Abstract. Activin A is a pleiotropic cytokine belonging to the transforming growth factor β superfamily. Abnormal expression of activin A is associated with tumorigenesis. Multiple myeloma is characterized by the development of osteolytic disease, which ultimately leads to cachexia. However, the involvement of activin A in myeloma cell viability and apoptosis remains to be fully elucidated. For this purpose, mouse myeloma NS-1 cells were treated with activin A, and subsequently subjected to 5-bromo-2'-deoxyuridine analysis, Hoechst 33342 staining, flow cytometry and western blot analysis. The results revealed that activin A significantly suppressed NS-1 cell viability, and induced NS-1 cell apoptosis. In addition, activin A-induced promotion of NS-1 cell apoptosis was accompanied by upregulated expression of BCL2 associated X, apoptosis regulator (Bax), but downregulated expression of B cell lymphoma-2 (Bcl-2), resulting in an increase of the Bax/Bcl-2 ratio. Furthermore, cytochrome c and caspase-3 protein expression also increased following treatment with activin A. These data suggest that activin A induces apoptosis in mouse myeloma NS-1 cells via the mitochondrial pathway, providing a novel insight into multiple myeloma treatment.

Activin A, a multifunctional cytokine, is a member of transforming growth factor-β (TGF-β) superfamily. It is associated with a variety of pathophysiological processes, including inflammation, fibrosis, and tumorigenesis. Chronic or prolonged endoplasmic reticulum (ER) stress can lead to cells apoptosis. However, whether ER stress-related proteins, such as CHOP, GADD34 are involved in activin A-induced myeloma cell apoptosis remains unknown. In the present study, it was revealed that activin A inhibited the proliferation of myeloma cell line NS-1 cells and induced NS-1 cell apoptosis. Activin A upregulated the expression of CHOP, GADD34, caspase-3, and caspase-12. Moreover, both Smad3 and p-Smad3 levels were increased with treatment of activin A. Further studies revealed that the overexpression of activin signaling protein Smad3 in NS-1 cells increased the levels of CHOP, caspase-3, and p-Smad3. These data indicated that the CHOP protein of the ER stress pathway may be involved in activin A-induced NS-1 cell apoptosis, and also indicated the potential therapy of activin A-induced apoptosis via CHOP signaling for multiple myeloma.