1. SPECIFIC AIMS The long-term goal of this research is to understand the function and regulation of the mammalian INK4 family of CDK inhibitors. All four INK4 proteins specifically bind to and inhibit the kinase activity of cyclin D-dependent CDK4 and CDK6, thereby retaining the growth suppressive activity of the retinoblastoma family proteins and preventing G1-to-S transition. Through concerted efforts by many laboratories over the past six years, the biochemical mechanisms underlying the inhibition of CDK4/6 by INK 4 inhibitors are now relatively well understood. However, both in vivo functions of INK4 genes and signals regulating INK4 gene expression remain poorly defined. The aims of this proposal are directed toward both issues, with focus on two members of the family: p18/INK4c and p19/INK4d. AIM 1. THE FUNCTION OF P18/INK4C IN TUMOR SUPPRESSION 1. Determine the tumor susceptibility of p18-deficient mice. 2. Determine whether p18 functional interact with p53 3. Examine the status of the p18 functional interact with p53. 4. Identifying gene(s) collaborating with p189 loss in lymphomagenesis by pro-virus insertional mutagenesis. AIM II. REGULATION OF P18/INK4C AND P27/KIP1 BY MEN GENES 1. Determine whether p18 and p27 are regulated by menin tumor suppressor 2. Determine whether p18 and p27 are regulated by RET proto-oncogene. AIM III. FUNCTION OF P18/INK4C IN CELL DIFFERENTIATION 1. Determine the function of p18 and p27 in maintaining terminal arrest of myotubes 2. Determine the function of p18 in inducing terminal arrest of adipocytes AIM IV. GENETIC FUNCTION OF P19/INK4D 1. Determine the function of p19 in controlling cellular proliferation 2. Determine the basis for the phenotypic difference between two INK4d mutant mice 3. Determine whether E2F1 and p53 are the downstream targets of p19 loss-induced apoptosis. 4. Determine the cell cycle kinetics of p19- and p18-deficient embryo fibroblasts