A Molecular Biologic Approach to Immune Activation

Siebenlist, U.

Abstract

The project is focused on the elucidation of molecular mechanisms that operate during immune activation. In particular, we wish to delineate the response of mitogenically activated T cells at the genetic level as well as elucidating the signal-transducing events which preceed the genetic response. We have previously cloned many novel immediate-early induced genes of T cells. These genes encode for various transcription factors, including NF-kappaB and multiple cytokines,receptors and a number of intracellular signal-transducing components. We have extended these studies to clone additional genes induced later during the activation cascade. The main focus of our research has been the activation of the transcription factor NF-kappaB. This factor is critical for the immune function of stimulated T cells because it regulates the expression of many immunomodulatory gene products. In addition, NF-kappaB regulates several viruses including HIV. NF-kappaB also plays an important role during the HTLV I virus encoded Tax protein induced transformation and activation of T cells. We have discovered that a primary mechanism of NF-kappaB activation involves site-specific phosphorylation and degradation of the IkappaB-alpha inhibitory protein, the main cytoplasmic inhibitor of NF-kappaB. We are studying the membrane-proximal events which occur during stimulation of immune cells with TNF-alpha, a potent activator of NF-kappaB and have begun to dissect the molecular events which occur subsequent to receptor stimulation. In addition, we are investigating the signaling paths which lead from the TNF- and the T cell-receptor to activation of NF-kappaB. Within this context we are elucidating the roles of MAPKinase-like pathways, including a pathway defined by a novel kinase we have cloned.