HUMAN FETAL LUNG (IMR-90) CELLS - MYOFIBROBLASTS WITH SMOOTH MUSCLE-LIKE CONTRACTILE PROPERTIES

Single cells displaying many characteristics in common with smooth mus cle are now being identified in many organs. Although their origin rem ains elusive, they are nonetheless known to play a major role in fibro proliferative diseases and stromal reactions by virtue of their contra ctile properties. We have investigated the contractile properties and expression of smooth muscle-associated proteins in such a cell line de rived from human foetal lung (IMR-90). For almost two decades, these c ells have served as model fibroblasts in a wide variety of studies. An d yet, IMR-90 cells manifest many features characteristic of different iated smooth muscle cells: they exhibit the same elongated, slender fo rm and the strikingly regular, longitudinal alignment of their actin-a ttachment sites, which are indispensable for coordinated contraction. Moreover, these adhaerens junctions also contain metavinculin, the smo oth muscle analogue of vinculin, the stable expression of which has no t previously been demonstrated in cultured cells. Since sm 22, as well as the smooth muscle-associated a-actin isoform and calponin are also expressed, IMR-90 cells must now be classified as myofibroblasts. Whe n cultivated on a rubbery silicon surface, IMR-90 cells respond to sti mulation with a rate of contraction which is considerably faster than that exhibited by fibroblasts derived from other established lines. Ta ken together, the regular longitudinal orientation of the adhaerens ju nctions, the stable expression of metavinculin, and the rapid speed of shortening in IMR-90 cells suggest, by implication, that the periodic ity of actin attachment sites is a fundamental determinant of contract ile efficiency in smooth muscle cells; this spacing may be mediated by metavinculin. (C) 1996 Wiley-Liss, Inc.