Methylation and silencing of the Thrombospondin-1 promoter in human cancer

Neovascularization is a common feature of many human cancers, but relativel y few molecular defects have been demonstrated in genes regulating angiogen esis. Decreased expression of Thrombospondin-1 (THBS1), a P53 and Rb regula ted angiogenesis inhibitor, has been observed in some human tumors, includi ng glioblastoma multiforme (GBM). To study whether methylation-associated i nactivation is involved in down-regulating THBS1 expression in cancer, we a nalysed the methylation status of THBS1 in several cell lines and primary t umors. Three cell lines (RKO, CEM and RAJI) were completely methylated at s everal CpG sites within the THBS1 5' CpG island, and had no detectable expr ession ba RT-PCR, THBS1 expression,vas readily reactivated using the methyl ation-inhibitor 5-deoxy-azacytidine in all three lines, Furthermore, THBS1 methylation was present in 33% (14/42) of primary GBMs, Thus, de novo methy lation may serve as a potential way to inactivate THBS1 expression in human neoplasms.