Carnosic acid and promotion of monocytic differentiation of HL60-G cells initiated by other agents

Background. Carnosic acid is a plant-derived polyphenol food preservative w ith chemoprotective effects against carcinogens when tested in animals. Rec ently, we showed that carnosic acid potentiates the effects of l alpha ,25- dihydroxyvitamin D-3(1 alpha ,25[OH](2)D-3) and of all-trans-retinoic acid (ATRA) on differentiation of human leukemia cells. We now examine the mecha nisms associated with carnosic acid-induced enhancement of cell differentia tion (in subline HL60-G) initiated by 1 alpha ,25(OH)(2)D-3, ATRA, or 12-O- tetradecanoylphorbol-13-acetate (TPA). Methods: We evaluated monocytic diff erentiation markers (CD11b, CD14, and monocytic serine esterase), cell cycl e parameters, and cell proliferation rates after treatment of cells with di fferent agents with or without carnosic acid. We also assessed the abundanc e of the vitamin D receptor (VDR), retinoid X receptor (RXR)-alpha, retinoi c. acid receptor (RAR)-alpha, and cell cycle-associated proteins by immunob lot analysis (p27, early growth response gene [EGR]-1, and p35Nck5a), the e xpression of corresponding genes by reverse transcription-polymerase chain reaction (RT-PCR), and the activity of VDR by electrophoretic mobility shif t analysis. The two-sided nonparametric Kruskal-Wallis one-way analysis-of variance test with Dunn's adjustment was used for statistical analyses. Res ults: Monocytic differentiation induced by low (1 nM) concentrations of 1 a lpha ,25(OH)(2)D-3, ATRA, or TPA was enhanced by carnosic acid (10 muM), as shown by the increased expression of monocytic serine esterase (P < .001, P < .001, and P =.043, respectively) and of CD11b (P =.008, P =.046, and P =.041, respectively). Increased expression of CD14 was seen only for 1 alph a ,25(OH)(2)D-3 and ATRA (P =.009 and P =.048, respectively) and also for s everal cell cycle-associated proteins. Carnosic acid in combination with 1 alpha ,25(OH)(2)D-3 and ATRA resulted in decreased cell proliferation and b locked the cell cycle transition from G(1) to S phase (P < .05). Carnosic a cid alone increased the expression of VDR and RXR-alpha, but the expression was greatly enhanced in the presence of 1 alpha ,25(OH)(2)D-3 and ATRA. In combination with TPA, carnosic acid potentiated the expression of VDR and RAR-alpha. Conclusion: Carnosic acid enhances a program of gene expression consistent Nvith 1 alpha ,25(OH)(2)D-3-, ATRA-, or TPA-induced monocytic di fferentiation of HL60-G cells.