Kuk-Wha Lee

Abstract

The Insulin-like Growth Factor (IGF) system is an important local regulator of osteoblast proliferation, the primary determinant of bone formation. Six IGF Binding Proteins (IGFBPs) either inhibit or enhance IGF actions. Previous studies have shown that IGFBP-4 is an important negative regulator of osteoblast cell proliferation and that agents such as PTH which increase intracellular cAMP significantly increase expression of IGFBP-4 at the protein and mRNA levels. The underlying molecular mechanism which accounted for IGFBP-4 expression had not been determined and was the focus of my dissertation. Agents which increase intracellular cAMP rapidly increased IGFBP-4 mRNA levels. Nuclear run-off experiments indicated that cAMP increased the IGFBP-4 gene transcription rate at 2 hours. Cloning and sequence analysis of the human IGFBP-4 gene promoter and first intron revealed the presence of putative cAMP responsive elements which might function to mediate the cAMP effect.

To investigate mechanisms regulating osteoblast IGFBP-4 expression, I determined the role of two major post-receptor signal transduction pathways, the Protein Kinase A (PKA) and Protein Kinase C (PKC) pathways, on IGFBP-4 mRNA expression. PKA inhibitors and PKC stimulators reduced IGFBP-4 mRNA levels. PKC inhibitors increased IGFBP-4 expression and synergistically interacted with cAMP to increase IGFBP-4 mRNA levels. These studies indicated the PKA and PKC pathways had opposing effects on IGFBP-4 gene expression. These findings increase our understanding of parathyroid hormone (PTH) action on bone. PTH acts through the PKA and PKC pathways to affect bone cell proliferation. High doses of PTH (10-8 M) inhibit bone cell proliferation. We found that high concentrations of PTH increased IGFBP-4 expression while PKA inhibitors blocked this stimulation. These findings were used to propose a model for catabolic PTH actions. In this model, high doses of PTH activate PKA, stimulate IGFBP-4 expression and inhibit cell proliferation.

LLU Discipline

Microbiology and Molecular Genetics

School

Graduate School

First Advisor

Donna D. Strong

Second Advisor

Thomas A. Linkhart

Third Advisor

Subburaman Mohan

Fourth Advisor

John Rossi

Fifth Advisor

Junichi Ryu

Sixth Advisor

John F. Sands

Degree Name

Doctor of Philosophy (PhD)

Degree Level

Ph.D.

Year Degree Awarded

1994

Date (Title Page)

12-1994

Language

English

Library of Congress/MESH Subject Headings

Insulin-Like Growth Factor I; Insulin-Like Growth Factor II; Cyclic AMP-Dependent Protein Kinases; Protein Kinase C; Signal Transduction

Type

Dissertation

Page Count

2 xi; 199

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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