A novel target of mizoribine inhibiting mesangial cell proliferation: S phase kinase-associated protein 2.

BACKGROUND/AIMS: Mizoribine (MZR) can inhibit mesangial cell (MC) proliferation, but the mechanism remains unknown. In this study, we investigated the inhibitory effect of MZR on MC proliferation via a cell cycle regulatory protein-dependent mechanism.

METHODS

We investigated the effect of MZR on MC proliferation and expression of cell cycle regulatory proteins such as cyclin D1, cyclin-dependent kinase 2 and p27(kip1) in primary cultured rat MCs. We further focused on analyzing the effects of MZR on S phase kinase-associated protein 2 (Skp2), which played a crucial role in p27(kip1) degradation.

RESULTS

MZR effectively inhibited MC proliferation in primary cultured rat MCs, reduced the expression of cyclin D1 and cyclin-dependent kinase 2, while it dramatically increased the protein level of p27(kip1), maintained the nucleus location of p27(kip1) and induced G1/S arrest. In contrast to the protein level, MZR produced no changes in p27(kip1) mRNA abundance. MZR impaired p27(kip1) degradation through downregulating the expression of Skp2 and this effect was not dependent on its inhibition on DNA synthesis. Skp2 overexpression abolished MZR-induced p27(kip1) accumulation.

CONCLUSION

These results suggested that MZR-induced p27(kip1) accumulation was at least partly mediated by Skp2, and that Skp2 might be a novel target of MZR inhibiting MC proliferation.