Bone mass is balanced by opposing processes of resorption and formation. Insulin-like growth factor-I (IGF-I) is an important bone growth factor that enhances replication of less differentiated bone cells and matrix collagen synthesis by osteoblasts. Parathyroid hormone and prostaglandin E2 increase cAMP levels in osteoblasts, and intermittent administration of either agent stimulates bone formation. These hormones act in part through a process that relies on cAMP dependent protein kinase A, inducing osteoblasts to express IGF-I. The investigator has identified a C/EBP site that is necessary and sufficient for cAMP-dependent IGF-I promoter activation, found C/EBP delta to be the functional trans-acting transcription factor in fetal rat osteoblasts, and also found that estrogen directly suppresses the stimulatory effect of cAMP on C/EBP delta-mediated IGF-I activation, but not on cAMP synthesis. This is estrogen receptor dependent and does not require an identifiable estrogen response elements or AP-1 binding sequence. The proposed studies will examine protein:protein interactions that influence C/EBP mediated IGF-I activation, and the counter-regulatory suppressive effect of estrogen on IGF-I gene activation. The investigator will determine the molecular actions of PGE2 and l7beta-estradiol on C/EBP delta and C/EBP beta expression by characterizing functional cis- and trans-acting elements that regulate their promoter function, and determine the ability of these agents to modulate C/EBP mRNA stability. He will determine the influence of PKA activation in the absence or presence of l7beta-estradiol co-treatment on translocation of C/EBP delta and beta from the cytoplasm to the nucleus and analyze changes in C/EBP phosphorylation under these conditions. Finally, he will determine the physiologic role of C/EBP delta and beta in cAMP activated IGF-I expression, interactions with estrogen, and ultimately in regulating bone mass in C/EBP knockout animals. Bone mass studies will be conducted using peripheral quantitative computer tomography, and will be correlated with basal and activated skeletal IGF-I expression.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK056310-02
Application #
6381626
Study Section
Endocrinology Study Section (END)
Program Officer
Margolis, Ronald N
Project Start
2000-05-01
Project End
2004-04-30
Budget Start
2001-05-01
Budget End
2002-04-30
Support Year
2
Fiscal Year
2001
Total Cost
$245,250
Indirect Cost
Name
Yale University
Department
Surgery
Type
Schools of Medicine
DUNS #
082359691
City
New Haven
State
CT
Country
United States
Zip Code
06520
McCarthy, Thomas L; Centrella, Michael (2015) Androgen receptor activation integrates complex transcriptional effects in osteoblasts, involving the growth factors TGF-? and IGF-I, and transcription factor C/EBP?. Gene 573:129-40
Dhawan, Puneet; Peng, Xiaorong; Sutton, Amelia L M et al. (2005) Functional cooperation between CCAAT/enhancer-binding proteins and the vitamin D receptor in regulation of 25-hydroxyvitamin D3 24-hydroxylase. Mol Cell Biol 25:472-87
Chang, Weizhong; Parra, Macarena; Centrella, Michael et al. (2005) Interactions between CCAAT enhancer binding protein delta and estrogen receptor alpha control insulin-like growth factor I (igf1) and estrogen receptor-dependent gene expression in osteoblasts. Gene 345:225-35
Centrella, Michael; Christakos, Sylvia; McCarthy, Thomas L (2004) Skeletal hormones and the C/EBP and Runx transcription factors: interactions that integrate and redefine gene expression. Gene 342:13-24
Chang, Weizhong; Rewari, Amar; Centrella, Michael et al. (2004) Fos-related antigen 2 controls protein kinase A-induced CCAAT/enhancer-binding protein beta expression in osteoblasts. J Biol Chem 279:42438-44
Centrella, Michael; McCarthy, Thomas L; Chang, Wei-Zhong et al. (2004) Estren (4-estren-3alpha,17beta-diol) is a prohormone that regulates both androgenic and estrogenic transcriptional effects through the androgen receptor. Mol Endocrinol 18:1120-30
McCarthy, Thomas L; Chang, Wei-Zhong; Liu, Yuan et al. (2003) Runx2 integrates estrogen activity in osteoblasts. J Biol Chem 278:43121-9
Ji, Changhua; Chang, Weizhong; Centrella, Michael et al. (2003) Activation domains of CCAAT enhancer binding protein delta: regions required for native activity and prostaglandin E2-dependent transactivation of insulin-like growth factor I gene expression in rat osteoblasts. Mol Endocrinol 17:1834-43
McCarthy, T L; Centrella, M (2001) Local IGF-I expression and bone formation. Growth Horm IGF Res 11:213-9
Centrella, M; McCarthy, T L (2001) Targeted disruption of C-type natriuretic peptide: a focused assault on cartilaginous bone. Trends Endocrinol Metab 12:235-6

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