p21-activated kinase (PAK) in gestational trophoblastic neoplasia

Abstract

Background and Objectives: The p21-activated kinase (Pak) family of serine/threonine kinases were effectors of the Rho GTPases and found to promote malignant progression by affecting cell proliferation, motility and apoptosis. In the present study, we aim at determining the expression of Paks1, 2 and 4 in trophoblastic tissues and correlate it with clinicopathological parameters, proliferative and apoptotic indices. Materials and Methods: Immunohistochemistry for Pak1, phosphor (p)-Pak2 Ser20 and Pak4 was performed on archived tissues including 10 first-trimester placentas, 8 term placentas and 7 spontaneous miscarriages, 43 hydatidiform moles, 5 choriocarcinomas and 4 placental site trophoblastic tumors. Western blotting for Paks 1, 2 and 4 and p-Pak2 Ser20 and real-time polymerase chain reaction (PCR) for Paks1, 2 and 4 on cases with available frozen blocks along with two choriocarcinoma cell lines (JAR and JEG-3) and one normal trophoblast cell line (TEV-1) were also done. Results: Pak1, p-Pak2 Ser20 and Pak4 were predominantly expressed in cytotrophoblast and villous intermediate trophoblast. Their expressions were significantly higher in carcinoma than in normal placentas and hydatidiform moles but no correlation with development of gestational trophoblastic neoplasia was found. An elevated expression of Pak1, p-Pak2 Ser20 and Pak4 was also observed in placental site trophoblastic tumour when compared with extravillous implantation site intermediate trophoblast. Such in vivo differential expression and the in vitro increased expression in choriocarcinoma were confirmed by Western blotting and real-time PCR. While Pak1, p-Pak2 Ser20 and Pak4 expression correlated with proliferative indices MCM7 (P = 0.015, P = 0.01 and P<0.001) and Ki67 (P=0.023, P=0.011, P<0.001), only p-Pak2 Ser20 and Pak4, but not Pak1, expression correlated with apoptotic index M30 CytoDeath antibody (P = 0.001 and P<0.001). Conclusions: Increased expression of Pak1, p-Pak2 Ser20 and Pak4 was observed in choriocarcinoma and PSTT. Such observation sugguested that Paks may play a role in their pathogenesis possibly by regulating the proliferation and apoptosis of trophoblastic tissues.