Human platelets contain a glycosylated estrogen receptor beta

Platelets play an important role in the coronary thrombus formation that leads to myocardial ischemia and infarction. Gender differences in the development of coronary heart disease and its outcomes are partly regulated by estrogen and its receptors, but the roles of the latter in thrombogenicity are less well-defined. We previously demonstrated the presence of estrogen receptor (ER) beta in cells of the megakaryocytic lineage. In this study, we characterize human platelet ERbeta and its expression using biochemical and molecular biological techniques. Western immunoblotting showed that platelet ERbeta migrated with an apparent molecular mass approximately 3.7 kDa larger than ERbeta in a variety of cell lines (including those of prostate and breast origin). A rigorous investigation of platelet ERbeta mRNA by reverse transcriptase-polymerase chain reaction revealed normal transcripts and a single alternately spliced mRNA. However, this variant form was smaller, lacking exon 2, and could not account for the larger protein size seen in platelets. Treatment of ERbeta with N-glycosidase F, which removes core carbohydrate residues, caused a more rapid migration through polyacrylamide gels but had no effect on ERbeta from human cell lines. We conclude that the larger form of ERbeta in human platelets is not attributable to alternate mRNA splicing but primarily to tissue-specific glycosylation.