Abstract C04: In vivo upregulation of bone morphogenic protein 4 (BMP4) in esophageal cancer is through tumor-stroma crosstalk

Bone morphogenic proteins (BMPs) are multi-functional growth factors that belong to the transforming growth factor-beta (TGFβ;) superfamily. Amongst them, BMP4 is becoming increasingly attractive due to its crucial role in the development of many cancers. Whereas in malignancies such as glioblastoma and myeloma high levels of BMP4 are associated with benign features, in gastrointestinal cancers BMP4 possesses tumorigenic capacities. In these cancers, BMP4 acts on tumor epithelial cells enhancing their pro-metastatic behavior and chemo-resistance. However, whether BMP4 is being secreted by the epithelial cells or by the stroma, has not been well established yet, in part due to a lack of specific anti-BMP4 antibodies.

To elucidate the functional implications of the origin of BMP4 production, we made use of a novel esophageal adenocarcinoma (EAC) tumor xenograft model and a newly generated Llama-derived anti-BMP4 antibody. Using in vivo molecular imaging techniques we find that BMP4 expression in the tumor is increased after engraftment of BMP4 negative human EAC tumor cells into immunodeficient mice. Immunohistochemical studies of the engrafted tissue reveal both a mouse and a human origin of BMP4 protein, suggesting that both epithelial as well as stromal cells are involved in BMP4 secretion. This implies that whereas the stroma directly secretes BMP4; it also produces molecules that activate autocrine BMP4 production by the cancer epithelial cells. In vitro analysis such as co-cultures with different stromal cells, revealed the functional effects of stroma-derived BMP4 on tumor cells, and how our anti-BMP4 antibodies can inhibit these. Further, these studies also uncovered the stromal components that induce BMP4 secretion by the human epithelial cells.

In sum, these studies suggest a pivotal role of the microenvironment in regulating both directly and indirectly BMP4 expression in a model of esophageal cancer. As BMP4 has also been shown to be responsible for tumor progression in other gastrointestinal cancers, stromal regulation of BMP4 production might not be restricted to EAC, and might be a common feature in gastrointestinal cancers. Finally, as our anti-BMP4 Llama-derived antibodies can inhibit these effects in vitro, they might represent a novel therapy in targeting stromal function and preventing metastasis.

Citation Format: Silvia Calpe, Matthew Read, Maria del Carmen Sancho-Serra, Danielle Straub, Nick Clemons, David Liu, Wayne Phillips, Kausilia K. Krishnadath. In vivo upregulation of bone morphogenic protein 4 (BMP4) in esophageal cancer is through tumor-stroma crosstalk. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr C04.

Mutations in the selenocysteine insertion sequence-binding protein 2 gene lead to a multisystem selenoprotein deficiency disorder in humans

Selenium, a trace element that is fundamental to human health, is incorporated into some proteins as selenocysteine (Sec), generating a family of selenoproteins. Sec incorporation is mediated by a multiprotein complex that includes Sec insertion sequence-binding protein 2 (SECISBP2; also known as SBP2). Here, we describe subjects with compound heterozygous defects in the SECISBP2 gene. These individuals have reduced synthesis of most of the 25 known human selenoproteins, resulting in a complex phenotype. Azoospermia, with failure of the latter stages of spermatogenesis, was associated with a lack of testis-enriched selenoproteins. An axial muscular dystrophy was also present, with features similar to myopathies caused by mutations in selenoprotein N (SEPN1). Cutaneous deficiencies of antioxidant selenoenzymes, increased cellular ROS, and susceptibility to ultraviolet radiation-induced oxidative damage may mediate the observed photosensitivity. Reduced levels of selenoproteins in peripheral blood cells were associated with impaired T lymphocyte proliferation, abnormal mononuclear cell cytokine secretion, and telomere shortening. Paradoxically, raised ROS in affected subjects was associated with enhanced systemic and cellular insulin sensitivity, similar to findings in mice lacking the antioxidant selenoenzyme glutathione peroxidase 1 (GPx1). Thus, mutation of SECISBP2 is associated with a multisystem disorder with defective biosynthesis of many selenoproteins, highlighting their role in diverse biological processes.