The signal transduction pathways activated in glomerular mesangial cells by inflammatory cytokines and in renal tubular epithelial cells in response to ATP depletion are poorly understood. This is particularly true for pathways leading to the nucleus and the activation of the transcription factors controlling the genetic response to these stimuli. The Stress-activated protein kinases, or SAPKs, are activated in response to IL-1beta, and by reperfusion of ischemic kidney or reversible ATP depletion in MDCK cells. These kinases are the major c-Jun amino-terminal kinases activated by ischemia. Since phosphorylation of c-Jun within the amino-terminus is associated with increased trans acting activity, it is likely that the SAPKs are transducing an important ischemia-induced signal to the nucleus via activation of c-Jun. The SAPKs also target ATF-2 and c- Jun to various promoter elements in response to ischemia and reversible ATP depletion. Although these data suggest the SAPKs may be critical to the genetic response to ischemia and reversible ATP depletion, their role in activating transcription remains unclear. The kinase which appears to regulate the SAPK cascade has recently been identified. It is a human homolog of a class of kinases, Ste20s, which regulate the response to a wide variety of environmental stresses in yeast. The identification of GC kinase as an activator of the SAPK cascade confirmed a remarkable evolutionary conservation and defined the first physiologic function of a member of the class of mammalian Ste2Os pathway of activation from the IL-1 receptor to GC kinase and the rest of the SAPK cascade incomplete, however. The specific goals of the proposal are:
Specific Aim 1. Characterize the pathways of activation of the SAPKs and p38 in response to IL-1beta. We propose to characterize this signalling pathway, starting from the IL-1 receptor and proceeding downstream toward the SAPKs and another IL-1beta-activated MAP kinase, p38, using a variety of techniques, including the yeast interaction trap.
Specific Aim 2. Determine the role of the SAPKs in the transcriptional response of cells to reversible ATP depletion and IL-1beta. We will attempt to directly implicate the SAPKs in the regulation of transcription by determining whether they are responsible for the activation of transcription from defined promoters and from promoters of genes actually induced by IL-1beta or ATP depletion. The findings should more clearly define the role played by the SAPKs in the response of the kidney to inflammatory cytokines and energy depletion.
