Down-regulation of p21-activated kinase 1 by progestin and its increased expression in the eutopic endometrium of women with endometriosis

BACKGROUND: P21-activated kinase I (PakI) integrates various signaling pathways that are vital to cell survival and function. This study was performed to evaluate whether sex steroids may regulate the expression of Pak I in endometrial cells as well as whether its expression is increased in the eutopic endometrium of women with endometriosis. METHODS: Following in vitro estradiol (E 2 ) and/or medroxyprogesterone acetate (MPA) treatment of Ishikawa cells and endometrial stromal cells (ESCs), PakI protein was analyzed utilizing western blot analysis and immunocytochemistry. Immunohistochemistry was performed to evaluate PakI immunoreactivity semiquantitatively in women with endometriosis and in controls. To assess the role of PakI on endometrial cell viability, crystal violet assay was performed following transfection of Ishikawa cells with PakI small interfering RNA (siRNA). RESULTS: In vitro treatment with E 2 plus MPA or MPA alone led to a significant decrease of PakI protein in Ishikawa cells and ESCs (both P < 0.05 versus control). Immunohistochemistry also revealed that PakI protein is significantly decreased during the secretory phase in both epithelial and stromal cells in the control subjects (P < 0.001 and P < 0.01, respectively). The immunoreactivity of PakI in glandular cells was significantly increased in the eutopic endometrium of women with endometriosis compared with the controls during the secretory phase (P < 0.01). Crystal violet assay has shown that transfection of Ishikawa cells with PakI siRNA led to a significant decrease of cellular viability (P < 0.05). CONCLUSIONS: These findings suggest that PakI is down-regulated by progesterone during the secretory phase in normal endometrium and increased PakI activity during the secretory phase might lead to establishment of endometriosis.