Matrine Inhibits the Activity of Translation Factor eIF4E through Dephosphorylation of 4E-BP1 in Gastric MKN45 Cells

Matrine, from Sophora flavescens , could remarkably inhibit tumor growth and induce apoptosis in various cancer cells in vitro . eIF4E and its inhibitor 4E-BP1 play key roles in regulating mRNA translation and cell proliferation. However, it remained elusive whether matrine inhibited cancer cells growth through attenuating the activity of 4E-BP1. In this study, we analyzed the effects of matrine on 4E-BP1 and eIF4E in gastric cancer MKN45 cells. Immunoblots showed that matrine inhibited the activity of eIF4E through dephosphorylation of 4E-BP1 in a dose- and time-dependent manner. We found that matrine inactivated Erk1/2, an upstream regulator of 4E-BP1 and eIF4E, and remarkably reduced the phosphorylation level of 4E-BP1 and eIF4E, whereas 4E-BP1 was little influenced by JNK, p38 or Akt/mTOR. Inactivation of PP2A obviously decreased the phosphorylation of 4E-BP1 in matrine-treated cells. These findings suggested that matrine inhibits the activity of eIF4E by dephosphorylating 4E-BP1, which partly counts for the growth inhibition in gastric MKN45 cells. Abbreviations 4E-BP:4E-binding protein DMSO:dimethyl sulfoxide EDTA:ethylenediaminetetraacetic acid eIF:eukaryotic initiation factor Erk1/2:extracellular-signal regulated kinase 1/2 GAPDH:glyceraldehyde-3-phosphate dehydrogenase JNK:Jun-N-terminal kinase MAPK:mitogen-activated protein kinase mTOR:mammalian target of rapamycin MTT:3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide PBS:phosphate-buffered saline TBS/T:Tris buffer saline/Tween-20 PMSF:phenylmethylsulfonyl fluoride PP2A:protein phosphatase 2A TRAIL:tumor necrosis factor α-related apoptosis inducing ligand