Serine 216 Phosphorylation of Estrogen Receptor α in Neutrophils: Migration and Infiltration into the Mouse Uterus

Background: Whereas estrogen receptors are present in immune cells, it is not known if they are phosphorylated to regulate immune cell functions. Here we determined the phosphorylation status of estrogen receptor alpha (ER alpha) at residue serine 216 in mouse neutrophils and examined its role in migration and infiltration. Serine 216 is the conserved phosphorylation site within the DNA binding domains found in the majority of nuclear receptors. Methodology/Principal Findings: A phospho-peptide antibody specific to phosphorylated serine 216 and ER alpha KO mice were utilized in immunohistochemistry, double immuno-staining or Western blot to detect phosphorylation of ER alpha in peripheral blood as well as infiltrating neutrophils in the mouse uterus. Transwell assays were performed to examine migration of neutrophils. An anti-Ly6G antibody identified neutrophils. About 20% of neutrophils expressed phosphorylated ER alpha at serine 216 in peripheral white blood cells (WBC) from C3H/HeNCrIBR females. Phosphorylation was additively segregated between C3H/HeNCrIBR and C57BL/6 females. Only neutrophils that expressed phosphorylated ER alpha migrated in Transwell assays as well as infiltrated the mouse uterus during normal estrous cycles. Conclusions/Significance: ER alpha was phosphorylated at serine 216 in about 20% of mouse peripheral blood neutrophils. Only those that express phosphorylated ER alpha migrate and infiltrate the mouse uterus. This phosphorylation was the first to be characterized in endogenous ER alpha found in normal tissues and cells. Phosphorylated ER alpha may have opened a novel research direction for biological roles of phosphorylation in ER alpha actions and can be developed as a drug target for treatment of immune-related diseases.