VDR and Familial prostate cancer: Given that S179D PRL upregulates the VDR and sensitizes prostate cancer cells to calcitriol, it was possible that combination therapy with the relatively low doses of calcitriol used would upregulate the VDR in other tissues and thereby reproduce the toxic effects of hypervitaminosis D. Histological analyses of both liver and kidneys, however, showed no signs of toxicity.