Estradiol binding after sialidase and sialyltransferase treatment of MCF-7 cells

Sialyltransferase activity and serum sialic acid concentration are higher in certain malignancies. Also the estrogen receptor can be modified post-translationally. We have investigated the effect of sialidase and sialyltransferase on estrogen receptors from MCF-7 cytosol. Specific estradiol binding was measured using the radioligand essay. Although the K-d values (0.7 +/- 0.2 nM) remained essentially unaltered, whether treated or not with sialidase or sialyltransferase (p>0.06), the specific binding capacity changed from 27.2 +/- 5 fmol mg(-1) protein (untreated) to 42.0 +/- 4 and 17.0 +/- 2 following treatment with sialidase and sialyltransferase respectively. Positive and negative correlations were respectively obtained with increasing concentrations of sialidase (r=0.9429) or sialyltransferase (r=-1.0000) with specific estradiol binding. These results suggest that the specific binding of estradiol to estrogen receptors can be post-translationally altered by sialidase and sialyltransferase treatment.