**11. Protein protein interactions during naER internalization following estradiol binding**

The studies reported from our laboratory (Sreeja & Thampan, 2004 b) have indicated that the internalization of naER from the plasma, following estradiol binding to the receptor was a clathrin-coated vesicle (CCV)-mediated mechanism. A 55 kDa protein of the CCV, apparently carrying the internalization signal (Trowbridge at al, 1993) is the target protein for naER in CCV. The internalized naER interacts with a 58kDa nuclear transport protein, the actin binding p58, that recognizes the nuclear localization signal (NLS) on the receptor. Prior to recognizing p58, the site involved on the naER is bound by Hsp-90.Estradiol binding to naER promotes dissociation of Hsp-90 from the receptor (Anilkumar at al., 2010). Confocal microscopic studies presented in this study showed that in goat endometrial cells in culture exposure of the cells to estradiol resulted in the intracellular movement of both naER and Hsp-90. It was observed that both naER and Hsp-90 entered the nuclei within a matter of 3 hours following the exposure of the cells to estradiol. The functional significance of Hsp-90 in the nuclei remains to be known.naER is transformed into nuclear estrogen receptor II (nERII) within the nucleus. It is evident that this change in identity is associated with a distinct structural change in the protein. Possibly, this transformation that takes place within the nucleus is chaperoned by Hsp-90.
