The Integrin αvβ3-5 Ligand MFG-E8 Is a p63/p73 Target Gene in Triple-Negative Breast Cancers but Exhibits Suppressive Functions in ER+ and erbB2+ Breast Cancers

Abstract

The progression from preinvasive lesion to invasive carcinoma is a critical step contributing to breast cancer lethality. We identified downregulation of milk fat globule-EGF factor 8 (MFG-E8) as a contributor to breast cancer progression using microarray analysis of laser capture microdissected (LCM) tissues. We first identified MFG-E8 downregulation in invasive lesions in transgenic mammary tumor models, which were confirmed in LCM-isolated human invasive ductal carcinomas compared with patient-matched normal tissues. In situ analyses of MFG-E8 expression in estrogen receptor (ER) positive cases confirmed its downregulation during breast cancer progression and small inhibitory MFG-E8 RNAs accelerated ER þ breast cancer cell proliferation. MFG-E8 also decreased in erbB2 þ human cancers and erbB2 transgenic mice lacking MFG-E8 showed accelerated tumor formation. In contrast, MFG-E8 expression was present at high levels in triple-negative (ER À , PgR À , erbB2 À ) breast cancers, cell lines, and patient sera. Knockdown, chromatin immunoprecipitation, and reporter assays all showed that p63 regulates MFG-E8 expression, and MFG-E8 knockdowns sensitized triple-negative breast cancers to cisplatin treatment. Taken together, our results show that MFG-E8 is expressed in triple-negative breast cancers as a target gene of the p63 pathway, but may serve a suppressive function in ER þ and erbB2 þ breast cancers. Its potential use as a serum biomarker that contributes to the pathogenesis of triple-negative breast cancers urges continued evaluation of its differential functions. Cancer Res; 71(3); 937-45. Ó2010 AACR.

MFG-E8/lactadherin regulates cyclins D1/D3 expression and enhances the tumorigenic potential of mammary epithelial cells

“…Our analysis of gene expression data revealed that MFG-E8 is highly expressed in primary and metastatic breast cancers and that its high expression is significantly associated with lack of ER expression as reported previously (Yang et al, 2011). We also found that high levels of MFG-E8 can be present in tumors expressing ErbB2, but not in those with the highest levels of ErbB2 (possibly bearing gene amplification).…”

“…Years ago MFG-E8, originally called BA46, was found to be expressed in some breast carcinomas and breast carcinoma cell lines and to be present in the sera of patients with advanced breast cancer, but not in that of healthy individuals (Ceriani et al, 1982;Peterson et al, 1990;Larocca et al, 1991). Schmidt and co-workers recently confirmed and extended these observations, showing that MFG-E8 is highly expressed in triplenegative breast cancers, but that it is downregulated during progression in estrogen receptor (ER)-positive carcinomas, suggesting that it may perform different functions in different breast cancer subtypes (Yang et al, 2011). These findings underscore the putative value of MFG-E8 as a biomarker and likely therapeutic target in breast carcinomas, and the need to better understand its functional properties.…”

“…The fact that MFG-E8 increases the tumorigenicity of 168FARN cells in NOD/SCID mice without an apparent induction of tumor angiogenesis suggests that this protein has additional functions in a developing mammary tumor, independent of, or not limited to, endothelial cell activation (Silvestre et al, 2005;Neutzner et al, 2007) and Treg-lymphocytemediated immune suppression (Jinushi et al, 2008). Yang et al (2011) have reported that whereas MFG-E8 may promote the progression of triple-negative breast carcinomas, it appears to inhibit the progression of ER-and ErbB2-positive tumors that in their study are characterized by a reduced basal expression of this protein. They also found that MFG-E8 downregulation in ER-positive cells stimulates their proliferation.…”

“…It has been shown that functionally blocking anti-MFG-E8 antibodies induced the regression of experimental breast cancers (Ceriani et al, 1987) and acted synergistically with conventional chemotherapy to reduce experimental colon carcinomas, melanomas and lymphomas (Jinushi et al, 2009); in addition, triple-negative breast cancer cells in which MFG-E8 expression was silenced were more sensitive to cisplatin treatment (Yang et al, 2011). Taken together with this published evidence, our present results support the idea that combinatorial therapies that include MFG-E8 blockade may be operative in the treatment of some breast cancer patients.…”

“…For this reason, it is critical to better elucidate MFG-E8 signaling properties and intracellular partners to identify novel mechanisms that can be therapeutically targeted. Moreover, as MFG-E8 function appears to vary in different breast cancer subtypes (Yang et al, 2011), it is important to identify those cancer types that will respond to anti-MFG-E8 therapies.…”