ROLE OF p38 MAPK IN THE EFFECTS OF CHOLESTEROL BIOSYNTHESIS INHIBITION ON CELL CYCLE PROGRESSION IN HL-60 CELLS

Introduction. Cells require cholesterol for proliferation and correct progression of the cell cycle. In the absence of cholesterol, the cells fail to undergo cytokinesis and polynucleated cells are generated. These effects could be mediated by stress signal transduction pathways. Objective. To study the effects of cholesterol biosynthesis inhibition on the activity of p38 MAPK and to evaluate the role of this pathway on cell cycle progression. Methodology. Human leukemia cells (HL-60) were incubated in the presence of SKF 104976, an inhibitor of cholesterol biosynthesis. In some cases inhibitors of p38 MAPK and ERK1/2, namely SB 203580 and PD 98059, were added to the medium. Cell cycle progression was studied by flow citometry, both DNA content and bromodeoxyuridine incorporation into DNA, and protein expression of p38 MAPK was analyzed by western blot. Results. Inhibition of cholesterol biosynthesis led to accumulation of cells in G2/M and a transient activation of p38 MAPK. These effects were reversed by supplementing the medium with LDL. The addition of SB 203580 accelerated DNA replication, which was accompanied by an increase of polyploidy. By contrast, the addition of PD 98059 inhibited DNA synthesis. Lastly, neither the inhibition of p38 MAPK nor ERK affected the division of cells treated with the cholesterol biosynthesis inhibitor following LDL provision, or mitosis completion from methaphase of cells previously synchronized with nocodazole. Conclusions. Cholesterol deficiency induces p38 MAPK pathway activation in order to prevent polyploidy, but has no effect on mitosis completion.