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Tumor necrosis factor receptor superfamily member 21 (TNFRSF21), also known as death receptor (DR6) TNFRSF21 (also known as death receptor 6 (DR6), CD358, BM-018) is highly expressed in differentiating neurons as well as in the adult brain, and is upregulated in injured neurons. DR6 negatively regulates neurondendrocyte, axondendrocyte, and oligodendrocyte survival, hinders axondendrocyte and oligodendrocyte regeneration and its inhibition has a neuro-protective effect in nerve injury. It activates nuclear factor kappa-B (NFkB) and mitogen-activated protein kinase 8 (MAPK8, also called c-Jun N-terminal kinase 1), and induces cell apoptosis by associating with TNFRSF1A-associated via death domain (TRADD), which is known to mediate signal transduction of tumor necrosis factor receptors. TNFRSF21 plays a role in T-helper cell activation, and may be involved in inflammation and immune regulation. Its possible ligand is alpha-amyloid precursor protein (APP), hence probably involved in the development of Alzheimer's disease; when released, APP binds in an autocrine/paracrine manner to activate a caspase-dependent self-destruction program that removes unnecessary or connectionless axons. Increasing beta-catenin levels in brain endothelium upregulates TNFRSF21 and TNFRSF19, indicating that these death receptors are downstream target genes of Wnt/beta-catenin signaling, which has been shown to be required for blood-brain barrier development. DR6 is up-regulated in numerous solid tumors as well as in tumor vascular cells, including ovarian cancer and may be a clinically useful diagnostic and predictive serum biomarker for some adult sarcoma subtypes.
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