15-Deoxy-Δ12,14-prostaglandin J2 Induces Epithelial-tomesenchymal Transition in Human Breast Cancer Cells and Promotes Fibroblast Activation

Abstract

In inflammation-associated carcinogenesis, COX-2 is markedly overexpressed, resulting in accumulation of various prostaglandins. 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) is one of the terminal products of COX-2-catalyzed arachidonic acid catabolism with oncogenic potential. Epithelial-to-mesenchymal transition (EMT) is a process by which epithelial cells lose their polarity and adhesiveness, and thereby gain migratory and invasive properties. Treatment of human breast cancer MCF-7 cells with 15d-PGJ(2) induced EMT as evidenced by increased expression of Snail and ZEB1, with concurrent down-regulation of E-cadherin. Nuclear extract from 15d-PGJ(2) treated MCF-7 cells showed the binding of Snail and ZEB1 to E-box sequences present in the E-cadherin promoter, which accounts for repression of E-catherin expression. Unlike 15d-PGJ(2), its non-electrophilic analogue 9,10-dihydro-15d-PGJ(2) failed to induce EMT, suggesting that the alpha,beta-unsaturated carbonyl group located in the cyclopentenone ring of 15d-PGJ(2) is essential for its oncogenic function. Notably, the mRNA level of interleukin-8 (IL-8)/CXCL8 was highly elevated in 15d-PGJ(2)-stimulated MCF-7 cells. 15d-PGJ(2)-induced up-regulation of IL-8/CXCL8 expression was abrogated by silencing of Snail short interfering RNA. Treatment of normal fibroblast with conditioned medium obtained from cultures of MCF-7 cells undergoing EMT induced the expression of activated fibroblast marker proteins, alpha-smooth muscle actin and fibroblasts activation protein-alpha. Co-culture of normal fibroblasts with 15d-PGJ(2)-stimulated MCF-7 cells also activated normal fibroblast cells to cancer associated fibroblasts. Taken together, above findings suggest that 15d-PGJ(2) induces EMT through up-regulation of Snail expression and subsequent production of CXCL8 as a putative activator of fibroblasts, which may contribute to tumor-stroma interaction in inflammatory breast cancer microenvironment.