Upregulation of p27 cyclin-dependent kinase inhibitor and a C-terminus truncated form of p27 contributes to G1 phase arrest

Takayuki Satoh,Daisuke Kaida

doi:10.1038/srep27829

Abstract

Potent anti-cancer compounds FR901464 and its methyl-ketal derivative spliceostatin A (SSA) inhibit cell cycle progression at G1 and G2/M phases. These compounds bind to the spliceosome and inhibit the splicing reaction. However, the molecular mechanism underlying G1 arrest after SSA treatment remains unknown. In this study, we found that ~90% of SSA-treated cells arrested at G1 phase after cell cycle synchronization. SSA treatment caused upregulation of the p27 cyclin-dependent kinase inhibitor both at mRNA and protein levels. In addition to p27, we observed expression of p27*, a C-terminal truncated form of p27 that is translated from CDKN1B (p27) pre-mRNA accumulated after splicing inhibition. Overexpression of p27 or p27* inhibited the exit from G1 phase after a double thymidine block. Conversely, knocking down of p27 by siRNA partially suppressed the G1 phase arrest caused by SSA treatment. There results suggest that G1 arrest in SSA-treated cells is caused, at least in part, by upregulation of p27 and p27*.

Highlights

Potent anti-cancer compounds FR901464 and its methyl-ketal derivative spliceostatin A (SSA) inhibit cell cycle progression at G1 and G2/M phases
It is difficult to distinguish whether cell cycle progression is arrested at G1 and G2/M phases or if cell cycle progression is only delayed at these phases using non-synchronized cells
To investigate if SSA causes G1 arrest, we examined the effect of SSA treatment on cell cycle progression of synchronized cells

Summary

Introduction

Potent anti-cancer compounds FR901464 and its methyl-ketal derivative spliceostatin A (SSA) inhibit cell cycle progression at G1 and G2/M phases. These compounds bind to the spliceosome and inhibit the splicing reaction. SSA treatment caused upregulation of the p27 cyclin-dependent kinase inhibitor both at mRNA and protein levels. SSA and FR901464 cause cell cycle arrest at G1 and G2/M phases, and this cell cycle arrest is thought to be the mechanism underlying the anti-cancer activity[16,18]. Splicing inhibition causes accumulation of intron 1, and translation from the start codon in exon 1 to the first in-frame stop codon in intron 1 leads to production of p27*, which inhibits Cdk[2] activity[16]. We investigated the molecular mechanism underlying G1 arrest after SSA treatment and the potential involvement of p27 and p27*in SSA-mediated cell cycle arrest

Methods

Results

Conclusion