Abstract
The active transport of iodide into thyroid cells is mediated by the Na+/I- symporter (NIS) located in the basolateral membrane. Strong intracellular staining with anti-NIS antibodies has been reported in thyroid and breast cancers. Proper NIS targeting to the plasma membrane in such cells could potentially increase the efficiency of radiotherapy for thyroid cancer and facilitate the use of radioiodide in the treatment and diagnosis of breast tumors. Our initial objective was to screen tumor samples for intracellular NIS staining and then to study the mechanisms underlying the altered subcellular localization of the transporters. Immunostaining using three different anti-NIS antibodies was performed on paraffin-embedded tissue sections from 114 thyroid or breast cancers. Western blot experiments were also carried out to determine the amount of NIS protein in some samples. Using three different anti-NIS antibodies, we observed intracellular staining in a majority of thyroid tumor samples. Control immunohistochemistry and western blot experiments indicated that this intracellular staining was due to nonspecific binding of the antibodies. In breast tumors, very weak intracellular staining was observed in some samples. Western blot experiments suggest that this labeling is also nonspecific. Our results strongly indicate that the NIS protein level is low in thyroid and breast cancers and that the intracellular staining obtained with anti-NIS antibodies corresponds to a nonspecific signal. This work was supported by grants from EDF. Alejandro Ondo was funded by ECOS-Nord/Colciencias/ICFES/ICETEX.