DESCRIPTION (Applicant's abstract): The long-term goal of the research in our laboratory is to understand the molecular mechanisms that regulate growth factor-stimulated cell cycle progression. Most cells in adult, higher organisms are generally in a quiescent non-proliferative state, referred to as the GO phase of the cell cycle. If activated by an appropriate extracellular mitogen, these cells can exit from the resting state and reinitiate cell proliferation. In the context of vascular biology, the onset of endothelial cell (EC) proliferation is associated with the pathogenesis of numerous "angiogenic diseases" (e.g., cancer, diabetic retinopathy) while smooth muscle cell (SMC) accumulation occurs during the development of atherosclerosis, transplant-associated arteriosclerosis and restenosis after vessel wall injury. It is likely that fibroblast growth factor (FGF)- 1 and FGF-2 play an important role in vascular cell growth control. These factors act by binding and thereby activating specific transmembrane receptor tyrosine kinases. This triggers downstream intracellular events, including the stimulation of protein phosphorylation cascades and the transcriptional activation of specific genes. We have used a differential display approach to identify FGF-inducible genes in NIH 3T3 cells and vascular cells. One of these genes, named Fnk, is an immediate-early response gene encoding a member of the polo family of structurally-related serine/threonine kinases. We hypothesize that Fnk expression and enzymatic activity is critical for growth factor-stimulated cell cycle progression. The specific aims of this proposal are: 1) To determine whether the addition of FGF-2 to quiescent murine NIH 3T3 cells promotes changes in Fnk synthesis, phosphoamino acid content, enzymatic activity and subcellular localization, 2) To identify candidate Fnk regulatory proteins and substrates by screening for Fnkbinding proteins, 3) To determine whether Fnk overexpression or underexpression alters NIH 3T3 cell, human microvascular EC, or human aortic SMC proliferation in vitro, and 4) To determine the phenotypic consequences of Fnk deficiency in vivo. It is anticipated that these studies will provide important information on the biological functions of the Fnk protein and its potential role in vascular cell growth control in vivo.