Sodium iodide symporter and pendrin expression in human thyroid tissues

Thyroid cells synthesize thyroid hormones through a multistep process durin g which iodide is transported through the basolateral and the apical membra nes of thyrocytes. Two genes that participate in these transports and the c orresponding proteins, namely sodium iodide symporter (NIS) and pendrin, th e product of the Pendred syndrome gene, have recently been characterized. W e studied NIS and pendrin expression at the mRNA and protein levels by a qu antitative reverse transcription-polymerase chain reaction (RT-PCR) method and by single and double immunostaining in normal and pathological human th yroid tissues. In normal tissue, NIS and pendrin were detected in about 20% and 40%-60% of thyrocytes, respectively. The number of NIS- and pendrin-po sitive cells was much higher in hyperfunctioning tissue from Graves' diseas e or toxic adenoma. In hypofunctioning adenomas and carcinomas, the number of NIS- and pendrin-positive cells was low or nonexistent. Three types of f ollicular cells were observed in positive tissues: NIS-negative/pendrin-neg ative cells, NIS-positive/pendrin-positive cells, and NIS-negative/pendrin- positive cells. The first two types of cells appear to be resting and activ e cells, respectively, but the functional status of NIS-negative/pendrin-po sitive thyrocytes remains to be determined.