Thioredoxin and Thioredoxin Reductase Expression in Thyroid Cancer Depends on Tumour Aggressiveness

Thyroid cancer is the second most common malignancy following breast cancer in Arab females. Thioredoxin (TRX) is a small multi-functional redox protein with both intracellular and extracellular functions. The protein exists in either a reduced form (thioredoxin-SH2) or an oxidized form (thioredoxin-S2). TRX acts as an enhancement for growth factors and stimulates the growth of cancer cells. In this study of thyroid neoplasms, involving 121 female and 62 male patients, expression of TRX and TRX-R was studied using purified mouse anti-human TRX monoclonal antibody and antihuman TRX-R antiserum from rabbits, respectively. In order to delineate tumour cell growth, proliferating cell nuclear antigen (PCNA) polyclonal antibody was used. Compared to normal thyroid tissue, expression of TRX and TRX-R was increased in the cytoplasm and nuclei of thyroid cancer cells. Furthermore, TRX expression correlated with that of TRX-R. Of the 183 thyroid neoplasms investigated, overexpression of TRX-R was found in different types of neoplasms. The majority of carcinomas showed a correlation between strongly positive TRX and TRX-R expression and neoplastic cellular proliferation, as measured by PCNA. This indicates that increased TRX and TRX-R expression may be associated with tumourigenesis by acting as an autocrine growth stimulus. This study suggests that TRX immunoreactivity in thyroid tumours is a function of malignancy and cancer progression. In addition, secreted TRX can also act as an extracellular growth factor for both normal and tumour cells and enhance sensitivity of the cells. Furthermore, this study emphasizes the potential benefits of anti-TRXITRX-R agents in cancer therapeutics in the treatment of thyroid cancer.