Health & Environmental Research Online (HERO)


Print Feedback Export to File
9218528 
Journal Article 
Nongenomic activation of phosphatidylinositol 3-kinase signaling by thyroid hormone receptors 
Sui, Li; Wang, J; Li, BaoM; , 
2008 
1 
Neurochemical Research
ISSN: 0364-3190
EISSN: 1573-6903 
SPRINGER/PLENUM PUBLISHERS 
NEW YORK 
1065-1076 
English 
18097751 
WOS:000254964800014 
Thyroid hormone (T3) is critical in growth, development, differentiation, and maintenance of metabolic homeostasis. Recent studies suggest that thyroid hormone receptors (TRs) not only mediate the biological activities of T3 via nucleus-initiated transcription, but also could act via nongenomic pathways. The striking phenotype of thyroid cancer exhibited by a knockin mutant mouse that harbors a dominant negative TRbeta mutant (TRbeta(PV/PV) mouse) allows the elucidation of novel oncogenic activity of a TRbeta mutant (PV) via extra-nuclear actions. PV physically interacts with the regulatory p85alpha subunit of phosphatidylinositol 3-kinase (PI3K) to activate the downstream AKT-mammalian target of rapamycin (mTOR) and p70(S6K) and PI3K-integrin-linked kinase-matrix metalloproteinase-2 signaling pathways. The PV-mediated PI3K activation results in increased cell proliferation, motility, migration, and metastasis. Remarkably, a nuclear receptor corepressor (NCoR) was found to regulate the PV-activated PI3K signaling by competing with PV for binding to the C-terminal SH2 domain of p85alpha. Over-expression of NCoR in thyroid tumor cells of TRbeta(PV/PV) mice reduces AKT-mTOR-p70(S6K) signaling. Conversely, lowering cellular NCoR by siRNA knockdown in tumor cells leads to over-activated PI3K-AKT signaling to increase cell proliferation and motility. Furthermore, NCoR protein levels are significantly lower in thyroid tumor cells than in wild type thyrocytes, allowing more effective binding of PV to p85alpha to activate PI3K signaling, thereby contributing to tumor progression. Thus, PV, an apo-TRbeta, could act via direct protein-protein interaction to mediate critical oncogenic actions. These studies also uncovered a novel extra-nuclear role of NCoR in modulating the nongenomic actions of a mutated TRbeta in controlling thyroid carcinogenesis.