Progesterone/RANKL is a major regulatory axis in the human breast.

Estrogens and progesterones are major drivers of breast development but also promote carcinogenesis in this organ. Yet, their respective roles and the mechanisms underlying their action in the human breast are unclear. Receptor activator of nuclear factor κB ligand (RANKL) has been identified as a pivotal paracrine mediator of progesterone function in mouse mammary gland development and mammary carcinogenesis. Whether the factor has the same role in humans is of clinical interest because an inhibitor for RANKL, denosumab, is already used for the treatment of bone disease and might benefit breast cancer patients. We show that progesterone receptor (PR) signaling failed to induce RANKL in PR(+) breast cancer cell lines and in dissociated, cultured breast epithelial cells. In clinical specimens from healthy donors and intact breast tissue microstructures, hormone response was maintained and RANKL expression was under progesterone control, which increased RNA stability. RANKL was sufficient to trigger cell proliferation and was required for progesterone-induced proliferation. The findings were validated in vivo where RANKL protein expression in the breast epithelium correlated with serum progesterone levels and the protein was expressed in a subset of luminal cells that express PR. Thus, important hormonal control mechanisms are conserved across species, making RANKL a potential target in breast cancer treatment and prevention.

Simple mucin-type carbohydrate antigens (T, sialosyl T, Tn and sialosyl-Tn) in breast carcinogenesis

Immunohistochemical analysis of the expression of simple mucin-type carbohydrate antigens (Tn, sialyl-Tn and T) was performed in a series of 43 cases of intraductal hyperplasia without atypia, 9 cases of intraductal hyperplasia with atypia, 54 cases of ductal carcinoma in situ (DCIS) and 26 cases of invasive breast carcinoma. We also studied 36 cases of isolated breast normal epithelium, 20 cases of 'normal' breast epithelium adjacent to neoplasms and 14 cases of apocrine metaplasia. All antigens were detected in different frequencies in normal, hyperplastic, metaplastic and neoplastic breast epithelium. Tn and sialyl-Tn are expressed more frequently in malignant than in benign breast epithelium; while Tn expression increases from normal to invasive carcinomas, sialyl-Tn increases until DCIS and drops in invasive carcinomas, suggesting that either there is a failure of a proportion of DCIS to progress to invasive carcinoma or loss of expression of sialyl-Tn when some carcinomas become invasive. The high frequency of Tn and sialyl-Tn expression in breast intraductal proliferations probably reflects incomplete glycosylation in these lesions, which is a well-known tumour-associated phenomenon and supports the assumption that such lesions are putative precursors of breast cancer. T antigen was expressed in all groups studied, but its prevalence differed significantly between normal and neoplastic epithelium. The expression of these antigens in epithelium adjacent to carcinomas is similar to that found in isolated normal breast epithelium, whereas apocrine metaplasia has a pattern of simple mucin-type glycosylation that is specific and distinct from that of the normal breast epithelium, with a high frequency of marked expression of Tn and sialyl-Tn. The similarity of the pattern of expression of simple mucin-type antigens in metaplasia and malignant neoplasia reduces the usefulness of these markers from a diagnostic standpoint.

The effect of protein tyrosine phosphatase SHP1 on tumorigenicity of the MDA -MB231 breast cancer cells

SHP1 is a cytosolic protein tyrosine phosphatase that contains two SH2 domains. It is highly expressed in hematopoietic cells and expressed in normal epithelium at lower levels. While SHP1 in hematopoietic cells is thought to be a negative regulator of cellular signaling by associating with and dephosphorylating various receptors and their downstream effectors after they become activated, its precise function in epithelium remains to be understood. The potential involvement of SHP1 in human tumorigenesis has been hypothesized from the findings that SHP1 can interact with, dephosphorylate, and regulate the activity of several protein tyrosine kinases (PTKs) implicated in human cancer. These PTKs include epidermal growth factor receptor (EGFR) and Src. Such speculation is also supported by the report that SHP1 is overexpressed in human ovarian cancers. ^ Here we report, for the first time, that the levels of SHP1 expression and activity are altered in human breast cancer cells in comparison with normal breast epithelium. In particular, SHP1 expression is nearly lost in the breast cancer cell lines MDA-MB231 and MDA-MB435. After the re-introduction of SHP1 both in wild type (wt) and enzymatically inactive (dn) forms, into the MDA-MB231 cells, we observed no changes in cellular proliferation. However, the overexpression of wt SHP1 led to increased anchorage-independent growth in the MDA-MB231 cells. SHP1 phosphatase activity is essential for such an increase since the overexpression of dn SHP1 had no effect. Enhanced turnorigenicity in nude mice was also observed in the MDA-MB231 cells overexpressing wt SHP1, but not dn SHP1, suggesting the crucial function of SHP1 enzymatic activity in this process. Our observations in this study indicate that SHP1 promotes tumorigenesis by a mechanism or mechanisms apart from enchancing angiogenesis. In addition, we have found no evidence that the overexpression of SHP1 could affect metastatic potential in the MDA-MB231 cells. ^ In the MDA-MB231 cells stably transfected with either wt or dn SHP1 the peak level of EGFR tyrosine phosphorylation induced by EGF, as well as the sensitivity to EGF stimulation, was not altered. However, the overexpression of wt SHP1 led to a slight increase in the kinetics of EGFR dephosphorylation, whereas the overexpression of dn SHP1 led to slightly delayed kinetics of EGFR dephosphorylation. The overexpression of either the wt or dn SHP1 did not lead to any significant increase in Src kinase activity. ^ In NIH3T3 cells, the transient overexpression of SHP1 led to no significant changes in MAP kinase (ERK2) activation by EGF or Akt activation by PDGF. In 3T3H4 cells, the transient overexpression of SHP1 led to no significant changes in MAP kinase (ERK2) activation by heregulin. The transient overexpression of wt SHP1 in the MDA-MB231 cells caused an apparent increase, ranging from 10% to 20%, in the G0/G1 population of the cells with a corresponding decrease in the S phase population. ^ In order to understand the mechanisms by which SHP1 exerts its positive effect on the tumorigenic potential of the MDA-MB231 cells, we employed two-dimensional electrophoresis in an attempt to identify cellular protein(s) with significantly altered tyrosine phosphorylation level upon wt SHP1 overexpression. The overexpression of wt SHP1 but not dn SHP1, leads increased tyrosine phosphorylation of a protein with a molecular weight of approximately 40 kDa and a pI between 5.9 to 6.6. ^

Antagonistic roles of Notch and p63 in controlling mammary epithelial cell fates.

The breast epithelium has two major compartments, luminal and basal cells, that are established and maintained by poorly understood mechanisms. The p53 homolog, p63, is required for the formation of mammary buds, but its function in the breast after birth is unknown. We show that in primary human breast epithelial cells, maintenance of basal cell characteristics depends on continued expression of the p63 isoform, DeltaNp63, which is expressed in the basal compartment. Forced expression of DeltaNp63 in purified luminal cells confers a basal phenotype. Notch signaling downmodulates DeltaNp63 expression and mimics DeltaNp63 depletion, whereas forced expression of DeltaNp63 partially counteracts the effects of Notch. Consistent with Notch activation specifying luminal cell fate in the mammary gland, Notch signaling activity is specifically detected in mice at sites of pubertal ductal morphogenesis where luminal cell fate is determined. Basal cells in which Notch signaling is active show decreased p63 expression. Both constitutive expression of DeltaNp63 and ablation of Notch signaling are incompatible with luminal cell fate. Thus, the balance between basal and luminal cell compartments of the breast is regulated by antagonistic functions of DeltaNp63 and Notch.Cell Death and Differentiation advance online publication, 9 April 2010; doi:10.1038/cdd.2010.37.

Müllerian adenosarcoma of the uterus with sarcomatous overgrowth following tamoxifen treatment for breast cancer

Müllerian adenosarcoma with sarcomatous overgrowth presented by a 52-year-old female patient after adjuvant tamoxifen treatment for breast carcinoma is described. The diagnosis was made on histological basis after curettage and complementary total hysterectomy with bilateral salpingo-oophorectomy. The immunohistochemical study showed high expression of estrogen receptors in the epithelial component of the lesion and irregularly positive findings in the stroma. The proliferative activity evaluated by Ki-67 immunoexpression was higher in the stroma than the epithelium. Some of the stromal cells showed rhabdomyoblastic differentiation. The association of tamoxifen use and development of mesenchymal neoplasms is discussed.

Bcl9/Bcl9l are critical for Wnt-mediated regulation of stem cell traits in colon epithelium and adenocarcinomas.

Canonical Wnt signaling plays a critical role in stem cell maintenance in epithelial homeostasis and carcinogenesis. Here, we show that in the mouse this role is critically mediated by Bcl9/Bcl9l, the mammalian homologues of Legless, which in Drosophila is required for Armadillo/beta-catenin signaling. Conditional ablation of Bcl9/Bcl9l in the intestinal epithelium, where the essential role of Wnt signaling in epithelial homeostasis and stem cell maintenance is well documented, resulted in decreased expression of intestinal stem cell markers and impaired regeneration of ulcerated colon epithelium. Adenocarcinomas with aberrant Wnt signaling arose with similar incidence in wild-type and mutant mice. However, transcriptional profiles were vastly different: Whereas wild-type tumors displayed characteristics of epithelial-mesenchymal transition (EMT) and stem cell-like properties, these properties were largely abrogated in mutant tumors. These findings reveal an essential role for Bcl9/Bcl9l in regulating a subset of Wnt target genes involved in controlling EMT and stem cell-related features and suggest that targeting the Bcl9/Bcl9l arm of Wnt signaling in Wnt-activated cancers might attenuate these traits, which are associated with tumor invasion, metastasis, and resistance to therapy.

Breast stem cells and hormonal mechanisms in carcinogenesis

A woman's risk of breast cancer is strongly affected by her reproductive history. The hormonal milieu is also a key determinant of the course of the disease. Combining mouse genetics with tissue recombination techniques, we have established that the female reproductive hormones, estrogens, progesterone, and prolactin, act sequentially on the mammary epithelium to trigger distinct developmental steps. The hormones impinge directly on a subset of luminal mammary epithelial cells that express the respective hormone receptors and act as sensor cells translating and amplifying systemic signals into local stimuli. Local signaling is stage and age specific. During puberty, estrogens promote proliferation using the EGF family member, amphiregulin, as essential paracrine mediator. In adulthood, progesterone, rather than estrogen, is the major inducer of stem cell activation and cell proliferation of the mammary epithelium. Hormonal signaling modulates crucial developmental pathways that impinge on mammary stem cell populations, while Notch signaling, by inhibiting p63, is central to mammary cell fate determination. Cell proliferation occurs in two waves. The first results from direct stimulation of the small fraction of hormone receptor positive cells. It is followed by a second wave of progesterone-induced proliferation involving mostly hormone receptor negative cells, in which RANKL is a key mediator. A model in which repeated activation of paracrine signaling by progesterone with resulting stem cell activation promotes breast carcinogenesis is proposed.

Characterization of BMP signaling in breast development and tumorigenesis

Résumé L'influence des hormones reproductives sur le développement du cancer du sein a été établie au travers de nombreuse études épidémiologiques. Nous avons précédemment démontré que le gène Wnt-4 est un médiateur essentiel de la progestérone dans le développement lobulo-alvéolaire de l'épithélium mammaire. De plus, le rôle de la voie de signalisation Wnt dans la tumorigénèse de la glande mammaire mutine est largement établi. Pour comprendre sa fonction dans le cancer du sein, nous avons activée cette voie en surexprimant le gène Wnt-1 dans des cellules épithéliales primaires de sein, au moyen d'un rétrovirus. Ceci a conduit à la transformation oncogénique de ces cellules et à l'obtention d'un modèle de carcinogénèse du sein dénommé Wnt-1 HMEC. L'analyse de l'expression des gènes induits par la surexpression de Wnt-1 dans ces cellules, a permis d'identifier les gènes BMP4 et 7. Alors que des analyses de RT-PCR ont montré leur forte expression dans les cellules Wnt-1-HMECs, la présence d'une grande quantité de la protéine BMP7 a été constatée dans les tumeurs dérivées de ces cellules. L'importante phosphorylation des Smad 1, 5, S dans les Wnt-1 HMECs indique l'activation de la voie BMP, possiblement due à la stimulation ce celle-ci par BMP7. L'activation de la voie Wnt par la ß-Caténine, conduit à la transcription de BMP7, identifiant ainsi ce gène comme un gène cible de la voie canonique. La pertinence de nos observations a par ailleurs été confirmée par le fait que BMP7 est surexprimé dans les tumeurs de seins humains. Afin d'élucider la fonction de la voie BMP dans le sein, nous avons utilisé le modèle mutin. L'expression du gène BMP7 dans les souris transgéniques MMTV Wnt-1 s'est avérée élevée, démontrant qu'il est aussi un gène cible de la voie Wnt in-vivo. L'expression de l'ARN messager .codant pour la protéine BMP7 est induite lors du développement lobulo-alvéolaire, qui se fait sous l'influence de la progestérone et de Wnt-4. Ensemble, ces observations corroborent le fait qu'une stimulation avec de la progestérone suffit à induire la transcription du gène dans les 24h. Nos résultats coïncident d'autre part avec le fait que BMP7 est exprimé dans la couche myoépithéliale de l'épithélium où la voie Wnt est activée. L'analyse de souris reportrices de l'activité de la voie BMP, suggère une activation dans la couche luminale de l'épithélium durant tout le développement de la glande mammaire. Curieusement, cette même voie est active dans le mésenchyme lors de la mammogénèse embryonnaire. Finalement, nos analyses d'immunofluorescence démontrent la capacité de prolifération des cellules ayant activé BMP, ainsi que leur nette ségrégation d'avec les cellules exprimant le récepteur à la progestérone. Nos résultats démontrent que le gène BMP7 est un gène cible de la voie Wnt canonique dans le sein. Son expression dans la couche myoépitheliale est induite par Wnt-4, lui-même sécrété par les cellules luminales sensibles à la progestérone. La sécrétion de la protéine BMP7 conduit finalement à l'activation de la voie BMP dans les cellules négatives pour le récepteur à la progestérone. Abstract Epidemiological studies highlight the repetitive exposure to circulating progesterone as a major risk in the development of breast cancer. Work in our laboratory showed that Wnt-4 is an essential mediator of progesterone-driven side-branch formation, while Wnt signaling has long been established as strongly oncogenic in the mouse mammary gland. To address the role of Wnt in breast tumorigenesis we activated the pathway in primary human breast epithelial cells by means of refroviral Wnt-1 expression. This resulted in a Wnt1-induced breast carcinogenesis model, being referred to as Wnt-1-HMECs. Gene expression profiling revealed the Bone Morphogenetic Protein 4 and 7 (BMP4 and 7) a mong the most upregulated gene by ectopic Wnt-1 expression in primary HMECs. RT-PCR analysis confirmed elevated BMP4 and 7 mRNA levels in Wnt-1-infected HMECs, as well as strong BMP7 expression in the tumors derived from these cells. Smad 1, 5, 8 phosphorylation was high in Wnt-1HMECs whereas below detection limit in primary HMECs suggesting that the increased expression of BMP-7 results in activation of downstream signaling. Ectopic expressíon of a stabilized form of ßcatenin in primary HMECs resulted in increased transcription of BMP-7 suggesting that it is a target of canonical Wnt signaling. The clinical relevance of our observations was confirmed by the finding of BMP7 being upregulated in human breast tumor samples. To elucidate the role of BMP ligands in the breast in-vivo, we made use of the mouse model. Expression of the BMP7 gene was found to be increased in MMTV-Wnt-1 transgenic animals, suggesting that BMP7 may also be a Wnt 1 target gene in vivo. Expression of BMP7 was upregulated in mid-pregnancy which coincides with progesterone/Wnt induced side branching. BMP7 was induced within 24 hours by progesterone. Consistent with it being a target of canonical Wnt signaling, we demonstrated preferential expression of this ligand in the myoepithelial cells, the target cells of Wnt signals. In-vivo analysis of BMP signaling using a reporter mouse revealed the activation of the pathway in the luminal layer of the epithelium throughout postnatal development. Interestingly, during embryonic mammogenesis the pathway was found to be active in the mesenchyme. Immunofluorescence studies demonstrated that cells with BMP activity can proliferate. They also revealed a clear segregation between progesterone receptor positive cells and cells with active BMP signaling. Together our observations suggest that BMP-7 is a canonical Wnt signaling target both in HMECs and in the mouse mammary gland in-vivo. It is expressed in the myoepithelium possibly in response to Wnt-4, which is secreted by steroid receptor positive cells in response to progesterone. BMP-7 in turn may impinge on lumina) epithelial cells and activate BMP signaling in PR negative cells.

The Effects of Estradiol, Androgens and the Selective Estrogen Modulators: Ospemifene, Raloxifene and Tamoxifen on Explant Cultures of Human Breast Tissue

The impact of menopausal hormone therapy (MHT) on increasing the risk for breast cancer (BC) remains controversial. To understand MHT-elicited cellular breast effects and the potential risks, included with using this therapy, a further investigation into this controversy is the subject of this thesis. In this thesis, to study the effects of estrogen, progestin, androgens and selective estrogen receptor modulators (SERMs), a modified tissue explant culture system was used. The different types of human breast tissues (HBTs) used in this study were normal HBTs, obtained from reduction mammoplasties of premenopausal women (prem-HBTs) or postmenopausal (postm-HBTs) women and peritumoral HBTs (peritum-HBTs) which were obtained from surgeries on postmenopausal BC patients. The explants were cultured up to three weeks in the presence or absence of estradiol (E2), medroxyprogesterone acetate (MPA), testosterone (T), dihydrotestosterone (DHT) and SERMs - ospemifene (OSP), raloxifene (RAL) and tamoxifen (TAM). The cultured HBTs maintained morphological integrity and responded to hormonal treatment in vitro. E2, MPA or E2/MPA increased proliferative activity and was associated with increased cyclin-D1 and caused changes in the cell cycle inhibitors p21 and p27, whereas the androgens T and DHT inhibited proliferation and increased apoptosis in HBT epithelia and opposed E2-stimulated proliferation and cell survival. The postm-HBTs were more sensitive to E2 than prem-HBTs. The effects of OSP, RAL and TAM on HBT epithelium were antiproliferative. E2, androgens and SERMs were associated with marked changes in the proportions of epithelial cells expressing steroid hormone receptors: E2 increased ERα expressing cells and decreased androgen receptor (AR) positive cells, whereas T and DHT had opposite effects. The OSP, RAL and TAM, also decreased a proportion of ERα positive cells in HBT epithelium. At 100 nM, these compounds maintained the relative number of AR positive cells, present at control level, which may partly explain proliferative inhibition. In conclusion, the proliferative activity of E2, in the epithelium of postm-HBTs, is opposed by T and DHT, which suggests that the inclusion of androgens in MHT may decrease the risk for developing BC.

Triiodothyronine and breast cancer

The thyroid hormones (THs), triiodothyronine (T3) and thyroxine (T4), are essential for survival; they are involved in the processes of development, growth, and metabolism. In addition to hyperthyroidism or hypothyroidism, THs are involved in other diseases. The role of THs in the development and differentiation of mammary epithelium is well established; however, their specific role in the pathogenesis of breast cancer (BC) is controversial. Steroid hormones affect many human cancers and the abnormal responsiveness of the mammary epithelial cells to estradiol (E2) in particular is known to be an important cause for the development and progression of BC. The proliferative effect of T3 has been demonstrated in various types of cancer. In BC cell lines, T3 may foster the conditions for tumor proliferation and increase the effect of cell proliferation by E2; thus, T3 may play a role in the development and progression of BC. Studies show that T3 has effects similar to E2 in BC cell lines. Despite controversy regarding the relationship between thyroid disturbances and the incidence of BC, studies show that thyroid status may influence the development of tumor, proliferation and metastasis.

TWIST and p-Akt immunoexpression in normal oral epithelium, oral dysplasia and in oral squamous cell carcinoma

Objectives: The aim of this study was to evaluate the immunoexpression of TWIST and p-Akt proteins in oral leukoplakia (OL) and oral squamous cell carcinoma (OSCC), correlating their expressions with the histological features of the lesions. Study design: Immunohistochemical studies were carried out on 10 normal oral epithelium, 30 OL and 20 OSCC formalin-fixed, paraffin-embedded tissue samples. Immunoperoxidase reactions for TWIST and p-Akt proteins were applied on the specimens and the positivity of the reactions was calculated for 1000 epithelial cells. Results: Kruskal-Wallis and Dunn's post tests revealed a significant difference in TWIST and p-Akt immunoexpression among normal oral mucosa, OL and OSCC. In addition, a significant positive correlation was found between TWIST and p-Akt expressions according to the Pearson's correlation test. Conclusions: The results obtained in the current study suggest that TWIST and p-Akt may participate of the multi-step process of oral carcinogenesis since its early stages.

{\it In vivo\/} induction of DNA changes in cervicovaginal epithelium by perinatal estrogen exposure

Epidemiological studies have associated estrogens with human neoplasm such as the endometrium, cervix, vagina, breast, and liver. Perinatal exposure to natural (17$\beta$-estradiol (17$\beta$-E$\sb2)\rbrack$ and synthetic (diethylstilbestrol (DES)) estrogens induces neoplastic changes in humans and rodents. Previous studies demonstrated that neonatal 17$\beta$-E$\sb2$ treatment increased the nuclear DNA content of mouse cervicovaginal epithelium that preceded histologically evident neoplasia. In order to determine whether this effect was specific to 17$\beta$-E$\sb2,$ associated with chromosomal changes, and relevant to the human, female BALB/c mice were treated neonatally with either 17$\alpha$-estradiol (17$\alpha$-E$\sb2)$ and 5$\beta$-dihydrotestosterone ($5\beta$-DHT), both inactive steroids in adult reproductive tissue, or 17$\beta$-E$\sb2.$ Ten-day-old mice received pellet implants of 17$\beta$-E$\sb2,$ 17$\alpha$-E$\sb2,$ $5\beta$-DHT, or cholesterol. Seventy-day-old cervicovaginal tracts were examined histologically and flow cytometrically. 17$\beta$-E$\sb2$-treated animals were evaluated by fluorescent in situ hybridization (FISH) using a probe specific for chromosome 1. Trisomy of chromosomes 1, 7, 11, and 17 was evaluated by FISH in cervicovaginal material from 19 DES-exposed and 19 control patients.^ $17\beta$-E$\sb2, 17\alpha$-E$\sb2$, and $5\beta$-DHT-induced dramatic developmental and histological changes in the cervicovaginal tract, including hypospadia, hyperplasia, and persistent cornification. The changes induced by 17$\alpha$-E$\sb2$ were equivalent to 17$\beta$-E$\sb2.$ Neonatal 17$\alpha$-E$\sb2$-induced adenosquamous cervicovaginal tumors at 24 months. 17$\alpha$-E$\sb2$ and $5\beta$-DHT significantly increased the nuclear DNA content over control animals, but at significantly lower levels than 17$\beta$-E$\sb2.$ DNA ploidy changes were highest (80%) in animals treated neonatally and secondarily with 17$\beta$-E$\sb2.$ Secondary 17$\alpha$-E$\sb2$ and $5\beta$-DHT administration, unlike 17$\beta$-E$\sb2,$ didn't significantly increase DNA content. Chromosome 1 trisomy incidence was 66% in neonatal 17$\beta$-E$\sb2$-treated animals. Trisomy was evident in 4 DES-exposed patients: one patient with trisomy of chromosomes 1, 7, and 11; one patient with chromosome 7 trisomy; and two patients with chromosome 1 trisomy. These data demonstrated the biological effects of 17$\alpha$-E$\sb2$ and $5\beta$-DHT were age-dependent, 17$\alpha$-E$\sb2$ was equivalent to 17$\beta$-E$\sb2$ and tumorigenic when administered neonatally, and histological changes were not steroid specific. Chromosomal changes were associated with increased nuclear DNA content and chromosomal changes may be an early event in the development of tumors in human DES-exposed tissues. ^

INTERACTION BETWEEN BRK AND HER2 IN BREAST CANCER

INTERACTION BETWEEN BRK AND HER2 IN BREAST CANCER Midan Ai, Ph.D. Supervisory Professor: Zhen Fan, M.D. Breast tumor kinase (Brk) is a nonreceptor protein-tyrosine kinase that is highly expressed in approximately two thirds of breast cancers but is not detectable or is expressed at very low levels in normal mammary epithelium. Brk plays important roles in promoting proliferation, survival, invasion, and metastasis of breast cancer cells, but the mechanism(s) of which remain largely unknown. Recent studies showed that Brk is frequently co-overexpressed with human epidermal growth factor receptor-2 (HER2) and is physically associated with HER2 in breast cancer. The mechanism needs to be determined. In my studies, I found that high expression of HER2 is correlated with high expression of Brk in breast cancer cell lines. Silencing HER2 expression via RNA interference in HER2 over-expressed breast cancer cells resulted in Brk protein decrease and overexpression of HER2 in HER2 low-expressed breast cancer cells up-regulated Brk expression. The mechanism study indicated that overexpression of HER2 increased Brk protein stability. Brk was degraded through a Ca2+-dependent protease pathway involving calpain and HER2 stimulated Brk expression via inhibiting calpain activity. Calpastatin is a calpain endogenous inhibitor and the calpain-calpastatin system has been implicated in a number of cell physiological functions. HER2 restrained calpain activation via up-regulating calpastatin expression and HER2 downstream signaling, MAPK pathway, was involved in the regulation. Furthermore, silencing of Brk expression by RNA interference in HER2-overexpressing breast cancer cells decreased HER2-mediated cell proliferation, survival, invasion/metastasis potential and increased cell sensitivity to HER2 kinase inhibitor, lapatinib, treatment, indicating that Brk plays important roles in regulating and mediating the oncogenic functions of HER2. The Stat3 pathway played important roles in Brk mediated cell survival and invasion/metastasis in the context of HER2-overexpressing breast cancer cells. However, transgenic mice with inducible expression of constitutively active Brk (CA) in the mammary epithelium failed to develop malignant change in the mammary glands after Brk induction for 15 months which indicated that expression of Brk protein alone was not sufficiently to induce spontaneous breast tumor. Bitransgenic mice with co-expression of HER2/neu and inducible expression of Brk in the mammary epithelium developed multifocal mammary tumors, but there were no significant difference in the tumor occurring time, tumor size, tumor weight and tumor multiplicity between the mouse group with co-expression of Brk and HER2/neu and the mouse group with HER2/neu expression only.

Nuclear Factor-κB (NF-κB) Regulates Proliferation and Branching in Mouse Mammary Epithelium

The nuclear factor-κB (NF-κB) family of transcription factors has been shown to regulate proliferation in several cell types. Although recent studies have demonstrated aberrant expression or activity of NF-κB in human breast cancer cell lines and tumors, little is known regarding the precise role of NF-κB in normal proliferation and development of the mammary epithelium. We investigated the function of NF-κB during murine early postnatal mammary gland development by observing the consequences of increased NF-κB activity in mouse mammary epithelium lacking the gene encoding IκBα, a major inhibitor of NF-κB. Mammary tissue containing epithelium from inhibitor κBα (IκBα)-deficient female donors was transplanted into the gland-free mammary stroma of wild-type mice, resulting in an increase in lateral ductal branching and pervasive intraductal hyperplasia. A two- to threefold increase in epithelial cell number was observed in IκBα-deficient epithelium compared with controls. Epithelial cell proliferation was strikingly increased in IκBα-deficient epithelium, and no alteration in apoptosis was detected. The extracellular matrix adjacent to IκBα-deficient epithelium was reduced. Consistent with in vivo data, a fourfold increase in epithelial branching was also observed in purified IκBα-deficient primary epithelial cells in three-dimensional culture. These data demonstrate that NF-κB positively regulates mammary epithelial proliferation, branching, and functions in maintenance of normal epithelial architecture during early postnatal development.

A novel plant toxin, persin, with in vivo activity in the mammary gland, induces Bim-dependent apoptosis in human breast cancer cells

Phytochemicals have provided an abundant and effective source of therapeutics for the treatment of cancer. Here we describe the characterization of a novel plant toxin, persin, with in vivo activity in the mammary gland and a p53-, estrogen receptor-, and Bcl-2-independent mode of action. Persin was previously identified from avocado leaves as the toxic principle responsible for mammary gland-specific necrosis and apoptosis in lactating livestock. Here we used a lactating mouse model to confirm that persin has a similar cytotoxicity for the lactating mammary epithelium. Further in vitro studies in a panel of human breast cancer cell lines show that persin selectively induces a G(2)-M cell cycle arrest and caspase-dependent apoptosis in sensitive cells. The latter is dependent on expression of the BH3-only protein Bim. Bim is a sensor of cytoskeletal integrity, and there is evidence that unique structure of the compound, persin could represent a novel class of microtubule-targeting agent with potential specificity for breast cancers.