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

Mammary Localization and Abundance of Laminin, Fibronectin, and Collagen IV Proteins in Prepubertal Heifers

The objective was to determine localization and abundance of extracellular matrix proteins fibronectin, laminin, and collagen in mammary tissues from ovariectomized or intact prepubertal heifers. Mammary parenchyma and fat pad tissues were collected from 14 6-mo-old heifers: eight were ovariectomized between 1 to 3 mo of age, and six were used as intact controls. Distribution of total collagen was assessed by Sirius Red staining of tissue sections. Fibronectin, laminin, and type IV collagen were assessed by immunohistochemistry. Abundance of fibronectin and laminin was also analyzed by western blotting. Total mammary mass was much less in ovariectomized animals (130 +/- 21 vs. 304 +/- 25 g). Histological structure differed as parenchyma from intact animals contained abundant, complex branching epithelial terminal ductular units, whereas terminal ductular units from ovariectomized animals were mostly major ductal structures with little or no branching. Collagen fibers were abundant and densely packed throughout interlobular stroma and were less abundant and more diffuse within intralobular stroma. Type IV collagen was primarily in basal lamina of mature ducts, whereas fibronectin and laminin staining were present throughout parenchymal stroma, in both intact and ovariectomized animals. Using western blotting, fibronectin was more abundant within parenchyma than in the fat pad and significantly higher in parenchyma from ovariectomized heifers. Laminin was more abundant in parenchyma from intact than ovariectomized animals (30 vs. 17 densitometric units/mg of tissue), but laminin was similar between parenchyma and fat pad. These results provide initial evidence that fibronectin, laminin, and collagen participate in regulation of heifer prepubertal mammary development.

Cathepsin L plays an active role in involution of the mouse mammary gland

Involution of the mammary gland after weaning occurs in two stages. The first stage is reversible, whereas the second stage is characterized by the irreversible collapse of the alveolar structure. A differential display analysis using cDNAs from tissues obtained at various times after forced weaning of pups identified cathepsin L as up-regulated during early involution. Levels of cathepsin L mRNA were dramatically increased within 24 hr after weaning. Cathepsin L protein detected by immunoblot was also increased during involution, reaching near maximal levels by 36 hr after weaning. In situ immunohistochemistry detected pronounced cathepsin L protein in the cytoplasm and cell periphery. Mice treated with a specific inhibitor of cathepsin L exhibited substantially reduced numbers of apoptotic cells at times up to 72 hr after weaning when compared with untreated animals. The cathepsin L inhibitor did not alter levels of cathepsin L detected in immunoblots or influence molecular weight of the cathepsin L species detected. These data suggest that cathepsin L plays a regulatory role early in the process of mammary gland involution.

Broad-spectrum matrix metalloproteinase inhibitor marimastat-induced musculoskeletal side effects in rats

OBJECTIVE

To characterize the clinical and histopathologic changes in a rat model of broad-spectrum matrix metalloproteinase (MMP)-induced musculoskeletal syndrome (MSS), and to facilitate research into the causes and treatments of MSS in humans.

METHODS

Male Lewis rats weighing 150-180 gm were administered 10-30 mg of the broad-spectrum MMP inhibitor marimastat over a 2-week period via surgically implanted subcutaneous osmotic pumps. The animals were monitored and scored for the onset and severity of MSS, using clinical and histologic parameters.

RESULTS

Marimastat-treated rats exhibited various clinical signs, including compromised ability to rest on their hind feet, high-stepping gait, reluctance or inability to move, and hind paw swelling. Histologically, marimastat-treated rat joints were characterized by soft tissue and bone changes, such as increased epiphyseal growth plate, synovial hyperplasia, and increased cellularity in the joint capsule and extracapsular ligaments. The severity of MSS, as judged by clinical criteria (2 blinded observers using 3 clinical parameters), paw volume, and histologic score, was nearly identical. The observed changes were indistinguishable from those reported for primate models and mimic MSS in humans.

CONCLUSION

This simple and sensitive model of MSS is an attractive alternative for studying the pathology of MSS.

Mast cell chymase induces smooth muscle cell apoptosis by a mechanism involving fibronectin degradation and disruption of focal adhesions

OBJECTIVE

Chymase released from activated mast cells has been shown to induce apoptosis of vascular smooth muscle cells (SMCs) in vitro. The proteolytic activity of chymase is essential for the proapoptotic effect, but the mechanism of chymase-induced apoptosis has remained unknown.

METHODS AND RESULTS

Here we show by means of FACS analysis, immunohistochemistry, and Western blotting that mast cell-derived chymase induces SMC apoptosis by a mechanism involving degradation of an extracellular matrix component, fibronectin (FN), with subsequent disruption of focal adhesions. The FN degradation products induced SMC apoptosis of similar magnitude and with similar changes in outside-in signaling, as did chymase. Sodium orthovanadate, an inhibitor of tyrosine phosphatases, inhibited the chymase-induced SMC apoptosis. Focal adhesion kinase (FAK), one of the key mediators of integrin-extracellular matrix interactions and cell survival, was rapidly degraded in the presence of chymase or FN degradation products. Loss of phosphorylated FAK (p-FAK) resulted in a rapid dephosphorylation of the p-FAK-dependent downstream mediator Akt.

CONCLUSIONS

The results suggest that chymase-secreting mast cells can mediate apoptosis of neighboring SMCs through a mechanism involving degradation of pericellular FN and disruption of the p-FAK-dependent cell-survival signaling cascade.

The not-so innocent bystander: the microenvironment as a therapeutic target in cancer

The microenvironment in which cancer arises is often regarded as a bystander to the clonal expansion and acquisition of malignant characteristics of the tumour. However, a major function of the microenvironment is to suppress cancer, and its disruption is required for the establishment of cancer. In addition, tumour cells can further distort the microenvironment to promote growth, recruit non-malignant cells that provide physiological resources, and facilitate invasion. In this review, the authors discuss the contribution of the microenvironment, i.e., the stroma and its resident vasculature, inflammatory cells, growth factors and the extracellular matrix (ECM), in the development of cancer, and focus on two components as potential therapeutic targets in breast cancer. First, the ECM, which imparts crucial signalling via integrins and other receptors, is a first-line barrier to invasion, modulates aggressive behaviour and may be manipulated to provide novel impediments to tumour growth. Second, the authors discuss the involvement of TGF-beta1 as an example of one of many growth factors that can regulate ECM composition and degradation and that play complex roles in cancer. Compared to the variable routes taken by cells to become cancers, the response of tissues to cancer is relatively consistent. Therefore, controlling and eliminating cancer may be more readily achieved indirectly via the tissue microenvironment.

Extracellular matrix remodeling and metalloproteinase involvement during intestine regeneration in the sea cucumber Holothuria glaberrima

The sea cucumber, Holothuria glaberrima, has the capacity to regenerate its internal organs. Intestinal regeneration is accomplished by the thickening of the mesenteric border and the invasion of this thickening by mucosal epithelium from the esophagus and the cloaca. Extracellular matrix (ECM) remodeling has been associated with morphogenetic events during embryonic development and regeneration. We have used immunohistochemical techniques against ECM components to show that differential changes occur in the ECM during early regeneration. Labeling of fibrous collagenous components and muscle-related laminin disappear from the regenerating intestine and mesentery, while fibronectin labeling and 4G7 (an echinoderm ECM component) are continuously present. Western blots confirm a decrease in fibrous collagen content during the first 2 weeks of regeneration. We have also identified five 1,10-phenanthroline-sensitive bands in collagen gelatin zymographs. The gelatinolytic activities of these bands are enhanced during early stages of regeneration, suggesting that the metalloprotease activity is associated with ECM remodeling. Inhibition of MMPs in vivo with 1,10-phenanthroline, p-aminobenzoyl-Gly-Pro-D-Leu-D-Ala hydroxamate or N-CBZ-Pro-Leu-Gly hydroxamate produces a reversible inhibition of intestinal regeneration and ECM remodeling. Our results show that significant changes in ECM content occur during intestine regeneration in the sea cucumber and that the onset of these changes is correlated to the proteolytic activities of MMPs.

Matrix metalloproteinases mediate the dismantling of mesenchymal structures in the tadpole tail during thyroid hormone-induced tail resorption

It has been suggested that a family of tissue remodelling enzymes called matrix metalloproteinases (MMPs) play a causal role in the process of tail resorption during thyroid hormone-induced metamorphosis of the anuran tadpole; however, this hypothesis has never been directly substantiated. We cloned two new Xenopus MMPs, gelatinase A (MMP-2) and MT3-MMP (MMP-16), and the MMP inhibitor TIMP-2. These clones were used along with several others to perform a comprehensive expression study. We show that all MMPs and TIMP-2 are dramatically induced in the resorbing tail during spontaneous metamorphosis and are spatially coexpressed, primarily in the remodelling mesenchymal tissues. By Northern blotting, we show that all the examined MMPs/TIMP-2 are also induced by treatment of organ-cultured tails with thyroid hormone (T(3)). Using the organ culture model, we provide the first direct evidence that MMPs are required for T(3)-induced tail resorption by showing that a synthetic inhibitor of MMP activity/expression can specifically retard the resorption process. By gelatin zymography, we also show T(3) induction of a fifth MMP, preliminarily identified as gelatinase B (GelB; MMP-9). Moreover, T(3) not only induces MMP/TIMP expression but also MMP activation, and we provide evidence that TIMP-2 participates in the latter process. These findings suggest that MMPs and TIMPs act in concert to effect the dismantling of mesenchymal structures during T(3)-induced metamorphic tadpole tail resorption.

A von Willebrand factor-derived heparin-binding peptide regulates cell--substrate adhesive strength and chemokinesis behavior

The ability of a soluble heparin-binding oligopeptide sequence derived from the von Willebrand factor (vWF) to modulate the adhesion and chemokinetic migration behavior of arterial smooth muscle cells was assessed using a novel glass microsphere centrifugation assay and automated time-lapse fluorescence videomicroscopy, respectively. Treatment of cells grown on fibronectin-coated substrates with the heparin-binding peptide resulted in the disassembly of focal adhesions, as assessed by immunohistochemical staining. These observations were consistent with six-fold decrease in cell--substrate adhesive strength (P<0.001), a biphasic effect on migration speed (P<0.05), as well as a dose-dependent reduction in the percentage of motile cells and the cell dispersion coefficient (mu=S(2)T/2). The specificity of this response to the vWF-derived heparin-binding peptide was supported by the absence of an observed effect in the presence of either a scrambled peptide or a consensus heparin-binding peptide sequence of similar heparin affinity. These data support the notion that competitive interactions between cell surface heparan sulfates with heparin-binding peptide domains located in soluble peptide fragments may modulate chemokinetic cell migration behavior and other adhesion-related processes.

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.