CCNE1 and E2F1 Partially Suppress G1 Phase Arrest Caused by Spliceostatin A Treatment.

Kei Kikuchi,Daisuke Kaida

doi:10.3390/ijms222111623

Abstract

The potent splicing inhibitor spliceostatin A (SSA) inhibits cell cycle progression at the G1 and G2/M phases. We previously reported that upregulation of the p27 cyclin-dependent kinase inhibitor encoded by CDKN1B and its C-terminal truncated form, namely p27*, which is translated from CDKN1B pre-mRNA, is one of the causes of G1 phase arrest caused by SSA treatment. However, the detailed molecular mechanism underlying G1 phase arrest caused by SSA treatment remains to be elucidated. In this study, we found that SSA treatment caused the downregulation of cell cycle regulators, including CCNE1, CCNE2, and E2F1, at both the mRNA and protein levels. We also found that transcription elongation of the genes was deficient in SSA-treated cells. The overexpression of CCNE1 and E2F1 in combination with CDKN1B knockout partially suppressed G1 phase arrest caused by SSA treatment. These results suggest that the downregulation of CCNE1 and E2F1 contribute to the G1 phase arrest induced by SSA treatment, although they do not exclude the involvement of other factors in SSA-induced G1 phase arrest.

Highlights

Sci. 2021, 22, 11623. https://doi.org/Cell cycle progression is closely controlled by cell cycle regulators
CCNE1 and E2F1 in combination with CDKN1B knockout partially suppressed G1 phase arrest caused by spliceostatin A (SSA) treatment. These results suggest that the downregulation of CCNE1 and E2F1 contribute to the G1 phase arrest induced by SSA treatment, they do not exclude the involvement of other factors in SSA-induced G1 phase arrest
These results prompted us to investigate whether upregulation of p27 and p27* expression is the reason for G1 phase arrest induced by splicing inhibition; we found that upregulation of p27 and p27* expression causes G1 phase arrest but knockdown of p27 and p27* is not sufficient for complete suppression of SSA-induced G1 phase arrest [23]

Summary

Introduction

Cell cycle progression is closely controlled by cell cycle regulators Among these regulators, cyclin family proteins and cyclin-dependent kinases (CDKs) promote cell cycle progression [1,2]. In G1/S phase transition, cyclin E1 and cyclin E2 (collectively known as cyclin E), along with Cdk, are the key players that phosphorylate a variety of substrates [3,4,5,6]. Rb is a substrate of the cyclin E–Cdk complex; it binds the E2F1 transcription factor and represses the transcriptional activity of E2F1 [7,8]. After phosphorylation by cyclin E–Cdk, Rb releases E2F1, and E2F1, in turn, activates the transcription of numerous genes that drive the initiation of the S phase. The genes encoding cyclin E are controlled by E2F1, and the cyclin E–Cdk complex and E2F1 form a positive feedback loop that promotes

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