// <![CDATA[ $('.header-date').hide();$('#titleAuthors').hide();$('#abstractHeader').hide(); // ]]> Muhammad Mushtaq1, Raja Hashim Ali2, Vladimir Kashuba1, 3, George Klein1, Elena Kashuba1, 4 1Department of Microbiology, Tumor and Cell Biology (MTC), Karolinska Institute, Stockholm, S-17177, Sweden 2KTH Royal Institute of Technology, Science for Life Laboratory, School of Computer Science and Communication, Solna, SE-17 177, Sweden 3Institute of Molecular Biology and Genetics of NASU, Kyiv, 03680, Ukraine 4R.E. Kavetsky Institute of Experimental Pathology, Oncology and Radiobiology, NASU, Kyiv, 03022, Ukraine Correspondence to: Elena Kashuba, email: Elena.Kashuba@ki.se Keywords: mitochondrial ribosomal proteins, MRPS18 family, phylogenetic analysis, evolutionary trace analysis, genetic polymorphism Received: April 07, 2016 Accepted: July 10, 2016 Published: July 30, 2016

Stemness encompasses the capability of a cell for self-renewal and differentiation. The stem cell maintains a balance between proliferation, quiescence, and regeneration via interactions with the microenvironment. Previously, we showed that ectopic expression of the mitochondrial ribosomal protein S18-2 (MRPS18-2) led to immortalization of primary fibroblasts, accompanied by induction of an embryonic stem cell (ESC) phenotype. Moreover, we demonstrated interaction between S18-2 and the retinoblastoma-associated protein (RB) and hypothesized that the simultaneous expression of RB and S18-2 is essential for maintaining cell stemness. Here, we experimentally investigated the role of S18-2 in cell stemness and differentiation. Concurrent expression of RB and S18-2 resulted in immortalization of Rb1^−/− primary mouse embryonic fibroblasts and in aggressive tumor growth in severe combined immunodeficiency mice. These cells, which express both RB and S18-2 at high levels, exhibited the potential to differentiate into various lineages in vitro, including osteogenic, chondrogenic, and adipogenic lineages. Mechanistically, S18-2 formed a multimeric protein complex with prohibitin and the ring finger protein 2 (RNF2). This molecular complex increased the monoubiquitination of histone H2A^Lys119, a characteristic trait of ESCs, by enhanced E3-ligase activity of RNF2. Furthermore, we found enrichment of KLF4 at the S18-2 promoter region and that the S18-2 expression is positively correlated with KLF4 levels. Importantly, knockdown of S18-2 in zebrafish larvae led to embryonic lethality. Collectively, our findings suggest an important role for S18-2 in cell stemness and differentiation and potentially also in cancerogenesis. Significance We here describe the essential roles of RB and MRPS18-2 (S18-2) in homeostasis of cell stemness. Mouse primary cells expressing both S18-2 and RB (designated as RH18RB) exhibited a stem cell phenotype. As a proof of principle, we demonstrated decreased expression of stem-cell–related genes in human mesenchymal stem cells upon down-regulation of S18-2 and RB. Notably, loss of the S18-2 protein resulted in embryonic lethality in zebrafish. To reveal putative molecular mechanisms, we demonstrated that S18-2, in a multimeric complex with RB, enhanced the E3-ubiquitin ligase activity of RNF2 toward histone H2A. Finally, based on our observation that RH18RB cells generated tumors in severe combined immunodeficiency mice, S18-2 could be a promising target in the development of cancer therapies.

The Warburg effect is one of the hallmarks of cancer and rapidly proliferating cells. It is known that the hypoxia-inducible factor 1-alpha (HIF1A) and MYC proteins cooperatively regulate expression of the HK2 and PDK1 genes, respectively, in the Burkitt lymphoma (BL) cell line P493-6, carrying an inducible MYC gene repression system. However, the mechanism of aerobic glycolysis in BL cells has not yet been fully understood. Western blot analysis showed that the HIF1A protein was highly expressed in Epstein–Barr virus (EBV)-positive BL cell lines. Using biochemical assays and quantitative PCR (Q-PCR), we found that—unlike in lymphoblastoid cell lines (LCLs)—the MYC protein was the master regulator of the Warburg effect in these BL cell lines. Inhibition of the transactivation ability of MYC had no influence on aerobic glycolysis in LCLs, but it led to decreased expression of MYC-dependent genes and lactate dehydrogenase A (LDHA) activity in BL cells. Our data suggest that aerobic glycolysis, or the Warburg effect, in BL cells is regulated by MYC expressed at high levels, whereas in LCLs, HIF1A is responsible for this phenomenon.

Viruses play an important role in cancerogenesis. It is estimated that approximately 20% of all cancers are linked to infectious agents. The viral genes modulate the physiological machinery of infected cells that lead to cell transformation and development of cancer. One of the important adoptive responses by the cancer cells is their metabolic change to cope up with continuous requirement of cell survival and proliferation. In this review we will focus on how DNA viruses alter the glucose metabolism of transformed cells. Tumor DNA viruses enhance “aerobic” glycolysis upon virus‐induced cell transformation, supporting rapid cell proliferation and showing the Warburg effect. Moreover, viral proteins enhance glucose uptake and controls tumor microenvironment, promoting metastasizing of the tumor cells.

Mitochondrial ribosomal protein S18-2 is highly expressed in endometrial cancers along with free E2F1