Mechanisms for Temporal Information Coding in Inflammatory JNK Signaling

Abstract

JNK (c‐Jun‐N‐terminal kinase) is a stress‐activated protein kinase that plays key roles in mediating stress and inflammatory response such as cell death, proliferation, and cytokine production. Several studies have uncovered that the duration of JNK signaling determines the specificity of downstream cellular events that lead to either cell‐death or survival. However, the question of how JNK is dynamically regulated in cells remains elusive. In this study, we aimed to reveal the physiological importance of the dynamics of JNK signaling in downstream gene expression by elucidating how inflammatory cytokine IL‐1β regulates a temporal pattern of JNK signaling in living HeLa cells. Here, using fluorescence imaging and our novel JNK activity reporter based on FRET, we succeeded in the quantitative evaluation of JNK dynamics at single cell resolution upon IL‐1β stimulation. Periodic pulsatile IL‐1β‐stimuli to cells were employed to analyze the regulatory mechanism of JNK activity. Our analysis revealed that JNK can be activated either transiently or repeatedly depending on the interval of stimulation pulses, while the initial peak amplitude of JNK activity was almost the same. We found that a simple negative‐feedback loop from a MAPK phosphatase MKP1 to its upstream kinase p38 MAPK accounts for the observed temporal dynamics of JNK activity, which was further verified by biochemical analysis and mathematical model simulation. The temporal aspects of IL‐1β stimulation were reflected in the gene expression profile obtained from HeLa cells after stimulation, in which the specific set of JNK‐dependent genes were more upregulated by repetitive IL‐1β stimulation pulses compared to that by continuous IL‐1β exposure. Our results indicate that the dynamic behavior of JNK in response to IL‐1β stimulation is regulated through dephosphorylation of JNK by MKP1 whose expression is positively regulated by p38 MAPK and down‐regulated by its phosphatase activity on p38 MAPK. In addition, JNK activity as well as downstream gene expression specificity could be modulated just by altering the temporal pattern of input IL‐1β stimuli. In conclusion, we demonstrated that the information of temporally fluctuating cytokine stimulation can be converted into the activation dynamics of JNK signaling, and the downstream gene expression specificity can be encoded by the temporal dynamics of JNK activity. Such a temporal information coding mechanism may have physiological relevance for inducing an adequate cellular response to a wide range of fluctuating cytokine levels through precise control of gene expression.Support or Funding InformationThis work was supported in part by JSPS KAKENHI [Grant numbers JP19K06548, JP17H06017 to T.T., JP18K06859 to S.A‐A.].