Different molecular mechanisms of vitamin D(3) receptor antagonists.

Two structurally different antagonists of the nuclear hormone 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)], the 25-carboxylic ester ZK159222 and the 26,23-lactone TEI-9647, have recently been described. In this study, the molecular mechanisms and the efficacy of both antagonists were compared. ZK159222 showed similar potency and sensitivity to 1alpha,25(OH)(2)D(3) in ligand-dependent gel shift assays using the vitamin D receptor (VDR), the retinoid X receptor, and specific DNA binding sites, whereas TEI-9647 displayed reduced potency and >10-fold lower sensitivity in this assay system. Limited protease digestion and gel shift clipping assays showed that the two antagonists stabilized individual patterns of VDR conformations. Both antagonists prevented the interaction of the VDR with coactivator proteins, as demonstrated by GST-pull-down and supershift assays; like the natural hormone, however, they were able to induce a dissociation of corepressor proteins. Interestingly, ZK159222 demonstrated functional antagonism in reporter gene assays both in HeLa and MCF-7 cells, whereas TEI-9647 functioned as a less sensitive antagonist only in MCF-7 cells. In conclusion, the two 1alpha,25(OH)(2)D(3) analogs act in part via different molecular mechanisms, which allows us to speculate that ZK159222 is a more complete antagonist and TEI-9647 a more selective antagonist.

Allelic loss of the retinoblastoma tumor suppressor gene: a marker for aggressive parathyroid tumors?

Allelic loss of the retinoblastoma tumor suppressor gene has recently been shown to be highly specific for parathyroid carcinoma. It has been proposed that this genetic abnormality may have diagnostic and prognostic implications for parathyroid carcinoma, but to date no further studies are available to substantiate these findings. In the present study, three cases of atypical recurrent hyperparathyroidism were examined: a patient with parathyroid carcinoma and an autotransplanted adenoma that progressed into carcinoma, a patient with recurrent juvenile hyperparathyroidism, and a patient with severe recurrent secondary hyperparathyroid disease due to rapidly growing autotransplant. Six pairs each of sporadic parathyroid adenoma and secondary parathyroid disease were also studied for comparison. Allelic losses of RB and D13S71 at 13q14 was found in the parathyroid carcinoma and the corresponding autotransplant that had previously been considered benign tissue and in the case of recurrent juvenile hyperparathyroidism, but not in any of the other tumors. Our findings support the findings of the previous study that RB or 13q loss is specific for parathyroid tumors with increased aggressiveness and might be of clinical significance.