A novel mechanism of natural vitamin E tocotrienol activity: involvement of ERβ signal transduction

Comitato R, Nesaretnam K, Leoni G, Ambra R, Canali R, Bolli A, Marino M, Virgili F. A novel mechanism of natural vitamin E tocotrienol activity: involvement of ER beta signal transduction. Am J Physiol Endocrinol Metab 297: E427-E437, 2009. First published June 2, 2009; doi: 10.1152/ajpendo.00187.2009.-Vitamin E is a generic term used to indicate all tocopherol (TOC) and tocotrienol (TT) derivates. In the last few years, several papers have shown that a TT-rich fraction (TTRF) extracted from palm oil inhibits proliferation and induces apoptosis in a large number of cancer cells. However, the molecular mechanism(s) involved in TT action is still unclear. In the present study, we proposed for the first time a novel mechanism for TT activity that involves estrogen receptor (ER) signaling. In silico simulations and in vitro binding analyses indicated a high affinity of TTs for ER alpha but not for ER beta. In addition, in ER beta-containing MDA-MB-231 breast cancer cells, we demonstrated that TTs increase the ER beta translocation into the nucleus, which in turn activates estrogen-responsive genes (MIC-1, EGR-1 and cathepsin D), as demonstrated by cell preincubation with the ER inhibitor ICI-182,780. Finally, we observed that TT treatment is associated with alteration of cell morphology, DNA fragmentation, and caspase-3 activation. Altogether, these experiments elucidated the molecular mechanism underling gamma- and delta-TT effects.