Up-regulation of thrombospondin-1 gene by epidermal growth factor and transforming growth factor β in human cancer cells - Transcriptional activation and messenger RNA stabilization

Thrombospondin-1 (TSP-1), a multifunctional matrix protein, affects tumor growth through modulation of angiogenesis and other stromal biological functions. In several of nine human cancer cell lines derived from liver, brain, pancreas, and bone, expression of TSP-1 was up-regulated in response to the two most representative growth factors, epidermal growth factor (EGF) and transforming growth factor β1 (TGFβ1). Expression of TSP-1 was markedly enhanced in hepatic HuH-7 cells by EGF but not by TGFβ1. In contrast, expression of TSP-1 was markedly enhanced by TGFβ1, but not by EGF, in osteosarcoma MG63 cells. EGF induced activation of TSP-1 promoter-driven luciferase activity in HuH-7 cells, and the elements between -267 and -71 on the 5′ region of TSP-1 gene containing two GC boxes to which Sp1 bound, were found to be responsible for the promoter activation by EGF. However, EGF did not alter TSP-1 mRNA stability in hepatic cells. On the other hand, no such enhancement of the TSP-1 promoter activity by TGFβ1 appeared in MG63 cells. Enhanced expression of TSP-1 by TGFβ1 in MG63 cells was partially blocked by exogenous addition of SB203580, an inhibitor of p38 mitogen-activated protein kinase. TGFβ was found to induce marked elongation of TSP-1 mRNA longevity in osteosarcoma cells when mRNA degradation was assayed in the presence of α-amanitin. The up-regulation of TSP-1 by EGF and TGFβ might play a critical role in modulation of angiogenesis and formation of matrices in tumor stroma.