Akt1 is essential for postnatal mammary gland development, function, and the expression of Btn1a1

Cancer invasion and metastasis: Insights from murine pubertal mammary gland morphogenesis

Cancer invasion and metastasis accounts for the majority of cancer related mortality. A better understanding of the players that drive the aberrant invasion and migration of tumors cells will provide critical targets to inhibit metastasis. Postnatal pubertal mammary gland morphogenesis is characterized by highly proliferative, invasive, and migratory normal epithelial cells. Identifying the molecular regulators of pubertal gland development is a promising strategy since tumorigenesis and metastasis is postulated to be a consequence of aberrant reactivation of developmental stages. In this review, we summarize the pubertal morphogenesis regulators that are involved in cancer metastasis and revisit pubertal mammary gland transcriptome profiling to uncover both known and unknown metastasis genes. Our updated list of pubertal morphogenesis regulators shows that most are implicated in invasion and metastasis. This review highlights molecular linkages between development and metastasis and provides a guide for exploring novel metastatic drivers.

The double faced role of xanthine oxidoreductase in cancer

Xanthine oxidoreductase (XOR) is a critical, rate-limiting enzyme that controls the last two steps of purine catabolism by converting hypoxanthine to xanthine and xanthine to uric acid. It also produces reactive oxygen species (ROS) during the catalytic process. The enzyme is generally recognized as a drug target for the therapy of gout and hyperuricemia. The catalytic products uric acid and ROS act as antioxidants or oxidants, respectively, and are involved in pro/anti-inflammatory actions, which are associated with various disease manifestations, including metabolic syndrome, ischemia reperfusion injury, cardiovascular disorders, and cancer. Recently, extensive efforts have been devoted to understanding the paradoxical roles of XOR in tumor promotion. Here, we summarize the expression of XOR in different types of cancer and decipher the dual roles of XOR in cancer by its enzymatic or nonenzymatic activity to provide an updated understanding of the mechanistic function of XOR in cancer. We also discuss the potential to modulate XOR in cancer therapy.

Proteomic analysis of a murine model of lung hypoplasia induced by oligohydramnios

Severe oligohydramnios (OH) due to prolonged loss of amniotic fluid can cause pulmonary hypoplasia. Animal model of pulmonary hypoplasia induced by amniotic fluid drainage is partly attributed to changes in mechanical compression of the lung. Although numerous studies on OH-model have demonstrated changes in several individual proteins, however, the underlying mechanisms for interrupting normal lung development in response to a decrease of amniotic fluid volume are not fully understood. In this study, we used a proteomic approach to explore differences in the expression of a wide range of proteins after induction of OH in a mouse model of pulmonary hypoplasia to find out the signaling/molecular pathways involved in fetal lung development. Liquid chromatography-massspectromery/mass spectrometry analysis found 474 proteins that were differentially expressed in OH-induced hypoplastic lungs in comparison to untouched (UnT) control. Among these proteins, we confirmed the downregulation of AKT1, SP-D, and CD200, and provided proof-of-concept for the first time about the potential role that these proteins could play in fetal lung development.

Endogenous Cyclin D1 Promotes the Rate of Onset and Magnitude of Mitogenic Signaling via Akt1 Ser473 Phosphorylation

Cyclin D1 encodes the regulatory subunit of a holoenzyme that phosphorylates RB and functions as a collaborative nuclear oncogene. The serine threonine kinase Akt plays a pivotal role in the control of cellular metabolism, survival, and mitogenic signaling. Herein, Akt1-mediated phosphorylation of downstream substrates in the mammary gland is reduced by cyclin D1 genetic deletion and is induced by mammary-gland-targeted cyclin D1 overexpression. Cyclin D1 is associated with Akt1 and augments the rate of onset and maximal cellular Akt1 activity induced by mitogens. Cyclin D1 is identified in a cytoplasmic-membrane-associated pool, and cytoplasmic-membrane-localized cyclin D1—but not nuclear-localized cyclin D1—recapitulates Akt1 transcriptional function. These studies identify a novel extranuclear function of cyclin D1 to enhance proliferative functions via augmenting Akt1 phosphorylation at Ser473.

Chen et al. show that the rate of onset and maximal cellular Akt1 activity induced by mitogens was augmented by cyclin D1. Cyclin D1 bound and phosphorylated Akt1 at Ser473. These studies identify a novel extranuclear function of cyclin D1 to enhance proliferative functions via augmenting Akt1 phosphorylation at Ser473.

Transcriptome Analysis Reveals the Potential Role of Long Non-coding RNAs in Mammary Gland of Yak During Lactation and Dry Period

The mammary gland is a remarkably dynamic organ of milk synthesis and secretion, and it experiences drastic structural and metabolic changes during the transition from dry periods to lactation, which involves the expression and regulation of numerous genes and regulatory factors. Long non-coding RNA (lncRNA) has considered as a novel type of regulatory factors involved in a variety of biological processes. However, their role in the lactation cycle of yak is still poorly understood. To reveal the involved mechanism, Ribo-zero RNA sequencing was employed to profile the lncRNA transcriptome in mammary tissue samples from yak at two physiological stages, namely lactation (LP) and dry period (DP). Notably, 1,599 lncRNA transcripts were identified through four rigorous steps and filtered through protein-coding ability. A total of 59 lncRNAs showed significantly different expression between two stages. Accordingly, the results of qRT-PCR were consistent with that of the transcriptome data. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated that target genes of differentially expressed lncRNAs (DELs) were involved in pathways related to lactation, such as ECM-receptor interaction, PI3K-Akt signaling pathway, biosynthesis of amino acids and focal adhesion etc. Finally, we constructed a lncRNA-gene regulatory network containing some well known candidate genes for milk yield and quality traits. This is the first study to demonstrate a global profile of lncRNA expression in the mammary gland of yak. These results contribute to a valuable resource for future genetic and molecular studies on improving milk yield and quality, and help us to gain a better understanding of the molecular mechanisms underlying lactogenesis and mammary gland development of yak.

Spleen tyrosine kinase regulates mammary epithelial cell proliferation in mammary glands of dairy cows

Spleen tyrosine kinase (SYK) is a nonreceptor tyrosine kinase that has been considered a hematopoietic cell-specific signal transducer involved in cell proliferation and differentiation. However, the role of SYK in normal mammary gland is still poorly understood. Here we show that SYK is expressed in mammary glands of dairy cows. Expression of SYK was higher in dry period mammary tissues than in lactating mammary tissues. Knockdown and overexpression of SYK affected dairy cow mammary epithelial cell proliferation as well as the expression of signal molecules involved in proliferation, including protein kinase B (PKB, also known as AKT1), p42/44 mitogen-activated protein kinase (MAPK), and signal transducer and activator of transcription 5 (STAT5). Dual-luciferase reporter assay showed that SYK increased the transcriptional activity of the AKT1 promoter, and cis-elements within the AKT1 promoter region from -439 to -84 bp mediated this regulation. These results suggest that SYK affects mammary epithelial cell proliferation by activating AKT1 at the transcriptional level in mammary glands of dairy cows, which is important for the mammary remodeling process in dry cows as well as for increasing persistency of lactation in lactating cows.

In utero exposure of rats to high-fat diets perturbs gene expression profiles and cancer susceptibility of prepubertal mammary glands

Human studies suggest that high-fat diets (HFDs) increase the risk of breast cancer. The 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis rat model is commonly used to evaluate the effects of lifestyle factors such as HFD on mammary tumor risk. Past studies focused primarily on the effects of continuous maternal exposure on the risk of offspring at the end of puberty (PND50). We assessed the effects of prenatal HFD exposure on cancer susceptibility in prepubertal mammary glands and identified key gene networks associated with such disruption. During pregnancy, dams were fed AIN-93G-based diets with isocaloric high olive oil, butterfat or safflower oil. The control group received AIN-93G. Female offspring were treated with DMBA on PND21. However, a significant increase in tumor volume and a trend of shortened tumor latency were observed in rats with HFD exposure against the controls (P=.048 and P=.067, respectively). Large-volume tumors harbored carcinoma in situ. Transcriptome profiling identified 43 differentially expressed genes in the mammary glands of the HFBUTTER group as compared with control. Rapid hormone signaling was the most dysregulated pathway. The diet also induced aberrant expression of Dnmt3a, Mbd1 and Mbd3, consistent with potential epigenetic disruption. Collectively, these findings provide the first evidence supporting susceptibility of prepubertal mammary glands to DMBA-induced tumorigenesis that can be modulated by dietary fat that involves aberrant gene expression and likely epigenetic dysregulation.

Phosphatidylinositol 3-kinase/Akt signaling as a key mediator of tumor cell responsiveness to radiation

The phosphatidylinositol 3-kinase (PI3K)/Akt pathway is a key cascade downstream of several protein kinases, especially membrane-bound receptor tyrosine kinases, including epidermal growth factor receptor (EGFR) family members. Hyperactivation of the PI3K/Akt pathway is correlated with tumor development, progression, poor prognosis, and resistance to cancer therapies, such as radiotherapy, in human solid tumors. Akt/PKB (Protein Kinase B) members are the major kinases that act downstream of PI3K, and these are involved in a variety of cellular functions, including growth, proliferation, glucose metabolism, invasion, metastasis, angiogenesis, and survival. Accumulating evidence indicates that activated Akt is one of the major predictive markers for solid tumor responsiveness to chemo/radiotherapy. DNA double-strand breaks (DNA-DSB), are the prime cause of cell death induced by ionizing radiation. Preclinical in vitro and in vivo studies have shown that constitutive activation of Akt and stress-induced activation of the PI3K/Akt pathway accelerate the repair of DNA-DSB and, consequently, lead to therapy resistance. Analyzing dysregulations of Akt, such as point mutations, gene amplification or overexpression, which results in the constitutive activation of Akt, might be of special importance in the context of radiotherapy outcomes. Such studies, as well as studies of the mechanism(s) by which activated Akt1 regulates repair of DNA-DSB, might help to identify combinations using the appropriate molecular targeting strategies with conventional radiotherapy to overcome radioresistance in solid tumors. In this review, we discuss the dysregulation of the components of upstream regulators of Akt as well as specific modifications of Akt isoforms that enhance Akt activity. Likewise, the mechanisms by which Akt interferes with repair of DNA after exposure to ionizing radiation, will be reviewed. Finally, the current status of Akt targeting in combination with radiotherapy will be discussed.

Estetrol is a weak estrogen antagonizing estradiol-dependent mammary gland proliferation

Estetrol (E4) is a natural estrogen produced exclusively by the human fetal liver during pregnancy. Its physiological activity remains unknown. In contrast to ethinyl estradiol and estradiol (E2), E4 has a minimal impact on liver cell activity and could provide a better safety profile in contraception or hormone therapy. The aim of this study was to delineate if E4 exhibits an activity profile distinct from that of E2 on mammary gland. Compared with E2, E4 acted as a low-affinity estrogen in both human in vitro and murine in vivo models. E4 was 100 times less potent than E2 to stimulate the proliferation of human breast epithelial (HBE) cells and murine mammary gland in vitro and in vivo respectively. This effect was prevented by fulvestrant and tamoxifen, supporting the notion that ERα (ESR1) is the main mediator of the estrogenic effect of E4 on the breast. Interestingly, when E4 was administered along with E2, it significantly antagonized the strong stimulatory effect of E2 on HBE cell proliferation and on the growth of mammary ducts. This study characterizes for the first time the impact of E4 on mammary gland. Our results highlight that E4 is less potent than E2 and exhibits antagonistic properties toward the proliferative effect of E2 on breast epithelial cells. These data support E4 as a potential new estrogen for clinical use with a reduced impact on breast proliferation.

Hepatocyte growth factor-like protein is a positive regulator of early mammary gland ductal morphogenesis

The Ron receptor tyrosine kinase regulates multiple cellular processes and is important during mammary gland development and tumor progression. Hepatocyte growth factor-like protein [HGFL] is the only known ligand for the Ron receptor and recent studies have identified major roles for HGFL during breast cancer metastasis. Understanding the functional importance HGFL during mammary gland development will provide significant insights onto its contribution during tumor development and metastasis. In this study, we assessed the role of HGFL during postnatal mammary gland development using mice that were either proficient [HGFL +/+] or deficient [HGFL-/-] for HGFL. Postnatal ductal morphology and stromal cell associations were analyzed at multiple time points through puberty until adulthood. HGFL deficiency resulted in several mammary gland developmental defects including smaller terminal end buds [TEBs], significantly fewer TEBs, and delayed ductal outgrowth during early puberty. Additionally, HGFL deficient animals exhibited significantly altered TEB epithelial cell turnover with decreased proliferation and increased apoptosis coupled with decreased TEB diameter. Macrophage recruitment to the TEBs was also significantly decreased in the HGFL-/- mice compared to controls. Moreover, the levels of STAT3 mRNA as well as the phosphorylation status of this protein were lower in the HGFL-/- mammary glands compared to controls. Taken together, our data provide the first evidence for HGFL as a positive regulator of mammary gland ductal morphogenesis by controlling overall epithelial cell turnover, macrophage recruitment, and STAT3 activation in the developing mammary gland. With a function in early mammary gland development, HGFL represents a potential target for the development of novel breast cancer therapies.

Genetically engineered mouse models of PI3K signaling in breast cancer

Breast cancer is the most common type of cancer in women. A substantial fraction of breast cancers have acquired mutations that lead to activation of the phosphoinositide 3-kinase (PI3K) signaling pathway, which plays a central role in cellular processes that are essential in cancer, such as cell survival, growth, division and motility. Oncogenic mutations in the PI3K pathway generally involve either activating mutation of the gene encoding PI3K (PIK3CA) or AKT (AKT1), or loss or reduced expression of PTEN. Several kinases involved in PI3K signaling are being explored as a therapeutic targets for pharmacological inhibition. Despite the availability of a range of inhibitors, acquired resistance may limit the efficacy of single-agent therapy. In this review we discuss the role of PI3K pathway mutations in human breast cancer and relevant genetically engineered mouse models (GEMMs), with special attention to the role of PI3K signaling in oncogenesis, in therapeutic response, and in resistance to therapy. Several sophisticated GEMMs have revealed the cause-and-effect relationships between PI3K pathway mutations and mammary oncogenesis. These GEMMs enable us to study the biology of tumors induced by activated PI3K signaling, as well as preclinical response and resistance to PI3K pathway inhibitors.

Atbf1 regulates pubertal mammary gland development likely by inhibiting the pro-proliferative function of estrogen-ER signaling

ATBF1 is a candidate tumor suppressor that interacts with estrogen receptor (ER) to inhibit the function of estrogen-ER signaling in gene regulation and cell proliferation control in human breast cancer cells. We therefore tested whether Atbf1 and its interaction with ER modulate the development of pubertal mammary gland, where estrogen is the predominant steroid hormone. In an in vitro model of cell differentiation, i.e., MCF10A cells cultured in Matrigel, ATBF1 expression was significantly increased, and knockdown of ATBF1 inhibited acinus formation. During mouse mammary gland development, Atbf1 was expressed at varying levels at different stages, with higher levels during puberty, lower during pregnancy, and the highest during lactation. Knockout of Atbf1 at the onset of puberty enhanced ductal elongation and bifurcation and promoted cell proliferation in both ducts and terminal end buds of pubertal mammary glands. Enhanced cell proliferation primarily occurred in ER-positive cells and was accompanied by increased expression of ER target genes. Furthermore, inactivation of Atbf1 reduced the expression of basal cell markers (CK5, CK14 and CD44) but not luminal cell markers. These findings indicate that Atbf1 plays a role in the development of pubertal mammary gland likely by modulating the function of estrogen-ER signaling in luminal cells and by modulating gene expression in basal cells.

Pleiotrophin (PTN) expression and function and in the mouse mammary gland and mammary epithelial cells

Expression of the heparin-binding growth factor, pleiotrophin (PTN) in the mammary gland has been reported but its function during mammary gland development is not known. We examined the expression of PTN and its receptor ALK (Anaplastic Lymphoma Kinase) at various stages of mouse mammary gland development and found that their expression in epithelial cells is regulated in parallel during pregnancy. A 30-fold downregulation of PTN mRNA expression was observed during mid-pregnancy when the mammary gland undergoes lobular-alveolar differentiation. After weaning of pups, PTN expression was restored although baseline expression of PTN was reduced significantly in mammary glands of mice that had undergone multiple pregnancies. We found PTN expressed in epithelial cells of the mammary gland and thus used a monoclonal anti-PTN blocking antibody to elucidate its function in cultured mammary epithelial cells (MECs) as well as during gland development. Real-time impedance monitoring of MECs growth, migration and invasion during anti-PTN blocking antibody treatment showed that MECs motility and invasion but not proliferation depend on the activity of endogenous PTN. Increased number of mammospheres with laminin deposition after anti-PTN blocking antibody treatment of MECs in 3D culture and expression of progenitor markers suggest that the endogenously expressed PTN inhibits the expansion and differentiation of epithelial progenitor cells by disrupting cell-matrix adhesion. In vivo, PTN activity was found to inhibit ductal outgrowth and branching via the inhibition of phospho ERK1/2 signaling in the mammary epithelial cells. We conclude that PTN delays the maturation of the mammary gland by maintaining mammary epithelial cells in a progenitor phenotype and by inhibiting their differentiation during mammary gland development.