Paracrine control of differentiation in the alveolar carcinoma, A549, by human foetal lung fibroblasts

Abstract

Summary Synthesis of pulmonary surfactant (PS) is necessary for normal functioning of the lungs and its production is indicative of normal differentiated lung. The human alveolar carcinoma, A549, has been found to synthesis and secrete PS in vitro. The purpose of this study was to optimise the culture conditions for PS synthesis by A549 as well as to determine the potential role of foetal lung fibroblasts in the induction of PS by glucocorticoids. A549 cells growing in filter wells produced higher levels of PS in response to steroid, a 5-fold increase on the filter well compared to only a 1.5-fold increase when the cells were cultured on a conventional plastic substrate. A549 cells grown in filter wells responded to coculture with fibroblasts whether in direct contact or separated co-culture. A 20-fold increase in PS over control values was observed in separated steroid-treated co-cultures, suggesting the presence of a diffusible factor. A partially purified factor was isolated from fibroblast conditioned medium which was capable of inducing differentiation and other phenotypic changes in A549, namely induction of PS, reduction of plasminogen activator activity and reduction in the in vivo growth of A549 xenografts in nude mice. These results suggest that, under the correct conditions, A549 cells, although transformed, still retain the capacity to respond to differentiation-inducing signals from normal fibroblasts.

Induction of tumor suppression and glandular differentiation of A549 lung carcinoma cells by dominant-negative IGF-I receptor

“…Hence, induction of tumor cell dierentiation may underlie the tumor suppressive eect of dnIGF-IR. Consistent with paracrine control of dierentiation, a partially purified factor isolated from ®broblast conditioned medium has been shown to inhibit the growth of A549 cells as established xenografts in nude mice and induce stromal in®ltration and glandular-like or duct-like differentiation (Speirs et al, 1991). In spite of its transformed phenotype, A549 cells can still respond to paracrine control of dierentiation via a soluble factor.…”

Activation of paracrine growth factors by heparan sulphate induced by glucocorticoid in A549 lung carcinoma cells

“…In vitro, the synthesis of pulmonary surfactant and alkaline phosphatase can be induced in A549, a cell line derived from a human lung adenocarcinoma (Giard et al 1972), of reputedly type II cell origin (Lieber et al, 1976), by conditioned medium from lung fibroblasts (CM) (Speirs et al, 1991). Whereas induction of PS synthesis by CM was enhanced by treating the fibroblasts with dexamethasone (DX) before and during the conditioning process, DX was not required for the action of the CM on the A549 cells (Speirs et al, 1991). It is, however, required for the induction of alkaline phosphatase by CM and by several cytokines, such as oncostatin M (OSM), interleukin 6 (IL-6), and interferons a and [3, and by insulin (McCormick et al, 1995;McCormick and Freshney, 1996).…”

“…Perinatal induction of differentiation is mediated by glucocorticoids and a paracrine factor, or factors, from mesenchymally derived cells in the lung (Caniggia et al, 1991). In vitro, the synthesis of pulmonary surfactant and alkaline phosphatase can be induced in A549, a cell line derived from a human lung adenocarcinoma (Giard et al 1972), of reputedly type II cell origin (Lieber et al, 1976), by conditioned medium from lung fibroblasts (CM) (Speirs et al, 1991). Whereas induction of PS synthesis by CM was enhanced by treating the fibroblasts with dexamethasone (DX) before and during the conditioning process, DX was not required for the action of the CM on the A549 cells (Speirs et al, 1991).…”

“…A partially purified factor from DX-treated lung fibroblasts was shown to inhibit growth of A549 cells grown as xenografts in nude mice (Speirs et al, 1991). Separate studies have demonstrated that paracrine factors are present in CM from fibroblasts Speirs et al, 1991;McCormick et al, 1995 (1995) showed that pure, cloned, cytokines are active singly, provided that DX is present, so there are some stable active inducers of AP, many of which are reasonable candidates for paracrine factors released by lung fibroblasts.…”

“…A partially purified factor from DX-treated lung fibroblasts was shown to inhibit growth of A549 cells grown as xenografts in nude mice (Speirs et al, 1991). Separate studies have demonstrated that paracrine factors are present in CM from fibroblasts Speirs et al, 1991;McCormick et al, 1995 (1995) showed that pure, cloned, cytokines are active singly, provided that DX is present, so there are some stable active inducers of AP, many of which are reasonable candidates for paracrine factors released by lung fibroblasts. As their activity is dependent on DX however, it is important to determine the nature of this dependence, on the one hand to understand better the mechanism of growth factor and cytokine action and, on the other, to determine whether a purified activating factor could substitute for DX, which may not always be appropriate for clinical treatment, particularly if it is prolonged and repeated.…”