Effect of Valproic Acid on the Expression of P27^Kip1 and Multidrug Resistance in HL60 Cells.

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. P27^Kip1 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 P27^Kip1 and P170 of HL60 cells in vitro. HL60/HT cells were induced from HL60 cells by harringtonine (HT) in gradient concentrations. The P27^Kip1 expression and P170 expression were tested in flow cytometry. We tested the expression of P27^Kip1 and P170 in normal mononuclear cells, HL60 cells and HL60/HT cells, also the effects of VPA on P27^Kip1 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 P27^Kip1 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 P27^Kip1 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 P27^Kip1 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 P27^Kip1 expression in normal mononuclear cells were higher than that in leukemia cells (HL60 cells), and the P27^Kip1 expression in common HL60 cells were higher than that in MDR HL60/HT cells. VPA could increase the expression of P27^Kip1 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.