Methylation patterns of the E-cadherin 5 ' CpG island are unstable and reflect the dynamic, heterogeneous loss of E-cadherin expression during metastatic progression

Metastatic progression of most common epithelial tumors involves a heteroge neous, transient loss of expression of the homotypic cell adhesion protein, E-cadherin, rather than the uniform loss of a functional protein resulting from coding region mutation. Indeed, whereas E-cadherin loss may promote i nvasion, reexpression may facilitate cell survival within metastatic deposi ts. The mechanisms underlying such plasticity are unclear. We now show that the heterogeneous loss of E-cadherin expression in primary human breast ca ncers reflects a heterogeneous pattern of promoter region methylation, whic h begins early prior to invasion. In cultured human tumor cells, such heter ogeneous methylation is dynamic, varying from allele to allele and shifting in relation to the tumor microenvironment. Following invasion in vitro whi ch favors diminished E-cadherin expression, the density of promoter methyla tion markedly increased. When these cells were cultured as spheroids, which requires homotypic cell adhesion, promoter methylation decreased dramatica lly, and E-cadherin was reexpressed, These data show that the methylation a ssociated with E-cadherin loss in human breast cancer is heterogeneous and unstable and suggest that such epigenetic plasticity may contribute to the dynamic, phenotypic heterogeneity that drives metastatic progression.