Regulation of a novel immediate early response gene, IEX-1, in keratinocytes by 1alpha,25-dihydroxyvitamin D3

1alpha,25-Dihydroxyvitamin D3 [1alpha,25(OH)2D3] regulates cellular growth and differentiation. We show that in keratinocytes, 1alpha, 25(OH)2D3 reduces concentrations of the messenger RNA of IEX-1, the product of which blocks Fas- or tumor necrosis factor type alpha-induced apoptosis in various cells. In sub-confluent keratinocyte cultures, the addition of 1alpha,25(OH)2D3, in amounts that induce growth arrest, reduces IEX-1 mRNA concentrations. In confluent cells, 1alpha,25(OH)2D3 initially reduces and then increases IEX-1 mRNA concentrations. IEX-1 protein is localized in the nucleus and perinuclear region of keratinocytes. In sub-confluent cells, 1alpha,25(OH)2D3 translocates IEX-1 protein from the nucleus to the perinuclear region and cytoplasm. Since IEX-1 has recently been shown to regulate cell survival and number, we suggest that IEX-1 may play a role in keratinocyte growth and differentiation and that 1alpha,25(OH)2D3 may reduce keratinocyte growth via a reduction in IEX-1 mRNA and a change in the intracellular distribution of IEX-1 protein.     

Vitamin D receptor expression, 24-hydroxylase activity, and inhibition of growth by 1alpha,25-dihydroxyvitamin D3 in seven human prostatic carcinoma cell lines

Although prostatic cancer is often viewed as an androgen-dependent malignancy, a number of other hormones including 1alpha, 25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] are now recognized to modulate its growth and differentiated phenotype. Seven different continuous human prostatic carcinoma cell lines were examined for the presence of biologically active receptors for 1alpha,25(OH)2D3. All seven lines were found to contain mRNA for the vitamin D receptor using an RNase protection assay. Six of the seven cell lines were found to have high-affinity saturable binding sites for 1alpha,25(OH)2D3. The seventh line was found to contain vitamin D receptors by sucrose gradient analysis. All seven lines were found to express 24-hydroxylase activity by a HPLC assay that measures the conversion of 25-hydroxyvitamin D3 to 24,25-dihydroxyvitamin D3. 24-Hydroxylase activity was up-regulated in all seven cell lines by preincubation with 1alpha,25(OH)2D3. In the presence of fetal bovine serum, the growth of four of the seven cell lines was inhibited. In the majority of cell lines growth inhibition was related not only to the number of receptors per cell, but also in inverse proportion to the 24-hydroxylase activity of each cell line. The ubiquitous presence of vitamin D receptor and 24-hydroxylase activity in human prostatic carcinoma cells suggests new alternatives for the pharmacological treatment of advanced prostatic cancer and implies that chemoprevention strategies could also make use of this endocrine axis.     

Growth inhibitory effects of 1,25-dihydroxyvitamin D3 and its synthetic analogue, 1alpha,25-dihydroxy-16-ene-23yne-26,27-hexafluoro-19-nor-cholecalcifero l (Ro 25-6760), on a human colon cancer xenograft

The effect of 1,25-dihydroxyvitamin D3 and its synthetic analogue, 1alpha,25-dihydroxy-16-ene-23yne-26,27-hexafluoro-19-n or-cholecalciferol (Ro 25-6760), have been evaluated both in vitro and in vivo in human colorectal cancer cell lines expressing high (HT-29) and low (SW-620) levels of vitamin D receptor. 1,25-Dihydroxyvitamin D3 caused significant dose-dependent growth inhibition of HT-29 cells at concentrations ranging from 10(-11) to 10(-6). The antiproliferative effect of Ro 25-6760 on HT-29 cells was also dose-dependent with cell counts on day 6, ranging from 98% of control at 10(-11) M to 14% of control at 10(-6) M. However, 1,25-dihydroxyvitamin D3 and Ro 25-6760 did not have any growth inhibitory effect on SW-620 at all concentrations. In mice with HT-29 tumor xenografts, administration of vitamin D at 0.1 and 0.2 microg/injection i.p. three times/week did not cause any significant tumor growth delay, whereas synthetic analogue Ro 25-6760, at both concentrations, caused a significant tumor growth inhibition in comparison with the control arm. In 30% of mice treated by R0 25-6760 the tumors disappeared on average after the second injection, and tumor growth did not resume after drug withdrawal. However, both 1,25-dihydroxyvitamin D3 or Ro 25-6760 had no growth inhibitory effect at all applied concentrations in mice with the SW-620 tumor xenografts. The mechanism for this impressive growth inhibition is not yet elucidated and warrants further investigation.