MRPS18-2 protein immortalizes primary rat embryonic fibroblasts and endows them with stem cell-like properties.

We report that the overexpression of mitochondrial ribosomal protein MRPS18-2 (S18-2) can immortalize primary rat embryonic fibroblasts (REFs). The immortalized cells (18IM) lose contact inhibition, form foci, and are capable of anchorage-independent growth. Concurrently, mesodermal markers, such as vimentin, smooth muscle actin, and Fut4, disappear completely. 18IM cells express embryonic stem cell markers, such as SSEA-1, Sox2, and Oct3/4. In confluent cultures, a portion of cells also express ectoderm- and endoderm-specific pan-keratin, ectoderm-specific beta-III-tubulin, mesoderm-specific MHC class II, and become stainable for fat with Oil red O. None of these changes was detected in c-myc+Ha-ras (MR)-transformed cells. In immunodeficient mice, 18IM cells formed small transiently growing tumors that have down-regulated SSEA-1 and showed pan-keratin staining. We conclude that S18-2 can immortalize REFs and induces them to express stem cell traits.

Epstein-Barr virus encoded EBNA-3 binds to vitamin D receptor and blocks activation of its target genes.

Epstein-Barr virus (EBV) is a human gamma herpes virus that infects B cells and induces their transformation into immortalized lymphoblasts that can grow as cell lines (LCLs) in vitro. EBNA-3 is a member of the EBNA-3-protein family that can regulate transcription of cellular and viral genes. The identification of EBNA-3 cellular partners and a study of its influence on cellular pathways are important for understanding the transforming action of the virus. In this work, we have identified the vitamin D receptor (VDR) protein as a binding partner of EBNA-3. We found that EBNA3 blocks the activation of VDR-dependent genes and protects LCLs against vitamin-D3-induced growth arrest and/or apoptosis. The presented data shed some light on the anti-apoptotic EBV program and the role of the EBNA-3-VDR interaction in the viral strategy.