Granulocyte-macrophage colony-stimulating factor and interleukin-3 induce cell cycle progression through the synthesis of c-Myc protein by internal ribosome entry site-mediated translation via phosphatidylinositol 3-kinase pathway in human factor-dependent leukemic cells.
To investigate the roles of c-myc during hematopoietic proliferation induced by growth factors, we used factor-dependent human leukemic cell lines (MO7e and F36P) in which proliferation, cell cycle progression, and c-Myc expression were strictly regulated by granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3). In these cell lines, both c-myc mRNA and c-Myc protein stability were not affected by GM-CSF and IL-3, suggesting a regulation of c-Myc protein at the translational level. However, rapamycin, an inhibitor of cap-dependent translation, did not block c-myc induction by GM-CSF and IL-3. Thus, we studied the cap-independent translation, the internal ribosome entry site (IRES), during c-Myc protein synthesis using dicistronic reporter gene plasmids and found that GM-CSF and IL-3 activated c-myc IRES to initiate translation. c-myc IRES activation, c-Myc protein expression, and cell cycle progression were all blocked by a phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002. In another factor-dependent cell line, UT7, we observed the cell cycle progression and up-regulation of c-Myc protein, c-myc mRNA, and c-myc IRES simultaneously, which were all inhibited by LY294002. Results indicate that hematopoietic growth factors induce cell cycle progression via IRES-mediated translation of c-myc though the PI3K pathway in human factor-dependent leukemic cells.
Kobayashi
Norihiko
N
Department of Hematology, Research Institute, International Medical Center of Japan, 1-21-1 Toyama, Shinjuku-ku, Tokyo 162-8655, Japan.
Saeki
Kumiko
K
Yuo
Akira
A
D002453:Cell Cycle / Q000187:drug effects*; D045744:Cell Line, Tumor; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology / Q000502:physiology*; D006133:Growth Substances / Q000494:pharmacology; D006801:Humans; D007377:Interleukin-3 / Q000494:pharmacology / Q000502:physiology*; D007938:Leukemia / Q000473:pathology*; D010442:Peptide Chain Initiation, Translational / Q000187:drug effects; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D014176:Protein Biosynthesis / Q000187:drug effects*; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000096:biosynthesis; D012270:Ribosomes; D015398:Signal Transduction; D015854:Up-Regulation / Q000187:drug effects
D006133:Growth Substances; D007377:Interleukin-3; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D019869:Phosphatidylinositol 3-Kinases