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Published on: June 15, 2017
Selective modulation of protein kinase A I and II reveals distinct roles in thyroid cell gene expression and growth
Davide Calebiro1, Tiziana de Filippis, Simona Lucchi
1Department of Medical Sciences, University of Milan, Milan, Italy.
Abstract:
A global gene expression profiling of TSH stimulation on differentiated (FRTL5) and partially dedifferentiated [FRT/TSHR (TSH receptor)] rat thyroid cells was performed. A total of 123 TSH-regulated genes (95 newly described) were identified in FRTL5, whereas no significant transcriptional modifications were seen in FRT/TSHR cells. Because regulatory subunit IIbeta (RIIbeta) of protein kinase A (PKA), a key element downstream of cAMP, was expressed in FRTL5 but not in cAMP-refractory FRT/TSHR cells, we hypothesized that this gene may play an important role in TSH signaling. We therefore performed a series of experiments to investigate the involvement of RIIbeta and the different PKA isoforms. A positive effect of PKA II- but not of PKA I-selective activation on gene transcription and proliferation in FRTL5 cells, as well as an impairment of TSH nuclear effects after RIIbeta silencing were observed, suggesting that PKA II plays an essential role in TSH signaling. This view was supported by the restoration of TSH nuclear effects after reexpression of RIIbeta in FRT/TSHR cells. Because PKA I stimulation could increase iodide uptake in FRTL5 cells without affecting gene transcription, PKA I may mediate TSH actions at posttranscriptional levels. Analyses on three human cancer cell lines confirmed the possible loss of RIIbeta expression and antiproliferative activity of PKA I-selective cAMP analogs ( approximately 60% at 200 microm in BRAF-mutated cells). The inhibitory effect of PKA I apparently required constitutive MAPK activation and was associated with an inhibition of ERK phosphorylation. These findings may open new therapeutic perspectives in patients with thyroid cancer.
Insights
Protein Kinase A (PKA) II is essential for thyroid-stimulating hormone (TSH) signaling in thyroid cells, mediating gene transcription and proliferation. PKA I may regulate TSH actions post-transcriptionally, offering potential thyroid cancer therapies.
Area of Science:
- Molecular Biology
- Cell Biology
- Endocrinology
Background:
- Thyroid-stimulating hormone (TSH) regulates thyroid cell function through complex signaling pathways.
- Understanding the specific roles of downstream effectors like Protein Kinase A (PKA) is crucial for deciphering TSH action.
- Differentiated (FRTL5) and dedifferentiated (FRT/TSHR) cell models offer distinct insights into TSH signaling.
Purpose of the Study:
- To investigate the role of PKA regulatory subunit IIbeta (RIIbeta) in TSH-mediated gene expression and cellular responses.
- To differentiate the functions of PKA I and PKA II isoforms in thyroid cells.
- To explore the therapeutic potential of PKA modulators in thyroid cancer.
Main Methods:
- Global gene expression profiling of TSH-stimulated FRTL5 and FRT/TSHR cells.
- Investigating the effects of PKA isoform-selective activation and RIIbeta silencing/reexpression.
- Analyzing iodide uptake and cell proliferation.
- Evaluating PKA I-selective cAMP analogs in human thyroid cancer cell lines.
Main Results:
- TSH stimulation induced significant gene expression changes in FRTL5 cells but not in FRT/TSHR cells.
- RIIbeta expression correlated with TSH-responsive gene transcription and proliferation; RIIbeta silencing impaired TSH effects.
- PKA II activation promoted gene transcription and proliferation, while PKA I activation enhanced iodide uptake without affecting transcription.
- PKA I-selective analogs showed antiproliferative effects in human thyroid cancer cells, particularly those with BRAF mutations, linked to MAPK pathway inhibition.
Conclusions:
- PKA II, via RIIbeta, plays a critical role in mediating TSH-induced gene transcription and proliferation in thyroid cells.
- PKA I may mediate TSH actions at a post-transcriptional level, such as iodide uptake.
- Targeting PKA signaling, particularly with PKA I-selective analogs, presents a potential therapeutic strategy for thyroid cancer.
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