This is a competing renewal application of a MERIT Award designed to continue studies in intestina phosphate absorption at the physiological and molecular levels. These studies will test the hypothesis that intestinal phosphate absorption involves proteins encoded by sodium phosphate-lib (NaPi-lIb), sodium phosphate-Ill (NaPi-lll), and Phosphate encoding gene with Homologies to Endopeptidases on the X chromosome (PHEX) genes. Understanding the regulation of these key genes will provide valuable insight into the overall phosphate homeostasis. The studies will utilize state-of-the-art in vivo and in vitro experiments that are designed to gain further information on the regulation and interrelationship between NaPi-llb, NaPi-lll, and PHEX genes in relationship to bone health during maturation. We have been exceedingly productive during the last funding period with significant advances being made in cloning the NaPi-llb, NaPi-lll. and the promoter region for both the phosphate transporters and the PHEX promoter. The current studies are designed to address four specific aims. The first aim is designed to characterize basal and hormone-stimulated regulation of the human and murine NaPi-llb genes. The second aim is designed to decipher the basal and vitamin DS-stimulated transcriptional regulation of the murine NaPi-lll gene. Specific Aim 3 is designed to determine if fibroblast growth factor-23(FGF-23) is a possible PHEX substrate which is involved in the regulation of intestinal phosphate absorption. Specific Aim 4 is designed to utilize a novel proteomic approach to search for putative PHEX substrate and for downstream targets in the intestinal epithelium. The finaJ aim is designed to investigate basal and glucocortJcoid-mediated [unreadable] transcriptional regulation of the murine PHEX gene. These studies will likely yield significant new information in regard to these important genes which are involved in the phosphate homeostasis. These studies will allow us to develop newerapproaches to the treatment of bone disorders during maturation. PERFORMANCE SfTEfS)(onjanizBrfoo. dty. slafa) Steele Memorial Children's Research Center /*/ /v/ v&n-'i/T'-i of- ft&-' ~E- 0/v [unreadable] Tucson, Arizona KEY PERSONNEL Seainstructions on Page 11. Use continuationpag*s as needed to provide the required information Inthe format shown below. Name Organization Rol[unreadable]on Project Fayez K. Ghishan, M.D P.I. James F. Collins, Ph.D. Co P.I. Shougang Zhuang, M.D Res Asst Prof Hua Xu Res Specialist Sr PHS 398 (Rev. 4/98) Page 2->[unreadable] BB Mumper pages consecutively at me Bottom mroupnoul rue ano|fcatien Do not use suffixes sueh.as.3a. 3b. CC Prinj^al InvestlgatoryProgram Director(Last,ffrei,middle): ^Jlhan, Fayez K. Type the name of the principal investigator/programdirector at the top of each printed page and each continuation page. (For Type specifications, see instructions on page6.) RESEARCH GRANT TABLE OF CONTENTS Pago Numbers Face Page -\ Description,