RUNX2 correlates with subtype-specific breast cancer in a human tissue microarray,and ectopic expression of Runx2 perturbs differentiation in the mouse mammary gland

RUNX2, a master regulator of osteogenesis, is oncogenic in the lymphoid lineage; however, little is known about its role in epithelial cancers. Upregulation of RUNX2 in cell lines correlates with increased invasiveness and the capacity to form osteolytic disease in models of breast and prostate cancer. However, most studies have analysed the effects of this gene in a limited number of cell lines and its role in primary breast cancer has not been resolved. Using a human tumour tissue microarray, we show that high RUNX2 expression is significantly associated with oestrogen receptor (ER)/progesterone receptor (PR)/HER2-negative breast cancers and that patients with high RUNX2 expression have a poorer survival rate than those with negative or low expression. We confirm RUNX2 as a gene that has a potentially important functional role in triple-negative breast cancer. To investigate the role of this gene in breast cancer, we made a transgenic model in which Runx2 is specifically expressed in murine mammary epithelium under the control of the mouse mammary tumour virus (MMTV) promoter. We show that ectopic Runx2 perturbs normal development in pubertal and lactating animals, delaying ductal elongation and inhibiting lobular alveolar differentiation. We also show that the Runx2 transgene elicits age-related, pre-neoplastic changes in the mammary epithelium of older transgenic animals, suggesting that elevated RUNX2 expression renders such tissue more susceptible to oncogenic changes and providing further evidence that this gene might have an important, context-dependent role in breast cancer.KEY WORDS: RUNX2, Breast cancer, Transgenic model, Mammary development     

The roles of BECN1 and autophagy in cancer are context dependent

Malignant tissue contains a rare population of multi-potent cells known as cancer stem-like cells (CSCs). Autophagy is an important mechanism in cancer cell survival and tumor growth; it can both suppress malignant transformation and promote the growth of established cancers. However, the molecular mechanisms underlying the tumor-promoting and tumor-suppressing functions of autophagy in CSCs are not understood. Our work demonstrates that a prosurvival autophagic pathway is critical for breast CSC maintenance. Notably, we provide new evidence for the existence of two separate, context-dependent, autophagic programs that are regulated in opposite ways by BECN1.     

Relationship between RUNX1 and AXIN1 in ER-negative versus ER-positive Breast Cancer

RUNX1 plays opposing roles in breast cancer: a tumor suppressor in estrogen receptor-positive (ER⁺) disease and an oncogenic role in ER-negative (ER^?) tumors. Potentially mediating the former, we have recently reported that RUNX1 prevents estrogen-driven suppression of the mRNA encoding the tumor suppressor AXIN1. Accordingly, AXIN1 protein expression was diminished upon RUNX1 silencing in ER⁺ breast cancer cells and was positively correlated with AXIN1 protein expression across tumors with high levels of ER. Here we report the surprising observation that RUNX1 and AXIN1 proteins are strongly correlated in ER^? tumors as well. However, this correlation is not attributable to regulation of AXIN1 by RUNX1 or vice versa. The unexpected correlation between RUNX1, playing an oncogenic role in ER^? breast cancer, and AXIN1, a well-established tumor suppressor hub, may be related to a high ratio between the expression of variant 2 and variant 1 (v2/v1) of AXIN1 in ER^? compared with ER⁺ breast cancer. Although both isoforms are similarly regulated by RUNX1 in estrogen-stimulated ER⁺ breast cancer cells, the higher v2/v1 ratio in ER^? disease is expected to weaken the tumor suppressor activity of AXIN1 in these tumors.     

Frequent Mutation of rs13281615 and Its Association with PVT1 Expression and Cell Proliferation in Breast Cancer

The q24 band of chromosome 8 （8q24） is frequently amplified in human cancers including breast cancer, and several SNPs （single nucleotide polymorphisms） at 8q24, including rs13281615, have been identified for their association with cancer risks. These SNPs are in a ＂gene desert＂ region, and their functions in cancer development remain to be illustrated, although several of the SNPs appear to influence the genes in the ＂desert＂ in a long-range manner, including the v-myc avian myelocytomatosis viral oncogene homolog （MYC） and the non- protein coding plasmacytoma variant translocation 1 （PVT1）, both of which have been implicated in human cancers. In the current study, we examined rs13281615 for its potential role in breast cancer using normal and cancer tissues from 121 Chinese women with breast cancer. In addition to confirming the association of the GG genotype of rs 13281615 with breast cancer risk, we found that germline GG genotype was significantly associated with estrogen receptor （ER） positivity, higher tumor grade and higher proliferation index. We also found frequent somatic mutations （22/121 or 18.2%） of this SNP in breast cancer. Interestingly, the majority of the mutations （17/22 or 77%） involved a G→ A change, resulting in a decrease in the number of cancers with the GG risk genotype and subsequent loss of GG association with higher tumor grade and proliferation index in cancers. Furthermore, PVT1 expression was increased in cancers, and the increase was associated with the GG genotype of rs13281615. These results suggest that the GG genotype of SNP rs13281615 plays a role in breast cancer likely by influencing PVT1 expression, and that during oncogenesis, ＂protective＂ mutations could occur.     

Breast cancer subtypes express distinct receptor repertoires for tumor-associated macrophage derived cytokines

Infiltration of the tumor microenvironment by macrophages is associated with poor outcomes in breast cancer and other solid tumors, however the identity and roles of many of the soluble factors these macrophages produce remains to be elucidated in detail. In addition to producing angiogenic factors (e.g. VEGF), proteases (e.g. MMP9) and immunomodulatory factors (e.g. IL10) which, by modifying the local microenvironment, likely contribute to progression in the majority of solid tumors, we have evaluated the extent to which macrophage cytokines may differentially affect distinct breast cancer subtypes. We identified 23 cytokines produced in a culture model of human tumor-associated macrophages and report that basal and luminal breast cancer cell lines express different repertoires of receptors for these cytokines. These data suggest that tumor-associated macrophages make specific contributions to different breast cancer subtypes and that understanding the importance of these interactions will be crucial to developing subtype-specific therapies targeting the macrophage component of the breast tumor microenvironment.     

Folate Receptor-α (FOLR1) Expression and Function in Triple Negative Tumors

Folate receptor alpha (FOLR1) has been identified as a potential prognostic and therapeutic target in a number of cancers. A correlation has been shown between intense overexpression of FOLR1 in breast tumors and poor prognosis, yet there is limited examination of the distribution of FOLR1 across clinically relevant breast cancer subtypes. To explore this further, we used RNA-seq data from multiple patient cohorts to analyze the distribution of FOLR1 mRNA across breast cancer subtypes comprised of estrogen receptor positive (ER+), human epidermal growth factor receptor positive (HER2+), and triple negative (TNBC) tumors. FOLR1 expression varied within breast tumor subtypes; triple negative/basal tumors were significantly associated with increased expression of FOLR1 mRNA, compared to ER+ and HER2+ tumors. However, subsets of high level FOLR1 expressing tumors were observed in all clinical subtypes. These observations were supported by immunohistochemical analysis of tissue microarrays, with the largest number of 3+ positive tumors and highest H-scores of any subtype represented by triple negatives, and lowest by ER+ tumors. FOLR1 expression did not correlate to common clinicopathological parameters such as tumor stage and nodal status. To delineate the importance of FOLR1 overexpression in triple negative cancers, RNA-interference was used to deplete FOLR1 in overexpressing triple negative cell breast lines. Loss of FOLR1 resulted in growth inhibition, whereas FOLR1 overexpression promoted folate uptake and growth advantage in low folate conditions. Taken together, our data suggests patients with triple negative cancers expressing high FOLR1 expression represent an important population of patients that may benefit from targeted anti-FOLR1 therapy. This may prove particularly helpful for a large number of patients who would typically be classified as triple negative and who to this point have been left without any targeted treatment options.     

Bone Marrow Stromal Antigen 2 (BST-2) DNA Is Demethylated in Breast Tumors and Breast Cancer Cells

Background

Bone marrow stromal antigen 2 (BST-2) is a known anti-viral gene that has been recently identified to be overexpressed in many cancers, including breast cancer. BST-2 is critical for the invasiveness of breast cancer cells and the formation of metastasis in vivo. Although the regulation of BST-2 in immune cells is unraveling, it is unknown how BST-2 expression is regulated in breast cancer. We hypothesized that meta-analyses of BST-2 gene expression and BST-2 DNA methylation profiles would illuminate mechanisms regulating elevated BST-2 expression in breast tumor tissues and cells.

Materials and Methods

We performed comprehensive meta-analyses of BST-2 gene expression and BST-2 DNA methylation in The Cancer Genome Atlas (TCGA) and various Gene Expression Omnibus (GEO) datasets. BST-2 expression levels and BST-2 DNA methylation status at specific CpG sites on the BST-2 gene were compared for various breast tumor molecular subtypes and breast cancer cell lines.

Results

We show that BST-2 gene expression is inversely associated with the methylation status at specific CpG sites in primary breast cancer specimens and breast cancer cell lines. BST-2 demethylation is significantly more prevalent in primary tumors and cancer cells than in normal breast tissues or normal mammary epithelial cells. Demethylation of the BST-2 gene significantly correlates with its mRNA expression. These studies provide the initial evidence that significant differences exist in BST-2 DNA methylation patterns between breast tumors and normal breast tissues, and that BST-2 expression patterns in tumors and cancer cells correlate with hypomethylated BST-2 DNA.

Conclusion

Our study suggests that the DNA methylation pattern and expression of BST-2 may play a role in disease pathogenesis and could serve as a biomarker for the diagnosis of breast cancer.     

Identification of RUNX3 as a component of the MST/Hpo signaling pathway

Recent genetic screens of fly mutants and molecular analysis have revealed that the Hippo (Hpo) pathway controls both cell proliferation and cell death. Deregulation of its human counterpart (the MST pathway) has been implicated in human cancers. However, how this pathway is linked with the known tumor suppressor network remains to be established. RUNX3 functions as a tumor suppressor of gastric cancer, lung cancer, bladder cancer, and colon cancer. Here, we show that RUNX3 is a principal and evolutionarily conserved component of the MST pathway. SAV1/WW45 facilitates the close association between MST2 and RUNX3. MST2, in turn, stimulates the SAV1-RUNX3 interaction. In addition, we show that siRNA-mediated RUNX3 knockdown abolishes MST/Hpo-mediated cell death. By establishing that RUNX3 is an endpoint effector of the MST pathway and that RUNX3 is capable of inducing cell death in cooperation with MST and SAV1, we define an evolutionarily conserved novel regulatory mechanism loop for tumor suppression in human cancers.     

RUNX1 and RUNX2 transcription factors function in opposing roles to regulate breast cancer stem cells

Breast cancer stem cells (BCSCs) are competent to initiate tumor formation and growth and refractory to conventional therapies. Consequently BCSCs are implicated in tumor recurrence. Many signaling cascades associated with BCSCs are critical for epithelial-to-mesenchymal transition (EMT). We developed a model system to mechanistically examine BCSCs in basal-like breast cancer using MCF10AT1 FACS sorted for CD24 (negative/low in BCSCs) and CD44 (positive/high in BCSCs). Ingenuity Pathway Analysis comparing RNA-seq on the CD24^−/low versus CD24^+/high MCF10AT1 indicates that the top activated upstream regulators include TWIST1, TGFβ1, OCT4, and other factors known to be increased in BCSCs and during EMT. The top inhibited upstream regulators include ESR1, TP63, and FAS. Consistent with our results, many genes previously demonstrated to be regulated by RUNX factors are altered in BCSCs. The RUNX2 interaction network is the top significant pathway altered between CD24^−/low and CD24^+/high MCF10AT1. RUNX1 is higher in expression at the RNA level than RUNX2. RUNX3 is not expressed. While, human-specific quantitative polymerase chain reaction primers demonstrate that RUNX1 and CDH1 decrease in human MCF10CA1a cells that have grown tumors within the murine mammary fat pad microenvironment, RUNX2 and VIM increase. Treatment with an inhibitor of RUNX binding to CBFβ for 5 days followed by a 7-day recovery period results in EMT suggesting that loss of RUNX1, rather than increase in RUNX2, is a driver of EMT in early stage breast cancer. Increased understanding of RUNX regulation on BCSCs and EMT will provide novel insight into therapeutic strategies to prevent recurrence.