ΔNp73 expression is a potentially useful prognostic marker to predict development of persistent gestational trophoblastic neoplasia requiring chemotherapy in patients suffering from complete hydatidiform moles

Abstract

Background ΔNp73 is an anti-apoptotic, NH2-terminal truncated isoform encoded by p73 gene. ΔNp73 overexpression has been found in some cancers but its expression in gestational trophoblastic diseases (GTD) has never been reported.

Aims of study (1) to investigate ΔNp73 expression in normal placentas and GTD (2) to compare ΔNp73 expression in choriocarcinoma cell lines treated by demethylating agent with untreated controls (3) to correlate ΔNp73 expression with development of persistent gestational trophoblastic neoplasia (GTN) and occurrence of metastases.

Method Immunohistochemical study was performed for ΔNp73 expression on 73 paraffin sections including first trimester placenta (11), term placenta (6), partial moles (12), complete moles (33), choriocarcinoma (5) and hydropic abortion (6). Western blotting analysis was performed on first trimester placenta (3), term placenta (3), hydatidiform moles (7), 1 normal extravillous trophoblast cell line and 2 choriocarcinoma cell lines (JEG-3 and JAR). Two choriocarcinoma cell lines (JEG-3 and JAR) were treated with demethylating agent 5-aza-2’deoxycytidine. Total RNA was extracted from these treated cell lines, as well as from untreated controls. Reverse transcription followed by real-time polymerase chain reaction was then performed to assess ΔNp73 expression.

Results ΔNp73 was expressed in villous cytotrophoblasts, intervillous trophoblast islands, syncitiotrophoblasts, deciduas and extravillous trophoblasts. ΔNp73 expression decreased with advancing gestation, with lower expression in term placentas compared with first trimester placentas (p<0.001). Significant difference was found in ΔNp73 expression with normal placentas showing the strongest expression, followed by hydatidiform moles and choriocarcinoma (p<0.001). Western blotting analysis showed strong expression in normal placentas but markedly reduced expression in choriocarcinoma cell lines. ΔNp73 expression was significantly higher in 5-aza-2’deoxycytidine-treated choriocarcinoma cell lines than in untreated controls. Complete moles which subsequently developed persistent GTN requiring chemotherapy showed significantly higher ΔNp73 expression than those which regressed spontaneously (p=0.034). There was no significant difference in ΔNp73 expression between cases of persistent GTN with metastases and cases without.

Conclusion ΔNp73 may play a role in the development of hydatidiform moles and choriocarcinoma. It is a potentially useful prognostic marker to predict development of persistent GTN requiring chemotherapy in patients with complete moles. The unexpected down-regulation of ΔNp73, which is supposed to be anti-apoptotic, in choriocarcinoma may be contributed by aberrant methylation of the p73 gene promoter region.