Lysine-specific Demethylase 2B (KDM2B)-let-7-Enhancer of Zester Homolog 2 (EZH2) Pathway Regulates Cell Cycle Progression and Senescence in Primary Cells

Alexandros Tzatsos,Polina Paskaleva,Stephania Lymperi,Gianmarco Contino,Svetlana Stoykova,Zhao Chen,Kwok-Kin Wong,Nabeel Bardeesy

doi:10.1074/jbc.m111.257667

Abstract

Sustained expression of the histone demethylase, KDM2B (Ndy1/FBXL10/JHDM1B), bypasses cellular senescence in primary mouse embryonic fibroblasts (MEFs). Here, we show that KDM2B is a conserved regulator of lifespan in multiple primary cell types and defines a program in which this chromatin-modifying enzyme counteracts the senescence-associated down-regulation of the EZH2 histone methyltransferase. Senescence in MEFs epigenetically silences KDM2B and induces the tumor suppressor miRNAs let-7b and miR-101, which target EZH2. Forced expression of KDM2B promotes immortalization by silencing these miRNAs through locus-specific histone H3 K36me2 demethylation, leading to EZH2 up-regulation. Overexpression of let-7b down-regulates EZH2, induces premature senescence, and counteracts immortalization of MEFs driven by KDM2B. The KDM2B-let-7-EZH2 pathway also contributes to the proliferation of immortal Ink4a/Arf null fibroblasts suggesting that, beyond its anti-senescence role in primary cells, this histone-modifying enzyme functions more broadly in the regulation of cellular proliferation.

Highlights

KDM2B Is Conserved Regulator of EZH2 Activity and of Onset of Senescence in Primary Cells—We have shown previously that KDM2B is the only Jumonji domain containing histone demethylase that is down-regulated in mouse embryonic fibroblasts (MEFs) undergoing senescence [2]
We found that cell passage induces a repressive epigenetic signature at the KDM2B promoter characterized by increased tri-methylation of H3K27, a repressive histone mark, and reduced trimethylation of H3K4, a permissive histone mark (Fig. 1D)
We show that epigenetic silencing of KDM2B contributes to the senescence of multiple types of primary embryonic and adult cells, and we define a let-7b-EZH2 pathway as an important component of KDM2B-mediated proliferative control and bypass of the senescence checkpoint

Summary

Introduction

Senescence [1, 2, 4]. Reciprocally, KDM2B overexpression immortalizes MEFs in a Jumonji-dependent manner [1, 2]. A number of miRNAs that regulate EZH2 abundance by targeting its 3Ј-UTR have been identified and are potential candidates for control of EZH2 expression during senescence; these include the let-7/98 family, miR-101, and miR-26 tumor suppressor miRNAs (supplemental Fig. S1F) [15, 18, 19].

Results

Conclusion