The effect of extracellular signal-regulated kinases signaling pathway inhibition on histone phosphorylation and gene expression in colorectal canoer cells

Abstract

Objective To study the effects of extracellular-signal regulated kinase mitogenactivated protein kinase (ERK-MAPK) signaling pathway inhibition on histone phosphorylation and the related gene expression in human colorectal cancer cells.Methods Two human colorectal cancer cell lines (SW1116 and HCT116) were cultured and treated with gradient(0,20,40/μmol/L) doses of ERK-MAPK signaling pathway inhibitor U0126.Cell viability was determined by cell counting kit 8 (CCK-8) assay.Cell cycle distribution was assessed by flow cytometry.The expression levels of histone H3 kinases including ribosomal S6 serine-threonine kinase (RSK-2) and mitogen-and stressactivated protein kinase 1 and 2 (MSK1 and MSK2),and the levels of histone H3 (Ser10) phosphorylation and c-Fos protein were detected using Western blotting.Results Treatment of these two human colorectal cancer cell lines with ERK-MAPK inhibitor resulted in a time and dose-dependent inhibition of cell proliferation significantly. Proliferation rate of HCT116 was reduced to 47% at 72 hours after 40/μmol/L U0126 treatment. Cell cycle analysis showed that the percentage of phase G0/G1 cells significantly increased (P<0. 01) and the percentage of phase S cells decreased (P<0.01) after treatment with ERK-MAPK inhibitor. The expression of MSK1 and RSK2 reduced obviously in both of human colorectal cancer cell lines treated with U0126, which resulted in a 28% and 40% reduction of levels of MSK1 and RSK2 as compared with control HCT116 cells respectively,while no detectable change in the expression of MSK2 was found. Consistent with this, the expression level of histone H3 (ser10) phosphorylation was markedly down-regulated by ERK-MAPK inhibitor, and the related protein c-Fos expression decreased accordantly. Conclusions Decreased ERK-MAPK signaling pathway may reduce histone H3 (Ser10) phosphorylation via suppression of the activity of histone H3 kinase including MSK1 and RSK2, but not MSK2, consequently decrease the expression of c-Fos protein, which results in the inhibition of colorectal cancer cells proliferation. Key words: Cell line,Tumor; Extracellular signal-regulated kinases; Cell cycle; Histone phosphorylation