Cellular geometry and epithelial-mesenchymal plasticity intersect with PIEZO1 in breast cancer cells.

Differences in shape can be a distinguishing feature between different cell types, but the shape of a cell can also be dynamic. Changes in cell shape are critical when cancer cells escape from the primary tumor and undergo major morphological changes that allow them to squeeze between endothelial cells, enter the vasculature, and metastasize to other areas of the body. A shift from rounded to spindly cellular geometry is a consequence of epithelial-mesenchymal plasticity, which is also associated with changes in gene expression, increased invasiveness, and therapeutic resistance. However, the consequences and functional impacts of cell shape changes and the mechanisms through which they occur are still poorly understood. Here, we demonstrate that altering the morphology of a cell produces a remodeling of calcium influx via the ion channel PIEZO1 and identify PIEZO1 as an inducer of features of epithelial-to-mesenchymal plasticity. Combining automated epifluorescence microscopy and a genetically encoded calcium indicator, we demonstrate that activation of the PIEZO1 force channel with the PIEZO1 agonist, YODA 1, induces features of epithelial-to-mesenchymal plasticity in breast cancer cells. These findings suggest that PIEZO1 is a critical point of convergence between shape-induced changes in cellular signaling and epithelial-mesenchymal plasticity in breast cancer cells.

Identification of aberrant luminal progenitors and mTORC1 as a potential breast cancer prevention target in BRCA2 mutation carriers.

Inheritance of a BRCA2 pathogenic variant conveys a substantial life-time risk of breast cancer. Identification of the cell(s)-of-origin of BRCA2-mutant breast cancer and targetable perturbations that contribute to transformation remains an unmet need for these individuals who frequently undergo prophylactic mastectomy. Using preneoplastic specimens from age-matched, premenopausal females, here we show broad dysregulation across the luminal compartment in BRCA2mut/+ tissue, including expansion of aberrant ERBB3lo luminal progenitor and mature cells, and the presence of atypical oestrogen receptor (ER)-positive lesions. Transcriptional profiling and functional assays revealed perturbed proteostasis and translation in ERBB3lo progenitors in BRCA2mut/+ breast tissue, independent of ageing. Similar molecular perturbations marked tumours bearing BRCA2-truncating mutations. ERBB3lo progenitors could generate both ER+ and ER- cells, potentially serving as cells-of-origin for ER-positive or triple-negative cancers. Short-term treatment with an mTORC1 inhibitor substantially curtailed tumorigenesis in a preclinical model of BRCA2-deficient breast cancer, thus uncovering a potential prevention strategy for BRCA2 mutation carriers.

Three-dimensional genome architecture coordinates key regulators of lineage specification in mammary epithelial cells.

Although lineage-specific genes have been identified in the mammary gland, little is known about the contribution of the 3D genome organization to gene regulation in the epithelium. Here, we describe the chromatin landscape of the three major epithelial subsets through integration of long- and short-range chromatin interactions, accessibility, histone modifications, and gene expression. While basal genes display exquisite lineage specificity via distal enhancers, luminal-specific genes show widespread promoter priming in basal cells. Cell specificity in luminal progenitors is largely mediated through extensive chromatin interactions with super-enhancers in gene-body regions in addition to interactions with polycomb silencer elements. Moreover, lineage-specific transcription factors appear to be controlled through cell-specific chromatin interactivity. Finally, chromatin accessibility rather than interactivity emerged as a defining feature of the activation of quiescent basal stem cells. This work provides a comprehensive resource for understanding the role of higher-order chromatin interactions in cell-fate specification and differentiation in the adult mouse mammary gland.

Towards resolution of the intron retention paradox in breast cancer.

BACKGROUND: After many years of neglect in the field of alternative splicing, the importance of intron retention (IR) in cancer has come into focus following landmark discoveries of aberrant IR patterns in cancer. Many solid and liquid tumours are associated with drastic increases in IR, and such patterns have been pursued as both biomarkers and therapeutic targets. Paradoxically, breast cancer (BrCa) is the only tumour type in which IR is reduced compared to adjacent normal breast tissue. METHODS: In this study, we have conducted a pan-cancer analysis of IR with emphasis on BrCa and its subtypes. We explored mechanisms that could cause aberrant and pathological IR and clarified why normal breast tissue has unusually high IR. RESULTS: Strikingly, we found that aberrantly decreasing IR in BrCa can be largely attributed to normal breast tissue having the highest occurrence of IR events compared to other healthy tissues. Our analyses suggest that low numbers of IR events in breast tumours are associated with poor prognosis, particularly in the luminal B subtype. Interestingly, we found that IR frequencies negatively correlate with cell proliferation in BrCa cells, i.e. rapidly dividing tumour cells have the lowest number of IR events. Aberrant RNA-binding protein expression and changes in tissue composition are among the causes of aberrantly decreasing IR in BrCa. CONCLUSIONS: Our results suggest that IR should be considered for therapeutic manipulation in BrCa patients with aberrantly low IR levels and that further work is needed to understand the cause and impact of high IR in other tumour types.

In vivo genome-editing screen identifies tumor suppressor genes that cooperate with Trp53 loss during mammary tumorigenesis.

Breast cancer is a heterogeneous disease that comprises multiple histological and molecular subtypes. To gain insight into mutations that drive breast tumorigenesis, we describe a pipeline for the identification and validation of tumor suppressor genes. Based on an in vivo genome-wide CRISPR/Cas9 screen in Trp53+/- heterozygous mice, we identified tumor suppressor genes that included the scaffold protein Axin1, the protein kinase A regulatory subunit gene Prkar1a, as well as the proof-of-concept genes Pten, Nf1, and Trp53 itself. Ex vivo editing of primary mammary epithelial organoids was performed to further interrogate the roles of Axin1 and Prkar1a. Increased proliferation and profound changes in mammary organoid morphology were observed for Axin1/Trp53 and Prkar1a/Trp53 double mutants compared to Pten/Trp53 double mutants. Furthermore, direct in vivo genome editing via intraductal injection of lentiviruses engineered to express dual short-guide RNAs revealed that mutagenesis of Trp53 and either Prkar1a, Axin1, or Pten markedly accelerated tumor development compared to Trp53-only mutants. This proof-of-principle study highlights the application of in vivo CRISPR/Cas9 editing for uncovering cooperativity between defects in tumor suppressor genes that elicit mammary tumorigenesis.

Calcium Signalling in Medulloblastoma: An In Silico Analysis of the Expression of Calcium Regulating Genes in Patient Samples.

Dysregulation in calcium signalling is implicated in several cancer-associated processes, including cell proliferation, migration, invasion and therapy resistance. Modulators of specific calcium-regulating proteins have been proposed as promising future therapeutic agents for some cancers. Alterations in calcium signalling have been extensively studied in some cancers; however, this area of research is highly underexplored in medulloblastoma (MB), the most common paediatric malignant brain tumour. Current MB treatment modalities are not completely effective and can result in several long-lasting mental complications. Hence, new treatment strategies are needed. In this study, we sought to probe the landscape of calcium signalling regulators to uncover those most likely to be involved in MB tumours. We investigated the expression of calcium signalling regulator genes in MB patients using publicly available datasets. We stratified the expression level of these genes with MB molecular subgroups, tumour metastasis and patient survival to uncover correlations with clinical features. Of particular interest was CACNA1 genes, in which we were able to show a developmentally-driven change in expression within the cerebellum, MB's tissue of origin, highlighting a potential influence on tumour incidence. This study lays a platform for future investigations into molecular regulators of calcium signalling in MB formation and progression.

Single cell transcriptome atlas of mouse mammary epithelial cells across development.

BACKGROUND: Heterogeneity within the mouse mammary epithelium and potential lineage relationships have been recently explored by single-cell RNA profiling. To further understand how cellular diversity changes during mammary ontogeny, we profiled single cells from nine different developmental stages spanning late embryogenesis, early postnatal, prepuberty, adult, mid-pregnancy, late-pregnancy, and post-involution, as well as the transcriptomes of micro-dissected terminal end buds (TEBs) and subtending ducts during puberty. METHODS: The single cell transcriptomes of 132,599 mammary epithelial cells from 9 different developmental stages were determined on the 10x Genomics Chromium platform, and integrative analyses were performed to compare specific time points. RESULTS: The mammary rudiment at E18.5 closely aligned with the basal lineage, while prepubertal epithelial cells exhibited lineage segregation but to a less differentiated state than their adult counterparts. Comparison of micro-dissected TEBs versus ducts showed that luminal cells within TEBs harbored intermediate expression profiles. Ductal basal cells exhibited increased chromatin accessibility of luminal genes compared to their TEB counterparts suggesting that lineage-specific chromatin is established within the subtending ducts during puberty. An integrative analysis of five stages spanning the pregnancy cycle revealed distinct stage-specific profiles and the presence of cycling basal, mixed-lineage, and 'late' alveolar intermediates in pregnancy. Moreover, a number of intermediates were uncovered along the basal-luminal progenitor cell axis, suggesting a continuum of alveolar-restricted progenitor states. CONCLUSIONS: This extended single cell transcriptome atlas of mouse mammary epithelial cells provides the most complete coverage for mammary epithelial cells during morphogenesis to date. Together with chromatin accessibility analysis of TEB structures, it represents a valuable framework for understanding developmental decisions within the mouse mammary gland.

Activation of the Ion Channel TRPV4 Induces Epithelial to Mesenchymal Transition in Breast Cancer Cells.

Epithelial to mesenchymal transition (EMT) in cancer is important in therapeutic resistance and invasiveness. Calcium signaling is key to the induction of EMT in breast cancer cells. Although inhibition of specific calcium-permeable ion channels regulates the induction of a sub-set of EMT markers in breast cancer cells, it is still unclear if activation of a specific calcium channel can be a driver for the induction of EMT events. In this study, we exploited the availability of a selective pharmacological activator of the calcium-permeable ion channel TRPV4 to assess the direct role of calcium influx in EMT marker induction. Gene association studies revealed a link between TRPV4 and gene-ontologies associated with EMT and poorer relapse-free survival in lymph node-positive basal breast cancers. TRPV4 was an important component of the calcium influx phase induced in MDA-MB-468 breast cancer cells by the EMT inducer epidermal growth factor (EGF). Pharmacological activation of TRPV4 then drove the induction of a variety of EMT markers in breast cancer cells. These studies demonstrate that calcium influx through specific pathways appears to be sufficient to trigger EMT events.

Transient receptor potential cation channel subfamily V and breast cancer.

Transient receptor potential cation channel subfamily V (TRPV) channels play important roles in a variety of cellular processes. One example includes the sensory role of TRPV1 that is sensitive to elevated temperatures and acidic environments and is activated by the hot pepper component capsaicin. Another example is the importance of the highly Ca2+ selective channels TRPV5 and TRPV6 in Ca2+ absorption/reabsorption in the intestine and kidney. However, in some cases such as TRPV4 and TRPV6, breast cancer cells appear to overexpress TRPV channels. Moreover, TRPV mediated Ca2+ influx may contribute to enhanced breast cancer cell proliferation and other processes important in tumor progression such as angiogenesis. It appears that the overexpression of some TRPV channels in breast cancer and/or their involvement in breast cancer cell processes, processes important in the tumor microenvironment or pain may make some TRPV channels potential targets for breast cancer therapy. In this review, we provide an overview of TRPV expression in breast cancer subtypes, the roles of TRPV channels in various aspects of breast cancer progression and consider implications for future therapeutic approaches.

NCS-1 expression is higher in basal breast cancers and regulates calcium influx and cytotoxic responses to doxorubicin.

Neuronal calcium sensor-1 (NCS-1) is a positive modulator of IP3 receptors and was recently associated with poorer survival in breast cancers. However, the association between NCS-1 and breast cancer molecular subtypes and the effects of NCS-1 silencing on calcium (Ca2+ ) signaling in breast cancer cells remain unexplored. Herein, we report for the first time an increased expression of NCS-1 in breast cancers of the basal molecular subtype, a subtype associated with poor prognosis. Using MDA-MB-231 basal breast cancer cells expressing the GCaMP6m Ca2+ indicator, we showed that NCS-1 silencing did not result in major changes in cytosolic free Ca2+ increases as a result of endoplasmic reticulum Ca2+ store mobilization. However, NCS-1 silencing suppressed unstimulated basal Ca2+ influx. NCS-1 silencing in MDA-MB-231 cells also promoted necrotic cell death induced by the chemotherapeutic drug doxorubicin (1 µm). The effect of NCS-1 silencing on cell death was phenocopied by silencing of ORAI1, a Ca2+ store-operated Ca2+ channel that maintains Ca2+ levels in the endoplasmic reticulum Ca2+ store and whose expression was significantly positively correlated with NCS-1 in clinical breast cancer samples. This newly identified association between NCS-1 and basal breast cancers, together with the identification of the role of NCS-1 in the regulation of the effects of doxorubicin in MDA-MB-231 breast cancer cells, suggests that NCS-1 and/or pathways regulated by NCS-1 may be important in the treatment of basal breast cancers in women.

MicroRNA-196a is regulated by ER and is a prognostic biomarker in ER+ breast cancer.

BACKGROUND: MicroRNAs are potent post-transcriptional regulators involved in all hallmarks of cancer. Mir-196a is transcribed from two loci and has been implicated in a wide range of developmental and pathogenic processes, with targets including Hox, Fox, Cdk inhibitors and annexins. Genetic variants and altered expression of MIR196A are associated with risk and progression of multiple cancers including breast cancer, however little is known about the regulation of the genes encoding this miRNA, nor the impact of variants therein. METHODS: Genomic data and chromatin interaction analysis were used to discover functional promoter and enhancer elements for MIR196A. Expression data were used to associate MIR196A with mechanisms of resistance, breast cancer subtypes and prognosis. RESULTS: Here we demonstrate that MIR196A displays complex and dynamic expression patterns, in part controlled by long-range transcriptional regulation between promoter and enhancer elements bound by ERα. Expression of this miRNA is significantly increased in drug-resistant models of hormone-receptor positive disease. The expression of MIR196A also proves to be a robust prognostic factor for patients with advanced and post-menopausal ER+ disease. CONCLUSION: This work sheds light on the normal and abnormal regulation of MIR196A and provides a novel stratification method for therapeutically resistant breast cancer.

ORAI1 and ORAI3 in Breast Cancer Molecular Subtypes and the Identification of ORAI3 as a Hypoxia Sensitive Gene and a Regulator of Hypoxia Responses.

The remodeling of specific calcium-permeable ion channels is a feature of some breast cancer subtypes. ORAI1 is a protein that forms a calcium-permeable ion channel responsible for store-operated calcium entry (SOCE) in a variety of cell types. ORAI3, a related isoform, is not a regulator of SOCE in most cell types. However, ORAI3 does control SOCE in many estrogen receptor-positive breast cancer cell lines, where it also controls proliferation. ORAI1 is a well-characterized regulator of the proliferation and migration of many basal breast cancer cells; however, the role of ORAI3 in these types of breast cancer cells remains unclear. Here, we sought to define ORAI1 and ORAI3 expression in breast cancer cell lines of different molecular subtypes and assess the potential role and regulation of ORAI3 in basal breast cancer cells. Our study demonstrates that elevated ORAI1 is a feature of basal-like breast cancers, while elevated ORAI3 is a feature of luminal breast cancers. Intriguingly, we found that ORAI3 is over-expressed in the mesenchymal subtype of triple-negative breast cancer. Given this, we assessed ORAI3 levels in the presence of two inducers of the mesenchymal phenotype, hypoxia and epidermal growth factor (EGF). Hypoxia induced ORAI3 levels in basal breast cancer cell lines through a pathway involving hypoxia-inducible factor-1 alpha (HIF1α. The silencing of ORAI3 attenuated hypoxia-associated phosphorylation of the EGF receptor (EGFR) and the expression of genes associated with cell migration and inflammatory/immune responses in the MDA-MB-468 model of basal breast cancer. Although elevated ORAI3 levels were not associated with survival; basal, estrogen receptor-negative and triple-negative breast cancers with high ORAI3 and low ORAI1 levels were associated with poorer clinical outcomes. This study defines ORAI3 as a potential fine-tuner for processes relevant to the progression of basal breast cancers.

MiR-29b-1-5p is altered in BRCA1 mutant tumours and is a biomarker in basal-like breast cancer.

Depletion of BRCA1 protein in mouse mammary glands results in defects in lactational development and increased susceptibility to mammary cancer. Extensive work has focussed on the role of BRCA1 in the normal breast and in the development of breast cancer, the cell of origin for BRCA1 tumours and the protein-coding genes altered in BRCA1 deficient cells. However, the role of non-coding RNAs in BRCA1-deficient cells is poorly understood. To evaluate miRNA expression in BRCA1 deficient mammary cells, RNA sequencing was performed on the mammary glands of Brca1 knockout mice. We identified 140 differentially expressed miRNAs, 9 of which were also differentially expressed in human BRCA1 breast tumours or familial non-BRCA1 patients and during normal gland development. We show that BRCA1 binds to putative cis-elements in promoter regions of the miRNAs with the potential to regulate their expression, and that four miRNAs (miR-29b-1-5p, miR-664, miR-16-2 and miR-744) significantly stratified the overall survival of basal-like tumours. Importantly the prognostic value of miR-29b-1-5p was higher in significance than several commonly used clinical biomarkers. These results emphasise the role of Brca1 in modulating expression of miRNAs and highlights the potential for BRCA1 regulated miRNAs to be informative biomarkers associated with BRCA1 loss and survival in breast cancer.

Canonical PRC2 function is essential for mammary gland development and affects chromatin compaction in mammary organoids.

Distinct transcriptional states are maintained through organization of chromatin, resulting from the sum of numerous repressive and active histone modifications, into tightly packaged heterochromatin versus more accessible euchromatin. Polycomb repressive complex 2 (PRC2) is the main mammalian complex responsible for histone 3 lysine 27 trimethylation (H3K27me3) and is integral to chromatin organization. Using in vitro and in vivo studies, we show that deletion of Suz12, a core component of all PRC2 complexes, results in loss of H3K27me3 and H3K27 dimethylation (H3K27me2), completely blocks normal mammary gland development, and profoundly curtails progenitor activity in 3D organoid cultures. Through the application of mammary organoids to bypass the severe phenotype associated with Suz12 loss in vivo, we have explored gene expression and chromatin structure in wild-type and Suz12-deleted basal-derived organoids. Analysis of organoids led to the identification of lineage-specific changes in gene expression and chromatin structure, inferring cell type-specific PRC2-mediated gene silencing of the chromatin state. These expression changes were accompanied by cell cycle arrest but not lineage infidelity. Together, these data indicate that canonical PRC2 function is essential for development of the mammary gland through the repression of alternate transcription programs and maintenance of chromatin states.

TRPC1 is a differential regulator of hypoxia-mediated events and Akt signalling in PTEN-deficient breast cancer cells.

Hypoxia is a feature of the tumour microenvironment that promotes invasiveness, resistance to chemotherapeutics and cell survival. Our studies identify the transient receptor potential canonical-1 (TRPC1) ion channel as a key component of responses to hypoxia in breast cancer cells. This regulation includes control of specific epithelial to mesenchymal transition (EMT) events and hypoxia-mediated activation of signalling pathways such as activation of the EGFR, STAT3 and the autophagy marker LC3B, through hypoxia-inducible factor-1α (HIF1α)-dependent and -independent mechanisms. TRPC1 regulated HIF1α levels in PTEN-deficient MDA-MB-468 and HCC1569 breast cancer cell lines. This regulation arises from effects on the constitutive translation of HIF1α under normoxic conditions via an Akt-dependent pathway. In further support of the role of TRPC1 in EMT, its expression is closely associated with EMT- and metastasis-related genes in breast tumours, and is enhanced in basal B breast cancer cell lines. TRPC1 expression is also significantly prognostic for basal breast cancers, particularly those classified as lymph node positive. The defined roles of TRPC1 identified here could be therapeutically exploited for the control of oncogenic pathways in breast cancer cells.

Long-range regulators of the lncRNA HOTAIR enhance its prognostic potential in breast cancer.

Predicting response to endocrine therapy and survival in oestrogen receptor positive breast cancer is a significant clinical challenge and novel prognostic biomarkers are needed. Long-range regulators of gene expression are emerging as promising biomarkers and therapeutic targets for human diseases, so we have explored the potential of distal enhancer elements of non-coding RNAs in the prognostication of breast cancer survival. HOTAIR is a long non-coding RNA that is overexpressed, promotes metastasis and is predictive of decreased survival. Here, we describe a long-range transcriptional enhancer of the HOTAIR gene that binds several hormone receptors and associated transcription factors, interacts with the HOTAIR promoter and augments transcription. This enhancer is dependent on Forkhead-Box transcription factors and functionally interacts with a novel alternate HOTAIR promoter. HOTAIR expression is negatively regulated by oestrogen, positively regulated by FOXA1 and FOXM1, and is inversely correlated with oestrogen receptor and directly correlated with FOXM1 in breast tumours. The combination of HOTAIR and FOXM1 enables greater discrimination of endocrine therapy responders and non-responders in patients with oestrogen receptor positive breast cancer. Consistent with this, HOTAIR expression is increased in cell-line models of endocrine resistance. Analysis of breast cancer gene expression data indicates that HOTAIR is co-expressed with FOXA1 and FOXM1 in HER2-enriched tumours, and these factors enhance the prognostic power of HOTAIR in aggressive HER2+ breast tumours. Our study elucidates the transcriptional regulation of HOTAIR, identifies HOTAIR and its regulators as novel biomarkers of patient response to endocrine therapy and corroborates the importance of transcriptional enhancers in cancer.

The calcium pump plasma membrane Ca(2+)-ATPase 2 (PMCA2) regulates breast cancer cell proliferation and sensitivity to doxorubicin.

Regulation of Ca(2+) transport is vital in physiological processes, including lactation, proliferation and apoptosis. The plasmalemmal Ca(2+) pump isoform 2 (PMCA2) a calcium ion efflux pump, was the first protein identified to be crucial in the transport of Ca(2+) ions into milk during lactation in mice. In these studies we show that PMCA2 is also expressed in human epithelia undergoing lactational remodeling and also report strong PMCA2 staining on apical membranes of luminal epithelia in approximately 9% of human breast cancers we assessed. Membrane protein expression was not significantly associated with grade or hormone receptor status. However, PMCA2 mRNA levels were enriched in Basal breast cancers where it was positively correlated with survival. Silencing of PMCA2 reduced MDA-MB-231 breast cancer cell proliferation, whereas silencing of the related isoforms PMCA1 and PMCA4 had no effect. PMCA2 silencing also sensitized MDA-MB-231 cells to the cytotoxic agent doxorubicin. Targeting PMCA2 alone or in combination with cytotoxic therapy may be worthy of investigation as a therapeutic strategy in breast cancer. PMCA2 mRNA levels are also a potential tool in identifying poor responders to therapy in women with Basal breast cancer.

The voltage gated Ca(2+)-channel Cav3.2 and therapeutic responses in breast cancer.

BACKGROUND: Understanding the cause of therapeutic resistance and identifying new biomarkers in breast cancer to predict therapeutic responses will help optimise patient care. Calcium (Ca(2+))-signalling is important in a variety of processes associated with tumour progression, including breast cancer cell migration and proliferation. Ca(2+)-signalling is also linked to the acquisition of multidrug resistance. This study aimed to assess the expression level of proteins involved in Ca(2+)-signalling in an in vitro model of trastuzumab-resistance and to assess the ability of identified targets to reverse resistance and/or act as potential biomarkers for prognosis or therapy outcome. METHODS: Expression levels of a panel of Ca(2+)-pumps, channels and channel regulators were assessed using RT-qPCR in resistant and sensitive age-matched SKBR3 breast cancer cells, established through continuous culture in the absence or presence of trastuzumab. The role of Cav3.2 in the acquisition of trastuzumab-resistance was assessed through pharmacological inhibition and induced overexpression. Levels of Cav3.2 were assessed in a panel of non-malignant and malignant breast cell lines using RT-qPCR and in patient samples representing different molecular subtypes (PAM50 cohort). Patient survival was also assessed in samples stratified by Cav3.2 expression (METABRIC and KM-Plotter cohort). RESULTS: Increased mRNA of Cav3.2 was a feature of both acquired and intrinsic trastuzumab-resistant SKBR3 cells. However, pharmacological inhibition of Cav3.2 did not restore trastuzumab-sensitivity nor did Cav3.2 overexpression induce the expression of markers associated with resistance, suggesting that Cav3.2 is not a driver of trastuzumab-resistance. Cav3.2 levels were significantly higher in luminal A, luminal B and HER2-enriched subtypes compared to the basal subtype. High levels of Cav3.2 were associated with poor outcome in patients with oestrogen receptor positive (ER+) breast cancers, whereas Cav3.2 levels were correlated positively with patient survival after chemotherapy in patients with HER2-positive breast cancers. CONCLUSION: Our study identified elevated levels of Cav3.2 in trastuzumab-resistant SKBR3 cell lines. Although not a regulator of trastuzumab-resistance in HER2-positive breast cancer cells, Cav3.2 may be a potential differential biomarker for survival and treatment response in specific breast cancer subtypes. These studies add to the complex and diverse role of Ca(2+)-signalling in breast cancer progression and treatment.

Non-coding RNAs in Mammary Gland Development and Disease.

Non-coding RNAs (ncRNAs) are untranslated RNA molecules that function to regulate the expression of numerous genes and associated biochemical pathways and cellular functions. NcRNAs include small interfering RNAs (siRNAs), microRNAs (miRNAs), PIWI-interacting RNAs (piRNAs), small nucleolar RNAs (snoRNAs) and long non-coding RNAs (lncRNAs). They participate in the regulation of all developmental processes and are frequently aberrantly expressed or functionally defective in disease. This Chapter will focus on the role of ncRNAs, in particular miRNAs and lncRNAs, in mammary gland development and disease.