Analysis of growth factor-dependent signalling in human epithelioid sarcoma cell lines: clues to the role of autocrine, juxtacrine and paracrine interactions in epithelioid sarcoma

Abstract

Human epithelioid sarcoma (ES) is an extremely aggressive soft tissue tumour of unknown histogenesis. Although growth factor-dependent signalling cascades significantly affect the biological behaviour of malignant tumours, little is known so far about their role in human ES. The present investigation, therefore, analyses the coexpression and function of different growth factors and their receptors in the human ES cell line GRU-1 and its clonal subpopulations (GRU-1A, GRU-1B and GRU-1C). As shown by Northern blot, flow cytometry, immunocytochemistry and MTT assay, all ES cell lines expressed transforming growth factor (TGF)-α and the epidermal growth factor receptor (EGF-R). Although no response to exogenous TGF-α was observed, antagonistic anti-EGF-R antibodies (at 20 μg/ml) induced significant ( P<0.05) growth inhibition in all cell lines. All cell lines showed coexpression of platelet-derived growth factor (PDGF)-A and the corresponding receptors. Neutralisation of ES-derived PDGF by anti-hPDGF antibodies resulted in significant ( P<0.05) growth inhibition of all clonal subpopulations. Although all cell lines expressed TGF-β 1 as well as TGF-β type I and type II receptors (TGF-BI-R and TGF-BII-R), growth inhibition ( P<0.05) by exogenous TGF-β 1 was achieved in the clonal subpopulations only and not in the parental cell line. No ES cell line expressed acidic fibroblast growth factor (FGF) but stimulation of FGF type 3 and type 4 receptors (FGF-3R and FGF-4R) by exogenous acidic FGF (aFGF) resulted in a marked ( P<0.05) acceleration of proliferation in all cell lines. In conclusion, our investigation suggests an intricate network of autocrine, juxtacrine and paracrine signalling between ES tumour cells and adjacent non-neoplastic stromal cells.