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

Abstract

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 1α,25-dihydroxy-vitamin D3 (1α,25[OH]2D3) 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 1α,25(OH)2D3, 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)-α, retinoic acid receptor (RAR)-α, 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 1α,25(OH)2D3, ATRA, or TPA was enhanced by carnosic acid (10 μM), as shown by the increased expression of monocytic serine esterase (P