Effect of Valproic Acid on the Expression of P27Kip1 and Multidrug Resistance in HL60 Cells.

Abstract

Multidrug resistance (MDR) was the main cause of treatment failure in leukemic chemotherapy. P170, the protein expressed from MDR-1 gene, play an important role in MDR. P27Kip1 was a member of cyclin dependent kinase inhibitor family. It was also a negative regulator in cell generation cycle. It also promoted cells apoptosis. Valproic acid (VPA) was a kind of histone deacetylace inhibitor which could inhibit cell cycle and induce apoptosis. In the current study, we investigated the effects of VPA on the expression of P27Kip1 and P170 of HL60 cells in vitro. HL60/HT cells were induced from HL60 cells by harringtonine (HT) in gradient concentrations. The P27Kip1 expression and P170 expression were tested in flow cytometry. We tested the expression of P27Kip1 and P170 in normal mononuclear cells, HL60 cells and HL60/HT cells, also the effects of VPA on P27Kip1 expression and P170 expression in HL60 cells and HL60/HT cells. The 50% inhibiting concentration (IC50) of vincristine for HL60/HT cells was 5.2 times higher than that for HL60 cells (0.078ug/ml vs. 0.015ug/ml). The IC50 of HT for HL-60/HT cells was 9.3 times higher than that for HL-60 cells (0.14μg/ml vs. 0.015μg/ml). The IC50 of Cytarabine for HL60/HT cells was 3.65 times higher than that for HL60 cells (0.73ug/ml vs. 0.20ug/ml). The expression of P27Kip1 in normal mononuclear cells was the highest, while that in HL60 cells was higher than HL60/HT cells (96.18±3.13% vs. 85.83±4.65% vs. 35.91±3.13%, one way ANOVA, P<0.05). The expression of P170 in normal mononuclear cells and HL60 cells had no significant difference (0.54±0.32% vs. 0.62±0.31%, P>0.05). But the P170 expression of HL60/HT cells was 6.71±1.61%, which was much higher than that of normal mononuclear cells or HL60 cells (P<0.05). In HL60 cells, the expression of P27Kip1 increased after cultured with 1mmol/L VPA (92.21±3.43% vs. 85.83±4.65%, P<0.05), but the expression of P170 didn't change significantly (0.65±0.18% vs. 0.62±0.31%, P>0.05). In HL60/HT cells, the expression of P27Kip1 increased after cultured with VPA (66.20±5.07% vs. 35.91±3.13%, P<0.05), and the expression of P170 didn't change significantly either (6.40±1.59% vs. 6.71±1.61%, P>0.05). These results indicate that the P27Kip1 expression in normal mononuclear cells were higher than that in leukemia cells (HL60 cells), and the P27Kip1 expression in common HL60 cells were higher than that in MDR HL60/HT cells. VPA could increase the expression of P27Kip1 in HL60 cells and HL60/HT cells. VPA had no effect on the expression of P170 in HL60 cells or HL60/HT cells. That means, The MDR-reverse effect of VPA may not come from the P170 descent mechanism.