Requirement of basement membrane for the suppression of programmed cell death in mammary epithelium

Spatial and temporal changes in Bax subcellular localization during anoikis

Bax, a member of the Bcl-2 family, translocates to mitochondria during apoptosis, where it forms oligomers which are thought to release apoptogenic factors such as cytochrome c. Using anoikis as a model system, we have examined spatial and temporal changes in Bax distribution. Bax translocates to mitochondria within 15 min of detaching cells from extracellular matrix, but mitochondrial permeabilization does not occur for a number of hours. The formation of Bax oligomers and perimitochondrial clusters occurs concomitant with caspase activation and loss of mitochondrial membrane potential, before nuclear condensation. Cells can be rescued from apoptosis if they are replated onto extracellular matrix within an hour, whereas cells detached for longer could not. The loss of ability to rescue cells from anoikis occurs after Bax translocation, but before the formation of clusters and cytochrome c release. Our data suggest that Bax regulation occurs at several levels, with formation of clusters a late event, and with critical changes determining cell fate occurring earlier.

Anoikis: roadblock to cell transplantation?

Cell therapy, in particular liver cell transplantation, holds great therapeutic potential and is partially hindered by the high rate of apoptosis during cell isolation, cryopreservation, and engraftment. Apoptosis occurring due to cell detachment from the extracellular matrix is a phenomenon termed "anoikis." The purpose of this review is to describe signaling mechanisms pertinent to anoikis in both immortalized cell lines, but particularly in primary normal epithelial cells. The mechanisms described include integrin signaling and survival molecules, caspase activation, and the role of mitochondrial proteins in anoikis. Strategies to prevent anoikis during isolation and cryopreservation of hepatocytes are discussed.

Early events in the anoikis program occur in the absence of caspase activation

Adhesion of many cell types to the extracellular matrix is essential to maintain their survival. In the absence of integrin-mediated signals, normal epithelial cells undergo a form of apoptosis termed anoikis. It has been proposed that the activation of initiator caspases is an early event in anoikis, resulting in Bid cleavage and cytochrome c release from mitochondria. We have previously demonstrated that the loss of integrin signaling in mammary epithelial cells results in apoptosis and that this is dependent upon translocation of Bax from the cytosol to the mitochondria. In this paper, we ask whether caspases are required for Bax activation and the associated changes within mitochondria. We show that Bax activation occurs extremely rapidly, within 15 min after loss of integrin-mediated adhesion to extracellular matrix. The conformational changes associated with Bax activation are independent of caspases including the initiator caspase-8. We also examined downstream events in the apoptosis program and found that cytochrome c release occurs after a delay of at least 1 h, with subsequent activation of the effector caspase-3. This delay is not due to a requirement for new protein synthesis, since cycloheximide has no effect on the kinetics of Bax activation, cytochrome c release, caspase-3 cleavage, or apoptosis. Together, our data indicate that the cellular decision for anoikis in mammary epithelial cells occurs in the absence of caspase activation. Moreover, although the conformational changes in Bax are rapid and synchronous, the subsequent events occur stochastically and with considerable delays.

Biological aspects of signal transduction by cell adhesion receptors

Cell adhesion receptors such as integrins, cadherins, selectins, and immunoglobulin family receptors profoundly modulate many signal transduction cascades. In this review we examine aspects of adhesion receptor signaling and how this impinges on key biological processes. We have chosen to focus on cell migration and on programmed cell death. We examine many of the cytoplasmic signaling molecules that interface with adhesion receptors, including focal adhesion kinase (FAK), phosphatidylinositol-3-kinase (PI3K), and elements of the Erk/MAP kinase pathway. In many cases these molecules impinge on both the regulation of cell movement and on control of apoptosis.

Developing a laboratory animal model for perinatal endocrine disruption: the hamster chronicles

At the biomedical, regulatory, and public level, considerable concern surrounds the concept that inappropriate exposure to endocrine-disrupting chemicals, especially during the prenatal and/or neonatal period, may disrupt normal reproductive tract development and adult function. The intent of this review was to 1. Describe some unique advantages of the hamster for perinatal endocrine disruptor (ED) studies, 2. Summarize the morphological and molecular consequences of exposure to the established perinatal ED, diethylstilbestrol, in the female and male hamster, 3. Present some new, histomorphological insight into the process of neonatal diethylstilbestrol-induced disruption in the hamster uterus, and 4. Introduce recent efforts and future plans to evaluate the potency and mechanism of action of other putative EDs in the hamster experimental system. Taken together, the findings indicate that the hamster represents a unique and sensitive in vivo system to probe the phenomenon of endocrine disruption. The spectrum of candidate endpoints includes developmental toxicity, neoplasia, and more subtle endpoints of reproductive dysfunction.

The mineralocorticoid receptor may compensate for the loss of the glucocorticoid receptor at specific stages of mammary gland development

To study the role of glucocorticoid receptor (GR) at different stages of mammary gland development, mammary anlage were rescued from GR-/- mice by transplantation into the cleared fat pad of wild-type mice. In virgin mice, GR-/- outgrowths displayed abnormal ductal morphogenesis characterized by distended lumena, multiple layers of luminal epithelial cells in some regions along the ducts, and increased periductal stroma. In contrast, the loss of GR did not result in overt phenotypic changes in mammary gland development during pregnancy, lactation, and involution. Surprisingly, despite the known synergism between glucocorticoids and prolactin in the regulation of milk protein gene expression, whey acidic protein and beta-casein mRNA levels were unaffected in GR-/- transplants as compared with wild-type transplants. That mineralocorticoid receptor (MR) might compensate for the loss of GR was suggested by the detection of MR in the mammary gland at d 1 of lactation. This hypothesis was tested using explant cultures derived from the GR-/- transplants in which the mineralocorticoid fludrocortisone was able to synergistically induce beta-casein gene expression in the presence of prolactin and insulin. These studies suggest that MR may compensate for the absence of GR at some, but not at all stages of mammary gland development.

Activation of BAD by therapeutic inhibition of epidermal growth factor receptor and transactivation by insulin-like growth factor receptor

Novel cancer chemotherapeutics are required to induce apoptosis by activating pro-apoptotic proteins. Both epidermal growth factor (EGF) and insulin-like growth factor (IGF) provide potent survival stimuli in many epithelia, and activation of their receptors is commonly observed in solid human tumors. Here we demonstrate that blockade of the EGF receptor by a new drug in phase III clinical trails for cancer, ZD1839, potently induces apoptosis in mammary epithelial cell lines and primary cultures, as well as in a primary pleural effusion from a breast cancer patient. We identified the mechanism of apoptosis induction by ZD1839. We showed that it prevents cell survival by activating the pro-apoptotic protein BAD. Moreover, we demonstrate that IGF transactivates the EGF receptor and that ZD1839 blocks IGF-mediated phosphorylation of MAPK and BAD. Many cancer therapies kill tumor cells by inducing apoptosis as a consequence of targeting DNA; however, the threshold at which apoptosis can be triggered through DNA damage is often different from that in normal cells. Our results indicate that by targeting a growth factor-mediated survival signaling pathway, BAD phosphorylation can be manipulated therapeutically to induce apoptosis.

Laminin-10/11 and fibronectin differentially prevent apoptosis induced by serum removal via phosphatidylinositol 3-kinase/Akt- and MEK1/ERK-dependent pathways

Cell adhesion to the extracellular matrix inhibits apoptosis, but the molecular mechanisms underlying the signals transduced by different matrix components are not well understood. Here, we examined integrin-mediated antiapoptotic signals from laminin-10/11 in comparison with those from fibronectin, the best characterized extracellular adhesive ligand. We found that the activation of protein kinase B/Akt in cells adhering to laminin-10/11 can rescue cell apoptosis induced by serum removal. Consistent with this, wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase, or ectopic expression of a dominant-negative mutant of Akt selectively accelerated cell death upon serum removal. In contrast to laminin-10/11, fibronectin rescued cells from serum depletion-induced apoptosis mainly through the extracellular signal-regulated kinase pathway. Cell survival on fibronectin but not laminin was significantly reduced by treatment with PD98059, a specific inhibitor of mitogen- or extracellular signal-regulated kinase kinase-1 (MEK1) and by expression of a dominant-negative mutant of MEK1. Laminin-10/11 was more potent than fibronectin in preventing apoptosis induced by serum depletion. These results, taken together, demonstrate laminin-10/11 potency as a survival factor and demonstrate that different extracellular matrix components can transduce distinct survival signals through preferential activation of subsets of multiple integrin-mediated signaling pathways.

Sensing the environment: a historical perspective on integrin signal transduction

Cell adhesion mediated by integrin receptors has a critical function in organizing cells in tissues and in guiding haematopoietic cells to their sites of action. However, integrin adhesion receptors have broader functions in regulating cell behaviour through their ability to transduce bi-directional signals into and out of the cell and to engage in reciprocal interactions with other cellular receptors. This historical perspective traces the key findings that have led to our current understanding of these important functions of integrins.

Cell-matrix interactions during development and apoptosis of the mouse mammary gland in vivo

Epithelial cell survival is dependent on extracellular signals provided by both soluble factors and by adhesion. In the mammary gland, extensive apoptosis of epithelial cells occurs rapidly when lactation ceases, but the mechanism of apoptosis induction is not known. In tissue culture, mammary epithelial cells require laminin as a survival ligand and specific beta1 integrins are necessary to suppress apoptosis. To explore the possibility that dynamic changes in cell-matrix interactions contribute to the onset of apoptosis during mammary involution in vivo, a detailed immunohistochemical analysis of the expression of integrin subunits and their extracellular matrix ligands during mouse mammary gland development has been performed. The kinetics of apoptosis were determined by using tissue samples obtained from virgin, pregnant, lactating, and involuting gland. The maximal elevation of apoptosis occurred within 24 hr of weaning as determined by histologic analysis and caspase-3 staining. A wide variety of laminin subunits, together with nidogen-1 and -2, and perlecan were identified within the basement membrane region of epithelial ducts, lobules, and alveoli in both human and mouse mammary gland. However, no change in the distribution of any of the basement membrane proteins or their cognate integrin receptors was observed during the transition from lactation to apoptosis. Instead, we discovered that altered ligand-binding conformation of the beta1 integrin to a nonbinding state coincided with the immediate onset of mammary apoptosis. This finding may provide a novel dynamic mechanism for inhibiting the transduction of extracellular matrix survival signals, thereby contributing to the onset of apoptosis in a developmental context in vivo.

Maspin is a tumour suppressor that inhibits breast cancer tumour metastasis in vivo

Maspin is a member of the serpin family of serine proteases and functions as a tumour suppressor. A study using a new syngeneic mouse model for breast cancer suggests that maspin can inhibit metastasis in vivo.

Suppression of p53 function in normal human mammary epithelial cells increases sensitivity to extracellular matrix-induced apoptosis

Little is known about the fate of normal human mammary epithelial cells (HMECs) that lose p53 function in the context of extracellular matrix (ECM)-derived growth and polarity signals. Retrovirally mediated expression of human papillomavirus type 16 (HPV-16) E6 and antisense oligodeoxynucleotides (ODNs) were used to suppress p53 function in HMECs as a model of early breast cancer. p53+ HMEC vector controls grew exponentially in reconstituted ECM (rECM) until day 6 and then underwent growth arrest on day 7. Ultrastructural examination of day 7 vector controls revealed acinus-like structures characteristic of normal mammary epithelium. In contrast, early passage p53- HMEC cells proliferated in rECM until day 6 but then underwent apoptosis on day 7. p53- HMEC-E6 passaged in non-rECM culture rapidly (8-10 passages), lost sensitivity to both rECM-induced growth arrest and polarity, and also developed resistance to rECM-induced apoptosis. Resistance was associated with altered expression of alpha3-integrin. Treatment of early passage p53- HMEC-E6 cells with either alpha3- or beta1-integrin function-blocking antibodies inhibited rECM-mediated growth arrest and induction of apoptosis. Our results indicate that suppression of p53 expression in HMECs by HPV-16 E6 and ODNs may sensitize cells to rECM-induced apoptosis and suggest a role for the alpha3/beta1-heterodimer in mediating apoptosis in HMECs grown in contact with rECM.

Extracellular matrix regulates alpha s1-casein gene expression in rabbit primary mammary cells and CCAAT enhancer binding protein (C/EBP) binding activity

Previous studies have shown that both the signal transducer and activator of transcription 5 (STAT5) and the CCAAT enhancer binding proteins (C/EBPs) are involved in the regulation of casein gene expression by mammary epithelial cells. Prolactin (Prl) activation of STAT5 is necessary for casein gene expression. The extracellular matrix (ECM) regulates also casein gene expression. Here, we have investigated whether ECM regulates C/EBPs activity in primary rabbit mammary epithelial cells. Isolated primary mammary cells were cultured on plastic or on floating collagen I gel. Prolactin induced alphas 1-casein gene expression when cells were cultured on collagen but not on plastic. It is noteworthy that activated STAT5 was detected in both culture conditions. Several STAT5 isoforms (STAT5a, STAT5b, and other STAT5 related isoforms, some with lower molecular weight than the full-length STAT5a and STAT5b) were detected under the different culture conditions. However, their presence was not related to the expression of alphas 1-casein gene. The binding of nuclear factors to a C/EBP specific binding site and the protein level of C/EBPbeta differed in cells cultured on plastic or on collagen but these parameters were not modified by Prl. This suggests that C/EBP binding activity was regulated by ECM and not by Prl. Interestingly, these modifications were correlated to the expression of the alphas 1-casein gene. Hence, the activation of the alphas 1-casein gene expression depends on two independent signals, one delivered by Prl via the activation of STAT5, the other delivered by ECM via C/EBP.

Human MCF10A mammary epithelial cells undergo apoptosis following actin depolymerization that is independent of attachment and rescued by Bcl-2

Many tumor cells are impaired in adhesion-regulated apoptosis, which contributes to their metastatic potential. However, suppression of this apoptotic pathway in untransformed cells is not mediated only by adhesion to the extracellular matrix but also through the resulting ability to spread and adopt a distinct morphology. Since cell spreading is dependent on the integrity of the actin microfilament cytoskeleton, we sought to determine if actin depolymerization was sufficient to induce apoptosis, even in the presence of continuous attachment. For this study, we used a human mammary epithelial cell line (MCF10A), which is immortalized but remains adhesion dependent for survival. Treatment of MCF10A cells with latrunculin-A (LA), an inhibitor of actin polymerization, rapidly led to disruption of the actin cytoskeleton and caused cell rounding but preserved attachment. Initiation of apoptosis in LA-treated MCF10A cells was detected by mitochondrial localization of the Bax apoptotic protein, which was prevented by overexpression of Bcl-2. DNA fragmentation and poly(ADP-ribose) polymerase (PARP) cleavage in LA-treated MCF10A cells indicated progression to the execution phase of apoptosis. The MDA-MB-453 cell line, which was derived from a metastatic human mammary tumor, was resistant to PARP cleavage and loss of viability in response to actin depolymerization. Stable overexpression of Bcl-2 in the untransformed MCF10A cells was able to recapitulate the resistance to apoptosis found in the tumor cell line. We demonstrate that inhibition of actin polymerization is sufficient to stimulate apoptosis in attached MCF10A cells, and we present a novel role for Bcl-2 in cell death induced by direct disruption of the actin cytoskeleton.

Coordinated expression of matrix Gla protein is required during endochondral ossification for chondrocyte survival

Matrix Gla protein (MGP) is a 14-kD extracellular matrix protein of the mineral-binding Gla protein family. Studies of MGP-deficient mice suggest that MGP is an inhibitor of extracellular matrix calcification in arteries and the epiphyseal growth plate. In the mammalian growth plate, MGP is expressed by proliferative and late hypertrophic chondrocytes, but not by the intervening chondrocytes. To investigate the functional significance of this biphasic expression pattern, we used the ATDC5 mouse chondrogenic cell line. We found that after induction of the cell line with insulin, the differentiating chondrocytes express MGP in a stage-specific biphasic manner as in vivo. Treatment of the ATDC5 cultures with MGP antiserum during the proliferative phase leads to their apoptosis before maturation, whereas treatment during the hypertrophic phase has no effect on chondrocyte viability or mineralization. After stable transfection of ATDC5 cells with inducible sense or antisense MGP cDNA constructs, we found that overexpression of MGP in maturing chondrocytes and underexpression of MGP in proliferative and hypertrophic chondrocytes induced apoptosis. However, overexpression of MGP during the hypertrophic phase has no effect on chondrocyte viability, but it does reduce mineralization. This work suggests that coordinated levels of MGP are required for chondrocyte differentiation and matrix mineralization.

Upregulated expression of human membrane type-5 matrix metalloproteinase in kidneys from diabetic patients

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that degrade the extracellular matrix (ECM). The membrane-type matrix metalloproteinases (MT-MMPs) are a new family of MMPs that differ from other MMPs in that they have a transmembrane domain that anchors them to the cell surface. MT-MMPs have been shown to function as receptors and activators for other MMPs and to localize extracellular matrix proteolysis at the pericellular region. Here we report on mRNA and protein expression of the fifth human MT-MMP (MT5-MMP), a 64-kDa protein that is capable of converting pro-MMP-2 to its active form, in human kidney as well as its upregulation in diabetes. We also demonstrate upregulation of the active form of MMP-2 in kidney samples from patients with diabetes. Through immunohistochemistry, MT5-MMP expression was localized to the epithelial cells of the proximal and distal tubules, the collecting duct, and the loop of Henle. Furthermore, the tubular epithelial cells that expressed MT5-MMP were associated with tubular atrophy. Because renal tubular atrophy is a significant factor in the pathogenesis of diabetic nephropathy and renal failure and the molecular mechanisms regulating this process remain unknown, it is hypothesized that the elevated expression of MT5-MMP contributes to the activation of pro-MMP-2, which participates in the remodeling of the proximal and distal tubules as well as in the collecting duct. These results provide the first evidence of the expression of a MT-MMP in diabetes and suggest a novel role for MT5-MMP in the pathogenesis of renal tubular atrophy and end-stage renal disease.

Escherichia coli induces apoptosis and proliferation of mammary cells

Mammary cell apoptosis and proliferation were assessed after injection of Escherichia coli into the left mammary quarters of six cows. Bacteriological analysis of foremilk samples revealed coliform infection in the injected quarters of four cows. Milk somatic cell counts increased in these quarters and peaked at 24 h after bacterial injection. Body temperature also increased, peaking at 12 h postinjection. The number of apoptotic cells was significantly higher in the mastitic tissue than in the uninfected control. Expression of Bax and interleukin-1beta converting enzyme increased in the mastitic tissue at 24 h and 72 h postinfection, whereas Bcl-2 expression decreased at 24 h but did not differ significantly from the control at 72 h postinfection. Induction of matrix metalloproteinase-9, stromelysin-1 and urokinase-type plasminogen activator was also observed in the mastitic tissue. Moreover, cell proliferation increased in the infected tissue. These results demonstrate that Escherichia coli-induced mastitis promotes apoptosis and cell proliferation.

Epithelial development and differentiation in the mammary gland is not dependent on alpha 3 or alpha 6 integrin subunits

In the mammary gland, both laminin and integrins have been shown to be required for normal ductal morphogenesis during development in vivo, and for functional differentiation in culture models. Major integrin receptors for laminins in the mammary gland are alpha 3 beta 1, alpha 6 beta 1, and alpha 6 beta 4. However, the specific subunits that contribute to laminin-mediated mammary cell function and development have not been identified. In this study, we use a genetic approach to test the hypothesis that laminin-binding integrins are required for the function of the mammary gland in vivo. Rudiments of embryonic mammary gland were shown to develop in the absence of these integrin subunits. Postnatal development of the mammary gland was studied in integrin null tissue that had been transplanted into the mammary fat pads of syngeneic hosts. In mammary epithelium lacking alpha 6 integrin, the beta 4 subunit was not apparent and hemidesmosome formation was only rudimentary. However, despite this deficiency, normal ductal morphogenesis and branching of the mammary gland occurred and myoepithelial cells were distributed normally with respect to luminal cells. Mammary alveoli devoid of alpha 3 or alpha 6 integrin formed in pregnancy and were histologically and functionally identical to those in wild-type mammary gland. The tissue underwent full morphological differentiation, and the epithelial cells retained the ability to synthesize beta-casein. This work demonstrates that mammary tissue genetically lacking major laminin-binding integrin receptors is still able to develop and function.

Overexpression of the integrin-linked kinase mesenchymally transforms mammary epithelial cells

Signals generated by the interaction of (β)1 integrins with laminin in the basement membrane contribute to mammary epithelial cell morphogenesis and differentiation. The integrin-linked kinase (ILK) is one of the signaling moieties that associates with the cytoplasmic domain of (β)1 integrin subunits with some specificity. Forced expression of a dominant negative, kinase-dead form of ILK subtly altered mouse mammary epithelial cell morphogenesis but it did not prevent differentiative milk protein expression. In contrast, forced overexpression of wild-type ILK strongly inhibited both morphogenesis and differentiation. Overexpression of wild-type ILK also caused the cells to lose the cell-cell adhesion molecule E-cadherin, become invasive, reorganize cortical actin into cytoplasmic stress fibers, and switch from an epithelial cytokeratin to a mesenchymal vimentin intermediate filament phenotype. Forced expression of E-cadherin in the latter mesenchymal cells rescued epithelial cytokeratin expression and it partially restored the ability of the cells to differentiate and undergo morphogenesis. These data demonstrate that ILK, which responds to interactions between cells and the extracellular matrix, induces a mesenchymal transformation in mammary epithelial cells, at least in part, by disrupting cell-cell junctions.

Matrix metalloproteinases and their inhibitors in oral lichen planus

BACKGROUND

Oral lichen planus (OLP) is characterized by a sub-epithelial lymphocytic infiltrate, basement membrane (BM) disruption, intra-epithelial T-cell migration and apoptosis of basal keratinocytes. BM damage and T-cell migration in OLP may be mediated by matrix metalloproteinases (MMPs).

METHODS

We examined the distribution, activation and cellular sources of MMPs and their inhibitors (TIMPs) in OLP using immunohistochemistry, ELISA, RT-PCR and zymography.

RESULTS

MMP-2 and -3 were present in the epithelium while MMP-9 was associated with the inflammatory infiltrate. MMP-9 and TIMP-1 secretion by OLP lesional T cells was greater than OLP patient (p < 0.01) and healthy control subject (p < 0.001) peripheral blood T cells. MMP-9 and TIMP-1 mRNA levels were greater in OLP lesional T cells compared with healthy control subject peripheral blood T cells p < 0.01). Tumor necrosis factor (TNF)-alpha upregulated OLP lesional T-cell MMP-9 (not TIMP-1) mRNA and secretion (p < 0.05). The in vitro activation rate of MMP-9 from OLP lesional T cells was greater than that from OLP peripheral blood T cells (p < 0.05).

CONCLUSION

T-cell-derived MMP-9 may be involved in the pathogenesis of OLP. Relative over-expression of MMP-9 (compared with TIMP-1) may cause BM disruption and facilitate intra-epithelial T-cell migration in OLP.

Apoptosis in normal and neoplastic mammary gland development

Apoptosis plays important roles in mammary development from early embryonic formation of the mammary gland to the regression that follows cessation of cycling. The most dramatic occurrence of apoptosis is found during mammary involution. Most of the secretory epithelium in the lactating breast undergoes apoptosis as the mammary gland regresses and is reorganized for another cycle of lactation. We used the morphology, biochemical changes, and gene expression detected in apoptotic mammary epithelium during involution as a model for studying cell death during other stages of mammary development and for approaching the failure of apoptosis found in mammary hyperplasia. Morphological studies and gene expression have suggested that apoptosis during involution is comprised of two phases: an early limited apoptosis in response to hormone ablation and later protease promoted widespread apoptosis in response to altered cell-matrix interactions and loss of anchorage. We examined protein expression during involution for changes associated with loss of hormone stimulation and altered cell-matrix interactions. One of the proteins whose expression is able to inhibit apoptosis, and is altered during mammary epithelial cell was the serine-threonine protein kinase, Akt 1. Akt 1 activation is common to hormone, growth factor, and anchorage-mediated survival of epithelial cells. We found regulated expression of activated Akt 1 in the mammary gland during involution. Akt 1 activation peaked in pregnancy and lactation, and decreased significantly during apoptosis in mammary involution. Mechanisms of Akt 1 action include modulation of the ratio bcl-2 family members implicated in control of apoptosis. Bcl-2 family proteins were also expressed in pattern consistent with Akt 1 regulation. These observations led us to examine expression of activated Akt 1 and bcl-2 family proteins in premalignant hyperplasias. Akt 1 activation was increased; expression of anti-apoptotic proteins bcl-2 and bcl-x was strongly increased while pro-apoptotic bax was greatly diminished in three different lines of transplantable premalignant mammary hyperplasia. This data suggest that activation of Akt 1 by hormone- or anchorage-mediated pathways regulates survival of mammary epithelium and can contribute to initiation of neoplasia. These data suggest that perturbation of normal cell turnover can contribute to initiation of neoplasia.

Inhibition of mammary epithelial apoptosis and sustained phosphorylation of Akt/PKB in MMTV-IGF-II transgenic mice

IGF-II is a growth factor implicated in human cancers and animal tumor models. While the mitogenic properties of IGF-II are well documented, its ability to suppress apoptosis in vivo has never been proven. We generated independent MMTV-IGF-II transgenic mice to examine the control of epithelial apoptosis at the morphological, cellular and molecular levels during the physiological event of postlactation mammary involution. Transgenic IGF-II expression was achieved in mammary epithelium and increased IGF-II bioactivity was confirmed by phosphorylation of the insulin receptor substrate-1, a signaling molecule downstream of the type I IGF receptor. IGF-II overexpression induced a delay in mammary involution, as evident by increased mammary gland to body weight ratios and persistence of both functionally intact lobulo-alveoli and mammary epithelial cellularity. The delayed mammary involution resulted from a significant reduction in mammary epithelial apoptosis, and not from increased epithelial proliferation. Recombinant IGF-II pellets implanted into involuting mammary glands of wild-type mice provided further evidence that IGF-II protein inhibited local epithelial apoptosis. At the molecular level, phosphorylated Akt/PKB, but not Erk1 or Erk2, persisted in IGF-II overexpressors and temporally correlated with reduced epithelial apoptosis. Levels of the phosphatase PTEN were unaltered in the transgenic tissue suggesting that the maintenance of Akt/PKB phosphorylation resulted from sustained phosphorylation rather than altered dephosphorylation of PIP-3. Together, this data reveal that IGF-II inhibits apoptosis in vivo and this effect correlates with prolonged phosphorylation of Akt/PKB

Discoidin domain receptor (DDR) 1 and 2: collagen-activated tyrosine kinase receptors in the cornea

Discoidin domain receptor (DDR) 1 and 2 have recently been found to serve as receptors for several collagen types. These receptors have been found to modulate cell proliferation and metalloprotease expression in response to collagen stimulation. The purpose of this study was to examine expression of DDR1 and DDR2 in the cornea and to determine the effect of several collagen types on proliferation and response to pro-apoptotic cytokines by corneal fibroblasts. DDR1 and DDR2 mRNAs were detected by RT-PCR. Proteins were detected by immunocytochemistry and immunoprecipitation with Western blotting. Cell proliferation in response to acetic acid-solubilized collagen type I, II, IV, IX or X was determined by cell counting. The effect of these collagen types on Fas-stimulating antibody-induced cell death was determined by trypan blue assay. DDR1 and DDR2 mRNAs were detected in each major human cell type of the cornea. Both were also detected in ex vivo human corneal epithelium. DDR1 and DDR2 proteins were detected in all three major cell types in culture and in human corneal tissue. Collagen types I, II, IV, IX and X stimulated proliferation, but had no effect on Fas-mediated apoptosis, of corneal fibroblasts. DDR1 and DDR2 tyrosine kinase receptors are expressed in the cornea. Collagen-stimulated mitosis of corneal fibroblasts in culture is likely mediated by the DDR receptors. Collagen had no effect on Fas-mediated apoptosis of corneal fibroblasts.

alpha3beta1 and alpha6beta4 integrin receptors for laminin-5 are not essential for epidermal morphogenesis and homeostasis during skin development

Continuous regeneration and homeostasis of the stratified epidermis requires coordinated regulation of cell proliferation, cell differentiation, and cell survival. Integrin-mediated cell adhesion to the extracellular matrix has important roles in regulating each of these processes. Integrins alpha3beta1 and alpha6beta4 are both receptors on epidermal keratinocytes for the basement membrane protein laminin-5, the major ligand for epidermal adhesion in mature skin. Ablation in mice of either alpha3beta1 or alpha6beta4, through null mutation of the gene encoding the alpha3, alpha6, or beta4 integrin subunit, results in epidermal blistering of varying severity. Our previous studies showed that, despite blistering, differentiation and stratification of the epidermis appeared essentially normal in mice that lacked either alpha3beta1 or alpha6beta4. However, these studies did not definitively address the specific developmental importance of each integrin, since they may have overlapping and/or compensatory functions. Given the individual importance of alpha3beta1 or alpha6beta4 in maintaining the dermo-epidermal junction in mature skin, we sought to determine the importance of these integrins for embryonic skin development and epidermal morphogenesis. In the current study, we analyzed skin development in mutant embryos that completely lack both integrins alpha3beta1 and alpha6beta4. Although alpha3beta1/alpha6beta4-deficient embryos displayed epidermal blistering by stage E15.5 of development, they also retained regions of extensive epidermal adhesion to the basement membrane through stage E16.5, indicating alternative adhesion mechanisms. Apoptosis was induced in detached epidermis of alpha3beta1/alpha6beta4-deficient embryos, exemplifying vividly the importance of epithelial attachment to the basement membrane for cell survival. However, apoptotic cells were completely absent from attached epidermis of alpha3beta1/alpha6beta4-deficient embryos, showing that epithelial adhesion that occurred independently of alpha3beta1 and alpha6beta4 also protected cells from apoptosis. Remarkably, in the absence of the known laminin-5 binding integrins (alpha3beta1, alpha6beta4, and alpha6beta1), keratinocytes retained the capacity to proliferate in the epidermis, and epidermal stratification and skin morphogenesis appeared normal prior to blister formation. These findings show that while alpha3beta1 and alpha6beta4 are both required for integrity of the dermo-epidermal junction, neither one is essential for epidermal morphogenesis during skin development.

1 alpha,25-dihydroxyvitamin D(3) inhibits angiogenesis in vitro and in vivo

Modulation of angiogenesis is now a recognized strategy for the prevention and treatment of pathologies categorized by their reliance on a vascular supply. The purpose of this study was to evaluate the effect of 1 alpha,25-dihydroxyvitamin D(3) [1, 25(OH)(2)D(3)], the active metabolite of vitamin D(3), on angiogenesis by using well-characterized in vitro and in vivo model systems. 1,25(OH)(2)D(3) (1 x 10(-9) to 1 x 10(-7) mol/L) significantly inhibited vascular endothelial growth factor (VEGF)-induced endothelial cell sprouting and elongation in vitro in a dose-dependent manner and had a small, but significant, inhibitory effect on VEGF-induced endothelial cell proliferation. 1, 25(OH)(2)D(3) also inhibited the formation of networks of elongated endothelial cells within 3D collagen gels. The addition of 1, 25(OH)(2)D(3) to endothelial cell cultures containing sprouting elongated cells induced the regression of these cells, in the absence of any effect on cells present in the cobblestone monolayer. Analysis of nuclear morphology, DNA integrity, and enzymatic in situ labeling of apoptosis-induced strand breaks demonstrated that this regression was due to the induction of apoptosis specifically within the sprouting cell population. The effect of 1,25(OH)(2)D(3) on angiogenesis in vivo was investigated by using a model in which MCF-7 breast carcinoma cells, which had been induced to overexpress VEGF, were xenografted subcutaneously together with MDA-435S breast carcinoma cells into nude mice. Treatment with 1,25(OH)(2)D(3) (12.5 pmol/d for 8 weeks) produced tumors that were less well vascularized than tumors formed in mice treated with vehicle alone. These results highlight the potential use of 1,25(OH)(2)D(3) in both the prevention and regression of conditions characterized by pathological angiogenesis.

Staurosporine-induced apoptosis in cultured chick embryonic neurons is reduced by polyethylenimine of low molecular weight used as a coating substrate

The survival of neurons largely depends on adhesion to extracellular matrix proteins. This study investigated the influence of polycationic macromolecules of different molecular weights used as coating substrates on apoptosis in primary cultures of chick embryonic neurons. Coating of the culture flasks with positively charged polyethylenimine (PEI) of 12, 32 and 1616 kDa led to different susceptibilities of the neurons to apoptosis induced by staurosporine and serum deprivation. In cultures grown as usual on polylysine (PL)-coated flasks, we found, after 24 h of incubation in medium with serum (controls), serum-free medium and staurosporine (200 nM)-containing serum-free medium, 15, 35 and 63% apoptotic neurons, respectively as evaluated by nuclear staining with Hoechst 33258. Using 12-kDa PEI as a coating substrate, only 11, 15 and 47% apoptotic neurons could be determined in controls, serum-deprived and staurosporine-treated cultures, respectively. No change in the percentage of apoptotic neurons was found after 24 h of serum deprivation or treatment with staurosporine in cultures grown on 32-kDa PEI compared with cultures grown on PL. However, in staurosporine-treated cultures grown on 1616-kDa PEI, the percentage of apoptotic neurons was even higher than in cultures grown on PL. Immunostaining using neurofilament (NF) antibodies revealed that the reduction of staurosporine-induced apoptosis using 12-kDa PEI instead of PL as a coating substrate was accompanied by a reduced disruption and aggregation of the neurofilaments. Thus, the usage of the newly synthesized 12-kDa PEI as a coating substrate enhanced neuronal resistance to apoptosis.

Fibronectin influences cellular proliferation and apoptosis similarly in LNCaP and PC-3 prostate cancer cell lines

The mechanisms responsible for the emergence of clinically advanced prostate cancer (PC) are incompletely understood. Recent studies suggest that altered tumoral apoptosis with disordered cell proliferation sustains advanced disease and may account for the phenomena of anti-androgen therapeutic resistance. Previous inquiry has focused primarily on faulty intracellular mechanisms with limited scrutiny of the extracellular matrix including fibronectin and collagen type 4. We evaluated cell proliferation with Ki-67 immunoassay/image analysis and apoptosis by TUNEL staining and Bcl-2 immunoassay/image analysis in LNCaP and PC-3 human PC cell lines at baseline and following propagation on fibronectin and collagen type 4-coated coverslip substrate. Cell cultures showed differing proliferative and apoptosis characteristics at baseline, with the LNCaP cell line showing relatively higher proliferation and apoptosis rates than the PC-3 cell line. Cell proliferation and apoptosis were statistically significantly decreased in both cell lines following propagation on fibronectin. Bcl-2 expression was significantly increased among both cell lines following propagation on fibronectin. In contrast, cell proliferation, apoptosis, and Bcl-2 expression showed insignificant changes in both cell lines following uncoated coverslip and collagen type 4 matrix propagation. Our findings showed that fibronectin influences cell proliferation, apoptosis, and Bcl-2 expression similarly among LNCaP and PC-3 PC cell lines. It is likely that the altered rates are independent of the androgen status of the cell line and are mediated through a nonhormonal mechanism.

Glucocorticoids maintain the extracellular matrix of differentiated mammary tissue during explant and whole organ culture

Mouse mammary whole organ culture (WOC) and explant culture of lactating tissue were used to investigate the mechanism by which glucocorticoids maintain secretory epithelium following lobuloalveolar development. The relative number of mammary epithelial cells expressing glucocorticoid receptors did not change with the loss of secretory epithelium during involution as demonstrated with competitive binding assays and immunohistochemistry for the glucocorticoid receptor. Furthermore, glucocorticoids did not inhibit AP-1 binding activity. However, Northern analysis demonstrated that genes associated with the breakdown of the extracellular matrix were not expressed in tissues cultured with glucocorticoids, in contrast to their upregulation during involution of mammary tissue cultured with insulin alone. Tissue inhibitor of metalloproteinase-1 (TIMP-1) mRNA expression was lowest in tissue cultured in the presence of glucocorticoids and increased 2.3-, 3.4-, and 9-fold when tissues were involuted in the presence of insulin (Ins) alone, Ins and hydrocortisone (Hyd) with 0. 005 mg/ml, or 0.01 mg/ml collagenase IV, respectively. These data indicate that glucocorticoids maintain mammary differentiation in part by inhibiting the turnover of basement membrane.

Mouse proximal tubular cell-cell adhesion inhibits apoptosis by a cadherin-dependent mechanism

Adhesion of epithelial cells to matrix is known to inhibit apoptosis. However, the role of cell-cell adhesion in mediating cell survival remains uncertain. Primary cultures of mouse proximal tubular (MPT) cells were used to examine the role of cell-cell adhesion in promoting survival. When MPT cells were deprived of both cell-matrix and cell-cell adhesion, they died by apoptosis. However, when incubated in agarose-coated culture dishes (to prevent cell-matrix adhesion) and at high cell density (to allow cell-cell interactions), MPT cells adhered to one another and remained viable. Expression of E-cadherin among suspended, aggregating cells increased with time. A His-Ala-Val (HAV)-containing peptide that inhibits homophilic E-cadherin binding prevented cell-cell aggregation and promoted apoptosis of MPT cells in suspension. By contrast, inhibition of potential beta(1)-integrin-mediated interactions between cells in suspension did not prevent either aggregation or survival of suspended cells. Aggregation of cells in suspension activated phosphatidylinositol 3-kinase (PI3K), an event that was markedly reduced by the presence of the HAV peptide. LY-294002, an inhibitor of PI3K, also inhibited survival of suspended cells. In summary, we provide novel evidence that MPT cells, when deprived of normal cell-matrix interactions, can adhere to one another in a cadherin-dependent fashion and remain viable. Survival of aggregated cells depends on activation of PI3K.

Integrin-mediated survival signals regulate the apoptotic function of Bax through its conformation and subcellular localization

Most normal cells require adhesion to extracellular matrix for survival, but the molecular mechanisms that link cell surface adhesion events to the intracellular apoptotic machinery are not understood. Bcl-2 family proteins regulate apoptosis induced by a variety of cellular insults through acting on internal membranes. A pro-apoptotic Bcl-2 family protein, Bax, is largely present in the cytosol of many cells, but redistributes to mitochondria after treatment with apoptosis-inducing drugs. Using mammary epithelial cells as a model for adhesion-regulated survival, we show that detachment from extracellular matrix induced a rapid translocation of Bax to mitochondria concurrent with a conformational change resulting in the exposure of its BH3 domain. Bax translocation and BH3 epitope exposure were reversible and occurred before caspase activation and apoptosis. Pp125FAK regulated the conformation of the Bax BH3 epitope, and PI 3-kinase and pp60src prevented apoptosis induced by defective pp125FAK signaling. Our results provide a mechanistic connection between integrin-mediated adhesion and apoptosis, through the kinase-regulated subcellular distribution of Bax.

Laminin-rich extracellular matrix association with mammary epithelial cells suppresses Brca1 expression

Brca1 mRNA was detectable in female mouse mammary gland tissue from adult virgins, during pregnancy and early lactation. It was associated with phases of mammary epithelial cell proliferation and differentiation but the pattern of Brca1 expression was dissociable from that of a true differentiation marker, beta-casein, by virtue of its significant expression in the virgin gland and termination of its expression in early lactation. In a primary cell culture model, association of a laminin-rich extracellular matrix (ECM) with mammary epithelial cells was required for cell survival and cell differentiation and suppressed Brca1 expression in these cells. ECM-association may significantly contribute to the final restriction in Brca1 expression in the lactating gland in vivo. Interestingly, our results suggest that mammary epithelial cells undergo apoptosis both when expressing and when not expressing Brca1, depending on whether the dying cell populations had been terminally differentiated or not.

MAP kinase pathway signalling is essential for extracellular matrix determined mammary epithelial cell survival

Mammary epithelial cells in primary cell culture require both growth factors and specific extracellular matrix (ECM)-attachment for survival. Here we demonstrate for the first time that inhibition of the ECM-induced Erk 1/Erk 2 (p42/44 MAPK) pathway, by PD 98059, leads to apoptosis in these cells. Associated with this cell death is a possible compensatory signalling through the p38 MAP kinase pathway the inhibition of which, by SB 203580, leads to a more rapid onset of apoptosis. This provides evidence for a hitherto undescribed Erk 1/Erk 2 to p38 MAP kinase pathway 'cross-talk' that is essential for the survival of these cells. The cell death associated with inhibition of these two MAP kinase pathways however, occurred in the presence of insulin that activates the classical PI-3 kinase-dependent Akt/PKB survival signals and Akt phosphorylation. Cell death induced by inhibition of the MAP kinase pathways did not affect Akt phosphorylation and may, thus, be independent of PI-3 kinase signalling.

Fibronectin fragments induce MMP activity in mouse mammary epithelial cells: evidence for a role in mammary tissue remodeling

Mammary gland form and function are regulated by interactions between epithelium and extracellular matrix. Major glycoprotein components of extracellular matrix have been identified that give survival, proliferation and differentiation signals to mammary epithelial cells. We provide evidence that proteolytic fragments of the extracellular matrix glycoprotein, fibronectin, suppress growth and can promote apoptosis of mouse mammary epithelial cells. During mammary gland involution, total fibronectin and fibronectin fragment levels are increased. The peak levels of fibronectin protein and fragments are observed 4–6 days post-weaning, coincident with the peak in epithelial cell death. Using a model for hormone withdrawal-induced death of mammary epithelium, elevated levels of fibronectin proteolytic fragments were associated with apoptosis in TM-6 cells, a tumorigenic mouse mammary epithelial cell line. Treatment of TM-6 cells with exogenous fibronectin fragments (FN120) reduced cell number, and induced apoptosis and matrix degrading protease activity. Inhibition of matrix protease activity rescued TM-6 cell viability, indicating that FN120-induced cell loss is mediated through matrix protease activity. In a three-dimensional model for mammary gland development, FN120 reduced alveolar-like and promoted ductal-like development by a matrix protease-dependent mechanism. These data suggest that during post-lactational involution, fibronectin fragments may contribute to epithelial cell loss and dissolution of mammary alveoli by inducing matrix degrading proteinases.

Cellular responses of embryonic hyaline cartilage to experimental wounding in vitro

It is well established that the reparative potential of many tissues is greatest during embryonic development. Despite the extensive literature documenting repair in nonembryonic cartilage models, there is no comparable wealth of experience relating to embryonic cartilage repair. With the embryonic chick sternum as a model of hyaline cartilage, this paper accounts cellular responses and alterations in extracellular matrix composition in response to experimental wounding in vitro. Creation of an experimental lesion induced a rapid (<20 minutes) apoptotic response in chondrocytes adjacent to the lesion edge; the presence of perichondrium delayed this response. Alterations in the extracellular matrix included immediate mechanical damage to type-II collagen fibrils and an increase in the expression of chondroitin-4 sulphate next to the lesion. Creation of the lesion induced an increased proliferative response in chondrocytes behind the zone of apoptosis and the expression of alpha5 and alpha6 integrin subunits.

Lymphoid adhesion promotes human thymic epithelial cell survival via NF-(kappa)B activation

Inside the thymus, thymic epithelial cells and thymocytes show an interdependent relationship for their functional differentiation and development. As regards possible interdependency for their mutual survival, it is clear that lympho-epithelial adhesion can control the survival of developing thymocytes whereas the effects of lymphoid adhesion on epithelial cell survival have never been described. To address this issue, we performed co-cultures between normal human thymic epithelial cells (TEC) and a mature lymphoid T cell line (H9) or unfractionated thymocytes. TEC were induced to apoptosis by growth factor deprivation and the level of cell death was measured by flow cytometry. TEC stimulated by cell adhesion showed a significant reduced apoptosis when compared to the control and this phenomenon was associated with increased binding activity of NF-(kappa)B, as measured by gel shift analysis. The activation of NF-(kappa)B was necessary to promote survival, since its inhibition by acetyl salicylic acid prevented the promoting effect. The mAb-mediated crosslinking of (alpha)(3)(beta)(1) was considered as a potential inducer of TEC survival, since we have previously demonstrated that the engagement of this integrin was able to induce NF-(kappa)B activation in TEC. The crosslinking of (alpha)(3)(beta)(1), which clustered at the lympho-epithelial contact sites, partially reproduced the promoting activity of cell adhesion. These results highlight that lympho-epithelial adhesion can control the survival of thymic epithelial cells through an intracellular pathway which requires the activation of NF-(kappa)B and is triggered by integrins of the (beta)(1) family.

Differentiation of separated mouse mammary luminal epithelial and myoepithelial cells cultured on EHS matrix analyzed by indirect immunofluorescence of cytoskeletal antigens

We have previously demonstrated that purified virgin mouse mammary luminal epithelial and myoepithelial cells promiscuously express cell type-specific cytokeratins when they are cloned in vitro. Changes in cytokeratin expression may be indicators of the loss or change of the differentiated identity of a cell. To investigate the factors that may be responsible for the maintenance of differentiated cellular identity, specifically cell-cell and cell-matrix interactions, we cloned flow-sorted mouse mammary epithelial cells on the extracellular matrix (ECM) derived from the Engelbreth-Holm-Swarm murine sarcoma (EHS matrix). Changes in cell differentiation on EHS, compared with culture on glass, were analyzed by comparing patterns of cytokeratin expression. The results indicate that ECM is responsible for maintenance of the differentiated identity of basal/myoepithelial cells and prevents the inappropriate expression of luminal antigens seen on glass or plastic. Luminal cell identity in the form of retention of luminal markers and absence of basal/myoepithelial antigens, on the contrary, appears to depend on homotypic cell-cell contacts and interactions. The results also show that luminal cells (or a subpopulation of them) can generate a cell layer that expresses only basal cytokeratin markers (and no luminal cytokeratin markers) and may form a pluripotent compartment. (J Histochem Cytochem 47:1513-1524, 1999)

Cell-based gene transfer to the pulmonary vasculature: Endothelial nitric oxide synthase overexpression inhibits monocrotaline-induced pulmonary hypertension

To circumvent the problems of in vivo transfection and avoid the use of viral vectors or proteins, we sought to establish whether smooth-muscle cells (SMCs) transfected ex vivo could be delivered via the systemic venous circulation into the pulmonary bed to achieve local transgene expression in the lung. Primary cultures of pulmonary artery SMCs from Fisher 344 rats were labeled with a fluorescent, membrane-impermeable dye chloromethyl trimethyl rhodamine or transfected with the beta-galactosidase (betaGal) reporter gene under the control of the cytomegalovirus (CMV) enhancer/promoter (pCMV-beta). Transfected or labeled SMCs (5 x 10(5) cells/animal) were delivered to syngeneic recipient rats by injection into the jugular vein; the animals were killed at intervals between 15 min and 2 wk; and the lungs, spleens, kidneys, and skeletal muscle were excised and examined. At 15 min after transplantation, injected cells were detected mainly in the lumen of small pulmonary arteries and arterioles, often in groups of three or more cells. After 24 h, labeled SMCs were found incorporated into the vascular wall of pulmonary arterioles, and transgene expression persisted in situ for 14 d with no evidence of immune response. Using simple geometric assumptions, it was calculated that approximately 57 +/- 5% of the labeled cells reintroduced into the venous circulation could be identified in the lungs after 15 min, 34 +/- 7% at 48 h, 16 +/- 3% at 1 wk, and 15 +/- 5% at 2 wk. Similar results were observed using cells transfected with the reporter gene betaGal. To determine whether this method of gene transfer could prove effective in inhibiting the development of pulmonary vascular disease, pulmonary artery SMCs were transfected with either the full-length coding sequence of endothelial nitric oxide synthase (NOS) under the control of the CMV enhancer/promoter or with the control vector (pcDNA3.1) and injected simultaneously with the pulmonary endothelial toxin monocrotaline. At 28 d after injection the right ventricular systolic pressure was significantly decreased from 50 +/- 4 mm Hg in animals injected with the null-transfected cells to 33 +/- 3 mm Hg in animals injected with the NOS-transfected cells (P < 0.01). These results suggest that a cell-based strategy of ex vivo transfection may provide an effective nonviral approach for the selective delivery of foreign transgenes to pulmonary microvessels in the treatment of pulmonary vascular disease.

Laminin and beta1 integrins are crucial for normal mammary gland development in the mouse

We have examined the role of integrin-extracellular matrix interactions in the morphogenesis of ductal structures in vivo using the developing mouse mammary gland as a model. At puberty, ductal growth from terminal end buds results in an arborescent network that eventually fills the gland, whereupon the buds shrink in size and become mitotically inactive. End buds are surrounded by a basement membrane, which we show contains laminin-1 and collagen IV. To address the role of cell-matrix interactions in gland development, pellets containing function-perturbing anti-beta1 integrin, anti-alpha6 integrin, and anti-laminin antibodies respectively were implanted into mammary glands at puberty. Blocking beta1 integrins dramatically reduced both the number of end buds per gland and the extent of the mammary ductal network, compared with controls. These effects were specific to the end buds since the rest of the gland architecture remained intact. Reduced development was still apparent after 6 days, but end buds subsequently reappeared, indicating that the inhibition of beta1 integrins was reversible. Similar results were obtained with anti-laminin antibodies. In contrast, no effect on morphogenesis in vivo was seen with anti-alpha6 integrin antibody, suggesting that alpha6 is not the important partner for beta1 in this system. The studies with beta1 integrin were confirmed in a culture model of ductal morphogenesis, where we show that hepatocyte growth factor (HGF)-induced tubulogenesis is dependent on functional beta1 integrins. Thus integrins and HGF cooperate to regulate ductal morphogenesis. We propose that both laminin and beta1 integrins are required to permit cellular traction through the stromal matrix and are therefore essential for maintaining end bud structure and function in normal pubertal mammary gland development.

Progelatinase A is produced and activated by rat hepatic stellate cells and promotes their proliferation

Activated hepatic stellate cells (HSCs) are a potential source of gelatinase A, which accumulates in fibrotic livers. Progelatinase A activation requires its binding to a complex of membrane-type matrix metalloproteinase (MT-MMP) and tissue inhibitor of metalloproteinases (TIMP)-2. These studies examine gelatinase A, MT1-MMP, and TIMP-2 synthesis by HSCs during activation in vitro and the potential role of gelatinase A in promoting HSC proliferation. Gelatinase A, MT1-MMP, and TIMP-2 messenger RNA (mRNA) were all upregulated in HSCs activated on plastic over 5 to 14 days. Gelatinase A expression was maximal at 7 days of culture, coinciding with the peak of HSC proliferation and the onset of procollagen I and alpha-smooth muscle actin (alpha-SMA) mRNA expression. Active forms of gelatinase A of 62 kd and 66 kd were secreted by activated HSCs and reached a maximum of 12.1% of total enzyme in 14-day culture supernatants. Treatment of HSCs with concanavalin A (con A) induced activation of MT1-MMP and enhanced secretion of activated gelatinase A, which reached a maximum of 44.4% of the total enzyme secreted into culture supernatants using 30 microgram/mL con A. [(14)C]-gelatin degradation assays confirmed the presence of gelatinolytic activity in activated HSC supernatants, which reached a maximum level at 7 days of culture. Antisense oligonucleotide inhibition of endogenous progelatinase A production, or the MMP inhibitor 1,10-phenanthroline inhibited (3)H-thymidine incorporation into HSC DNA by greater than 50%. We conclude that HSCs produce progelatinase A during activation in vitro and activate this enzyme coincident with MT1-MMP and TIMP-2 synthesis. Gelatinase A activity is required for maximal proliferation of HSCs in vitro suggesting this metalloproteinase is an autocrine proliferation factor for HSCs.

Modulation of mammary development and programmed cell death by the frequency of milk removal in lactating goats

1. Unilateral changes in mammary cell number are elicited when one gland is milked more or less frequently than the contralateral gland in lactating goats. These changes were investigated using histochemical and immunocytochemical markers of mammary cell types, and the degree of mammary apoptosis was determined by end-labelling of fragmented DNA. 2. Histological analysis confirmed that unilateral cessation of milking initiated involution and cell loss preferentially in the unmilked gland. The presence of fragmented DNA and morphological characteristics consistent with apoptosis demonstrated that these changes in mammary cell number in unmilked glands were, in part, the result of programmed alveolar cell death. 3. De-differentiation of the remaining secretory cells to ductal epithelial cells occurred with an increase in staining of cytokeratin markers and decreased staining by peanut lectin and casein antisera. 4. Differential once- and thrice-daily milking of lactating goats was also associated with unilateral changes in mammary cell number and milk yield. Milk yield and alveolar size were reduced after 4 weeks of infrequent milking. The latter was due to the increased loss of secretory cells by apoptosis, as indicated by a higher degree of fragmented DNA laddering. 5. After 10 weeks of differential milking, a homogeneous secretory morphology, albeit with smaller alveoli, was maintained in thrice-daily milked glands. Once-daily milked glands possessed a heterogeneous composition of terminal structures, resulting in the simultaneous presence of secretory and involuting alveoli as well as resting ductules. 6. The differences in programmed cell death and mammary morphology between unmilked and twice-daily milked glands, and between once- and thrice-daily milked glands, suggests that mammary apoptosis is subject to modulation by intra-mammary mechanisms sensitive to the frequency of milk removal.

Division of labor among the alpha6beta4 integrin, beta1 integrins, and an E3 laminin receptor to signal morphogenesis and beta-casein expression in mammary epithelial cells

Contact of cultured mammary epithelial cells with the basement membrane protein laminin induces multiple responses, including cell shape changes, growth arrest, and, in the presence of prolactin, transcription of the milk protein beta-casein. We sought to identify the specific laminin receptor(s) mediating the multiple cell responses to laminin. Using assays with clonal mammary epithelial cells, we reveal distinct functions for the alpha6beta4 integrin, beta1 integrins, and an E3 laminin receptor. Signals from laminin for beta-casein expression were inhibited in the presence of function-blocking antibodies against both the alpha6 and beta1 integrin subunits and by the laminin E3 fragment. The alpha6-blocking antibody perturbed signals mediated by the alpha6beta4 integrin, and the beta1-blocking antibody perturbed signals mediated by another integrin, the alpha subunit(s) of which remains to be determined. Neither alpha6- nor beta1-blocking antibodies perturbed the cell shape changes resulting from cell exposure to laminin. However, the E3 laminin fragment and heparin both inhibited cell shape changes induced by laminin, thereby implicating an E3 laminin receptor in this function. These results elucidate the multiplicity of cell-extracellular matrix interactions required to integrate cell structure and signaling and ultimately permit normal cell function.

(Alpha)3(beta)1 integrin regulates epithelial cytoskeletal organization

Epithelial cell morphology and cytoskeletal organization are determined by interactions, with both adjacent cells and the extracellular matrix, which are mediated by integrins and cadherins. Little is known, however, of the relative contributions of integrins and cadherins to maintaining the sub-cortical cytoskeleton characteristic of epithelial cells. Since most studies that utilize integrin-blocking antibodies result in a loss of both cell-cell adhesion and sub-cortical cytoskeletal organization, it has been difficult to distinguish whether integrins and cadherins both mediate cytoskeletal assembly in epithelial cells. Therefore, cells derived from kidney collecting ducts of (alpha)3(beta)1 integrin-deficient mice were used to examine the role of integrins in epithelial cell morphology and cytoskeletal organization. In primary cell culture, (alpha)3(beta)1 integrin-deficient kidney collecting duct cells maintain cadherin-mediated cell-cell adhesions but fail to form the sub-cortical cytoskeleton that is characteristic of epithelial cells, and instead assemble actin stress fibers. Moreover, the cell-cell junctions in mutant cells were irregular, rather than being uniformly oriented perpendicular to the culture substrate. These results demonstrated that integrins have an primary and essential function in establishing and maintaining the sub-cortical cytoskeleton that is characteristic of epithelial cells. To further study the role of (alpha)3(beta)1 integrin in establishing and maintaining cytoskeletal organization in tubular epithelial cells, we derived immortalized cell lines from wild-type and (alpha)3(beta)1 integrin-deficient kidney collecting ducts that duplicated the cytoskeletal and cadherin organization observed in primary cells. E-cadherin and (alpha)- and (beta)-catenin were complexed together in equal amounts in membranes of wild-type and (alpha)3(beta)1 integrin-deficient cells. However, association of the cadherin:catenin complex with (alpha)-actinin was greatly decreased in mutant cells, indicating that integrin-mediated assembly of the sub-cortical cytoskeleton is essential for subsequent association of the cytoskeleton with the cadherin:catenin complex. These results present direct evidence for integrin:cadherin cross-regulation in which cadherin function is dependent on the presence of an integrin.

Caspase activation is downstream of commitment to apoptosis of Ntera-2 neuronal cells

Death by apoptosis is widespread among different cell types, including neurones. Apoptosis consists of a phase during which cells commit to die, followed by an execution phase, characterized by conserved morphological changes. To prevent neuronal loss during disease, it is important to identify the events which define irreversible commitment to death. The present study has investigated the events accompanying the commitment and execution phases of the neuronal cell line Ntera-2. In response to serum starvation, Ntera-2 cells enter the execution phase and detach into the culture supernatant with an apoptotic morphology. This phase is associated with activation of caspases. The remaining adherent cells have a normal morphology and can adhere to extracellular matrix substrates. However, after 96 h of serum deprivation, 95% of these adherent cells fail to form colonies in a single cell cloning assay. When refed with serum, 70% of these cells become apoptotic within 24 h, suggesting that they had previously committed to die. A further 20% of the cells escape from commitment to apoptosis by beginning to differentiate. Inhibition of caspases fails to delay commitment. In response to serum deprivation, therefore, neuronal cells either differentiate or commit to cell death, and events upstream of caspase activation regulate this irreversible commitment. These results have significant therapeutic implications since they suggest that caspase inhibitors may not promote long-term survival of every neuronal cell type in every situation.

Extracellular matrix selectively modulates the response of mammary epithelial cells to different soluble signaling ligands

In adherent cells, cell-substratum interactions are essential for the propagation of some growth factor signaling events. However, it has not been resolved to what extent different types of extracellular matrix regulate the signals elicited by different soluble ligands. Our previous work has shown that prolactin signaling in mammary epithelium requires a specific cell interaction with the basement membrane and does not occur in cells plated on collagen I. We have now investigated whether the proximal signaling pathways triggered by insulin, epidermal growth factor (EGF), and interferon-gamma are differentially regulated in primary mammary epithelial cell cultures established on basement membrane and collagen I. Two distinct signaling pathways triggered by insulin exhibited a differential requirement for cell-matrix interactions. Activation of insulin receptor substrate (IRS) and phosphatidylinositol 3-kinase was restricted to cells contacting basement membrane, whereas the phosphorylation of Erk occurred equally in cells on both substrata. The amplitude and duration of insulin-triggered IRS-1 phosphorylation and its association with phosphatidylinositol 3-kinase were strongly enhanced by cell-basement membrane interactions. The mechanism for inhibition of IRS-1 phosphorylation in cells cultured on collagen I may in part be mediated by protein-tyrosine phosphatase activity since vanadate treatment somewhat alleviated this effect. In contrast to the results with insulin, cell adhesion to collagen I conferred greater response to EGF, leading to higher levels of tyrosine phosphorylation of the EGF receptor and Erk. The mechanism for increased EGF signaling in cells adhering to collagen I was partly through an increase in EGF receptor expression. The interferon-gamma-activated tyrosine phosphorylation of Jak2 and Stat3 was independent of the extracellular matrix. It is well recognized that the cellular environment determines cell phenotype. We now suggest that this may occur through a selective modulation of growth factor signal transduction resulting from different cell-matrix interactions.

Type IV collagen and laminin regulate glomerular mesangial cell susceptibility to apoptosis via beta(1) integrin-mediated survival signals

Postinflammatory scarring is characterized by changes in extracellular matrix (ECM) composition and progressive loss of normal resident cells. In glomerular inflammation there is now evidence that unscheduled apoptosis (programmed cell death) of mesangial and other resident cells may mediate progression to irreversible glomerulosclerosis. In the current study we examined the hypothesis that ECM components may differ in their capacity to support mesangial cell survival by suppression of apoptosis. Using a well-established in vitro model of mesangial cell apoptosis, we found that collagen IV and laminin, components of normal mesangial ECM, protected rat mesangial cells from apoptosis induced by serum starvation and DNA damage, by a beta(1) integrin-mediated, but arg-gly-asp (RGD)-independent mechanism. In contrast, collagen I, fibronectin, and osteonectin/SPARC, which are overexpressed in diseased glomeruli, failed to promote rat mesangial cell survival. However, the survival-promoting effect of collagen IV and laminin was not associated with changes in cellular levels of apoptosis regulatory proteins of the Bcl-2 family. These experiments demonstrate that glomerular mesangial cell survival is dependent on interactions with ECM and provide insights into potential mechanisms by which resident cell loss may occur during acute inflammation and postinflammatory scarring of the kidney and other organs.

Developmental regulation of Bcl-2 family protein expression in the involuting mammary gland

Epithelial cells within the mammary gland undergo developmental programmes of proliferation and apoptosis during the pregnancy cycle. After weaning, secretory epithelial cells are removed by apoptosis. To determine whether members of the Bcl-2 gene family could be involved in regulating this process, we have examined whether changes in their expression occur during this developmental apoptotic program in vivo. Bax and Bcl-x were evenly expressed throughout development. However, expression of Bak and Bad was increased during late pregnancy and lactation, and the proteins were present during the time of maximal apoptotic involution. Thereafter, their levels declined. In contrast, Bcl-w was expressed in pregnancy and lactation but was downregulated at the onset of apoptosis. Bcl-2 was not detected in lactating or early involuting mammary gland. Thus, the pro-apoptotic proteins Bax, Bak and Bad, as well as the death-suppressors Bcl-x, Bcl-2 and Bcl-w, are synthesised in mouse mammary gland, and dynamic changes in the expression profiles of these proteins occurs during development. To determine if changes in Bak and Bcl-w expression could regulate mammary apoptosis, their effect on cultured mouse mammary epithelial cells was examined in transient transfection assays. Enforced expression of Bak induced rapid mammary apoptosis, which could be suppressed by coexpression of Bcl-w. In extracts of mammary tissue in vivo, Bak heterodimerized with Bcl-x whereas Bax associated with Bcl-w, but Bak/Bcl-w heterodimers were not detected. Thus, Bak and Bcl-w may regulate cell death through independent pathways. These results support a model in which mammary epithelial cells are primed for apoptosis during the transition from pregnancy to lactation by de novo expression of the death effectors Bak and Bad. It is suggested that these proteins are prevented from triggering apoptosis by anti-apoptotic Bcl-2 family proteins until involution, when the levels of Bcl-w decline. Our study provides evidence that regulated changes in the expression of cell death genes may contribute to the developmental control of mammary apoptosis.