Thrombospondin 1 (TSP1) contributed to platelet-derived growth factor (PDGF) and transforming growth factor (TGF)β-induced contractile activation in normal fibroblasts via mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signalling pathways. (a) Normal fibroblasts were treated overnight with or without TGFβ or PDGF, plus the antagonists of activin-linked kinase 5 (ALK5), ERK and PDGF, and interferon (IFN)β prior to performing a floating gel contraction assay. TGFβ-induced contractile ability was significantly reduced by IFNβ as that by SB431542 and U0126 in normal fibroblasts. PDGF-induced cell contractility was impaired by PDGF receptor inhibitor (Gleevec). (b) Following floating gel contraction, the fibroblasts in floating gel samples were analysed by western blotting. TGFβ-induced TSP1 expression and p-ERK activations were inhibited by SB431542, U0126 or IFNβ. PDGF induced the overexpression of TSP1 inhibited by Gleevec, which also accompanied a retrained reaction for PDGF-induced p-ERK activation in normal fibroblasts. (c) The mRNAs from the fibroblasts in these floating gel samples were also assayed by reverse transcription (RT)-PCR. The TSP1 gene expression levels altered in a similar manner to the TSP1 protein expression level within the corresponding groups.