Type 1 5'-deiodinase is one of two isoenzymes that participate in conversion of prohormone thyroxine into triiodothyronine (T3). A decrease in type 1 5'-deiodinase expression was observed in renal clear cell carcinoma, thyroid cancer, and lung cancer. The aim of this study was to evaluate type 1 5'-deiodinase activity and mRNA level in breast cancer tissue and non-cancerous surrounding breast tissue. Material was collected from 36 patients undergoing radical mastectomy or local tumor resection. In all non-cancerous breast tissues, type 1 50-deiodinase activity was found to be at a very low or immeasurable level, and type 1 5'-deiodinase mRNA was detected only in 2 out of the 36 samples. By contrast, 20 out of the 36 breast cancer tissues, mainly grades G1 and G2, expressed abundant type 1 5'-deiodinase activity and/or a high mRNA level. Our data demonstrated the presence of type 1 5'-deiodinase in well-differentiated breast cancer tissue. High enzymatic activity of type 1 50-deiodinase can potentially lead to an increase in the production of T3, which may affect target gene transcription, including genes responsible for energy expenditure, growth, differentiation, and proliferation.
Type 1 iodothyronine deiodinase (D1) is a crucial enzyme which converts the prohormone thyroxine (T4) into active tri-iodothyronine (T3). There has been strong evidence that the metabolism of thyroid hormones is disturbed in some neoplastic tissues such as thyroid, renal, and breast cancer. However, there are few available data about D1 enzyme activity in benign tumors such as hemangioma, which is the most common primary liver tumor. Hence this study aimed to determine the enzymatic activity of D1 in hemangiomas in relation to healthy liver tissue. Seven tumors and healthy control tissues were obtained from patients who had liver resection due to hemangioma. The activity was assessed by measurement of radioactive iodine released by deiodination catalyzed by D1. It was found that D1 activity was significantly lower in the hemagiomas than in the healthy surrounding tissue (p = 0.0017). The results indicated that thyroid hormones play important roles not only in the regulation of cell metabolism, but also in cell growth, division, and apoptosis. The active form T3 acts through its nuclear receptors and influences the up- and down-regulation of target genes. Healthy liver tissue expresses a high level of D1, but disturbed D1 activity may result in changes in the local concentration of T3 which may impair gene transcription. These finding demonstrate a low enzymatic activity of D1 in liver hemangioma and suggest an as yet unknown role of thyroid hormones in this type of benign liver tumor.
IntroductionType 1 iodothyronine deiodinase (D1) converts thyroxin (T4) into tri-iodothyronine (T3). Strong evidence indicates that thyroid hormone metabolism is disturbed in neoplasms such as thyroid and breast cancer. However, there is limited data concerning the function of the D1 enzyme in liver tumors. We aimed to estimate the enzymatic activity of D1 in two different common liver tumors.Material and methodsWe obtained 20 tumor samples from patients who had undergone a liver resection. Of the tissue samples, there were 13 benign lesions of focal nodular hyperplasia (FNH) and 7 malignant lesions of hepatocellular carcinomas (HCC). The D1 activity was assessed by measuring the amount of radioactive iodine released in reaction to D1-catalysed deiodination. Groups were compared by the Mann-Whitney non-parametrical test for independent trials, and the Kruskal Wallis test.ResultsThe enzymatic activity of D1 was not significantly altered in the FNH group (median = 536 fmol/mg of protein/min; p = 0.972) and HCC group (367 fmol/mg; p = 0.128) when compared to matched normal liver parenchyma controls (546 fmol/mg and 556 fmol/mg, respectively).ConclusionsLiver parenchyma expresses high levels of D1. The results clearly revealed that D1 activity was not significantly different between benign and malignant tumors (FNH and HCC) compared to healthy liver parenchyma cells.
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