Milk Fat Globule EGF-8 Promotes Melanoma Progression through Coordinated Akt and Twist Signaling in the Tumor Microenvironment

Abstract

The pathogenesis of malignant melanoma involves the interplay of tumor cells with normal host elements, but the underlying mechanisms are incompletely understood. Here, we show that milk fat globule EGF-8 (MFG-E8), a secreted protein expressed at high levels in the vertical growth phase of melanoma, promotes disease progression through coordinated A v B 3 integrin signaling in the tumor microenvironment. In a murine model of melanoma, MFG-E8 enhanced tumorigenicity and metastatic capacity through Akt-dependent and Twist-dependent pathways. MFG-E8 augmented melanoma cell resistance to apoptosis, triggered an epithelial-tomesenchymal transition (EMT), and stimulated invasion and immune suppression. In human melanoma cells, MFG-E8 knockdown attenuated Akt and Twist signaling and thereby compromised tumor cell survival, EMT, and invasive ability. MFG-E8-deficient human melanoma cells also showed increased sensitivity to small molecule inhibitors of insulin-like growth factor I receptor and c-Met. Together, these findings delineate pleiotropic roles for MFG-E8 in the tumor microenvironment and raise the possibility that systemic MFG-E8 blockade might prove therapeutic for melanoma patients. [Cancer Res 2008;68(21):8889-98]

Milk fat globule—epidermal growth factor—factor VIII (MFGE8)/lactadherin promotes bladder tumor development

“…In addition, out of 15 studies with recorded invasiveness status, two cancers, prostate and bladder carcinomas, displayed significant (Po0.001) increase of MFGE8 expression during tumor progression. In agreement with the study of Jinushi et al (Jinushi et al, 2008), the MFGE8 messenger RNA was also upregulated during progression of primary human melanoma, but with a lower level of confidence (P ¼ 0.008) (Oncomine analysis of reference (Xu et al, 2008), data not shown).…”

“…Two recent articles have proposed a regulatory T cell-promoting role for Mfge8/lactadherin in mice: in atherosclerosis (Ait-Oufella et al, 2007), or in granulocyte monocyte-colony stimulating factor-dependent induction of anti-tumor immune responses (Jinushi et al, 2007). More recently, the latter group has shown that subcutaneous grafts of mouse melanoma cells transfected with Mfge8 were infiltrated with Mfge8-expressing macrophages, regulatory T cells, and poorly efficient cytotoxic T cells when transplanted in mice (Jinushi et al, 2008), and thus became more aggressive. In the mouse model of bladder carcinoma, our observation that Mfge8 requires a functional adaptive immune system to promote development also suggests a possible Treg-dependent protumoral role of Mfge8.…”

“…is overexpressed during human bladder tumor initiation and progression MFGE8 overexpression was recently observed by immunohistochemistry in biopsies of vertical growth phase melanoma, and MFGE8 was proposed to favor melanoma progression (Jinushi et al, 2008). We assessed whether this observation could be relevant to other types of human tumors, using publicly available transcriptome data compiled in the Oncomine website ( Figure 1a, Supplementary Table S1).…”

“…Like the macrophage markers, MS4A1 was significantly overexpressed in MFGE8-overexpressing tumors, whether total or only superficial carcinoma were considered (Po0.025, Wilcoxon test, data not shown), suggesting the possible presence of B lymphocytes in these tumors. In addition, as MFGE8-mediated phagocytosis of apoptotic tumor cells by macrophages has been shown to promote the differentiation of regulatory T cells (Tregs) (Jinushi et al, 2007(Jinushi et al, , 2008, we asked whether Tregs were present in the bladder tumors. FOXP3 is the transcription factor commonly used as a Treg marker, but the low signal of the probe sets for this gene in the Affymetrix expression data precluded their use to identify Tregs.…”

“…Presence of this protein in the serum of breast cancer patients, and in some tumor cells in vitro has been observed long ago (Ceriani et al, 1982;Larocca et al, 1991). More recently, an increased MFGE8 expression in human melanoma biopsies at the vertical growth stage, a reduced resistance to apoptosis of melanoma cell lines upon MFGE8 depletion, and an increased aggressiveness in vivo of a mouse melanoma cell line engineered to overexpress MFGE8 have been described (Jinushi et al, 2008). In addition, in a mouse genetic model of pancreatic cancer, Mfge8-deficiency led to development of slightly less invasive tumors (Neutzner et al, 2007).…”