Dietary I(-) absorption: expression and regulation of the Na(+)/I(-) symporter in the intestine

Thyroid hormones are critical for the normal development, growth, and functional maturation of several tissues, including the central nervous system. Iodine is an essential constituent of the thyroid hormones, the only iodine-containing molecules in vertebrates. Dietary iodide (I(-)) absorption in the gastrointestinal tract is the first step in I(-) metabolism, as the diet is the only source of I(-) for land-dwelling vertebrates. The Na(+)/I(-) symporter (NIS), an integral plasma membrane glycoprotein located in the brush border of enterocytes, constitutes a central component of the I(-) absorption system in the small intestine. In this chapter, we review the most recent research on structure/function relations in NIS and the protein's I(-) transport mechanism and stoichiometry, with a special focus on the tissue distribution and hormonal regulation of NIS, as well as the role of NIS in mediating I(-) homeostasis. We further discuss recent findings concerning the autoregulatory effect of I(-) on I(-) metabolism in enterocytes: high intracellular I(-) concentrations in enterocytes decrease NIS-mediated uptake of I(-) through a complex array of posttranscriptional mechanisms, e.g., downregulation of NIS expression at the plasma membrane, increased NIS protein degradation, and reduction of NIS mRNA stability leading to decreased NIS mRNA levels. Since the molecular identification of NIS, great progress has been made not only in understanding the role of NIS in I(-) homeostasis but also in developing protocols for NIS-mediated imaging and treatment of various diseases.

First published in 1943, Vitamins and Hormones is the longest-running serial published by Academic Press.

The Series provides up-to-date information on vitamin and hormone research spanning data from molecular biology to the clinic. A volume can focus on a single molecule or on a disease that is related to vitamins or hormones. A hormone is interpreted broadly so that related substances, such as transmitters, cytokines, growth factors and others can be reviewed.

This volume focuses on hormone and transport systems.

• Expertise of the contributors
• Coverage of a vast array of subjects
• In depth current information at the molecular to the clinical levels

First published in 1943, Vitamins and Hormones is the longest-running serial published by Academic Press. The Series provides up-to-date information on vitamin and hormone research spanning data from molecular biology to the clinic. A volume can focus on a single molecule or on a disease that is related to vitamins or hormones. A hormone is interpreted broadly so that related substances, such as transmitters, cytokines, growth factors and others can be reviewed. This volume focuses on hormone and transport systems. Expertise of the contributors Coverage of a vast array of subjects In depth current information at the molecular to the clinical levels