Nitric oxide (NO) is a free radical that mediates signal transduction, influencing a wide variety of biological processes. It is generated by three different nitric oxide synthase (NOS) isoforms (I to III). Among all NOS isoforms described in the thyroid cell, NOS III is the highest expressed. We reported that NO acts as regulator on TSH-induced gene expression. TSH also increases NO production and regulates NOS III mRNA expression.
The aim of this work was to analyze the signal pathway activated by TSH involved in the expression of NOS III in the thyroid cells FRTL-5.
TSH treatment for different time and concentration increases NOS III protein expression, indicating a TSH-dependent NOS expression. We evaluated a possible post-transcriptional effect developed by TSH stabilizing NOS III protein expression. A significant increase in NOS III protein half-life was induced by TSH treatment. In order to examine the signal pathway involved, we measured the effect of TSH on NOS III protein expression in the presence of different kinase inhibitors. We observed a significant inhibition of protein up-regulation in presence of PKA and Akt inhibitors. As Akt is cononical activated by PI3K, we evaluated the effect of PI3K inhibitors on NOS III up-regulation observing no evident inhibition. After that we evaluated Akt phophorilation in response to TSH. We found a TSH-dependent Akt-phosphorilation in dependence of PKA activity.
In conclussion, our results provide evidence of a novel pathway for TSH action in NOS III expression involving activation of the Akt pathway in dependence of PKA activation.
