Cancer cells on the move: Mechanisms of dissemination from breast tumors

Abstract

Most of breast cancer mortality stems from the ability of carcinoma cells to leave the primary tumor and colonize different organs; thus major efforts in breast cancer research are now focusing in understanding the signals/mechanisms governing the early steps of metastasis, invasion and intravasation.;Using an in vivo invasion assay, we set out to investigate whether Heregulin and CXCL12 could induce invasion within the tumor microenvironment and whether this invasive behavior was dependent on tumor-resident cells. We show, in both xenograft and transgenic breast cancer models, that Heregulin and CXCL12 enhance in vivo invasion of breast cancer cells in a macrophage dependent manner, with the EGF/CSF-1 paracrine interaction between these cells constituting a common mechanism of cancer cell invasion.;Although CXCL12 signaling has been found to be important both in tumor growth and metastasis by interacting with CXCR4 expressed in cancer cells, the recent discovery of CXCR7 as a second CXCL12 receptor that enhances primary tumor growth and experimental metastasis, has raised new questions on how CXCL12 affects the different steps of metastasis. To investigate the role of CXCL12/CXCR4 versus CXCL12/CXCR7 signaling in breast cancer metastasis, we overexpressed these receptors in MTLn3 cells. We show that CXCR4 and CXCR7 play opposite roles in breast cancer progression with CXCR7 enhancing primary tumor growth but impairing cancer cell invasion to CXCL12 and dissemination from the primary tumor, while CXCR4 has no effect in primary tumor growth but increases the motile and invasive behavior of cancer cells to CXCL12 and their ability to leave the primary tumor.;The main result of cancer cell invasion is the approach of blood vessels---the highways for dissemination. Since not many cancer cells actually intravasate, we hypothesized that intravasated cells exhibit a different gene expression profile compared to the average primary tumor cell. To evaluate these changes in gene expression, we used microarray technology. We orthotopically injected mice with GFP labeled breast cancer cells, extracted intravasated breast cancer cells via cardiac punctures and sorted them using Fluorescence Activated Cell Sorting. We report methods useful in amplification of small amounts of RNA and preliminary gene expression findings.