TY - JOUR
T1 - Human estrogen receptor introduced into the Xenopus oocyte represses expression from an artificial frog estrogen response element
AU - Watson, C. S.
N1 - Funding Information:
Acknowledgements--All expression and reporter plasmids and some helpful experimental suggestions were kindly provided by Dr Ming Jer Tsai of Baylor College of Medicine, Houston, TX. I also thank Dr Mary Thomas and Mr Todd Pappas of this institution for critical reading of my manuscript in preparation for submission. The excellent technical assistance of Ms Teri Tortes is gratefully acknowledged. This work was supported by NIH grant HD22746 and by the Pfeiffer Foundation.
PY - 1991/4
Y1 - 1991/4
N2 - Although the estrogen responsiveness and estrogen receptors of Xenopus hepatocytes have been well described, oocytes of this species have not previously been shown to contain estrogen receptors (ER). Recombinant human ER (HER) was expressed in oocytes in a dose dependent fashion as measured by [35S]methionine incorporation into newly synthesized proteins. Chloramphenicol acetyl transferase (CAT) reporter plasmids, driven by a herpes simplex thymidine kinase promotor with or without a 17 base pair estrogen response element (ERE) from the vitellogenin A2 gene, were also injected into oocytes. When injected without the accompanying HER sequences, the construct containing the ERE expressed 10-fold more CAT activity, and this response was saturable as demonstrated by injecting increasing amounts of reporter plasmid. These results suggest either the activity of small amounts of a Xenopus ER (measured here by LH-20 assay), or the presence of some endogenous oocyte protein other than the ER that can interact with this ERE. When HER was co-expressed with ERECAT, CAT expression was suppressed over a wide range of HER concentrations. This unexpected repression may be due to displacement of an estrogen receptor or other endogenous oocyte regulatory protein on the ERE. HER's positive regulatory activity may require transcription factors that are lacking or insufficient in the oocyte. Alternatively the simple 17 base pair ERE may not provide DNA binding sites for such transcription factors.
AB - Although the estrogen responsiveness and estrogen receptors of Xenopus hepatocytes have been well described, oocytes of this species have not previously been shown to contain estrogen receptors (ER). Recombinant human ER (HER) was expressed in oocytes in a dose dependent fashion as measured by [35S]methionine incorporation into newly synthesized proteins. Chloramphenicol acetyl transferase (CAT) reporter plasmids, driven by a herpes simplex thymidine kinase promotor with or without a 17 base pair estrogen response element (ERE) from the vitellogenin A2 gene, were also injected into oocytes. When injected without the accompanying HER sequences, the construct containing the ERE expressed 10-fold more CAT activity, and this response was saturable as demonstrated by injecting increasing amounts of reporter plasmid. These results suggest either the activity of small amounts of a Xenopus ER (measured here by LH-20 assay), or the presence of some endogenous oocyte protein other than the ER that can interact with this ERE. When HER was co-expressed with ERECAT, CAT expression was suppressed over a wide range of HER concentrations. This unexpected repression may be due to displacement of an estrogen receptor or other endogenous oocyte regulatory protein on the ERE. HER's positive regulatory activity may require transcription factors that are lacking or insufficient in the oocyte. Alternatively the simple 17 base pair ERE may not provide DNA binding sites for such transcription factors.
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U2 - 10.1016/0960-0760(91)90330-8
DO - 10.1016/0960-0760(91)90330-8
M3 - Article
C2 - 2031857
AN - SCOPUS:0025758245
SN - 0960-0760
VL - 38
SP - 423
EP - 431
JO - Journal of Steroid Biochemistry and Molecular Biology
JF - Journal of Steroid Biochemistry and Molecular Biology
IS - 4
ER -