Molecular and Cellular Biochemistry 262: 215–224, 2004. c  2004 Kluwer Academic Publishers. Printed in the Netherlands. 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 Krishanu Sengupta, 1,2 Snigdha Banerjee, 1,2 Neela K. Saxena, 1,2 Nira Ben Jonathan, 3 Donald R. Campbell 1,4 and Sushanta K. Banerjee 1,2 1 Cancer Research Unit, V.A. Medical Center; 2 Division of Oncology/Hematology, Department of Medicine, University of Kansas Medical Center, Kansas City, MO, USA; 3 Department of Cell Biology, University of Cincinnati Medical School, Cincinnati, OH, USA; 4 Saint Luke’s Hospital and University of Missouri, Kansas City, MO, USA Received 21 November 2003; accepted 15 December 2003 Abstract β -Estradiol (17β -E 2 ) augments VEGF-A expression in various estrogen targeted organs and cells including breast tumor derived cell lines, via an ER-α mediated pathway. Ironically, 17β -E 2 is able to regulate some genes via ER-α independent pathways. In the present study, we sought to determine whether 17β -E 2 can modulate VEGF-A expression in absence of ER-α, and therefore, three different cell lines including ER-α + MCF-7, and ER-α SKBR-3 and HMEC were used for this study. The present study demonstrates that 17β -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-α 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-α or overlapping signal in these cells. Consistent with this suggestion, the present studies demonstrate the existence of an ER-α 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 17β -E 2 by these cells suggest the ER-α var2 may act as active receptor in SKBR-3 cells. (Mol Cell Biochem 262: 215–224, 2004) Key words: 17β -estradiol, breast tumor cells, estrogen receptor, radio–ligand binding, vascular endothelial growth factor-A Introduction Vascular endothelial growth factor-A (VEGF-A; formerly known as VEGF) is a potent endothelial cell mitogen that plays a crucial role in endothelial cell proliferation and migration [1, 2] as well as, regulating the growth of cancer Address for offprints: S.K. Banerjee, Cancer Research Unit, V.A. Medical Center, Research Division, 151 VA Medical Center, 4801 East Linwood Blvd, Kansas City, MO 64128-2226, USA (E-mail: sbanerjee@kumc.edu) cells by autocrine and paracrine pathways [3, 4]. This growth factor is a homodimeric protein of molecular weight 34–42 kDa and exists in five molecular isoforms (i.e., VEGF 121 , VEGF 145 , VEGF 165 , VEGF 189 , and VEGF 206 ) with variable functions [5–7]. A variety of growth factors and cytokines such as PDGF, EGF, and TGF-β have been identified as