Demonstration of the Receptor Site for Thyroid Hormone on Integrin αvβ3

Integrin αvβ3 is one of the 24 heterodimeric structural proteins of the plasma membrane of animal cells. The extracellular domain of αvβ3 comprises about 80% of its mass and is devoted largely to interactions with extracellular matrix (ECM) proteins, such as vitronectin and fibronectin, and cell-cell interaction. The binding of specific ECM proteins is conveyed to the cell interior by signal transduction. In the past decade, integrin αvβ3 has been shown to bind small molecules, such as nonprotein hormones-thyroid hormone analogues and dihydrotestosterone-and the stilbene, resveratrol. The αvβ3-thyroid hormone interaction signal generated at the integrin is transduced into intracellular protein trafficking, nucleoprotein phosphorylation, and expression of specific genes. The hormone receptor on the integrin bears no structural homologies with nuclear thyroid hormone receptors (TRs). Because integrin αvβ3 is generously expressed on the surface of cancer cells and rapidly dividing endothelial cells, thyroid hormone actions initiated at the receptor on integrin not unexpectedly relate to cell proliferation, cancer cell survival pathways and to angiogenesis. In this chapter, we present methods for the definition of the receptor, for monitoring certain of its functions and for the downregulation of the gene for the integrin.