Cholesterol inhibits the nuclear entry of estrogen receptor activation factor (E-RAF) and its dimerization with the nonactivated estrogen receptor (naER) in goat uterus

✍ Scribed by Raghava Varman Thampan; Atya Zafar; N.S. Imam; S. Sreeja; K. Suma; M. Vairamani

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 386 KB
• Volume: 77
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/(sici)1097-4644(20000601)77:3<382::aid-jcb4>3.0.co;2-l

✦ Synopsis

An alternative form of estrogen receptor isolated from goat uterus, the nonactivated estrogen receptor (naER), has no DNA-binding function, although it is closely similar to the classical estrogen receptor (ER) in its hormone binding affinity and specificity. The naER dimerizes with a DNA binding protein, estrogen receptor activation factor (E-RAF). The heterodimer binds to the DNA. Assays carried out during the purification of E-RAF showed that an endogenous inhibitor that is heat stable and dialyzable bound to the E-RAF and prevented the formation of the heterodimer. The inhibitor has been isolated and purified. GC-MS analysis identifies this molecule to be cholesterol. Circular dichroism measurement has shown that the high-affinity binding of cholesterol to E-RAF results in subtle changes in the secondary and the tertiary structure of the protein. The E-RAF with altered conformation fails to dimerize with the naER. Instead of facilitating E-RAF entry into the nucleus, dimerization with the naER prevents it. Similarly, cholesterol binding blocks the nuclear entry of the protein, showing that E-RAF with altered conformation is incapable of interaction with the nuclear pore complex/membrane proteins. The naER-E-RAF heterodimer remains at the nuclear periphery, incapable of further transport. These results indicate the possibility that the dimerization between naER and the E-RAF takes place only within the nuclear compartment. The observation that cholesterol binding prevents nuclear entry of the E-RAF reflects the similarity of E-RAF with the sterol regulatory element (SRE) binding protein that enters the nucleus and binds to SRE only when the intracellular level of cholesterol remains low.