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Fibroblast growth factor receptor 3 gene transcription is suppressed by cyclic adenosine 3',5'-monophosphate.
D G McEwen1, R P Green, M C Naski
1Department of Molecular Biology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Abstract:
Signaling through fibroblast growth factor receptors (FGFRs) is critical for the development and patterning of the vertebrate skeleton. Gain-of-function alleles of fgfr2 and fgfr3 have been linked to several dominant skeletal disorders in humans, while null mutations in fgfr3 result in the overgrowth of long bones in a mouse model system. Interestingly, the expression pattern of fgfr3 in growth plate chondrocytes overlaps that of the parathyroid hormone (PTH)-related peptide (PTHrP) receptor, a signaling molecule that also regulates endochondral ossification. The coincident expression of these two receptors suggests that their signaling pathways may also interact. To gain insight into the regulatory mechanism(s) that govern the expression of the fgfr3 gene in chondrocytes, we have identified a cell-specific transcriptional regulatory element (CSRh) by measuring the activity of various promoter fragments in FGFR3-expressing (CFK2) and nonexpressing (RCJ) chondrocyte-like cell lines. Furthermore, we demonstrate that activation of PTH/PTHrP receptors, either by stimulation with PTH or through the introduction of activating mutations, represses CSRh-mediated transcriptional activity. Finally, the transcriptional repression of the CSRh element was mimicked by treatment with forskolin, 8-bromo-cAMP, and 3-isobutyl-1-methylxanthine or by overexpression of the catalytic subunit of protein kinase A. Together, these data suggest that protein kinase A activity is a critical factor that regulates fgfr3 gene expression in the proliferative or prehypertrophic compartment of the epiphyseal growth plate. Furthermore, these results provide a possible link between PTHrP signaling and fgfr3 gene expression during the process of endochondral ossification.
Insights
Fibroblast growth factor receptor 3 (FGFR3) gene expression in chondrocytes is regulated by protein kinase A activity. This suggests a link between parathyroid hormone (PTH)-related peptide signaling and FGFR3 during skeletal development.
Area of Science:
- Skeletal Biology
- Molecular Genetics
- Cell Signaling
Background:
- Fibroblast growth factor receptors (FGFRs) are crucial for vertebrate skeletal development and patterning.
- Dysregulation of FGFR signaling, particularly FGFR3, is implicated in human skeletal disorders and mouse models of bone overgrowth.
- FGFR3 expression in growth plate chondrocytes overlaps with the parathyroid hormone (PTH)-related peptide (PTHrP) receptor, suggesting potential pathway interactions.
Purpose of the Study:
- To investigate the regulatory mechanisms controlling fgfr3 gene expression in chondrocytes.
- To identify cell-specific transcriptional regulatory elements involved in fgfr3 gene expression.
- To explore the interaction between PTH/PTHrP receptor signaling and fgfr3 gene regulation.
Main Methods:
- Identification of a cell-specific transcriptional regulatory element (CSRh) by analyzing promoter activity in chondrocyte cell lines (CFK2 and RCJ).
- Assessment of CSRh-mediated transcriptional activity following PTH/PTHrP receptor stimulation or introduction of activating mutations.
- Evaluation of the effects of cAMP pathway activators (forskolin, 8-bromo-cAMP, IBMX) and protein kinase A (PKA) overexpression on CSRh activity.
Main Results:
- A cell-specific transcriptional regulatory element (CSRh) was identified that controls fgfr3 gene expression in chondrocytes.
- Activation of PTH/PTHrP receptors significantly represses CSRh-mediated transcriptional activity.
- Repression of CSRh activity was mimicked by cAMP pathway activation and PKA overexpression, indicating PKA's role.
Conclusions:
- Protein kinase A (PKA) activity is a critical regulator of fgfr3 gene expression in the proliferative/prehypertrophic zones of the epiphyseal growth plate.
- These findings establish a potential link between PTHrP signaling and fgfr3 gene expression during endochondral ossification.
- The study elucidates a novel regulatory mechanism for FGFR3 in skeletal development.