Shree Ram Singh, Ph.D.
Stem cells have an inherent ability to self-renew and to differentiate into several specialized cell types as well as control the maintenance of our tissues and organs. Failure of such maintenance results in several degenerative diseases and cancer. Stem cells have recently attracted significant attention, mainly because of their potential medical benefits in the fields of therapeutic cloning and regenerative medicine. Our current research is directed toward understanding the molecular genetic mechanism by which stem cells regulate tissue homeostasis, regeneration, and tumorigenesis. We are utilizing Drosophila and mouse models to understand the above mechanisms. Specifically, we are using adult testis, kidney and gastrointestinal tissues to characterize the genes/signaling pathways that regulate stem cell behavior and tumor formation. Further, we are focusing on lipid metabolism (lipolysis) on stem cell fate. The knowledge gained from investigating stem cell regulation in Drosophila and mouse models will provide a basis for understanding how human adult stem cells respond during normal and pathological conditions.
Stem cells are undifferentiated cells and play a critical role in tissue development, homeostasis, and regeneration. Stem cells self-renewal divisions are controlled by intrinsic and extrinsic factors. Failure of stem cells function in tissue maintenance results in degenerative diseases, on the other hand, the overproliferation of stem cells results in tumor development (Singh et al., Cell Research 2005; Singh et al., Journal of Cellular and Molecular Medicine 2011; Singh, Current Medicinal Chemistry 2012; Singh, Cancer Letters 2013). Our current research is directed toward understanding the molecular genetic mechanisms by which stem cells regulate tissue homeostasis, regeneration, and tumorigenesis. We are utilizing Drosophila and mouse models to understand the above mechanisms.
In 2006, we identified a novel gene, namely GEF (a small GTPase guanine nucleotide exchange factor), and demonstrated that a Rap-GEF/Rap signaling pathway regulates stem cell anchoring to the niche and organ formation by regulating DE-cadherin-mediated cell adhesion (Wang, Singh et al., Developmental Cell 2006; Singh et al., Development, Growth & Differentiation 2006). Further, we demonstrated that the Drosophila homologue of the human tumor suppressor gene BHD regulates male germline stem cells maintenance and functions downstream of the JAK/STAT and Dpp signal transduction pathways. These findings suggest that BHD regulates tumorigenesis by modulating stem cells in human (Singh et al., Oncogene 2006). Furthermore, we also demonstrated that germline and somatic stem cells coordinate their self-renewal and differentiation through the JAK/STAT signaling pathway during Drosophila spermatogenesis (Singh et al., Journal of Cellular Physiology 2010).
Our lab identified kidney stem cells in Drosophila and characterized the signaling pathways that are responsible for maintenance of these stem cells in renal tubules (Singh et al., Cell Stem Cell 2007; Singh and Hou, Journal of the American Society of Nephrology 2008; Singh and Hou, Journal of Experimental Biology 2008; Zeng et al., Journal of Cellular Physiology 2010). Recently, we also identified gastric stem cells in the adult Drosophila (Singh et al., Cell Cycle 2011). We further found that JAK-STAT signaling regulates gastric stem cell proliferation, Wingless signaling regulates gastric stem cell self-renewal, and Hedgehog signaling regulates gastric stem cell differentiation.
In the last few years, we have been focusing on identifying the genes responsible for gastrointestinal stem cell self-renewal and differentiation. Recently, we found that JAK-STAT signaling controls ISC proliferation and this ability is negatively regulated by Notch, at least through transcriptional control of the JAK-STAT signaling ligand, unpaired (Liu et al., Journal of Cellular Biochemistry 2010). More recently, we finished a genome-wide RNAi screen in Drosophila gastrointestinal tissues (Zeng et al., Cell Reports 2015) as well as in Drosophila testis (Liu et al. Nature Communications, 2016) and identified novel regulators in these two tissue systems. We are currently focusing on characterizing these genes. In addition, we also developed immunofluorescence labeling, and in situ hybridization techniques for the identification and characterization of stem cells and differentiated cells in different Drosophila tissues (Singh and Hou, Methods Mol Biol 2008; Singh et al., Methods Mol Biol 2013).
In collaborations, we have investigated the differentiation potential of osteoarthritic chondrocytes (OC) into iPSCs using defined transcription factors and explored the possibility of using these OC-derived iPSCs for chondrogenesis. We found that iPSCs could be generated from OCs using defined factors and that in vitro co-culture of TGF-β1-transfected OC-derived iPSCs with articular cartilages (ACs) in alginate matrix results in significantly improved chondrogenesis of iPSCs. In addition, in vivo study also revealed the obvious cartilage tissue formed in the co-culture of TGF-β1- transfected OC-derived iPSCs with ACs in alginate matrix. This combinational strategy will promote the use of iPSC-derived tissue in tissue engineering (Wei et al., European Cells & Materials 2012; Yin et al., Stem Cell Reviews and Reports 2015). Further, we are also focusing on the PDX model in colon cancer (Seol et al., Cancer Letters 2014), interaction of PhIP with curcumin in breast epithelial cells (Jain et al. Cancer Letters 2015), role of microRNAs in metabolism and tumor development (Seol et al., Cancer Letters 2014; Kim et al., Cancer Letters 2015; Chan et al., Cancer Letters 2015; Singh et al., Cancer Letters 2015), surface markers for gastric cancer stem cells (Fagoonee et al., Minerva Biotec 2015), role of histone demethylase KDM1A in oral cancer (Narayanan et al., Cancer Letters 2015), role of Riluzole on hepatocellular carcinoma (HCC) therapy (Seol et al., Cancer Letters, 2016), generation and characterization of PDX models of pancreatic ductal adenocarcinoma (Jung et al. Oncotarget 2016), role of complement proteins C7 and CFH on stemness of liver cancer cells (Seol et al., Cancer Letters, 2016) and circulating endothelial progenitor cells in Crohn's disease (Dietrich and Singh, Digestive Diseases and Sciences 2017).
Recently, we found that (Mtor)/Tpr, a nuclear matrix protein that regulates germline stem cell asymmetric division and maintenance through the spindle assembly checkpoint (SAC) complex in Drosophila testis. (Liu, Singh et al., PLoS Genet 2015). Further, we have identified that Mlf1-adaptor molecule (Madm), a novel tumor suppressor, regulates the competition between germline stem cells and somatic cyst stem cells for niche occupancy in Drosophila testis (Singh et al., Nature Communications 2016).
Recent studies suggest that cancer stem cells (CSCs) are responsible for tumor propagation, relapse, and the eventual death of most cancer patients (Hou and Singh, Current Topics in Developmental Biology, 2017). However, very little is known about the biology behind this resistance to therapeutics. Recently, we investigated a novel mechanism of stem-cell and transformed stem cell death using adult Drosophila digestive system. We found that knockdowns of the COPI/Arf1 pathways selectively killed normal and transformed stem cells through necrosis, by attenuating the lipolysis pathway. The dying stem cells were engulfed by neighboring differentiated cells through a Draper-Mbc/Rac1-JNK-dependent autophagy pathway. We further found that Arf1 inhibitors also killed CSCs in human cancer cell lines. These findings together suggest that normal or CSCs, like hibernating animals, primarily rely on lipid reserves for energy and blocking lipolysis starves them to death (Singh et al., Nature 2016).
My NCBI: Dr. Singh's Biography
Selected Recent Publications
- Nature. 538: 198-113, 2016. [ Journal Article ]
- Nature Communications. 7: 10473, 2016. [ Journal Article ]
The Nuclear Matrix Protein Megator Regulates Stem Cell Asymmetric Division through the Mitotic Checkpoint Complex in Drosophila Testes.PLoS Genetics. 11: e1005750, 2015. [ Journal Article ]
Genome-wide RNAi screen identifies networks involved in intestinal stem cell regulation in Drosophila.Cell Reports. 10: 1226-1238, 2015. [ Journal Article ]
- Cell Stem Cell. 1: 191-203, 2007. [ Journal Article ]
Dr. Shree Ram Singh obtained his Ph.D. in genetics from the Department of Zoology, Banaras Hindu University, India in 2001. Dr. Singh was a guest scientist at the Department of Molecular Cell Biology Biocenter, Johann Wolfgang Goethe University, Frankfurt, Germany in 1998 and in 2001 he received a UNESCO Biotechnology Action Council (BAC) fellowship at the Department of Plant Molecular Biology Biocenter, Johann Wolfgang Goethe University. Dr. Singh pursued his postdoctoral research studies at the University of Haifa, Israel, and at the National Cancer Institute at Frederick. Since 2011, he has served as a staff scientist at National Cancer Institute at Frederick. Dr. Singh was appointed as Lead Guest Editor in 2012 for a special issue of Current Medicinal Chemistry on Stem cells in regenerative medicine and cancer, in 2013 for a special issue of Cancer Letters on Cancer Stem Cells, in 2015 for a special issue of Cancer Letters on Cancer Metabolism, and in 2016 for a special issue of Cancer Letters on Tumor Microenvironment. He also serves as an Academic Editor of PLoS One and PeerJ, Associate Editor of BMC Genetics, Review Editor of Frontiers in Cell and Developmental Biology and an Editorial Board member of Scientific Reports, Signal Transduction and Targeted Therapy, and Cancer Letters.
|Beyonce Carrington||Student Intern (Werner H. Kirsten)|
|Nathan Pinto||Student Intern (Werner H. Kirsten)|