MM is an incurable B cell neoplasm, which is characterized by the clonal proliferation of plasma cells in the bone marrow (BM), accounts for approximately 10% of hematological malignancies. Insulin-like growth factor-1 (IGF-1) is a vital proliferation factor in myeloma cells, recent researches demonstrated that it may be involved in MM cell metastasis. In last decade, studies have demonstrated that IGF-1 induces epithelial-mesenchymal transition (EMT), which has been tightly correlated with increased motility and invasive capacity in several cancers including gastric cancer, hepatocellular carcinoma, and melanoma. However, it remains unclear whether IGF-1 induces EMT and promote myeloma progression.
In this study, we firstly observed the morphology of the myeloma cell line Karpas707 changed from tight polygon to loose spindle, a mesenchymal phenotype after treated with IGF-1 (50 ng/ml) after 72h. We supposed IGF-1 may induced EMT in myeloma cells. Furthermore, when serum-starved MM cell lines RPMI8226 and MM1.S were stimulated with 50ng/mL of IGF-1, we found that the expression of mesenchymal features was significantly upregulated in a time-dependent manner, as determined by both flow cytometry analysis and western blotting. Next we confirmed that IGF-1 can activate the PI3K/Akt signaling pathway by inducing the phosphorylation of Akt in MM cells. To investigated whether PI3K/Akt signaling pathway involved in the IGF-1 mediated EMT, we blocked PI3K/Akt signaling pathway using Akt inhibitor MK2206 in IGF-1 treated MM.1S cells. We found MK2206 reversed these changes of EMT markers. Moreover, we found the IGF-1-induced EMT promotes myeloma progression, including migration, invasion, adhesion and clone formation in MM cells, using transwell migration and invasion assay, cell adhesion assay, colony formation assay and flow cytometry. Furthermore, to further validate IGF-1-induced EMT promote MM progression, we knocked down mesenchymal marker vimentin using siRNA in MM.1S cells (VIM k/d cells). We detected that these function IGF-1 plays in myeloma was impaired in Vim k/d cells, indicating that IGF-1-induced EMT promotes MM progression. Finally, we validated that IGF1 expression is aberrantly upregulated and correlated with the expression of the EMT markers by analyzing the mRNA data of BM samples from normal donors and patients in different stages of plasma cell neoplasm from the GEO database. Taken together, these data demonstrate that the mesenchymal phenotype induced by IGF1 contributes to MM progression via PI3K/Akt pathway.
Disclosures
No relevant conflicts of interest to declare.
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