Selective expression of transthyretin in subtypes of lung cancer.

Transthyretin (TTR) is expressed primarily in liver, choroid plexus of brain and pancreatic islet A and B cells. It is also synthesized in some endocrine tumors. In the present study, the protein expression of TTR in lung cancer tissues and cell lines was investigated by western blot. The mRNA expression of TTR in 24 pairs of frozen lung cancer tissues was examined by RT-PCR. The specific expression and cellular distribution of TTR were also evaluated in 104 paraffin-embedded lung cancer samples and 3 normal lung tissues by immunohistochemistry. Similarly, the subcellular localization and expression of TTR were further analyzed in lung cancer cell lines. With the exception of mucinous adenocarcinoma, the expression of TTR protein was observed in all tested subtypes of lung carcinoma. Adenocarcinoma displayed the highest positive expression rate of TTR, accounting for 84.4 %, and the positive expression rate of TTR was up to 85.7 % at stages III and IV. The secretory bubbles with strong TTR staining were observed in luminal cells of lung cancer. Furthermore, the localization of TTR in the cytoplasm of lung cancer cells and the secretion of TTR into extracellular milieu were also confirmed. Taken together, TTR is selectively synthesized in lung cancer cells and can be secreted extracellularly.