fig6: Antiadhesive effects of LTBP-2 and its fragments are concentration dependent. (A) Concentration dependency analysis. Glass coverslips were coated with constant concentration of FN (10 μg/ml). Nonspecific binding sites were saturated with BSA, and the coverslips were incubated with increasing concentrations of LTBP-2 or its fragments L2-N* and L2-V*. Fibroblasts plated on BSA only served as a control. Fibroblasts were fixed 90 min after plating and stained for actin. Cells lost their adherent morphology when the concentrations of LTBP-2 or its fragments were increased. Bottom, quantification of cell spreading. Cell spreading was quantified from the coverslips (three independent fields). Note the differences in maximal effects of LTBP-2 and its fragments. (B) Comparison of LTBP-2 and tenascin-C effects on actin stress fiber formation. Actin stress fiber formation of cells was quantified from coverslips treated with increasing concentrations of LTBP-2 or tenascin-C.

Mentions: Next, we investigated the effects of LTBP-2 on actin cytoskeletons of cells attaching to FN. Full-length LTBP-2 and its NH2-terminal fragments had a dominant actin stress fiber formation–disrupting effect on fibroblasts when compared with cells plated on FN alone (Fig. 5 B). Actin staining was mainly localized to the cell periphery, including membrane ruffles and patch-like structures at the extremities of the cells, resembling very much the cells plated on LTBP-2 fragments only (compare with Fig. 4), whereas cells plated on FN formed extensive stress fibers. The effect resembled that of tenascin-C. In addition, cells cultured on LTBP-2/FN substratum were less spread than control cells (Fig. 6 A). The COOH-terminal control fragment L3-C* derived from LTBP-3 (Penttinen et al., 2002) did not exhibit any detectable effects on cell morphology or actin cytoskeleton formation (Fig. 5 B).

Hyytiäinen M, Keski-Oja J - J. Cell Biol. (2003)

Bottom Line: Unlike FN, this fragment did not augment actin stress fiber formation.Interestingly, the adhesion-mediating and cytoskeleton-disrupting effects were localized to the same NH2-terminal proline-rich region of LTBP-2.LTBP-2 and its antiadhesive fragment bound to FN in vitro, and the antiadhesive fragment associated with the extracellular matrix FN fibrils.

Affiliation: Department of Virology, The Haartman Institute and Helsinki University Hospital, University of Helsinki, Helsinki FIN-00014, Finland.

Abstract: We have analyzed the effects of latent TGF-beta binding protein 2 (LTBP-2) and its fragments on lung fibroblast adhesion. Quantitative cell adhesion assays indicated that fibroblasts do not adhere to full-length LTBP-2. Interestingly, LTBP-2 had dominant disrupting effects on the morphology of fibroblasts adhering to fibronectin (FN). Fibroblasts plated on LTBP-2 and FN substratum exhibited less adherent morphology and displayed clearly decreased actin stress fibers than cells plated on FN. These cells formed, instead, extensive membrane ruffles. LTBP-2 had no effects on cells adhering to collagen type I. Fibroblasts adhered weakly to the NH2-terminal fragment of LTBP-2. Unlike FN, this fragment did not augment actin stress fiber formation. Interestingly, the adhesion-mediating and cytoskeleton-disrupting effects were localized to the same NH2-terminal proline-rich region of LTBP-2. LTBP-2 and its antiadhesive fragment bound to FN in vitro, and the antiadhesive fragment associated with the extracellular matrix FN fibrils. These observations reveal a potentially important role for LTBP-2 as an antiadhesive matrix component.