Epithelial–Mesenchymal Transition Induces an Antitumor Immune Response Mediated by NKG2D Receptor

Abstract

Epithelial–mesenchymal transition (EMT) is a morphogenetic process characterized by the acquisition of mesenchymal properties linked with an invasive phenotype and metastasis of tumor cells. NK group 2, member D (NKG2D) is an NK cell–activating receptor crucially involved in cancer immunosurveillance. In this study, we show that induction of EMT by TGF-β stimulation of human keratinocytes, by glycogen synthase kinase-3β inhibition in several epithelial tumor cell lines, and by Snail1 overexpression in colorectal cancer cells strongly upregulated the expression of NKG2D ligands (NKG2DLs), MHC class I chain–related molecules A and B (MICA/B) and ULBP1-3. Overexpression of Snail1 and inhibition of glycogen synthase kinase-3β in colorectal tumor cells markedly induced the activity of Sp1 transcription factor, which plays a key role in the upregulation of NKG2DL expression during EMT. The stimulation of MICA/B expression by TGF-β treatment was independent of Sp1, but it involved posttranslational mechanisms mediated by mammalian target of rapamycin pathway. Accordingly, with the increased expression of NKG2DLs, triggering of EMT rendered cancer cells more susceptible to NKG2D-mediated killing by NK cells. In agreement, MICA/B were expressed in vivo in well-differentiated colorectal tumors with retained epithelial characteristics, whereas no expression of MICA/B was detected in poorly differentiated and invasive colorectal tumors that have lost epithelial characteristics. This decrease of MICA/B expression was associated with a dramatic increase of NKG2D+-tumor infiltrating lymphocytes. Overall, our findings indicate that EMT is a relevant checkpoint in the control of tumor progression through NKG2D-mediated immune responses.

Epithelial-mesenchymal transition leads to NK cell–mediated metastasis-specific immunosurveillance in lung cancer

“…Strongly supporting the above notion, our studies show that in addition to promoting an invasive phenotype (18,19,44), EMT renders cancer cells more susceptible to NK-mediated killing, in vitro, by modulating activating and inhibitory ligands. This is consistent with a singular in vitro study that showed increased susceptibility of a colon cancer cell line to NK cells (45). More importantly, for the first time to our knowledge, we have demonstrated the effect of this enhanced susceptibility on tumor metastasis in vivo in multiple mouse models.…”

Sulforaphane induces ROS mediated induction of NKG2D ligands in human cancer cell lines and enhances susceptibility to NK cell mediated lysis

“…Epithelial-mesenchymal transitions (EMT) induced the expression of NKG2DLs, rendering EMT tumor cells more susceptible to elimination by NK cells [36], thus supporting our observations of high MICA/B expression by the invasive cell line MDA-MB-231. U-937 monocytic cell lines have high surface expression as well as secrete MICA and MICB.…”

Drug-induced hyperploidy stimulates an antitumor NK cell response mediated by NKG2D and DNAM-1 receptors

“…Additionally, co-culture with hyperploid cancer cells induced the expression of NKG2D and DNAM-1 on NK cells, and experiments performed using blocking antibodies highlighted the relevance of these receptors in the cytotoxic response of NK cells against polyploid cancer cells. Altogether, we describe herein that, additionally to oncogenes, proliferative, tumor progression and stress signals, which are known to regulate NKG2D ligands expression in cancer, [26][27][28][29][30] the induction of hyperploidy is involved in the activation of the NKG2D-mediated cancer immunosurveillance.…”

“…22 Among NK cell receptors, NKG2D plays a key role in the immune response against cancer. 18,23 Genotoxic stress, 24 Sp1 transcription factors, 25 proliferative and tumor suppressor signaling pathways, 26,27 and tumor progression 28,29 are known to induce the expression of NKG2D ligands in cancer cells, initiating an antitumor immune response. [30][31][32] Activated NK cells are capable of killing a broad range of cancers and of regulating the innate and adaptive immune responses through the secretion of cytokines, such as IFN-g.…”