-22 overexpression correlates with poor clinical outcomes and silencing of the TET-miR-200 axis in patients. Taken together, our findings implicate miR-22 as a crucial epigenetic modifier and promoter of EMT and breast cancer stemness toward metastasis.
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•miR-22 triggers epithelial-mesenchymal transition, invasion, and metastasis•miR-22 enhances murine mammary gland side-branching, stemness, and tumor development•miR-22 antagonizes miR-200 by directly targeting TET family members•Elevated miR-22 expression is linked to poor clinical outcomes in patients
miR-22 targets TET family chromatin modifiers that promote demethylation of miR-200 promoters, dampening the expression of these miRNAs, which play a role in EMT. This pathway modulates tumorigenesis and metastasis in mammary glands and miR-22 could serve as a biomarker for breast cancer metastasis.
Patterns of genomic evolution between primary and metastatic breast cancer have not been studied in large numbers, despite patients with metastatic breast cancer having dismal survival. We sequenced ...whole genomes or a panel of 365 genes on 299 samples from 170 patients with locally relapsed or metastatic breast cancer. Several lines of analysis indicate that clones seeding metastasis or relapse disseminate late from primary tumors, but continue to acquire mutations, mostly accessing the same mutational processes active in the primary tumor. Most distant metastases acquired driver mutations not seen in the primary tumor, drawing from a wider repertoire of cancer genes than early drivers. These include a number of clinically actionable alterations and mutations inactivating SWI-SNF and JAK2-STAT3 pathways.
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•Metastases mostly disseminate late from primary breast tumors, keeping most drivers•Drivers at relapse sample from a wider range of cancer genes than in primary tumors•Mutations in SWI-SNF complex and inactivated JAK-STAT signaling enriched at relapse•Mutational processes similar in primary and relapse; radiotherapy can damage genome
By sequencing primary, locally relapsed, and metastatic breast cancers, Yates et al. show that clones seeding metastasis or relapse disseminate late from primary tumors but continue to acquire mutations, including clinically actionable alterations and mutations inactivating the SWI/SNF and JAK2-STAT3 pathways.
Although poly(ADP-ribose) polymerase (PARP) inhibitors are active in homologous recombination (HR)-deficient cancers, their utility is limited by acquired resistance after restoration of HR. Here, we ...report that dinaciclib, an inhibitor of cyclin-dependent kinases (CDKs) 1, 2, 5, and 9, additionally has potent activity against CDK12, a transcriptional regulator of HR. In BRCA-mutated triple-negative breast cancer (TNBC) cells and patient-derived xenografts (PDXs), dinaciclib ablates restored HR and reverses PARP inhibitor resistance. Additionally, we show that de novo resistance to PARP inhibition in BRCA1-mutated cell lines and a PDX derived from a PARP-inhibitor-naive BRCA1 carrier is mediated by residual HR and is reversed by CDK12 inhibition. Finally, dinaciclib augments the degree of response in a PARP-inhibitor-sensitive model, converting tumor growth inhibition to durable regression. These results highlight the significance of HR disruption as a therapeutic strategy and support the broad use of combined CDK12 and PARP inhibition in TNBC.
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•Dinaciclib is a potent inhibitor of CDK12 and disrupts homologous recombination•Residual HR is a cause of de novo PARP inhibitor resistance in BRCA-mutated cancer•Dinaciclib sensitizes resistant BRCA-mutated breast cancer models to PARP inhibition•In HR-deficient cancer, dinaciclib augments the response afforded by PARP inhibition
Johnson et al. show that CDK12 inhibition, mediated by the small molecule dinaciclib, disrupts residual or restored homologous recombination (HR) in BRCA-associated breast cancer, sensitizing to PARP inhibition. CDK12 inhibition also augments the degree of PARP inhibitor response in HR-deficient breast cancer. Combined CDK12-PARP inhibition is well tolerated in preclinical models.
Breast cancer is a heterogeneous disease with varied morphological appearances, molecular features, behavior, and response to therapy. Current routine clinical management of breast cancer relies on ...the availability of robust clinical and pathological prognostic and predictive factors to support clinical and patient decision making in which potentially suitable treatment options are increasingly available. One of the best-established prognostic factors in breast cancer is histological grade, which represents the morphological assessment of tumor biological characteristics and has been shown to be able to generate important information related to the clinical behavior of breast cancers. Genome-wide microarray-based expression profiling studies have unraveled several characteristics of breast cancer biology and have provided further evidence that the biological features captured by histological grade are important in determining tumor behavior. Also, expression profiling studies have generated clinically useful data that have significantly improved our understanding of the biology of breast cancer, and these studies are undergoing evaluation as improved prognostic and predictive tools in clinical practice. Clinical acceptance of these molecular assays will require them to be more than expensive surrogates of established traditional factors such as histological grade. It is essential that they provide additional prognostic or predictive information above and beyond that offered by current parameters. Here, we present an analysis of the validity of histological grade as a prognostic factor and a consensus view on the significance of histological grade and its role in breast cancer classification and staging systems in this era of emerging clinical use of molecular classifiers.
Cancer susceptibility has been attributed to at least one heterozygous genetic alteration in a tumor suppressor gene (TSG). It has been hypothesized that subtle variations in TSG expression can ...promote cancer development. However, this hypothesis has not yet been definitively supported in vivo. Pten is a TSG frequently lost in human cancer and mutated in inherited cancer-predisposition syndromes. Here we analyze Pten hypermorphic mice (Ptenhy/+), expressing 80% normal levels of Pten. Ptenhy/+ mice develop a spectrum of tumors, with breast tumors occurring at the highest penetrance. All breast tumors analyzed here retained two intact copies of Pten and maintained Pten levels above heterozygosity. Notably, subtle downregulation of Pten altered the steady-state biology of the mammary tissues and the expression profiles of genes involved in cancer cell proliferation. We present an alterative working model for cancer development in which subtle reductions in the dose of TSGs predispose to tumorigenesis in a tissue-specific manner.
Much interest is currently focused on the emerging role of tumor-stroma interactions essential for supporting tumor progression. Carcinoma-associated fibroblasts (CAFs), frequently present in the ...stroma of human breast carcinomas, include a large number of myofibroblasts, a hallmark of activated fibroblasts. These fibroblasts have an ability to substantially promote tumorigenesis. However, the precise cellular origins of CAFs and the molecular mechanisms by which these cells evolve into tumor-promoting myofibroblasts remain unclear. Using a coimplantation breast tumor xenograft model, we show that resident human mammary fibroblasts progressively convert into CAF myofibroblasts during the course of tumor progression. These cells increasingly acquire two autocrine signaling loops, mediated by TGF-β and SDF-1 cytokines, which both act in autostimulatory and cross-communicating fashions. These autocrine-signaling loops initiate and maintain the differentiation of fibroblasts into myofibroblasts and the concurrent tumor-promoting phenotype. Collectively, these findings indicate that the establishment of the self-sustaining TGF-β and SDF-1 autocrine signaling gives rise to tumor-promoting CAF myofibroblasts during tumor progression. This autocrine-signaling mechanism may prove to be an attractive therapeutic target to block the evolution of tumor-promoting CAFs.
Increased number of single nucleotide substitutions is seen in breast and ovarian cancer genomes carrying disease-associated mutations in BRCA1 or BRCA2. The significance of these genome-wide ...mutations is unknown. We hypothesize genome-wide mutation burden mirrors deficiencies in DNA repair and is associated with treatment outcome in ovarian cancer.
The total number of synonymous and non-synonymous exome mutations (Nmut), and the presence of germline or somatic mutation in BRCA1 or BRCA2 (mBRCA) were extracted from whole-exome sequences of high-grade serous ovarian cancers from The Cancer Genome Atlas (TCGA). Cox regression and Kaplan-Meier methods were used to correlate Nmut with chemotherapy response and outcome. Higher Nmut correlated with a better response to chemotherapy after surgery. In patients with mBRCA-associated cancer, low Nmut was associated with shorter progression-free survival (PFS) and overall survival (OS), independent of other prognostic factors in multivariate analysis. Patients with mBRCA-associated cancers and a high Nmut had remarkably favorable PFS and OS. The association with survival was similar in cancers with either BRCA1 or BRCA2 mutations. In cancers with wild-type BRCA, tumor Nmut was associated with treatment response in patients with no residual disease after surgery.
Tumor Nmut was associated with treatment response and with both PFS and OS in patients with high-grade serous ovarian cancer carrying BRCA1 or BRCA2 mutations. In the TCGA cohort, low Nmut predicted resistance to chemotherapy, and for shorter PFS and OS, while high Nmut forecasts a remarkably favorable outcome in mBRCA-associated ovarian cancer. Our observations suggest that the total mutation burden coupled with BRCA1 or BRCA2 mutations in ovarian cancer is a genomic marker of prognosis and predictor of treatment response. This marker may reflect the degree of deficiency in BRCA-mediated pathways, or the extent of compensation for the deficiency by alternative mechanisms.
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