We found that membrane attachment is important for Fas function and, unlike previous results with anti-Fas monoclonal antibodies, we show that dimerization is sufficient to trigger apoptosis. Using this system, we show that the Fas pathway is restricted to double-positive thymocytes in vivo, consistent with recent in vitro findings with thymocytes. This method promises to be more useful not only for developmental studies involving cell ablation, but also for studies involving the regulation of a wide variety of signaling molecules. AB - Extracellular growth and differentiation factors induce changes in gene expression in the nucleus by initiating a series of protein associations that alter the subcellular localization of intracellular signaling proteins. Initial events involve receptor homo- or heterodimerization and subsequent recruitment of cytosolic signaling proteins to the inner leaflet of the plasma membrane.
Intermediate events involve the translocation of proteins into the nucleus.
Late events involve the recruitment of transcriptional activators to the vicinity of specific genes in the nucleus, resulting in increased gene transcription. The ability to induce signals at each of these three phases of signaling pathways is illustrated by the use of a heterodimeric chemical inducer of dimerization that causes a proximal relationship between two different target proteins. To further understand the diverse roles of antigen receptor signaling throughout T cell development, we have identified a new NFATc family member, NFATc3, that is expressed at highest levels in the thymus. NFATc3 is the product of a gene on murine chromosome 8 that is not linked to the other NFATc genes. Additionally, thymic NFATc3 undergoes modifications in response to agents that mimic T cell receptor signaling, including a decrease in apparent molecular mass upon elevation of intracellular calcium that is inhibited by the immunosuppressant FK506.