Human platelets contain a glycosylated estrogen receptor β

Abstract

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) β in cells of the megakaryocytic lineage. In this study, we characterize human platelet ERβ and its expression using biochemical and molecular biological techniques. Western immunoblotting showed that platelet ERβ migrated with an apparent molecular mass ≈ 3.7 kDa larger than ERβ in a variety of cell lines (including those of prostate and breast origin). A rigorous investigation of platelet ERβ 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 ERβ with N-glycosidase F, which removes core carbohydrate residues, caused a more rapid migration through polyacrylamide gels but had no effect on ERβ from human cell lines. We conclude that the larger form of ERβ in human platelets is not attributable to alternate mRNA splicing but primarily to tissue-specific glycosylation.