Requirement of CIC-3 in G0/G1 to S Phase Transition Induced by IGF-1 via ERK1/2-Cyclins Cascade in Multiple Myeloma Cells

Background: CIC-3 is involved in the proliferation and migration of several cancer cells. However, CIC-3 expression and its role of cell-cycle control in multiple myeloma (MM) has not yet been investigated. Methods: MM cells were treated with different concentrations of IGF (30,100, 300 ng/mL), and their proliferation was examined by CCK-8. The effects of CIC-3 on cell cycle progression was detected by flow cytometry. Western blot was used to analyze the relative levels of C1C3, CD138, P21, P27, CDK, p-Erkl/2, and t-Erkl/2 protein expression. Transfection of RPMI8226 with gpCIC-3 cDNA and siRNA alters the expression of C1C-3. Results: We compared the expression of CIC-3 in primary myeloma cells and in MM cell lines (U266 and RPMI8266) with that in normal plasma cells (PCs) from normal subjects and found that myeloma cells from patients and MM cell lines had significantly higher expression of CIC-3. Additionally, silencing of CIC-3 with the small interfering RNA (siRNA) that targets human CIC-3 decreased proliferation of RPMI8226 after IGF-1 treatment and slowed cell cycle progression from G0/G1 to S phase, which was associated with diminished phosphorylation of ERK1/2, down-expression of cyclin E, cyclin D1 and up-regulation of p27 and p21. By contrast, overexpression of CIC-3 potentiated cell proliferation induced by IGF-1, raised the percentage of S phase cells, enhanced phosphorylation of ERK1/2, downregulated p27 and p21 and upregulated cyclin E and cyclin Dl. Conclusions: CIC-3 accelerated G0/G1 to S phase transition in the cell cycle by modulating ERK1/2 kinase activity and expression of Gl/S transition related proteins, making CIC-3 an attractive therapeutic target in MM.