Objective: To investigate the effects of PPARgamma ligand (rosiglitazone, RGZ) as well as combined with all trans-retinoic acid (ATRA) on human myeloma cells and try to explore the possible mechanism.
Methods: Human myeloma cell lines U266 and RPMI-8226 cells were treated with RGZ in the presence or absence of ATRA. Cell proliferation was evaluated by [(3)H] thymidine incorporation, cell cycle distribution and CD49e expression were analyzed by flow cytometry, morphology changes were evaluated by Wright-Giemsa staining, and p27(Kip1) and p21(Waf1) expression was detected by Western blotting.
Results: The exposure to RGZ induced proliferation inhibition in both cell lines in a dose-dependent manner. After cultured with 5 micromol/L RGZ, the proportion of U266 and RPMI-8226 cells in phase G(0)/G(1) was (45.2 +/- 6.7)% and (40.3 +/- 7.3)%, respectively (P < 0.05). The proportion of the cells in phase G(2)/M and S was (52.2 +/- 7.4)% and (57.4 +/- 9.5)%, respectively (P < 0.05). These changes were more evident when the RGZ concentration was increased to 10 micromol/L. A combination of RGZ with ATRA enhanced the growth inhibition and cell cycle arrest effects of RGZ. The RGZ-treated myeloma cells displayed morphological characteristics of cell differentiation, and more evident signs of differentiation were observed when RGZ was combined with ATRA. These changes were confirmed by the detection of CD49e expression. The expression of p27(Kip1) and p21(Waf1) in myeloma cells was up-regulated by RGZ and this change was more apparent when RGZ was used in combination with ATRA.
Conclusion: RGZ can induce cell cycle arrest and cell differentiation in myeloma cells which maybe caused by up-regulation of p27(Kip1) and p21(Waf1) expression. ATRA can enhance these effects of RGZ on multiple myeloma cells and combined use of these two drugs may show a synergistic effect on myeloma cells.