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 with chemoprotective effects against carcinogens when tested in animals. Recently, 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 mechanisms associated with carnosic acid-induced enhancement of cell differentiation (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 differentiation markers (CD11b, CD14, and monocytic serine esterase), cell cycle parameters, and cell proliferation rates after treatment of cells with different agents with or without carnosic acid. We also assessed the abundance of the vitamin D receptor (VDR), retinoid X receptor (RXR)-alpha, retinoic. acid receptor (RAR)-alpha, and cell cycle-associated proteins by immunoblot analysis (p27, early growth response gene [EGR]-1, and p35Nck5a), the expression of corresponding genes by reverse transcription-polymerase chain reaction (RT-PCR), and the activity of VDR by electrophoretic mobility shift analysis. The two-sided nonparametric Kruskal-Wallis one-way analysis-of variance test with Dunn's adjustment was used for statistical analyses. Results: Monocytic differentiation induced by low (1 nM) concentrations of 1 alpha ,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 alpha ,25(OH)(2)D-3 and ATRA (P =.009 and P =.048, respectively) and also for several cell cycle-associated proteins. Carnosic acid in combination with 1 alpha ,25(OH)(2)D-3 and ATRA resulted in decreased cell proliferation and blocked the cell cycle transition from G(1) to S phase (P < .05). Carnosic acid 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 differentiation of HL60-G cells.