Transfection of Mv1Lu mink lung type II alveolar cells with ␤1-6-N-acetylglucosaminyl transferase V is associated with the expression of large lysosomal vacuoles, which are immunofluorescently labeled for the lysosomal glycoprotein lysosomal-associated membrane protein-2 and the ␤1-6-branched N-glycan-specific lectin phaseolis vulgaris leucoagglutinin. By electron microscopy, the vacuoles present the morphology of multilamellar bodies (MLBs). Treatment of the cells with the lysosomal protease inhibitor leupeptin results in the progressive transformation of the MLBs into electron-dense autophagic vacuoles and eventual disappearance of MLBs after 4 d of treatment. Heterologous structures containing both membrane lamellae and peripheral electron-dense regions appear 15 h after leupeptin addition and are indicative of ongoing lysosome-MLB fusion. Leupeptin washout is associated with the formation after 24 and 48 h of single or multiple foci of lamellae within the autophagic vacuoles, which give rise to MLBs after 72 h. Treatment with 3-methyladenine, an inhibitor of autophagic sequestration, results in the significantly reduced expression of multilamellar bodies and the accumulation of inclusion bodies resembling nascent or immature autophagic vacuoles. Scrape-loaded cytoplasmic FITC-dextran is incorporated into lysosomal-associated membrane protein-2-positive MLBs, and this process is inhibited by 3-methyladenine, demonstrating that active autophagy is involved in MLB formation. Our results indicate that selective resistance to lysosomal degradation within the autophagic vacuole results in the formation of a microenvironment propicious for the formation of membrane lamella. INTRODUCTIONMultilamellar bodies (MLBs) are membrane-bound cellular organelles, which vary in size from 100-2400 nm, are composed of concentric membrane layers, and frequently exhibit an electron-dense core. MLBs are found in numerous cell types where they function in lipid storage and secretion (Schmitz and Mü ller, 1991). In lung type II alveolar cells, MLBs function as secretory granules whose exocytosis results in the deposition of the tubular myelin forms of surfactant on the surface of the alveolae (Hatasa and Nakamura, 1965;Ryan et al., 1975;Williams, 1977). The surfactant film over the alveolar epithelium regulates the surface tension at the air-cell interface and protects the alveola from collapse during respiration (Haagman and van Golde, 1991).Although the secretory function of MLBs in type II alveolar cells is well established, the precise mechanism of MLB biogenesis remains unclear. Autoradiographic studies of murine type II alveolar cells of mouse lungs showed that although phospholipids labeled with [ 3 H]choline are delivered directly from the Golgi to the MLB, proteins metabolically labeled with [ 3 H]leucine are visualized within multivesicular bodies before delivery to MLBs (Chevalier and Collet, 1972). Surfactant proteins A, B, and C are delivered via multivesicular bodies to MLBs, and multivesicular bodies are proposed as th...

The pleiotropic cytokines, transforming growth factor ␤1 (TGF␤1), and tumor necrosis factor (TNF) play critical roles in tissue homeostasis in response to injury and are implicated in multiple human diseases and cancer. We reported that the loss of Timp3 (tissue inhibitor of metalloproteinase 3) leads to abnormal TNF signaling and cardiovascular function. Here we show that parallel deregulation of TGF␤1 and TNF signaling in

Introduction Extensive mammographic density in women is associated with increased risk for breast cancer. Mouse models provide a powerful approach to the study of human diseases, but there is currently no model that is suited to the study of mammographic density.