title: Specific growth suppression of human cancer cells by targeted delivery of Dictyostelium mitochondrial ribosomal protein S4.
abstract: BACKGROUND
  In general, growth and differentiation are mutually exclusive but are cooperatively regulated throughout development. Thus, the process of a cell's switching from growth to differentiation is of great importance not only for the development of organisms but also for malignant transformation, in which this process is reversed. We have previously demonstrated using a Dictyostelium model system that the Dictyostelium mitochondrial ribosomal protein S4 (Dd-mrp4) gene expression is essential for the initiation of cell differentiation: Dd-mrp4-null cells fail to initiate differentiation, while the initial step of cell differentiation and the subsequent morphogenesis are markedly enhanced in mrp4 (OE) cells overexpressing the Dd-mrp4 in the extramitochondrial cytoplasm. This raised a possibility that the ectopically enforced expression of the Dd-mrp4 in human cells might inhibit their growth, particularly of malignant tumor cells, by inducing cell differentiation.
  
  
  METHODS
  FOUR KINDS OF HUMAN TUMOR CELL LINES WERE TRANSFECTED BY THREE KIND OF VECTOR CONSTRUCTS (THE EMPTY VECTOR: pcDNA3.1 (Mock); pcDNA3.1-rps4 bearing Dictyostelium cytoplasmic ribosomal protein S4; pcDNA3.1-mrp4 bearing Dictyostelium mitochondrial ribosomal protein S4). As controls, four kinds of human primary cultured cells were similarly transfected by the above vector constructs. After transfection, growth kinetics of cells was analyzed using cell viability assay, and also the TUNEL method was used for evaluation of apoptotic cells.
  
  
  RESULTS
  Ectopically expressed Dd-mrp4 suppressed cell proliferation through inducing apoptotic cell death specifically in the human lung adenocarcinoma (A549), epithelial cervical cancer (HeLa), hepatocellular carcinoma (HepG2) and colonic carcinoma (Caco-2), but not in primary cultured normal cells, such as human brain microvascular endothelial cells (HBMECs); human umbilical vein endothelial cells (HUVECs) and human normal hepatocytes (hHeps™), with one exception (human cardiac fibloblasts (HCF)).
  
  
  CONCLUSIONS
  The present finding that the ectopically enforced expression of Dd-mrp4 in human several tumor cell lines specifically suppresses their proliferation suggests strongly that the Dd-mrp4 gene derived from Dictyostelium mitochondria may provide a new promising therapeutic strategy for disrupting cell viability pathways in human cancers.
authors: Division of Molecular Neurobiology, Institute for Enzyme Research, The University of Tokushima, Kuramoto-cho, Tokushima 770-8503, Japan.
authors: Junji
authors: J
authors: Chida
authors: Division of Enzyme Chemistry, Institute for Enzyme Research, The University of Tokushima, Kuramoto-cho, Tokushima 770-8503, Japan.
authors: Hikaru
authors: H
authors: Araki
authors: Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aoba, Sendai 980-8578, Japan.
authors: Yasuo
authors: Y
authors: Maeda
keywords: Anticancer action; Apoptosis; Dd-mrp4; Dictyostelium discoideum; Differentiation; Human tumor; Mitochondrial ribosomal protein S4 (MRP4); Proliferation