IL-1β induced and p38MAPK-dependent activation of the mitogen-activated protein kinase (MAPK)-activated protein kinase (MK) 2 in hepatocytes: signal transduction with robust and concentration-independent signal amplification
Kulawik A, Engesser R, Ehlting C, Raue A, Albrecht U, Hahn B, Lehmann WD, Gaestel M, Klingmüller U, Häussinger D, Timmer J, Bode JG.
The Interleukin (IL)-1β induced activation of the p38MAPK/MK2 pathway in hepatocytes is important for the control of acute phase response and regulation of liver regeneration. Many aspects of regulatory relevance of this pathway have been investigated in immune cells in the context of inflammation. However, very little is known about concentration-dependent activation kinetics and signal propagation in hepatocytes and the role of MK2. We established a mathematical model for IL-1β induced activation of the p38MAPK/MK2 pathway in hepatocytes that was calibrated to quantitative data on time- and IL-1β concentration-dependent phosphorylation of p38MAPK and MK2 in primary mouse hepatocytes. This analysis showed that in hepatocytes signal transduction from IL-1β via p38MAPK to MK2 is characterized by strong signal amplification. Quantification of p38MAPK and MK2 revealed that in hepatocytes at maximum 11.3 % of p38MAPK molecules and 36.5 % of MK2 molecules are activated in response to IL-1β. The mathematical model was experimentally validated employing phosphatase inhibitors and the p38MAPK inhibitor SB203580. Model simulations predicted an IC50 of 1 μM - 1.2 μM for SB203580 in hepatocytes. In silico analyses and experimental validation demonstrated that kinase activity of p38MAPK determines signal amplitude while phosphatase activity affects both signal amplitude and duration. p38MAPK and MK2 concentrations and responsiveness towards IL-1β was quantitatively compared between hepatocytes and macrophages. In macrophages the absolute p38MAPK and MK2 concentration was significantly higher. Finally, in line with experimental observations the mathematical model predicted a significantly higher EC50 for IL-1β induced pathway activation in macrophages compared to hepatoyces underscoring the importance of cell-type specific differences in pathway regulation.