Cdc25C/cdc2/cyclin B, raf/MEK/ERK and PERK/eIF2α/CHOP pathways are involved in forskolin-induced growth inhibition of MM.1S cells by G2/M arrest and mitochondrion-dependent apoptosis

Multiple myeloma (MM) remains an incurable hematological malignancy characterized by proliferation and accumulation of plasma cells in the bone marrow. Innovative and effective therapeutic approaches that are able to improve the outcome and the survival of MM sufferers, especially the identification of novel natural compounds and investigation of their anti-MM mechanisms, are needed. Here, we investigated the effects and the potential mechanisms against MM of forskolin, a diterpene derived from the medicinal plant Coleus forskohlii, in MM cell line MM.1S. CCK-8 assay showed that forskolin significantly inhibited MM.1S cells viability in a time- and dose-dependent manner. Furthermore, we demonstrated that forskolin induced G2/M phase arrest with a remarkable increase of p-cdc25c, p-cdc2, and a decrease of cyclin B1, indicating the suppression of cdc25C/cdc2/cyclin B pathway. Moreover, we found that forskolin induced mitochondrion-dependent apoptosis which was accompanied by the increase of pro-apoptotic proteins Bax, Bad, Bim and Bid, the decrease of anti-apoptotic proteins Bcl-2 and Bcl-xl, the changes of the mitochondrial membrane potential (MMP) and increase of cleaved caspase-9, cleaved caspase-3 and cleaved PARP. Of note, we demonstrated that forskolin induced a decrease of p-C-Raf, p-MEK, p-ERK1/2 and p-p90Rsk, and an increase of p-PERK, p-eIF2 alpha and CHOP, which indicated that the inhibition of Raf/MEK/ERK pathway and activation of PERK/eIF2 alpha/CHOP pathway were involved, at least partially, in forskolin-induced MM.1S cells apoptosis. These findings confirm the anti-MM action of forskolin and extend the understanding of its anti-MM mechanism in MM.1S cells, as well as reinforcing the evidence for forskolin as a natural chemotherapeutic compound against MM.