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Reduced syncytin-1 expression in choriocarcinoma BeWo cells activates the calpain1-AIF-mediated apoptosis, implication for preeclampsia.

ABSTRACT: Placentas associated with preeclampsia are characterized by extensive apoptosis in trophoblast lineages. Syncytin-1 (HERVWE1) mediates the fusion of cytotrophoblasts to form syncytiotrophoblasts, which assume the placental barrier, fetal-maternal exchange and endocrine functions. While decreased syncytin-1 expression has been observed in preeclamptic placentas, it is not clear if this alteration is involved in trophoblast apoptosis. In the current study, we found that siRNA-mediated knockdown of syncytin-1 led to apoptosis in choriocarcinoma BeWo, a cell line of trophoblastic origin. Characterization of the apoptotic pathways indicated that this effect does not rely on the activation of caspases. Rather, decreased syncytin-1 levels activated the apoptosis inducing factor (AIF) apoptotic pathway by inducing the expression, cleavage, and nuclear translocation of AIF. Moreover, calpain1, the cysteine protease capable of cleaving AIF, was upregulated by syncytin-1 knockdown. Furthermore, treatment with calpain1 inhibitor MDL28170 effectively reversed AIF cleavage, AIF nuclear translocation, and cell apoptosis triggered by syncytin-1 downregulation, verifying the specific action of calpain1-AIF pathway in trophoblast apoptosis. We confirmed that preeclamptic placentas express lower levels of syncytin-1 than normal placentas, and observed an inverse correlation between syncytin-1 and AIF/calpain1 mRNA levels, a result consistent with the in vitro findings. Immunohistochemistry analyses indicated decreased syncytin-1 and increased AIF and calpain1 protein levels in apoptotic cells of preeclamptic placentas. These findings have for the first time revealed that decreased levels of syncytin-1 can trigger the AIF-mediated apoptosis pathway in BeWo cells. This novel mechanism may contribute to the structural and functional deficiencies of syncytium frequently observed in preeclamptic placentas.

SUBMITTER: Huang Q

PROVIDER: S-EPMC4644425 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature

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Reduced syncytin-1 expression in choriocarcinoma BeWo cells activates the calpain1-AIF-mediated apoptosis, implication for preeclampsia.

Huang Qiang Q Chen Haibin H Wang Fengchao F Brost Brian C BC Li Jinping J Gao Yu Y Li Zongfang Z Gao Ya Y Jiang Shi-Wen SW

Cellular and molecular life sciences : CMLS 20140112 16

Placentas associated with preeclampsia are characterized by extensive apoptosis in trophoblast lineages. Syncytin-1 (HERVWE1) mediates the fusion of cytotrophoblasts to form syncytiotrophoblasts, which assume the placental barrier, fetal-maternal exchange and endocrine functions. While decreased syncytin-1 expression has been observed in preeclamptic placentas, it is not clear if this alteration is involved in trophoblast apoptosis. In the current study, we found that siRNA-mediated knockdown of ...[more]

PMID: 24413738

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Project description:We have examined binding of [3H]nitrobenzylthioinosine (NBMPR) and influx of [3H]thymidine in adherent cultures of human choriocarcinoma (BeWo) cells and, for comparison, cervical-carcinoma (HeLa) cells. Specific association of NBMPR with BeWo cells at 22 degrees C required 1.5 h to reach an equilibrium between free and bound ligand, whereas association with HeLa cells required 20-30 min. Scatchard analysis of NBMPR binding to low-density cultures of BeWo cells revealed a total of 27 x 10(6) sites per cell, consisting of two distinct populations that differed in their affinities for NBMPR. One population bound NBMPR with 'high' affinity (Bmax.1 15.0 pmol/10(6) cells; Kd1 0.6 nM) and the other, larger, population bound NBMPR with 'low' affinity (Bmax.2 29.0 pmol/10(6) cells; Kd2 14.5 nM). By contrast, HeLa cells possessed only 4.1 x 10(5) sites per cell, and these sites all bound NBMPR with the same affinity (Bmax. 0.7 pmol/10(6) cells; Kd 0.5 nM). Interaction of NBMPR with both populations of sites in BeWo cells could be blocked by nitrobenzylthioguanosine (NBTGR), dilazep or dipyridamole. Concentration-effect relationships for dilazep inhibition of binding of 1 nM- and 25 nM-NBMPR to BeWo cells were monophasic, with virtually complete inhibition achieved at 0.1 microM and 1 microM respectively. Plasma-membrane preparations from BeWo cells also had high numbers of NBMPR-binding sites, and u.v. irradiation of site-bound [3H]NBMPR in such preparations labelled polypeptides that migrated in electrophoretograms as a broad band with a peak M(r) of 60,000. The concentration-effect relationship for NBMPR inhibition of thymidine transport by BeWo cells was biphasic, with an IC50 for inhibition of the 'NBMPR-sensitive' component of 1.6 nM and a substantial (15-20%) component of flux that was not inhibited by 10 microM-NBMPR and was thus 'NBMPR-insensitive'. Vmax. values for thymidine transport by BeWo cells were 20-30-fold larger than the corresponding values for transport by HeLa cells. Elimination of the Na+ gradient had no effect on initial rates of thymidine fluxes measured in either the presence or the absence of NBMPR. Our results demonstrate that BeWo cells have an unusually large capacity for NBMPR-sensitive nucleoside transport, apparently resulting from high levels of expression of 'erythrocyte-like' transport elements, identified by their high-affinity interaction with NBMPR. The relationship of the low-affinity binding sites to NBMPR-sensitive transporter elements is uncertain.

Dataset Information

Reduced syncytin-1 expression in choriocarcinoma BeWo cells activates the calpain1-AIF-mediated apoptosis, implication for preeclampsia.

Publications

Reduced syncytin-1 expression in choriocarcinoma BeWo cells activates the calpain1-AIF-mediated apoptosis, implication for preeclampsia.

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