# 1,25(OH)2D REGULATION OF PARATHYROID HORMONE ACTION

> **NIH NIH R01** · EMORY UNIVERSITY · 1991 · $164,370

## Abstract

The long-term objective of this project is to define the effects of
1,25-Dihydroxyvitamin D and glucocorticoids on the cAMP pathway for
parathyroid hormone (PTH) action on the osteoblast in culture, from the
point of PTH binding to cellular functional responses that can be
understood at the tissue level.  These studies relate to understanding the
mechanisms of glucocorticosteroid-induced osteoporosis, more effective and
rational, use of vitamin D metabolites in this disease, and the possibility
of devising other therapeutic agents which also antagonize the skeletal
effects of glucocorticoids.  The rationale for the approach originated with
our observations that 1,25(OH)2D completely antagonizes the effect of
glucocorticoid to increase the cAMP response of cell culture models of the
osteoblast to PTH .  Important new data show that these effects are
mediated predominantly at the level of PTH-R regulation and the effects are
transmitted to the next step in the cAMP pathway, the protein kinase.  We
have characterized PTH stimulation of mRNA for the tissue plasminogen
activator (tPA).  This enzyme is believed to play a crucial role in the
osteoblast's ability to signal the need for bone resorption.

Three hypotheses will be tested in the continuation of the project.  (1)
1,25D and GC have opposing regulatory effects on transduction of the PTH
signal into functional responses in normal osteoblasts.  (2) As a
consequence of modulating PKA activity, 1,25D and GC alter effects of PTH
cyclase catalytic subunit in order to accommodate the changes in PTH
receptor number that they induce.  For hypothesis (1) we shall:  (a)
determine the effects of 1,25D and GC on the dose-response relationship for
PTH stimulation of tPA mRNA; (b) demonstrate that PTH acts to increase
transcription of tPA mRNA; (c) identify the individual cells expressing tPA
mRNA in response to PTH as osteoblasts by showing they contain alkaline
phosphatase and do not synthesize type III collagen.  For hypothesis (2) we
shall determine, in ROS 17/2.8 cells, the effects of 1,25D and GC on (a)
the dose-response for PTH activation of protein phosphatase inhibitor-1 and
(b) the dose-response for PTH activation of the high affinity (Type III)
cAMP phosphodiesterase (PDE).  For hypothesis (3) we shall use both ROS
17/2.8 and UMR106 cells to (a) measure the effect of 1,25D and GC on the
amount and turnover number of the adenylate cyclase catalytic subunit and
its relationship to PTH receptor number and (b) demonstrate that the amount
of immunoreactive Gs (a) protein solubilized from membranes is in excess
relative to PTH receptor number and adenylate cyclase.

Routine procedures include primary culture of osteoblasts, radioimmunoassay
of cAMP, adenylate cyclase assay, PTH radioreceptor assay, electrophoresis
and DNA hybridization analysis of mRNA.  In situ hybridization of mRNA in
cultures will be performed with the collaboration of a local expert in this
technique.  Adenylate cyclase catalytic sub...

## Key facts

- **NIH application ID:** 3156223
- **Project number:** 2R01AR032196-07A1
- **Recipient organization:** EMORY UNIVERSITY
- **SAM.gov UEI:** S352L5PJLMP8
- **Principal Investigator:** BAYARD D CATHERWOOD
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 1991
- **Award amount:** $164,370
- **Award type:** 2
- **Project period:** 1987-04-01 → 1995-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/3156223

## Citation

> US National Institutes of Health, RePORTER application 3156223, 1,25(OH)2D REGULATION OF PARATHYROID HORMONE ACTION (2R01AR032196-07A1). Retrieved via MORVS 2026-10-25 from https://api.morvs.ai/grant/nih/3156223. Licensed CC0.

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