Laminin α-chain expression and basement membrane formation by MLE-15 respiratory epithelial cells

Abstract

-Basement membranes have a critical role in alveolar structure and function. Alveolar type II cells make basement membrane constituents, including laminin, but relatively little is known about the production of basement membrane proteins by murine alveolar type II cells and a convenient system is not available to study basement membrane production by murine alveolar type II cells. To facilitate study of basement membrane production, with particular focus on laminin chains, we examined transformed murine distal respiratory epithelial cells (MLE-15), which have many structural and biochemical features of alveolar type II cells. We found that MLE-15 cells produce laminin-␣5, a trace amount of laminin-␣3, laminins-␤1 and -␥1, type IV collagen, and perlecan. Transforming growth factor-␤1 significantly induces expression of laminin-␣1. When grown on a fibroblast-embedded collagen gel, MLE-15 cells assemble a basement membrane-like layer containing laminin-␣5. These findings indicate that MLE-15 cells will be useful in modeling basement membrane production and assembly by alveolar type II cells. murine alveolar type II cells; transforming growth factor-␤; extracellular matrix BASEMENT MEMBRANES ARE THIN sheets of extracellular matrix that serve as a structural support for cells. They also act as a selective barrier to various solutes and affect cell properties, including proliferation, differentiation, adhesion, and migration (for review, see Ref. 6). The major components of basement membranes are laminins, type IV collagens, entactins (nidogens), and perlecan. Basement membrane composition varies between tissues and even in the same tissue at different stages of development. Laminins contribute to the diversity of basement membranes. Laminins are a family of heterotrimeric glycoproteins in which each member contains an ␣-, ␤-, and ␥-chain. To date, five ␣-, three ␤-, and three ␥-chains forming 15 laminin isoforms have been described. Laminin-␥3 is the most recently described (23) laminin chain and is the only laminin chain that is not found in basement membranes. In the current model, basement membrane assembly occurs via linking of a type IV collagen network with a laminin network by entactin (41).In the lung, alveolar type I and alveolar type II cells rest on a continuous basement membrane; however, the composition of the basement membrane under both cell types is not the same. Differences exist in the location of basement membrane anionic sites beneath alveolar type I and type II cells (34). Subsets of alveolar type II cells have localized interruptions or discontinuities of the basement membrane where cytoplasmic processes extend and contact or closely approximate interstitial fibroblasts and extracellular matrix, whereas the basement membrane beneath type I cells does not (5).The alveolar epithelial basement membrane is complex in composition and undergoes changes during development. Recent studies (29, 30) highlight the variability of laminin ␣-chain expression in the lung. Laminin-␣1 and -␣2 are present in fet...

The Kindler Syndrome Protein Is Regulated by Transforming Growth Factor-β and Involved in Integrin-mediated Adhesion

“…The disruption of the integrity of the basement membrane caused by genetic defects in ␣ 3 and ␤ 1 integrin and kindlerin implicates these proteins in basement membrane assembly and maintenance and suggests that they are likely components of the same signaling pathway. TGF-␤ not only enhances kindlerin expression as shown in this report but also increases the abundance of integrins (61, 62) and extracellular matrix constituents such as fibronectin, collagen, and laminin (63)(64)(65)(66). Therefore, it is reasonable to postulate that organization of the newly synthesized extracellular matrix components by integrin and kindlerin complexes may be an important step in TGF-␤-stimulated cell motility.…”

Laminin-6 assembles into multimolecular fibrillar complexes with perlecan and participates in mechanical-signal transduction via a dystroglycan-dependent, integrin-independent mechanism

“…The alveolar cells of the lung lie on a basement membrane composed of a complex of matrix proteins (Miner et al, 1997;Nguyen et al, 2002). In the intact lung, the production of laminin subunits is developmentally regulated.…”

Increase in laminin expression in allergic airway remodelling and decrease by dexamethasone

“…Prior work by LEE et al [32] demonstrated that IL-13 induces lung fibrosis in mice by selective activation of transforming growth factor-b (TGF-b). TGF-b induces expression of laminin a1 chains in rat mesangial cells [33] and laminin c1 chains in mouse distal respiratory epithelial cells [34]. The ability of laminin, via a laminin/nidogen binding site, to form a lattice-type assembly with collagen in the lung matrix may lead to airway wall thickening.…”