Related Experiment Videos
Inhibition of thyroid hormone action by a non-hormone binding c-erbA protein generated by alternative mRNA splicing
R J Koenig1, M A Lazar, R A Hodin
1Department of Medicine, Brigham & Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115.
Abstract:
Thyroid hormone (T3) binds to a nuclear receptor protein which regulates gene expression by binding to specific DNA sequences near hormone-responsive genes. Proteins encoded by two cellular proto-oncogenes, c-erbA alpha and beta, bind T3 and can act as functional T3 receptors. In rats, alternative splicing of the alpha-gene transcript generates at least two distinct protein products, termed r-erbA alpha 1 and r-erbA alpha 2. Although these proteins bind to the same DNA sequence, r-erbA alpha 2 does not bind T3. We show here that expression of r-erbA alpha 2 inhibits the T3-dependent inductive effect of either r-erbA beta or r-erbA alpha 1 on expression of a T3-responsive test gene. Alternative splicing of the erbA alpha transcript thus generates products with opposing biological activities, suggesting a novel mechanism for the modulation of hormonal responsiveness.
Insights
Alternative splicing of the thyroid hormone (T3) receptor alpha gene generates two proteins with opposing effects. One protein binds T3 and regulates genes, while the other inhibits this process, suggesting a novel hormonal responsiveness mechanism.
Area of Science:
- Molecular endocrinology
- Gene regulation
- Proto-oncogene function
Background:
- Thyroid hormone (T3) exerts its effects by binding to nuclear receptors that regulate gene expression.
- Cellular proto-oncogenes c-erbA alpha and beta encode proteins that function as T3 receptors.
- Alternative splicing of the c-erbA alpha gene transcript in rats produces distinct protein isoforms, r-erbA alpha 1 and r-erbA alpha 2.
Purpose of the Study:
- To investigate the functional consequences of alternative splicing of the c-erbA alpha gene.
- To determine if the different r-erbA alpha isoforms exhibit distinct biological activities.
- To explore the potential for opposing roles in modulating thyroid hormone signaling.
Main Methods:
- Analysis of protein products from alternative splicing of the rat c-erbA alpha gene.
- Assessment of T3 binding capabilities of r-erbA alpha 1 and r-erbA alpha 2.
- Experimental evaluation of the effect of r-erbA alpha 2 expression on T3-responsive gene expression induced by r-erbA beta or r-erbA alpha 1.
Main Results:
- While both r-erbA alpha 1 and r-erbA alpha 2 bind to the same DNA sequences, only r-erbA alpha 1 binds T3.
- Expression of r-erbA alpha 2 was found to inhibit the T3-dependent induction of a T3-responsive test gene.
- This inhibition occurred even when co-expressed with functional T3 receptors like r-erbA beta or r-erbA alpha 1.
Conclusions:
- Alternative splicing of the erbA alpha transcript generates protein products with opposing biological activities.
- The r-erbA alpha 2 isoform acts as a dominant-negative inhibitor of T3 signaling.
- This suggests a novel mechanism for fine-tuning hormonal responsiveness through differential protein expression.