title: Graded mitogen-activated protein kinase activity precedes switch-like c-Fos induction in mammalian cells.
abstract: The mitogen-activated protein kinase (MAPK) pathway is an evolutionarily conserved signaling module that controls important cell fate decisions in a variety of physiological contexts. During Xenopus oocyte maturation, the MAPK cascade converts an increasing progesterone stimulus into a switch-like, all-or-nothing response. While the importance of such switch-like behavior is widely discussed in the literature, it is not known whether the MAPK pathway in mammalian cells exhibits a switch-like or graded response. For this study, we used flow cytometry and immunofluorescence to generate single-cell measurements of MAPK signaling in Swiss 3T3 fibroblasts. In contrast to the case in Xenopus oocytes, we found that ERK activation in individual mammalian cells is not ultrasensitive and shows a graded response to changes in agonist concentration. Thus, the conserved MAPK signaling module exhibits different systems-level properties in different cellular contexts. Furthermore, the graded ERK response was converted into a more switch-like behavior at the level of immediate-early gene induction and cell cycle progression. Thus, while MAPK signaling is involved in all-or-nothing cell fate decisions for both Xenopus oocyte maturation and mammalian fibroblast proliferation, the underlying mechanisms responsible for the switch-like nature of the cellular responses are different in these two systems, with the mechanism appearing to lie downstream of the kinase cascade in mammalian fibroblasts.
authors.affiliation: Department of Cell Biology, Harvard Medical School, 240 Longwood Ave., Boston MA 02115, USA.
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Mackeigan
authors.forename: Leon O
authors.initials: LO
authors.lastname: Murphy
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Dimitri
authors.forename: John
authors.initials: J
authors.lastname: Blenis
mesh_terms: D000818:Animals; D049109:Cell Proliferation; D004815:Epidermal Growth Factor / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000032:analysis / Q000378:metabolism*; D005347:Fibroblasts / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D020935:MAP Kinase Signaling System; D051379:Mice; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D041701:Swiss 3T3 Cells
chemical_list: D010982:Platelet-Derived Growth Factor; D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D004815:Epidermal Growth Factor; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases