S. Nayeri et al., THE ANTIPROLIFERATIVE EFFECT OF VITAMIN-D-3 ANALOGS IS NOT MEDIATED BY INHIBITION OF THE AP-1 PATHWAY, BUT MAY BE RELATED TO PROMOTER SELECTIVITY, Oncogene, 11(9), 1995, pp. 1853-1858
The hormone 1,25-dihydroxyvitamin D-3 (VD) is able to induce cellular
differentiation and to inhibit cellular proliferation, which provides
it with an interesting therapeutic potential in cancer. However, side
effects of VD on homeostasis (eg hypercalcemia) had made the need for
the development of VD analogues with low calcemic effect. On the human
breast cancer cell line MCF-7 we obtained with the VD analogue EB1089
an about 100-fold higher anti-proliferative effect than with VD. We f
ound that this difference in biological activity is neither related to
increased functional affinity to the VD receptor nor to repression of
AP-1 activity. The physiologically most prominent complex of the VD r
eceptor is a heterodimer with the retinoid X receptor that binds VD re
sponse elements formed two hexameric core binding motifs being arrange
d either as direct repeats spaced by 3 nucleotides (DR3s) or as invert
ed palindromes spaced by 9 nucleotides (IP9s). We observed that EB1089
stimulates transcriptional activation from IP9-type elements at clear
ly lower concentrations than from DR3-type elements. It is possible th
at IP9-type response elements play an important role in or contribute
to the control of cell proliferation, so that promoter-selectivity may
explain the high anti-proliferative effect of EB1089.