Lysyl Oxidase Interacts with Hormone Placental Lactogen and Synergistically Promotes Breast Epithelial Cell Proliferation and Migration

Noemi Polgar,Ben Fogelgren,J Michael Shipley,Katalin Csiszar

doi:10.1074/jbc.m609407200

Noemi Polgar, Ben Fogelgren + Show 2 more

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https://doi.org/10.1074/jbc.m609407200

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Abstract

Lysyl oxidase (LOX), an extracellular amine oxidase, catalyzes the cross-linking of collagen and elastin. LOX has been also shown to play an essential role in promoting the invasive and metastatic potential of breast tumor cells. However, the LOX-interacting factors in these processes are not known. In this study, we identified placental lactogen (PL), a member of the growth hormone/prolactin hormone family, as a LOX-interacting partner using yeast two-hybrid screens. PL is normally only expressed in placental syncytiotrophoblasts, but PL genes are amplified and expressed in a high percentage of invasive ductal breast carcinomas. We confirmed LOX-PL interactions using far Western and solid phase binding assays. In activity assays, PL was not a substrate or inhibitor of LOX. We further demonstrated that PL is expressed in breast tumor epithelial cells and detected LOX-PL interactions by coimmunoprecipitation in invasive breast cancer cells. In MCF-10A normal breast epithelial cells stably expressing LOX, PL, or both, LOX had no effect on cell proliferation, PL alone increased proliferation by 49%, and coexpression of LOX and PL led to a 121% increase in cell proliferation. Unlike in tumor cells, LOX did not induce a more migratory phenotype in MCF-10A cells; nor did PL. However, their coexpression resulted in a 240% increase in cell migration, suggesting that these interactions may be highly relevant to the transition of epithelial cells toward a migratory phenotype during the development and progression of breast carcinoma and a significant role for LOX-PL interactions in epithelial cell behavior.

Highlights

Lysyl oxidase (LOX)2 is a copper-dependent amine oxidase that catalyzes the enzymatic step for generating lysine-derived covalent cross-links that insolubilize collagen and elastin dur
To elucidate the factors that might play a role in these molecular mechanisms, we focused on LOX-protein interactions and identified human placental lactogen as a potential interacting partner of LOX from yeast two-hybrid screens
We have shown that the active LOX promoted migratory/invasive behavior in the noninvasive/poorly metastatic breast cancer cell lines MCF-7 and T47D [7] and that in normal epithelial cells, LOX overexpression induced changes toward a mesenchymal, fibroblastlike morphology [42]

Summary

Introduction

Lysyl oxidase (LOX) is a copper-dependent amine oxidase that catalyzes the enzymatic step for generating lysine-derived covalent cross-links that insolubilize collagen and elastin dur-. Recent studies suggested the implication of LOX in cell motility [3, 4], transcriptional regulation [5], embryonic development [2, 6], and pathological conditions, including cancer. Increases in the expression and enzymatic activity of LOX have been demonstrated in highly invasive cutaneous and uveal melanoma [7], invasive and metastatic breast cancer cell lines [7, 8], and metastatic breast tumors [9]. The proteolytic activation of LOX and its matrix cross-linking activity has been extensively studied, its significance in pathological conditions is less understood. PL is only expressed in the placenta during pregnancy, and it replaces the down-regulated pituitary PRL as the placental growth hormone (GH-V) replaces the down-regulated pituitary GH [16]. A trend was noted toward an increased incidence of lymph node metastases with amplification of the PL genes [22]

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