5'Deiodinase in two breast cancer cell lines: effect of triiodothyronine, isoproterenol and retinoids.

Thyroid hormones participate in the regulation of growth, development and energy expenditure of vertebrates. Type I (D1) and type II 5'deiodinases catalyze the peripheral conversion of the thyroid prohormone thyroxine to the active form triiodothyronine (T3). D1 is expressed in organs like liver, thyroid, and lactating mammary gland. This enzyme is regulated in an organ-specific manner by a wide number of factors like carbohydrates, T3, thyrotropin, and catecholamines. However, it has been shown that in several types of cancer the expression of D1 is reduced, lost, or regulated by different components. In the present work we describe the expression and regulation of 5'deiodinases in two breast cancer cell lines: MCF-7 (ovarian hormone-dependent) and MDA-MB-231 (ovarian hormone-independent). Our results showed that MCF-7 cells expressed D1 activity ( approximately 10 pmol I(-)/mg protein per h), which was stimulated only by retinoic acid treatments, but not by T3 or the beta-adrenergic agonist isoproterenol. In MDA-MB-231 cells, deiodinase activity was not detected in control conditions nor under any of these treatments. These results support the notion that D1 expression could represent a sensitive differentiation marker.