Endothelin-1 (ET-1) induces resistance to bortezomib in human multiple myeloma cells via a pathway involving the ETB receptor and upregulation of proteasomal activity

Abstract

Purpose

Bortezomib (BTZ) is used for the treatment of multiple myeloma (MM). However, a significant proportion of patients may be refractory to the drug. This study aimed to investigate whether the endothelin (ET-1) axis may act as an escape mechanism to treatment with bortezomib in MM cells.

Methods

NCI-H929 and RPMI-8226 (human MM cell lines) were cultured with or without ET-1, BTZ, and inhibitors of the endothelin receptors. ET-1 levels were determined by ELISA, while the protein levels of its receptors and of the PI3K and MAPK pathways' components by western blot. Effects of ET-1 on cell proliferation were studied by MTT and on the ubiquitin proteasome pathway by assessing the chymotryptic activity of the 20S proteasome in cell lysates.

Results

Endothelin receptors A and B (ET_AR and ET_BR, respectively) were found to be expressed in both cell lines, with the RPMI-8226 cells that are considered resistant to BTZ, expressing higher levels of ET_BR and in addition secreting ET-1. Treatment of the NCI-H929 cells with ET-1 increased proliferation, while co-incubation of these cells with ET-1 and BTZ decreased BTZ efficacy with concomitant upregulation of 20S proteasomal activity. Si-RNA silencing or chemical blockade of ET_BR abrogated the protective effects of ET-1. Finally, data suggest that the predominant signaling pathway involved in ET-1/ET_BR-induced BTZ resistance in MM cells may be the MAPK pathway.

Conclusion

Our data suggest a possible role of the ET-1/ET_BR axis in regulating the sensitivity of MM cells to BTZ. Thus, combining bortezomib with strategies to target the ET-1 axis could prove to be a novel promising therapeutic approach in MM.

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