Protein cross-linking mediated by tissue transglutaminase correlates with the maturation of extracellular matrices during lung development

At birth, the mammalian lung is still immature. The alveoli are not yet formed and the interairspace walls contain two capillary layers which are separated by an interstitial core. After alveolarization (first 2 postnatal weeks in rats) the alveolar septa mature: their capillary layers merge, the amount of connective tissue decreases, and the mature lung parenchyma is formed (second and third week). During the first 3 wk of life the role of tissue transglutaminase (tTG) was studied in rat lung by immunostaining of cryostat and paraffin sections, by Northern and Western blotting, and by a quantitative determination of gamma-glutamyl-epsilon-lysine. While enzyme activity and intracellular tTG were already present before term, the enzyme product (gamma-glutamyl-epsilon-lysine-crosslink) and extracellular tTG appeared between postnatal days 10 and 19 in the lung parenchyma. In large blood vessels and large airways, which mature earlier than the parenchyma, both the enzyme product and extracellular tTG had already appeared at the end of the first postnatal week. We conclude that tTG is expressed and externalized into the extracellular matrix of lung shortly before maturation of an organ area. Because tTG covalently and irreversibly crosslinks extracellular matrix proteins, we hypothesize that it may prevent or delay further remodeling of basement membranes and may stabilize other extracellular components, such as microfibrils

Wnts induce migration and invasion of myeloma plasma cells

Multiple myeloma is an incurable form of lymphoid cancer characterized by accumulation of neoplastic plasma cells in the bone marrow cavity. Little is known about the mechanisms regulating myeloma cell movement within the bone marrow and metastasis to secondary sites. Herein, we identify multiple members of the wingless/int (Wnt) family as promoters of myeloma cell migration/invasion. Wnt-mediated migration was associated with the Wnt/RhoA pathway and did not necessitate signaling through β-catenin. Activation of both RhoA and members of the protein kinase C (PKC) family, including PKCα, PKCβ, and PKCμ, were required for induction of migration. Activated RhoA and PKCα, PKCβ, and PKCμ appear to assemble in macromolecular signaling complexes that are associated with the cell membrane. These results suggest that Wnt responsiveness of myeloma plasma cells may be a significant factor in disease progression. (Blood. 2005;106: 1786-1793