Background/Aims: Choriocarcinoma is a trophoblastic tumour, most highly prevalent in Asian populations. The (pro)renin receptor ((P)RR) stimulates signalling pathways that enhance cancer progression (invasion, proliferation, and angiogenesis). We aimed to determine if (P)RR is involved in choriocarcinoma pathogenesis. To do this we used the BeWo choriocarcinoma cell line, which comprises both cytotrophoblast (mononuclear) and syncytiotrophoblast (multinuclear) cells. BeWo cells can be induced to syncytialise with forskolin. We aimed to determine which subset of these cells are more invasive and whether (P)RR affects the ability of BeWo cells to syncytialise and/or invade. Additionally, we aimed to determine if soluble (P)RR (s(P)RR) could be a biomarker for choriocarcinoma invasiveness and how it is cleaved from full-length (P)RR in BeWo cells.
Methods: BeWo choriocarcinoma cells were treated with (P)RR siRNA, Furin siRNA, negative control siRNA, DEC-RVKR-CMK (a furin enzyme inhibitor), or PF 429242 (a site 1 protease inhibitor), before treatment with forskolin (to induce syncytialisation) or vehicle (DMSO). Choriocarcinoma cell invasion was measured using the xCELLigence Real-time Cell Analysis system. Syncytialisation was measured by assessing E-cadherin (immunoblot/immunocytochemistry) and hCG secretion (ELISA). Soluble (P)RR levels were measured by ELISA.
Results: Forskolin successfully induced syncytialisation and significantly increased choriocarcinoma cell invasion (P<0.0001). (P)RR siRNA inhibited both syncytialisation (as evidenced by decreased hCG secretion (P=0.005) and the percent of nuclei in syncytia (P=0.05)) and invasion (P=0.046). Additionally, forskolin increased s(P)RR levels (P=0.02). (P)RR siRNA, Furin siRNA and DEC-RVKR-CMK significantly reduced s(P)RR secretion (all P<0.0001), PF 429242 had no effect.
Conclusions: The syncytiotrophoblast in choriocarcinoma is invasive and (P)RR knockdown decreases forskolin-induced syncytialisation and invasion. Hence, (P)RR could play a role in the pathogenesis of choriocarcinoma. Since s(P)RR levels reflect syncytialisation, invasion and (P)RR levels, we hypothesise that s(P)RR could be a marker of choriocarcinoma cell invasion. Furin, not site 1 protease, cleaves s(P)RR in choriocarcinoma cells.