Normal development of multi-cellular organisms relies on the balance between cell proliferation, differentiation and programmed cell death (PCD or apoptosis). Many types of human diseases including cancer appear to be associated with aberrant regulation of PCD and proliferation. Despite the wealth of information, mammalian-signaling pathways for survival and anti-PCD remain poorly understood. Survival and growth of hematopoietic cells as well as hematopoietic development depend on cytokines such as IL-3. We have been studying cell survival pathways using IL-3 signaling as a model system. Through a newly developed genetic screen, we have identified a number of novel factors as new components in survival signaling cascades. One of them is the Phox-homology (PX) domain containing serine/threonine kinase CISK (Cytokine-lndependent Survival Kinase). CISK is a new member of the SGK family kinases (SGK3), and the first to be shown capable of supporting cell survival. Our studies suggest that CISK may function downstream of PI-3 kinase and regulate Flightless homologue and GCF2 activities. The unique domain structure, tissue expression pattern, and subcellular localization of CISK also suggest that CISK plays a distinct role from Akt and other SGK family kinases. The overall objective of this proposal is to understand CISK signaling networks and to define the function of CISK in anti-apoptosis and development. The specific aims of this proposal are to: 1. Elucidate the signaling pathways modulated by CISK in vivo, by investigating the survival activity of endogenous CISK and its regulation of FLII and GCF2 function and activities. 2. Determine the biochemical mechanisms that control CISK activation and subcellular localization, by examining the regulation of its activities by cytokines and the unique domains of CISK. 3. Investigate the physiological role of CISK in cell survival and development in mice, by studying how CISK affects hematopoietic cell development and survival using chimeric and knock-out mouse models.