Dietary Polyphenols, Resveratrol and Pterostilbene Exhibit Antitumor Activity on an HPV E6-Positive Cervical Cancer Model: An in vitro and in vivo Analysis.

Human papilloma virus (HPV)-induced cervical cancer is one of the most frequent cancers in women residing in underdeveloped countries. Natural compounds like polyphenols continue to be of scientific interest as non-toxic effective alternative treatments. Our previous work showed the efficacy of two polyphenols, resveratrol, and pterostilbene on human HeLa cells. Here we explored the in vitro anti-cancer activity and in vivo anti-tumor potential of these two structurally similar compounds on HPV oncogene E6 and E7 positive murine TC1 cells. In vitro analysis confirmed the cytotoxic potential of both resveratrol and pterostilbene compounds with each having a low IC50 value and each showing the ability to downregulate viral oncogene E6. Further in vivo studies on TC1 tumors developing in mice indicated that treatment with either resveratrol or pterostilbene can significantly inhibit tumor development, with both compounds capable of downregulating E6 and VEGF tumor protein levels. Interestingly, the decrease in tumor size in pterostilbene was associated with tumor cell apoptosis, as indicated by an upregulation of activated caspase-3 whereas in resveratrol-treated mice it was accompanied by arrest of cell cycle, as indicated by a downregulation of PCNA. Thus, resveratrol and pterostilbene can serve as potential antineoplastic agents against HPV E6+ tumors and may suppress tumor growth via two different mechanisms.

Phytoestrogens: The current state of research emphasizing breast pathophysiology.

Phytoestrogens, a class of plant-derived compounds that are structural mimics of estrogen, can bind to estrogen receptors, acting as either agonists or antagonists. They have been implicated in estrogen-mediated physiology, which makes them interesting targets of study, especially for biomedical applications in woman's health. The 1998 Women's Health Initiative sparked considerable interest in natural alternatives to hormone replacement therapy, thereby triggering many additional studies on phytoestrogens. In this review, key advancements in dietary phytoestrogens are addressed, emphasizing their relation to breast pathophysiology. Recent developments such as clinical trials, precise bioassays for screening and selection of potential phytoestrogens, drug delivery systems to enhance bioavailability of therapeutically favorable phytoestrogens, regulatory guidelines on phytoestrogen-based supplements, and avenues that need further improvement are also discussed.

Resveratrol and Pterostilbene Exhibit Anticancer Properties Involving the Downregulation of HPV Oncoprotein E6 in Cervical Cancer Cells.

Cervical cancer is one of the most common cancers in women living in developing countries. Due to a lack of affordable effective therapy, research into alternative anticancer compounds with low toxicity such as dietary polyphenols has continued. Our aim is to determine whether two structurally similar plant polyphenols, resveratrol and pterostilbene, exhibit anticancer and anti-HPV (Human papillomavirus) activity against cervical cancer cells. To determine anticancer activity, extensive in vitro analyses were performed. Anti-HPV activity, through measuring E6 protein levels, subsequent downstream p53 effects, and caspase-3 activation, were studied to understand a possible mechanism of action. Both polyphenols are effective agents in targeting cervical cancer cells, having low IC50 values in the µM range. They decrease clonogenic survival, reduce cell migration, arrest cells at the S-phase, and reduce the number of mitotic cells. These findings were significant, with pterostilbene often being more effective than resveratrol. Resveratrol and to a greater extent pterostilbene downregulates the HPV oncoprotein E6, induces caspase-3 activation, and upregulates p53 protein levels. Results point to a mechanism that may involve the downregulation of the HPV E6 oncoprotein, activation of apoptotic pathways, and re-establishment of functional p53 protein, with pterostilbene showing greater efficacy than resveratrol.

Unique synergistic formulation of curcumin, epicatechin gallate and resveratrol, tricurin, suppresses HPV E6, eliminates HPV+ cancer cells, and inhibits tumor progression.

Curcumin (from curry) (C) is highly potent against cervical cancer cells (CCC), but poor bioavailability has limited its clinical use. Similar natural polyphenols resveratrol (from grapes) (R), and epicatechin gallate (from green tea) (E) also display activity against CCC. By treating CCC (HeLa) with C, E, or R, or combinations of these compounds, we computed combination indices and observed a strong synergism among C, E, and R at the unique molar ratio 4:1:12.5. This combination, named as TriCurin, rapidly down regulated HPV18 E6 and NF-kB expression while concomitantly inducing the tumor suppressor protein p53 in HeLa cells. In the mouse c-Ha-ras and HPV16 E6, E7-expressing TC-1 CCC, both C and TriCurin elicited suppression of E6, induction of both p53 and acetyl-p53 (activated p53), and activation of caspase-3, but the TriCurin-evoked changes were several-fold greater than that produced by curcumin (4.7-fold for E6 inhibition, and 2-fold, 6-fold, and 1.7-fold for the induction of p53, acetyl-p53, and active caspase-3, respectively). Consequently, TriCurin was more potent in killing TC-1 and HeLa cells. Intralesional TriCurin treatment of tumors generated in mice by subcutaneously implanting the TC-1 CCC caused an 80-90% decrease in tumor growth. The ability of C to eliminate HeLa cells was significantly stabilized when delivered as TriCurin than when delivered alone. Topical application of TriCurin dispersed in a cream base afforded efficient transfer of C across the skin. Subcutaneous TriCurin injection yielded no adverse effect in tumor-naïve healthy mice. Thus, TriCurin is a safe and promising therapeutic agent against HPV-associated disease.

UPLC-QTOFMS(E)-Guided Dereplication of the Endangered Chinese Species Garcinia paucinervis to Identify Additional Benzophenone Derivatives.

A number of Garcinia species accumulate benzophenone derivatives that may be useful for the treatment of breast cancer. The dereplication of new benzophenone derivatives from Garcinia species is challenging due to the occurrence of multiple isomers and the known compounds found in their extracts. In the current study, a strategy is described using the UPLC-QTOFMS(E) technique to identify tentatively the known and uncharacterized benzophenones of interest based upon the characteristic fragmentation ions. Several UPLC-QTOFMS peaks (a-ee) appeared to contain benzophenone derivatives, and 12 of these peaks contained compounds with MS ionization profiles not consistent with previously identified compounds from the seeds of Garcinia paucinervis, an endangered Chinese species. The targeted isolation of unidentified compounds of interest afforded five new benzophenones, paucinones E-I (1-5), which were determined by MS and NMR analysis and ECD spectroscopy. These compounds were evaluated for cytotoxicity against three breast cancer cell lines inclusive of MDA-MB-231, SKBR3, and MCF-7. These results indicate that the UPLC-QTOFMS(E)-guided isolation procedure is an efficient strategy for isolating new benzophenones from Garcinia species.

Comparative UPLC-QTOF-MS-based metabolomics and bioactivities analyses of Garcinia oblongifolia.

Garcinia oblongifolia Champ. ex Benth. (Clusiaceae) is a well-known medicinal plant from southern China, with edible fruits. However, the phytochemistry and bioactivity of the different plant parts of G. oblongifolia have not been studied extensively. Comparative metabolic profiling and bioactivities of the leaf, branch, and fruit of G. oblongifolia were investigated. A total of 40 compounds such as biflavonoids, xanthones, and benzophenones were identified using UPLC-QTOF-MS and MS(E), including 15 compounds reported for the first time from this species. Heatmap analyses found that benzophenones, xanthones, and biflavonoids were predominately found in branches, with benzophenones present in relatively high concentrations in all three plant parts. Xanthones were found to have limited distribution in fruit while biflavonoids were present at only low levels in leaves. In addition, the cytotoxic (MCF-7 breast cancer cell line) and antioxidant (ABTS and DPPH chemical tests) activities of the crude extracts of G. oblongifolia indicate that the branch extract exhibits greater bioactivity than either the leaf or the fruit extracts. Orthogonal partial least squares discriminate analysis was used to find 12 marker compounds, mainly xanthones, from the branches, including well-known antioxidants and cytotoxic agents. These G. oblongifolia results revealed that the variation in metabolite profiles can be correlated to the differences in bioactivity of the three plant parts investigated. This UPLC-QTOF-MS strategy can be useful to identify bioactive constituents expressed differentially in the various plant parts of a single species.

Diagnostic imaging of cervical intraepithelial neoplasia based on hematoxylin and eosin fluorescence.

BACKGROUND: Pathological classification of cervical intraepithelial neoplasia (CIN) is problematic as it relies on subjective criteria. We developed an imaging method that uses spectroscopy to assess the fluorescent intensity of cervical biopsies derived directly from hematoxylin and eosin (H&E) stained tissues. METHODS: Archived H&E slides were identified containing normal cervical tissue, CIN I, and CIN III cases, from a Community Hospital and an Academic Medical Center. Cases were obtained by consensus review of at least 2 senior pathologists. Images from H&E slides were captured first with bright field illumination and then with fluorescent illumination. We used a Zeiss Axio Observer Z1 microscope and an AxioVision 4.6.3-AP1 camera at excitation wavelength of 450-490 nm with emission captured at 515-565 nm. The 32-bit grayscale fluorescence images were used for image analysis. RESULTS: We reviewed 108 slides: 46 normal, 33 CIN I and 29 CIN III. Fluorescent intensity increased progressively in normal epithelial tissue as cells matured and advanced from the basal to superficial regions of the epithelium. In CIN I cases this change was less prominent as compared to normal. In high grade CIN lesions, there was a slight or no increase in fluorescent intensity. All groups examined were statistically different. CONCLUSION: Presently, there are no markers to help in classification of CIN I-III lesions. Our imaging method may complement standard H&E pathological review and provide objective criteria to support the CIN diagnosis.

Endocytic trafficking of laminin is controlled by dystroglycan and is disrupted in cancers.

The dynamic interactions between cells and basement membranes serve as essential regulators of tissue architecture and function in metazoans, and perturbation of these interactions contributes to the progression of a wide range of human diseases, including cancers. Here, we reveal the pathway and mechanism for the endocytic trafficking of a prominent basement membrane protein, laminin-111 (referred to here as laminin), and their disruption in disease. Live-cell imaging of epithelial cells revealed pronounced internalization of laminin into endocytic vesicles. Laminin internalization was receptor mediated and dynamin dependent, and laminin proceeded to the lysosome through the late endosome. Manipulation of laminin receptor expression revealed that the dominant regulator of laminin internalization is dystroglycan, a laminin receptor that is functionally perturbed in muscular dystrophies and in many cancers. Correspondingly, laminin internalization was found to be deficient in aggressive cancer cells displaying non-functional dystroglycan, and restoration of dystroglycan function strongly enhanced the endocytosis of laminin in both breast cancer and glioblastoma cells. These results establish previously unrecognized mechanisms for the modulation of cell-basement-membrane communication in normal cells and identify a profound disruption of endocytic laminin trafficking in aggressive cancer subtypes.

Na(+) /H(+) exchanger 1 (NHE1) function is necessary for maintaining mammary tissue architecture.

BACKGROUND: The mammary gland is an ideal model to study the link between form and function in normal tissue. Perhaps as interesting as the cues necessary to generate this structure are the signals required to maintain its branched architecture over the lifetime of the organism, since likely these pathways are de-regulated in malignancies. Previously, we have shown that the Na(+) /H(+) exchanger 1 (NHE1), a critical regulator of intracellular pH, was necessary for mammary branching morphogenesis. Here we provide strong evidence that NHE1 function is also necessary for maintaining mammary branched architecture. RESULTS: Inhibition of NHE1 with 5-N-Methy-N-isobutyl amiloride (MIA) on branched structures resulted in a rapid (within 24 hr) and reversible loss of branched architecture that was not accompanied by any overt changes in cell proliferation or cell death. NHE1 inhibition led to a significant acidification of intracellular pH in the branched end buds that preceded a number of events, including altered tissue polarity of myoepithelial cells, loss of NHE1 basal polarity, F-actin rearrangements, and decreased E-cadherin expression. CONCLUSIONS: Our results implicate NHE1 function and intracellular pH homeostasis as key factors that maintain mammary tissue architecture, thus, indirectly allowing for mammary function as a milk-providing (form) and -producing (function) gland.

Epimorphin is a novel regulator of the progesterone receptor isoform-a.

Epimorphin/syntaxin-2 is a membrane-tethered protein localized extracellularly (Epim) and intracellularly (Stx-2). The extracellular form Epim stimulates morphogenic processes in a range of tissues, including in murine mammary glands where its overexpression in luminal epithelial cells is sufficient to drive hyperplasia and neoplasia. We analyzed WAP-Epim transgenic mice to gain insight into how Epim promotes malignancy. Ectopic overexpression of Epim during postnatal mammary gland development led to early side-branching onset, precocious bud formation, and increased proliferation of mammary epithelial cells. Conversely, peptide-based inhibition of Epim function reduced side branching. Because increased side branching and hyperplasia occurs similarly in mice upon overexpression of the progesterone receptor isoform-a (Pgr-a), we investigated whether Epim exhibits these phenotypes through Pgr modulation. Epim overexpression indeed led to a steep upregulation of both total Pgr mRNA and Pgr-a protein levels. Notably, the Pgr antagonist RU486 abrogated Epim-induced ductal side branching, mammary epithelial cell proliferation, and bud formation. Evaluation of Epim signaling in a three-dimensional ex vivo culture system showed that its action was dependent on binding to its extracellular receptor, integrin-αV, and on matrix metalloproteinase 3 activity downstream of Pgr-a. These findings elucidate a hitherto unknown transcriptional regulator of Pgr-a, and shed light on how overexpression of Epim leads to malignancy.

First ayurvedic approach towards green drugs: anti cervical cancer-cell properties of Clerodendrum viscosum root extract.

The concept of Ayurvedic expert guided drug discovery and development is defined and put to test systematically for the first time in literature. Western Science has explored only ~5% of the approximately 25,000 species of higher plants for drug leads. The ancient medical science of Ayurveda has however employed a much larger spectrum of plants for clinical treatment. Clerodendrum viscosum (CV), a commonly growing weed in the Indian subcontinent has been employed by S. Nirmalananda (Ayurvedic expert) for the treatment of cervical cancer. Here we isolate and characterize a water extract fraction (Cv-AP) from the root of CV and evaluate its anticervical cancer cell bioactivity. Our results indicate that Cv-AP possesses pro-apoptotic, anti-proliferative, and anti-migratory activity in a dose-dependent fashion against cervical cancer cell lines. In contrast, primary fibroblasts (control healthy cells), when exposed to similar concentrations of this extract, fail to undergo apoptosis and remain relatively unaffected. These findings suggest that Clerodendrum viscosum (CV) is a readily available source of components with potent anti-cancer activity and selective bioactivity against cervical cancer cells. The major component in CV-AP was identified as a glycoprotein via SDS Page and Concanavalin-A binding studies. This study serves to illustrate that systematic collaboration with Ayurveda is a practical and powerful strategy in drug discovery and development.

Dendrimer-curcumin conjugate: a water soluble and effective cytotoxic agent against breast cancer cell lines.

Curcumin, which is derived from the plant Curcuma longa, has received considerable attention as a possible anti-cancer agent. In cell culture, curcumin is capable of inducing apoptosis in cancer cells at concentrations that do not affect normal cells. One draw-back holding curcumin back from being an effective anti-cancer agent in humans is that it is almost completely insoluble in water and therefore has poor absorption and subsequently poor bioavailability. Here we have generated a number of curcumin derivatives (tetrahydro-curcumin, curcumin mono-carboxylic acid, curcumin mono-galactose, curcumin mono-alkyne and dendrimer-curcumin conjugate) to test whether any of them display both cytotoxicity and water solubility. Of those tested only dendrimer-curcumin conjugate exhibited both water solubility and cytotoxicity against SKBr3 and BT549 breast cancer cells. When compared to curcumin dissolved in DMSO, dendrimer-curcumin conjugate dissolved in water was significantly more effective in inducing cytotoxicity, as measured by the MTT assay and effectively induced cellular apoptosis measured by caspase-3 activation. Since dendrimer-curcumin conjugate is water soluble and capable of inducing potent cytotoxic effects on breast cancer cell lines, it may prove to be an effective anti-cancer therapy to be used in humans.

A novel curcumin-based vaginal cream Vacurin selectively eliminates apposed human cervical cancer cells.

OBJECTIVE: Human papillomavirus (HPV) infections remain a leading cause of mortality worldwide. In the U.S. strategies via screening and vaccination prevent HPV-associated cervical neoplasms, but consume immense healthcare costs. The spice component curcumin has potent anticancer and antiviral properties, which have been difficult to harness as a treatment, due to its poor systemic bioavailability. This project tests the possibility of developing a curcumin-based therapy for cervical cancer. METHODS: Using four HPV(+) cervical cancer cell lines and normal fibroblasts we first tested the selectivity and potency of curcumin in eliminating HPV(+) cells. Subsequently, we developed a curcumin-based cervical cream and tested its efficacy in eliminating apposed HPV(+) cells and also its possible side effects on the vaginal epithelium of healthy mice. RESULTS: Curcumin selectively eliminates a variety of HPV(+) cervical cancer cells (HeLa, ME-180, SiHa, and SW756), suppresses the transforming antigen E6, dramatically inhibits the expression of the pro-cancer protein epidermal growth factor receptor (EGFR), and concomitantly induces p53. Additionally, Vacurin, a uniform colloidal solution of curcumin in a clinically used amphipathic vaginal cream, eliminates apposed HeLa cells while suppressing the expression of EGFR. In mice, daily intravaginal application of Vacurin for three weeks produced no change in body weight and when the mice were sacrificed, the vaginal tract epithelium showed no Vacurin-evoked adverse effects. CONCLUSION: We have developed a curcumin-based vaginal cream, which effectively eradicates HPV(+) cancer cells and does not affect non-cancerous tissue. Our preclinical data support a novel approach for the treatment of cervical HPV infection.

Nongenomic Mechanisms of PTEN Regulation.

A large amount of data supports the view that PTEN is a bona fide tumor suppressor gene. However, recent evidence suggests that derailment of cellular localization and expression levels of functional nonmutated PTEN is a determining force in inducing abnormal cellular and tissue outcomes. As the cellular mechanisms that regulate normal PTEN enzymatic activity resolve, it is evident that deregulation of these mechanisms can alter cellular processes and tissue architecture and ultimately lead to oncogenic transformation. Here we discuss PTEN ubiquitination, PTEN complex formation with components of the adherens junction, PTEN nuclear localization, and microRNA regulation of PTEN as essential regulatory mechanisms that determine PTEN function independent of gene mutations and epigenetic events.

Intracellular pH regulation by Na⁺/H⁺ exchanger-1 (NHE1) is required for growth factor-induced mammary branching morphogenesis.

Regulation of intracellular pH (pHi) and protection against cytosolic acidification is primarily a function of the ubiquitous plasma membrane Na+/H+exchanger-1 (NHE1), which uses a highly conserved process to transfer cytosolic hydrogen ions (H+) across plasma membranes in exchange for extracellular sodium ions (Na+). Growth factors, which are essential regulators of morphogenesis, have also been found to be key activators of NHE1 exchanger activity; however, the crosstalk between both has not been fully evaluated during organ development. Here we report that mammary branching morphogenesis induced by transforming growth factor-alpha (TGFα) requires PI3K-dependent NHE1-activation and subsequent pHi alkalization. Inhibiting NHE1 activity after TGFα stimulation with 10 µM of the NHE1-specific inhibitor N-Methyl-N-isobutyl Amiloride (MIA) dramatically disrupted branching morphogenesis, induced extensive proliferation, ectopic expression of the epithelial hyper-proliferative marker Keratin-6 and sustained activation of MAPK. Together these findings indicate a novel developmental signaling cascade involving TGFα>PI3K>NHE1>pHi alkalization, which leads to a permissible environment for MAPK negative feedback inhibition and thus regulated mammary branching morphogenesis.

Atp8a1 deficiency is associated with phosphatidylserine externalization in hippocampus and delayed hippocampus-dependent learning.

The molecule responsible for the enzyme activity plasma membrane (PM) aminophospholipid translocase (APLT), which catalyzes phosphatidylserine (PS) translocation from the outer to the inner leaflet of the plasma membrane, is unknown in mammals. A Caenorhabditis elegans study has shown that ablation of transbilayer amphipath transporter-1 (TAT-1), which is an ortholog of a mammalian P-type ATPase, Atp8a1, causes PS externalization in the germ cells. We demonstrate here that the hippocampal cells of the dentate gyrus, and Cornu Ammonis (CA1, CA3) in mice lacking Atp8a1 exhibit a dramatic increase in PS externalization. Although their hippocampi showed no abnormal morphology or heightened apoptosis, these mice displayed increased activity and a marked deficiency in hippocampus-dependent learning, but no hyper-anxiety. Such observations indicate that Atp8a1 plays a crucial role in PM-APLT activity in the neuronal cells. In corroboration, ectopic expression of Atp8a1 but not its close homolog, Atp8a2, caused an increase in the population (V(max) ) of PM-APLT without any change in its signature parameter K(m) in the neuronal N18 cells. Conversely, expression of a P-type phosphorylation-site mutant of Atp8a1 (Atp8a1*) caused a decrease in V(max) of PM-APLT without significantly altering its K(m) . The Atp8a1*-expressing N18 cells also exhibited PS externalization without apoptosis. Together, our data strongly indicate that Atp8a1 plays a central role in the PM-APLT activity of some mammalian cells, such as the neuronal N18 and hippocampal cells.

The metastasis-promoting protein S100A4 regulates mammary branching morphogenesis.

High levels of the S100 calcium binding protein S100A4 also called fibroblast specific protein 1 (FSP1) have been established as an inducer of metastasis and indicator of poor prognosis in breast cancer. The mechanism by which S100A4 leads to increased cancer aggressiveness has yet to be established; moreover, the function of this protein in normal mammary gland biology has not been investigated. To address the role of S100A4 in normal mammary gland, its spatial and temporal expression patterns and possible function in branching morphogenesis were investigated. We show that the protein is expressed mainly in cells of the stromal compartment of adult humans, and during active ductal development, in pregnancy and in involution of mouse mammary gland. In 3D culture models, topical addition of S100A4 induced a significant increase in the TGFα mediated branching phenotype and a concomitant increase in expression of a previously identified branching morphogen, metalloproteinase-3 (MMP-3). These events were found to be dependent on MEK activation. Downregulation of S100A4 using shRNA significantly reduced TGFα induced branching and altered E-cadherin localization. These findings provide evidence that S100A4 is developmentally regulated and that it plays a functional role in mammary gland development, in concert with TGFα by activating MMP-3, and increasing invasion into the fat pad during branching. We suggest that S100A4-mediated effects during branching morphogenesis provide a plausible mechanism for how it may function in breast cancer progression.

Dystroglycan controls signaling of multiple hormones through modulation of STAT5 activity.

Receptors for basement membrane (BM) proteins, including dystroglycan (DG), coordinate tissue development and function by mechanisms that are only partially defined. To further elucidate these mechanisms, we generated a conditional knockout of DG in the epithelial compartment of the mouse mammary gland. Deletion of DG caused an inhibition of mammary epithelial outgrowth and a failure of lactation. Surprisingly, loss of DG in vivo did not disrupt normal tissue architecture or BM formation, even though cultured Dag1-null epithelial cells failed to assemble laminin-111 at the cell surface. The absence of DG was, however, associated with a marked loss in activity of signal transducer and activator of transcription 5 (STAT5). Loss of DG perturbed STAT5 signaling induced by either prolactin or growth hormone. We found that DG regulates signaling by both hormones in a manner that is dependent on laminin-111 binding, but independent of the DG cytoplasmic domain, suggesting that it acts via a co-receptor mechanism reliant on DG-mediated laminin assembly. These results demonstrate a requirement for DG in the growth and function of a mammalian epithelial tissue in vivo. Moreover, we reveal a selective role for DG in the control of multiple STAT5-dependent hormone signaling pathways, with implications for numerous diseases in which DG function is compromised.

Interaction of E-cadherin and PTEN regulates morphogenesis and growth arrest in human mammary epithelial cells.

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a dual-function phosphatase with tumor suppressor function compromised in a wide spectrum of cancers. Because tissue polarity and architecture are crucial modulators of normal and malignant behavior, we postulated that PTEN may play a role in maintenance of tissue integrity. We used two nonmalignant human mammary epithelial cell lines that form polarized, growth-arrested structures (acini) when cultured in three-dimensional laminin-rich extracellular matrix gels (lrECM). As acini begin to form, PTEN accumulates both in the cytoplasm and at cell-cell contacts where it colocalizes with the E-cadherin/beta-catenin complex. Reduction of PTEN levels by shRNA in lrECM prevents formation of organized breast acini and disrupts growth arrest. Importantly, disruption of acinar polarity and cell-cell contact by E-cadherin function-blocking antibodies reduces endogenous PTEN protein levels and inhibits its accumulation at cell-cell contacts. Conversely, in Skbr-3 breast cancer cells lacking endogenous E-cadherin expression, exogenous introduction of E-cadherin gene causes induction of PTEN expression and its accumulation at sites of cell interactions. These studies provide evidence that E-cadherin regulates both the PTEN protein levels and its recruitment to cell-cell junctions in three-dimensional lrECM, indicating a dynamic reciprocity between architectural integrity and the levels and localization of PTEN. This interaction thus seems to be a critical integrator of proliferative and morphogenetic signaling in breast epithelial cells.

Nuclear translocation of beta-dystroglycan reveals a distinctive trafficking pattern of autoproteolyzed mucins.

Dystroglycan (DG) is an extracellular matrix receptor implicated in muscular dystrophies and cancers. DG belongs to the membrane-tethered mucin family and is composed of extracellular (alpha-DG) and transmembrane (beta-DG) subunits stably coupled at the cell surface. These two subunits are generated by autoproteolysis of a monomeric precursor within a distinctive protein motif called sea urchin-enterokinase-agrin (SEA) domain, yet the purpose of this cleavage and heterodimer creation is uncertain. In this study, we identify a functional nuclear localization signal within beta-DG and show that, in addition to associating with alpha-DG at the cell surface, the full-length and glycosylated beta-DG autonomously traffics to the cytoplasm and nucleoplasm in a process that occurs independent of alpha-DG ligand binding. The trafficking pattern of beta-DG mirrors that of MUC1-C, the transmembrane subunit of the related MUC1 oncoprotein, also a heterodimeric membrane-tethered mucin created by SEA autoproteolysis. We show that the transmembrane subunits of both MUC1 and DG transit the secretory pathway prior to nuclear targeting and that their monomeric precursors maintain the capacity for nuclear trafficking. A screen of breast carcinoma cell lines of distinct pathophysiological origins revealed considerable variability in the nuclear partitioning of beta-DG, indicating that nuclear localization of beta-DG is regulated, albeit independent of extracellular ligand binding. These findings point to novel intracellular functions for beta-DG, with possible disease implications. They also reveal an evolutionarily conserved role for SEA autoproteolysis, serving to enable independent functions of mucin transmembrane subunits, enacted by a shared and poorly understood pathway of segregated subunit trafficking.