Background:

The serum-and-glucocorticoid-inducible-kinase-1 (SGK1) is ubiquitously expressed and under genomic control by cell stress, hormones and further mediators. A most powerful stimulator of SGK1 expression is transforming growth factor TGFß1. SGK1 is activated by insulin and growth factors via phosphatidylinositol-3-kinase and the 3-phosphoinositide dependent kinase PDK1. As shown recently, SGK1 increases the store operated Ca²⁺ entry (SOCE), which is accomplished by the pore forming ion channel unit Orai. Most recent observations further revealed that SGK1 plays a critical role in the regulation of fertility. SGK1 is upregulated in the luminal epithelium of women with unexplained infertility but downregulated in decidualizing stromal cells of patients with recurrent pregnancy loss. The present study explored whether Orai1 is expressed in endometrium and sensitive to regulation by SGK1 and/or TGFß1.

Methods:

Orai1 protein abundance was determined by Western blotting and SOCE by Fura-2 fluorescence.

Results:

Orai1 is expressed in human endometrium and in human endometrial Ishikawa cells. Orai1 expression and SOCE in Ishikawa cells are increased by transfection with constitutively active ^S422DSGK1 but not by transfection with inactive ^K127NSGK1. The difference of SOCE between ^S422DSGK1 and ^K127NSGK1 transfected cells was virtually abrogated in the presence of Orai1 inhibitor 2-aminoethoxydiphenyl borate (2-APB, 10 µM). Similar to ^S422DSGK1 transfection TGFß1 treatment upregulated both, Orai1 protein abundance and SOCE.

Conclusions:

Orai1 is expressed in human endometrium and is up-regulated by SGK1 and TGFß1. The present observations thus uncover a novel element in SGK1 sensitive regulation of endometrial cells.