Differential expression of VEGF-A mRNA by 17β-estradiol in breast tumor cells lacking classical ER-α may be mediated through a variant form of ER-α

beta-Estradiol (17beta-E-2) augments VEGF-A expression in various estrogen targeted organs and cells including breast tumor derived cell lines, via an ER-alpha mediated pathway. Ironically, 17beta-E-2 is able to regulate some genes via ER-alpha independent pathways. In the present study, we sought to determine whether 17beta-E-2 can modulate VEGF-A expression in absence of ER-alpha, and therefore, three different cell lines including ER-alpha(+) MCF-7, and ER-alpha SKBR-3 and HMEC were used for this study. The present study demonstrates that 17beta-E-2 also induces VEGF-A mRNA expression in ER-negative SKBR-3 breast tumor cells in a manner similar to that observed in ER-positive MCF-7 cells. Blocking the induced-expression by antiestrogen ICI 182,780 indicates the induction pathway is ER dependent. While ER-alpha mRNA is absent in both HMEC and SKBR-3 cells, the impact of estrogen was found only in SKBR-3 cells, suggesting the existence of an analogue to ER-alpha or overlapping signal in these cells. Consistent with this suggestion, the present studies demonstrate the existence of an ER-alpha(var2) protein in MCF-7 and in SKBR-3 cells. This variant is predominantly localized in the nuclei of SKBR-3 cells. Importantly, specific binding of 17beta-E-2 by these cells suggest the ER-alpha(var2) may act as active receptor in SKBR-3 cells.