p57KIP2-mediated inhibition of human trophoblast apoptosis and promotion of invasion in vitro

Placental hypoxia serves a role in the early stages of normal pregnancy and is involved in the pathophysiology of preeclampsia. Previously, it was suggested that p57(kinase inhibitory protein (KIP)2) regulates the cell cycle during embryogenesis and apoptosis. Recent evidence has indicated that p57(KIP2) is increased in preeclamptic placentas and absence of p57(KIP2) induces preeclampsia-type symptoms in rats. However, effects of p57(KIP2) on apoptosis under hypoxic conditions remain to be elucidated. In the present study, HTR-8/SVneo trophoblasts were cultured under hypoxic conditions (2% O-2). Knockdown using small interfering (si)RNA and overexpression of p57(KIP2) were utilized to explore the biological function of p57(KIP2) in apoptosis and cell function in vitro. Furthermore, expression of p57(KIP2) and apoptosis were evaluated by western blotting, flow cytometry and TUNEL assays, and the response of trophoblasts to hypoxia and the role of p57(KIP2) in trophoblast migration and invasion was assessed. The role of p57(KIP2) in the JNK signaling pathway in HTR-8/SVneo trophoblasts was further studies. In vitro, protein expression of p57(KIP2) was increased in HTR-8/SVneo cells exposed to 2% O-2. Exogenous p57(KIP2) overexpression significantly decreased the expression of pro-apoptosis proteins, including p53, Bax and cleaved caspase3, under hypoxic conditions for 24 h. In addition, knockdown of p57(KIP2) increased the response to apoptosis following hypoxia for 24 h. The present study revealed that overexpres-sion of p57(KIP2) decreased the levels of phosphorylated-JNK. JNK inhibitor treatment combined with the overexpression of p57(KIP2) significantly decreased the levels of apoptosis and increased cell invasion and migration. Taken together, p57(KIP2) knockdown significantly increased apoptosis in HTR-8/SVneo cells exposed to 2% O-2, whereas overexpression of p57(KIP2) had opposite effects, mediated by the JNK/stress activated protein kinase (SAPK) signaling pathway. The results indicated that hypoxia-induced expression of p57(KIP2) promoted trophoblast migration and invasion by mediating the JNK/SAPK signaling pathway, which is crucial during placentation. These results may provide a novel molecular mechanism to understand the involvement of p57(KIP2) in the pathogenesis of preeclampsia.