Activated \u03b12-macroglobulin binding to cell surface GRP78 induces trophoblastic cell fusion

Daniel Bastida-Ruiz,Aude Pederencino,Salvatore Vincent Pizzo,Marie Cohen,Christine Wuillemin,Begoña Martinez De Tejada,Michal Yaron

doi:10.1038/s41598-020-66554-0

Daniel Bastida-Ruiz, Aude Pederencino + Show 5 more

Open Access

https://doi.org/10.1038/s41598-020-66554-0

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Abstract

The villous cytotrophoblastic cells have the ability to fuse and differentiate, forming the syncytiotrophoblast (STB). The syncytialisation process is essential for placentation. Nevertheless, the mechanisms involved in cell fusion and differentiation are yet to be fully elucidated. It has been suggested that cell surface glucose-regulated protein 78 (GRP78) was involved in this process. In multiple cancer cells, cell membrane-located GRP78 has been reported to act as a receptor binding to the active form of α2-macroglobulin (α2M*), activating thus several cellular signalling pathways implicated in cell growth and survival. We hypothesised that GRP78 interaction with α2M* may also activate signalling pathways in trophoblastic cells, which, in turn, may promote cell fusion. Here, we observed that α2M mRNA is highly expressed in trophoblastic cells, whereas it is not expressed in the choriocarcinoma cell line BeWo. We thus took advantage of forskolin-induced syncytialisation of BeWo cells to study the effect of exogenous α2M* on syncytialisation. We first demonstrated that α2M* induced trophoblastic cell fusion. This effect is dependent on α2M*-GRP78 interaction, ERK1/2 and CREB phosphorylation, and unfolded protein response (UPR) activation. Overall, these data provide novel insights into the signalling molecules and mechanisms regulating trophoblastic cell fusion.

Highlights

The villous cytotrophoblastic cells have the ability to fuse and differentiate, forming the syncytiotrophoblast (STB)
In order to determine the best model to study the effects of α2M* in trophoblastic cell fusion, we first evaluated the mRNA expression of α2M in placental villous cytotrophoblastic cells (vCTB) and in BeWo cells, which are commonly used as a model to mimic the syncytialisation of placental villous cytotrophoblast
BeWo cells were cultured for 48 h with or without Forskolin (FSK), a cell fusion inducer. mRNA expression of α2M was detected in primary trophoblastic cells observing that the α2M expression was independent of cell fusion rate, though it increased with gestational age (Fig. 2)

Summary

Introduction

The villous cytotrophoblastic cells have the ability to fuse and differentiate, forming the syncytiotrophoblast (STB). This effect is dependent on α2M*-GRP78 interaction, ERK1/2 and CREB phosphorylation, and unfolded protein response (UPR) activation Overall, these data provide novel insights into the signalling molecules and mechanisms regulating trophoblastic cell fusion. An acceleration of the fusion process may drain the regenerative pool of vCTB, whereas insufficient cell fusion may lead to an abnormal STB layer and subsequent functional deficits[12] For this reason, understanding the mechanisms involved in syncytialisation is essential to prevent aberrant placenta formation. Decreased expression of GRP78 at the cell surface of trophoblastic cells due to an impaired relocation mechanism[19] was observed in women who developed preeclampsia (PE), a maternal syndrome characterised by abnormal placentation[20] This information suggests cell surface-located GRP78 plays a role in trophoblastic syncytialisation. It was observed that in prostate cancer, GRP78-α2M* interaction induces UPR by increasing GRP78, eukaryotic translation initiation factor 2α (eIF2α), activating transcription factor (ATF)[4] and ATF6 expression[29]

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