title: Heterogeneous kinetics of AKT signaling in individual cells are accounted for by variable protein concentration.
abstract: In most solid cancers, cells harboring oncogenic mutations represent only a sub-fraction of the entire population. Within this sub-fraction the expression level of mutated proteins can vary significantly due to cellular variability limiting the efficiency of targeted therapy. To address the causes of the heterogeneity, we performed a systematic analysis of one of the most frequently mutated pathways in cancer cells, the phosphatidylinositol 3 kinase (PI3K) signaling pathway. Among others PI3K signaling is activated by the hepatocyte growth factor (HGF) that regulates proliferation of hepatocytes during liver regeneration but also fosters tumor cell proliferation. HGF-mediated responses of PI3K signaling were monitored both at the single cell and cell population level in primary mouse hepatocytes and in the hepatoma cell line Hepa1_6. Interestingly, we observed that the HGF-mediated AKT responses at the level of individual cells is rather heterogeneous. However, the overall average behavior of the single cells strongly resembled the dynamics of AKT activation determined at the cell population level. To gain insights into the molecular cause for the observed heterogeneous behavior of individual cells, we employed dynamic mathematical modeling in a stochastic framework. Our analysis demonstrated that intrinsic noise was not sufficient to explain the observed kinetic behavior, but rather the importance of extrinsic noise has to be considered. Thus, distinct from gene expression in the examined signaling pathway fluctuations of the reaction rates has only a minor impact whereas variability in the concentration of the various signaling components even in a clonal cell population is a key determinant for the kinetic behavior.
authors.affiliation: Division of Systems Biology of Signal Transduction, German Cancer Research Center (DKFZ), DKFZ-ZMBH Alliance Heidelberg, Germany.
authors.forename: René
authors.initials: R
authors.lastname: Meyer
authors.forename: Lorenza A
authors.initials: LA
authors.lastname: D'Alessandro
authors.forename: Sandip
authors.initials: S
authors.lastname: Kar
authors.forename: Bernhard
authors.initials: B
authors.lastname: Kramer
authors.forename: Bin
authors.initials: B
authors.lastname: She
authors.forename: Daniel
authors.initials: D
authors.lastname: Kaschek
authors.forename: Bettina
authors.initials: B
authors.lastname: Hahn
authors.forename: David
authors.initials: D
authors.lastname: Wrangborg
authors.forename: Johan
authors.initials: J
authors.lastname: Karlsson
authors.forename: Mats
authors.initials: M
authors.lastname: Kvarnström
authors.forename: Mats
authors.initials: M
authors.lastname: Jirstrand
authors.forename: Wolf-Dieter
authors.initials: WD
authors.lastname: Lehmann
authors.forename: Jens
authors.initials: J
authors.lastname: Timmer
authors.forename: Thomas
authors.initials: T
authors.lastname: Höfer
authors.forename: Ursula
authors.initials: U
authors.lastname: Klingmüller