11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1), catalyzing the intracellular activation of cortisone to cortisol, is currently considered a promising target to treat patients with metabolic syndrome; hence, there is considerable interest in the development of selective inhibitors. For preclinical tests of such inhibitors, the characteristics of 11β-HSD1 from the commonly used species have to be known. Therefore, we determined differences in substrate affinity and inhibitor effects for 11β-HSD1 from six species. The differences in catalytic activities with cortisone and 11-dehydrocorticosterone were rather modest. Human, hamster and guinea-pig 11β-HSD1 displayed the highest catalytic efficiency in the oxoreduction of cortisone, while mouse and rat showed intermediate and dog the lowest activity. Murine 11β-HSD1 most efficiently reduced 11-dehydrocorticosterone, while the enzyme from dog showed lower activity than those from the other species. 7-Ketocholesterol (7KC) was stereospecifically converted to 7β-hydroxycholesterol by recombinant 11β-HSD1 from all species analyzed except hamster, which showed a slight preference for the formation of 7α-hydroxycholesterol. Importantly, guinea-pig and canine 11β-HSD1 displayed very low 7-oxoreductase activities. Furthermore, we demonstrate significant species-specific variability in the potency of various 11β-HSD1 inhibitors, including endogenous compounds, natural chemicals and pharmaceutical compounds. The results suggest significant differences in the three-dimensional organization of the hydrophobic substrate-binding pocket of 11β-HSD1, and they emphasize that species-specific variability must be considered in the interpretation of results obtained from different animal experiments. The assessment of such differences, by cell-based test systems, may help to choose the appropriate animal for safety and efficacy studies of novel potential drug candidates.
Spyridon Arampatzis, Bert Kadereit, Daniela Schuster, Zoltan Balazs, Roberto A S Schweizer, Felix J Frey, Thierry Langer and Alex Odermatt
Márcia Faria, Daniela Félix, Rita Domingues, Maria João Bugalho, Paulo Matos and Ana Luísa Silva
Thyroid cancer (TC) is the most common endocrine malignancy. The sodium–iodide symporter (NIS), responsible for active transport of iodide into thyroid cells, allows the use of radioactive iodine (RAI) as the systemic treatment of choice for TC metastatic disease. Still, patients with advanced forms of TC often lose the ability to respond to RAI therapy, which results in worse survival rates. We have shown that the overexpression of RAC1b, a tumor-related RAC1 splice variant, is associated with less favorable clinical outcomes in differentiated TCs derived from the follicular epithelial (DTCs). RAC1b overexpression is also significantly associated with the presence of MAPK-activating BRAFV600E mutation, which has been previously implicated in the loss of NIS expression. Here, we show that increased RAC1b levels are associated with NIS downregulation in DTCs and demonstrate that ectopic overexpression of RAC1b in non-transformed thyroid cells is sufficient to decrease TSH-induced NIS expression, antagonizing the positive effect of the canonically spliced RAC1 GTPase. Moreover, we clearly document for the first time in thyroid cells that both NIS expression and iodide uptake are hampered by RAC1 inhibition, highlighting the role of RAC1 in promoting TSH-induced NIS expression. Our findings support a role for RAC1 and RAC1b signaling in the regulation of NIS expression in thyroid cells and suggest that RAC1b in cooperation with other cancer-associated signaling cues may be implicated in the response of DTCs to RAI therapy.