? The body's immediate response to serious trauma, denoted the Acute Phase Response (APR), coordinates a wide variety of inflammatory signals, and produces a common response, in the massive induction of protective proteins by the liver. While APR is designed for survival, severe or prolonged activation of this response can lead to organ failure and death, as its induction is inevitably associated with interruption of normal liver function. Evidence suggests that the APR's repression of steady-state liver function is a byproduct of its mode of induction. Further evidence suggests that this is a highly regulated process which shares an early cell state, and some signals with the proliferative response. Evidence is presented that negative regulation of differentiated genes may be mediated through phosphorylation of a small web of liver-specific transcription factors, particularly HNF-4. Better understanding of this process could potentially have therapeutic importance in allowing more reliable resolution of the acute phase.
The first aim i s to dissect where HNF-4 phosphorylation occurs, by phosphopeptide mapping, to identify what kinases and thus signal transduction pathways are involved. This will also generate original materials, in the form of altered HNF-4 molecules, to test the importance of this phosphorylation to APR and regeneration.
The second aim i s to trace the effect of this phosphorylation on the biochemical activities of HNF-4, namely its DNA binding and site selection, and changes in its interactions and activities in the cell, by diagnostic chromatin immunoprecipitation. Third, using DNA microarrays, a global picture of the genes regulated by HNF-4 and its modification will be obtained and compared to that from several acute phase inductions at early stages. This will test both the importance of HNF-4's modification, and establish what transcriptional events are common to the early phase of APR, when normal liver function retracts and the liver prepares for subsequent massive induction. ? ?
