MT1-MMP is a membrane-bound matrix metalloproteinase (MT-MMP) capable of mediating pericellular proteolysis of extracellular matrix components. MT1-MMP is therefore thought to be an important molecular tool for cellular remodeling of the surrounding matrix. To establish the biological role of this membrane proteinase we generated MT1-MMP-deficient mice by gene targeting. MT1-MMP deficiency causes craniofacial dysmorphism, arthritis, osteopenia, dwarfism, and fibrosis of soft tissues due to ablation of a collagenolytic activity that is essential for modeling of skeletal and extraskeletal connective tissues. Our findings demonstrate the pivotal function of MT1-MMP in connective tissue metabolism, and illustrate that modeling of the soft connective tissue matrix by resident cells is essential for the development and maintenance of the hard tissues of the skeleton.

Abstract. We have developed two rat mAbs that recognize different subunits of the human fibroblast fibronectin receptor complex and have used them to probe the function of this cell surface heterodimer. mAb 13 recognizes the integrin class 1 beta polypeptide and mAb 16 recognizes the fibronectin receptor alpha polypeptide. We tested these mAbs for their inhibitory activities in cell adhesion, spreading, migration, and matrix assembly assays using WI38 human lung fibroblasts, mAb 13 inhibited the initial attachment as well as the spreading of WI38 cells on fibronectin and laminin substrates but not on vitronectin. Laminin-mediated adhesion was particularly sensitive to mAb 13. In contrast, mAb 16 inhibited initial cell attachment to fibronectin substrates but had no effect on attachment to either laminin or vitronectin substrates. When coated on plastic, both mAbs promoted WI38 cell spreading. However, mAb 13 (but not mAb 16) inhibited the radial outgrowth of cells from an explant on fibronectin substrates, mAb 16 also did not inhibit the motility of individual fibroblasts on fibronectin in low density culture and, in fact, substantially accelerated migration rates. In assays of the assembly of an extracellular fibronectin matrix by WI38 fibroblasts, both mAbs produced substantial inhibition in a concentration-dependent manner. The inhibition of matrix assembly resulted from impaired retention of fibronectin on the cell surface. Treatment of cells with mAb 16 also resulted in a striking redistribution of cell surface fibronectin receptors from a streak-like pattern to a relatively diffuse distribution. Concomitant morphological changes included decreases in thick microfilament bundle formation and reduced adhesive contacts of the streak-like and focal contact type. Our results indicate that the fibrol~last fibronectin receptor (a) functions in initial fibroblast attachment and in certain types of adhesive contact, but not in the later steps of cell spreading; (b) is not required for fibroblast motility but instead retards migration; and (c) is critically involved in fibronectin retention and matrix assembly. These findings suggest a central role for the fibronectin receptor in regulating cell adhesion and migration.T HE interaction of cells with solid substrates is important for their anchorage, proliferation, migration, and differentiation. Cells can attach, spread, and migrate on a variety of extracellular glycoproteins including fibronectin, laminin, vitronectin, and collagen. These interactions occur through specific cell surface receptors. Many of these cell adhesion receptors belong to a large superfamily of related cell surface complexes called the integrins or the cytoadhesins (for reviews see 3,11,26,30,33,37,52). The integrins are noncovalent, heterodimeric glycoprotein complexes that consist of a 140,000-180,000-D alpha subunit and a 105,000-125,000-D beta subunit. The alpha subunit often consists of a small, transmembrane polypeptide of 20,000 D disulfide bonded to a larger, extracellular polypeptide ...

Mannose receptor–mediated uptake of collagen by M2-like macrophages is a major mechanism of collagen turnover in mice.

We have isolated the major cell surface glycoprotein of chick embryo fibroblasts, CSP, and added it to a variety of transformed cells in vitro. The transformed cells become more elongated, often more flattened, and show increased adhesion to the substratum. Several transformed cell lines also align in striking parallel arrays. This alignment is characterized by a decrease in the amount of nuclear overlapping, probably indicating restoration of contact inhibition of movement. The morphological changes are antagonized by antibody to CSP. These effects of CSP are not associated with an elevation of cellular 3':5'-cyclic AMP. Moreover, the morphological reversion is not accompanied by an alteration in growth properties. Our results are consistent with a role for CSP in cell adhesion and morphology but not in growth control.The major cell surface glycoprotein of chick embryo fibroblasts, CSP, is substantially decreased after transformation by oncogenic viruses. Similar proteins, designated "LETS" proteins, are decreased in other cell types after transformation (refs. 1-3; for other references see 4 and 5). We have isolated CSP and found that it will aggregate several cell types, including erythrocytes, embryonic chick cells, and transformed NRK (normal rat kidney) cells (6, 7), suggesting that CSP may play a physiological role in cell:cell adhesion. The agglutinin activity of CSP is destroyed by treatment with proteases and chelating agents and is greatly diminished in transformed chick cells (7). Since transformation is often accompanied by altered growth control, morphology, adhesion, and contact inhibition of movement, we investigated whether re-attaching this glycoprotein to the cell surface could restore a more normal phenotype to transformed cells. We find that CSP partially restores morphology, adhesion, and the alignment characteristic of untransformed fibroblasts.MATERIALS AND METHODS Isolation of CSP. We prepared CSP from secondary cultures of chick embryo fibroblasts as described previously; the protein is essentially homogeneous by electrophoresis in sodium dodecyl sulfate with or without 8 M urea at pH 7 or pH 11 (ref. 7; unpublished). We then added solid ammonium sulfate to 70% saturation and adjusted the pH to 7.4 with NH40H. After 30 min at 4°, the solution was centrifuged at 25,000 X g for 15 min. The pellet was solubilized in 1ko volume of buffer A (0.15 M NaCl, 1 mM CaCl2, 10 mM cyclohexylaminopropane sulfonic acid, pH 11.0) at about 1 mg/ml, dialyzed overnight against two changes of 400 volumes of buffer A, and stored at -70°. These conditions are optimal for maintaining a concentrated, nonaggregated preparation of CSP with high agglutinating activity (unpublished Cytoplasmic Area and Nuclear Overlap Ratio. SVT2 cells were plated at 1 X I04 per cm2 on glass coverslips in CSP-containing or control media. After 48 hr they were fixed and stained with hematoxylin (9). Cytoplasmic area was measured using the intersections of a 10 X 10 microscope eyepiece grid by the formula A = aCF/IN, where ...