Types 1 and 3 iodothyronine deiodinases are known to be selenocysteine-containing enzymes. Although a putative human type 2 iodothyronine deiodinase (D2) gene (hDio2) encoding a similar selenoprotein has been identified, basal D2 activity is not selenium (Se)-dependent nor has D2 been labeled with 75Se. A human mesothelioma cell line (MSTO- 211H) has recently been shown to have 40-fold higher levels of hDio2 mRNA than mesothelial cells. Mesothelioma cell lysates activate thyroxine (T4) to 3,5,3 -triiodothyronine with typical characteristics of D2 such as low Km (T4), 1.3 nM, resistance to propylthiouracil, and a short half-life ( 30 min). D2 activity is 30-fold higher in Se-supplemented than in Se-depleted medium. An antiserum prepared against a peptide deduced from the Dio2 mRNA sequence precipitates a 75Se protein of the predicted 31-kDa size from 75Se-labeled mesothelioma cells. Bromoadenosine 3 5 cy- clic monophosphate increases D2 activity and 75Se-p31 2.5-fold whereas substrate (T4) reduces both D2 activity and 75Se-p31 2–3-fold. MG132 or lactacystin (10 M), inhib- itors of the proteasome pathway by which D2 is degraded, increase both D2 activity and 75Se-p31 3–4-fold and prevent the loss of D2 activity during cycloheximide or substrate (T4) exposure. Immunocytochemical studies with affinity- purified anti-hD2 antibody show a Se-dependent increase in immunofluorescence. Thus, human D2 is encoded by hDio2 and is a member of the selenodeiodinase family ac- counting for its highly catalytic efficiency in T4 activation.
The Human Type 2 Iodothyronine Deiodinase Is a Selenoprotein Highly Expressed in a Mesothelioma Cell Line.
Cyntia Curcio, Munira M. A. Baqui, Domenico Salvatore, Bertrand H. Rihn, Steve Mohr, John W. Harney, P. Reed Larsen, and Antonio C. Bianco. Journal of Biological Chemistry. August 10, 2001. doi: 10.1074/jbc.C100325200