Association of estrogen receptor beta with plasma-membrane caveola components: implication in control of vitamin D receptor
Authors: Betty Schwartz
Liat Abovich Gilad
Journal: Journal of Molecular Endocrinology (2007)
Discipline: BIOLOGY & BIOCHEMISTRY
Keywords: caveolin-1; estrogen receptor beta; 7beta-estradiol; vitamin D receptor; compartmentalization
Affiliations: Faculty of Agricultural, Food and Environmental Quality Sciences, Institute of Biochemistry, Food Science and Nutrition, The Hebrew University of Jerusalem, Israel.

Abstract:  This study was designed to provide a direct demonstration of the importance of caveolin-1 in the compartmentalization of estrogen receptor beta (ERbeta) to the membrane, thus allowing 7beta-estradiol (E2) to control vitamin D receptor (VDR) transcription and expression. Our strategy was to obtain cell lines expressing different levels of caveolin-1. To this end, we transfected human embryonic kidney 293 cells with a caveolin-1-expressing vector and obtained three cell-line variants: one expressing high amounts of caveolin-1 (clone A), one expressing low amounts of caveolin-1 (clone B), and one expressing high amounts of the nonfunctional P132L caveolin-1 mutant (clone C), and compared these with parental (wild-type, WT) cells expressing negligible levels of caveolin-1. In clone A, ERbeta colocalized to membrane preparations and E2 treatment induced significant ERK 1/2 phosphorylation and enhanced VDR expression. In clones B and C and the WT, ERbeta did not localize to membrane preparations and E2 treatment was ineffective at inducing VDR upregulation associated with ERK 1/2 phosphorylation. Luciferase reporter gene expression assays showed that the human VDR promoter is only highly responsive to E2 treatment in clone A, except in the presence of the ER-specific inhibitor ICI182 780. Cotransfection of clone A with the VDR promoter and several mutants of MAPK kinase (MEK) demonstrated that the constitutively active form of MEK significantly increases VDR promoter activation, while the catalytically inactive construct is ineffective in this regard. In clone A cells transfected with an activation protein-1 (AP-1)-luciferase construct, E2 significantly upregulated the promoter activity, while ICI182 780 completely eliminated this E2-mediated effect. Clone A cells transfected with a VDR promoter bearing a targeted mutation towards the AP-1 site showed reduced E2-mediated activation of luciferase activity. Taken together, our data confirm the importance of caveolin-1 in the association of ERbeta to the membrane caveolae, allowing ERK 1/2 phosphorylation and upregulation of VDR. 

Retracted: No

PubPeer comments:
 Figure 1. * Red and blue boxes: b-actin lanes in panels A (representing HEK-293 cells) appear to look similar to b-actin lanes in panel B ( three cell lines transfected with caveolin-1 cDNA and then selected for high (clone A) and low (clone B) levels of caveolin-1 expression according to the text). Maybe I am misinterpreting the text, but it seems that the cells in A and B are not the same. Could the authors please clarify? ![file] , 
 Figure 2A. * Orange and green boxes focus attention to bands that look more similar than expected. ![file] , 
 Figure 7. * Boxes of the same color point out bands that look more similar than expected. ![file] , 
 The b-actin lanes in Figure 7A, B, and C also look similar to the GAPDH bands in Figure 4 of an older paper by some of the same authors, i.e., Liat Abovich Gilad, Oren Tirosh and Betty Schwartz, Journal of Endocrinology (2006), DOI: 10.1677 joe.1.06930, https: pubpeer.com publications 9B9041B0AA1A9E44A0B45A4AD6A1BF ![file] , 
 Four VDR lanes and four b-actin lanes in Figure 7E from this paper look similar to panels in Figure 5M of another paper by the same research group (not clear what the bottom blot represents), i.e. Tamara Jaffe and Betty Schwartz, Int. J. Cancer (2008), DOI: 10.1002 ijc.23821, https: pubpeer.com publications B5FEF5B4D3632FB17AC8528E2957AA ![file] ,