Cellular senescence mediated by p16INK4A-coupled miRNA pathways

Marita G Overhoff,Cleo L Bishop,David H Beach,James C Garbe,James Koh,Martha R Stampfer

doi:10.1093/nar/gkt1096

Abstract

p16 is a key regulator of cellular senescence, yet the drivers of this stable state of proliferative arrest are not well understood. Here, we identify 22 senescence-associated microRNAs (SA-miRNAs) in normal human mammary epithelial cells. We show that SA-miRNAs-26b, 181a, 210 and 424 function in concert to directly repress expression of Polycomb group (PcG) proteins CBX7, embryonic ectoderm development (EED), enhancer of zeste homologue 2 (EZH2) and suppressor of zeste 12 homologue (Suz12), thereby activating p16. We demonstrate the existence of a tight positive feedback loop in which SA-miRNAs activate and re-enforce the expression of other SA-miRNA members. In contrast, PcG members restrain senescence by epigenetically repressing the expression of these SA-miRNAs. Importantly, loss of p16 leads to repression of SA-miRNA expression, intimately coupling this effector of senescence to the SA-miRNA/PcG self-regulatory loop. Taken together, our findings illuminate an important regulatory axis that underpins the transition from proliferation to cellular senescence.

Highlights

With the exception of pluripotent embryonic stem cells, normal human cells in vitro [1] and in vivo [2,3] invariably undergo progressive cellular senescence, associated with the eventual cessation of cell division
To identify miRNAs that participate in cellular senescence (SA-miRNAs), we performed an unbiased functional screen for miRNAs that modulate p16 in normal human mammary epithelial cells (HMECs) and cross-referenced these data with microarray expression profiling of endogenous miRNAs that alter during spontaneous cellular senescence (Figure 1A)
We demonstrated that SA-miRNAs-26b, 181a, 210 and 424 drive cellular senescence by directly repressing a panel of Polycomb group (PcG) members

Summary

Introduction

With the exception of pluripotent embryonic stem cells, normal human cells in vitro [1] and in vivo [2,3] invariably undergo progressive cellular senescence, associated with the eventual cessation of cell division This state of proliferative arrest is induced by both endogenous and external influences that converge on either or both of the p16INK4a/retinoblastoma (p16/pRb) or p14ARF (p14)/p53 pathways. The relative involvement of these two tumour suppressor networks is known to be dependent on the cellular context [4] Both p16 and p14 are encoded by the highly complex INK/alternate reading frame (ARF) locus (9p21.3), which includes p15INK4b and the long non-coding RNA, ANRIL. This locus is associated with many ageingassociated diseases, such as cancer, type 2 diabetes [5,6,7] and cardiovascular disease [8,9]

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Conclusion