Knockout of MXRA8 in MDA-MB-231 cells
Matrix remodeling associated protein 8 or MXRA8 is a transmembrane protein that can binds arthritogenic alpha viruses like the Chikunggunya virus and provide viral entry into cells. MXRA8 can also interact with integrin ß3 and thus possibly regulate cell-cell interactions and binding to the extracellular matrix. While MXRA8 has been associated with reduced survival in patients with colorectal and renal clear cell cancers, the role of MXRA8 in breast cancer remains unexplored. Our previous work exploring genes that mediate the anti-tumor effects of the miR-200c/141 cluster in breast cancer identified MXRA8 as a potential suppressor of breast cancer growth and metastasis. In the current study, MXRA8 was knocked out in the human triple negative breast cancer cell line, MDA-MB-231. Loss of MXRA8 reduce cell proliferation in vitro but had no effect on apoptosis or migration in cultured cells. However, loss of MXRA8 significantly delayed tumor development and reduced metastatic dissemination to the lungs in a xenograft model. RNA sequencing identified three genes, ADMATS1, TIE1, and BMP2 whose expression were significantly reduced in MXRA8 knockout tumors compared to control tumors. MXRA8 staining of a human breast cancer tissue array revealed higher levels of MXRA8 in primary tumors and metastases of aggressive tumor subtypes (TNBC and HER2+) compared to less aggressive, ER+ breast cancers.  Our findings demonstrate for the first time that MXRA8 regulates the progression of human TNBC possibly through influencing the interaction of tumor cells with their microenvironment. Overall design: MXRA8 was knocked out in MDA-MB-231 cells using Crispr-Cas. RNA sequencing was performed on two different knockout clones and a control clone  grown in two dimensional culture and following injection into the mammary glands of NCG mice.