Regulation of phosphatidylinositol-phosphate kinase IIγ gene transcription by thyroid-stimulating hormone in thyroid cells

Abstract

This study was performed to evaluate the effects of thyroid-stimulating hormone (TSH) on phosphatidylinositol-4-phosphate 5-kinase type IIγ (PIPKIIγ) gene expression in the thyrocytes of FRTL-5 cells. Although PIPKIIγ mRNA was expressed constantly in the absence of added TSH, its expression increased remarkably in the presence of 10-9 M TSH. This increase started within 6 h of the addition of TSH, and reached a maximum at 8 h. The mRNA expression properties of PIPKIIγ in the cells were identified using inhibitors. Actinomycin D blocked PIPKIIγ transcription strongly, while cycloheximide did not. In an experiment using 5,6-dichlo-1-β-d-ribofuranosyl-benzimidaxole, the half-life of PIPKIIγ mRNA was approximately 6 h in the presence or absence of TSH, and it was not affected by the stability of the PIPKIIγ mRNA. The effects of TSH on PIPKIIγ gene expression were specific, and other growth factors examined (transferrin, insulin and hydrocortisone) did not alter its expression. It is possible that the mechanism of PIPKIIγ gene expression is involved in the permissive effects of the TSH-cAMP cascade proper. Our results indicate, for the first time, that the expression of PIPKIIγ is regulated transcriptionally by TSH in thyrocytes.