Mapping the genetic basis of breast microcalcifications and their role in metastasis

Asif Rizwan,Chao Zheng,Menglin Cheng,Santosh Kumar Paidi,Kristine Glunde,Ishan Barman

doi:10.1038/s41598-018-29330-9

Abstract

Breast cancer screening and early stage diagnosis is typically performed by X-ray mammography, which detects microcalcifications. Despite being one of the most reliable features of nonpalpable breast cancer, the processes by which these microcalcifications form are understudied and largely unknown. In the current work, we have investigated the genetic drivers for the formation of microcalcifications in breast cancer cell lines, and have investigated their involvement in disease progression. We have shown that stable silencing of the Osteopontin (OPN) gene decreased the formation of hydroxyapatite in MDA-MB-231 breast cancer cells in response to osteogenic cocktail. In addition, OPN silencing reduced breast cancer cell migration. Furthermore, breast cancer cells that had spontaneously metastasized to the lungs in a mouse model of breast cancer had largely elevated OPN levels, while circulating tumor cells in the same mouse model contained intermediately increased OPN levels as compared to parental cells. The observed dual roles of the OPN gene reveal the existence of a direct relationship between calcium deposition and the ability of breast cancer cells to metastasize to distant organs, mediated by common genetic factors.

Highlights

Breast cancer is the most common malignancy in women with an incidence rate of about 120 in 100,000 women in the United States[1]
The contribution of OPN to the migratory properties of the cancer cells was validated through in vivo studies by quantifying and comparing levels of OPN and CD44 expression in parental MDA-MB-231 cells orthotopically implanted in the mouse, MDA-MB-231 cells that have escaped from the primary tumor into the blood circulation, and MDA-MB-231 cells that have successfully metastasized to the lungs
Osteopontin expression increases with breast cancer cell aggressiveness and osteogenic cocktail treatment

Summary

Introduction

Breast cancer is the most common malignancy in women with an incidence rate of about 120 in 100,000 women in the United States[1]. Emerging evidence from us and others suggests that higher hydroxyapatite content in mammary microcalcifications is a marker for malignant disease whereas lower hydroxyapatite and a relatively higher calcium carbonate content is characteristic of benign breast lesions[6] Such studies have provided limited information about the mechanisms governing the genesis of microcalcifications and their role in disease progression. Bellahacene et al reported increased expression of bone matrix proteins, which are typically involved in physiological bone mineralization, in human breast cancer cells, and speculated that they may have a role in hydroxyapatite formation[9,10]. Osteopontin (OPN) is a secreted soluble glycoprotein that is present in most body fluids including milk and serum[12] It is overexpressed in a number of different carcinomas and has previously been implicated as an enhancer of mineralization in human breast cancer samples[9]. The contribution of OPN to the migratory properties of the cancer cells was validated through in vivo studies by quantifying and comparing levels of OPN and CD44 expression in parental MDA-MB-231 cells orthotopically implanted in the mouse, MDA-MB-231 cells that have escaped from the primary tumor into the blood circulation, and MDA-MB-231 cells that have successfully metastasized to the lungs

Methods

Results

Conclusion