title: Unraveling Growth Factor Signaling and Cell Cycle Progression in Individual Fibroblasts.
abstract: Cultured cells require the actions of growth factors to enter the cell cycle, but how individual members of a population respond to the same stimulus remains unknown. Here we have employed continuous monitoring by live cell imaging in a dual-reporter cell model to investigate the regulation of short-term growth factor signaling (protein kinase B (PKB/Akt) activity) and longer-term progression through the cell cycle (cyclin-dependent kinase 2 activity). In the total population, insulin-like growth factor-I (IGF-I)-enhanced cell cycle entry by >5-fold compared with serum-free medium (from 13.5 to 78%), but at the single cell level we observed a broad distribution in the timing of G1 exit (4-24 h, mean ∼12 h) that did not vary with either the amount or duration of IGF-I treatment. Cells that failed to re-enter the cell cycle exhibited similar responses to IGF-I in terms of integrated Akt activity and migration distance compared with those that did. We made similar observations with EGF, PDGF-AA, and PDGF-BB. As potential thresholds of growth factor-mediated cell cycle progression appeared to be heterogeneous within the population, the longer-term proliferative outcomes of individual cells to growth factor stimulation could not be predicted based solely on acute Akt signaling responses, no matter how robust these might be. Thus, although we could define a relationship at the population level between growth factor-induced Akt signaling dynamics and cell cycle progression, we could not predict the fate of individual cells.
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, Oregon 97239 and.
authors.forename: Sean M
authors.initials: SM
authors.lastname: Gross
authors.affiliation: the Department of Biomedical Sciences, Paul L. Foster School of Medicine, Texas Tech Health University Health Sciences Center, El Paso, Texas 79905 peter.rotwein@ttuhsc.edu.
authors.forename: Peter
authors.initials: P
authors.lastname: Rotwein
mesh_terms: D000818:Animals; D002453:Cell Cycle; D002460:Cell Line; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D051379:Mice; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D007334:Insulin-Like Growth Factor I; D051057:Proto-Oncogene Proteins c-akt; D051357:Cyclin-Dependent Kinase 2
keywords: Akt PKB; cell proliferation; cell signaling; growth factor; signal transduction