LIV-1 promotes prostate cancer epithelial-to-mesenchymal transition and metastasis through HB-EGF shedding and EGFR-mediated ERK signaling

LIV-1, a zinc transporter, is an effector molecule downstream from soluble growth factors. This protein has been shown to promote epithelial-to-mesenchymal transition (EMT) in human pancreatic, breast, and prostate cancer cells. Despite the implication of LIV-1 in cancer growth and metastasis, there has been no study to determine the role of LIV-1 in prostate cancer progression. Moreover, there is no clear delineation of the molecular mechanism underlying LIV-1 function in cancer cells. In this study, we found increased LIV-1 expression in a progresssive manner in benign, PIN, primary and bone metastatic human prostate cancer. We characterized the mechanism by which LIV-1 drives prostate cancer EMT in an androgen-refractory human prostate cancer cell (ARCaP) bone metastasis model. LIV-1, when overexpressed in ARCaPE cells (derivative cells of ARCaP with epithelial phenotype), promoted EMT irreversibly. LIV-1 overexpressed ARCaPE cells had elevated levels of HB-EGF and matrix metalloproteinase (MMP) 2 and MMP 9 proteolytic enzyme activities, without affecting intracellular zinc concentration. The activation of MMPs resulted in the shedding of heparin binding-epidermal growth factor (HB-EGF) from ARCaP E cells, eliciting constitutive epidermal growth factor receptor (EGFR) phosphorylation and its downstream extracellular signal regulated kinase (ERK) signaling. Further investigation of the HB-EGF promoter revealed that both Stat3 and AP-1 controlled HB-EGF promoter activity. Ectopic LIV-1 overexpression induced AP-1 and Stat3 activation. Blockade of both Stat3 and AP-1 by specific inhibitors or dominant negative expression vectors diminished the HB-EGF promoter activity induced by LIV-1 overexpression. These results suggest that LIV-1 is involved in prostate cancer progression as an intracellular target of growth factor receptor signaling which promotes EMT and cancer metastasis. LIV-1 could be an attractive therapeutic target for the eradication of pre-existing human prostate cancer and bone and soft tissue metastases.;INDEX WORDS: LIV-1, EMT, Prostate cancer progression, EGFR, HB-EGF, ERK, AP-1, Stat3.