Expression and activation of mitogen-activated protein kinase in the human endometrium during the menstrual cycle

The purpose of this study was to investigate the fluctuation of expression and activation of mitogen-activated protein kinase in normal human endometrium throughout the menstrual cycle.

Thirty-three normal endometrial tissues were obtained from fertile women who had undergone hysterectomies for reasons other than endometrial disease. Extracellular signal-regulated kinase, -1, and -2 expression were studied by immunohistochemistry. Moreover, extracellular signal-regulated kinase activity was analyzed by gel kinase assay.

Western blotting analysis with anti-pan-extracellular signal-regulated kinase antibody mainly demonstrated an immunoreactive band of 42 kd that corresponded to extracellular signal-regulated kinase 2 in the endometrium. The expression of extracellular signal-regulated kinase 2 tended to increase in the secretory phase. Immunohistochemical analysis for extracellular signal-regulated kinase 1 in endometrial sections revealed a weak staining of glands and almost no staining of stromal cells. Immunohistochemical analysis for extracellular signal-regulated kinase 2 in endometrial sections revealed a distinct staining of glands in both proliferative and secretory phases and a weak staining of stromal cells. Although the intensity of staining for extracellular signal-regulated kinase 2 in stromal cells did not change during the secretory phase, in the glands the extracellular signal-regulated kinase 2 was highly stained in the mid-to-late secretory phase. In gel kinase assay revealed that extracellular signal-regulated kinase activity was increased significantly in the mid-to-late secretory phase.

Expression and activation of extracellular signal-regulated kinase in the human endometrium was increased particularly during the secretory phase. We suggest that fluctuation of extracellular signal-regulated kinase in the human endometrium may be induced by ovarian steroid hormones.