%0 Journal Article
%T Self-Renewal Signalling in Presenescent Tetraploid IMR90 Cells
%A Anda Huna
%A Kristine Salmina
%A Elina Jascenko
%A Gunars Duburs
%A Inna Inashkina
%A Jekaterina Erenpreisa
%J Journal of Aging Research
%D 2011
%I Hindawi Publishing Corporation
%R 10.4061/2011/103253
%X Endopolyploidy and genomic instability are shared features of both stress-induced cellular senescence and malignant growth. Here, we examined these facets in the widely used normal human fibroblast model of senescence, IMR90. At the presenescence stage, a small (2¨C7%) proportion of cells overcome the 4n-G1 checkpoint, simultaneously inducing self-renewal (NANOG-positivity), the DNA damage response (DDR; ¦Ã-H2AX-positive foci), and senescence (p16inka4a- and p21CIP1-positivity) signalling, some cells reach octoploid DNA content and divide. All of these markers initially appear and partially colocalise in the perinucleolar compartment. Further, with development of senescence and accumulation of p16inka4a and p21CIP1, NANOG is downregulated in most cells. The cells increasingly arrest in the 4n-G1 fraction, completely halt divisions and ultimately degenerate. A positive link between DDR, self-renewal, and senescence signalling is initiated in the cells overcoming the tetraploidy barrier, indicating that cellular and molecular context of induced tetraploidy during this period of presenescence is favourable for carcinogenesis. 1. Introduction Cellular senescence is a condition in which the cells remain alive but are unable to proliferate. Premature senescence can be triggered by certain stresses independently of the number of cell divisions or telomere length [1], possibly as a result of protracted DNA damage signalling [2]. Oncogene-induced senescence is thought to behave similarly, driven at the very early stages of tumour development where it serves as a barrier to cancer progression [3]. Subsequent progression to full-blown malignancy is favoured when tumour stem cells acquire further mutations that impair the senescence pathway, for example, mutations in TP53 or CDKN2a [4, 5]. During in vitro culture, human fibroblast cells undergo a presenescence phenomenon whereby they display evidence of chromosome instability (CIN) within an apparently highly heterogenous population with signs of chromosomal damage, and the appearance of polyploid interphase cells and their divisions [4, 6¨C12]. Whereas the frequency of diploid mitotic cells at presenescence is declining, the number of polyploid mitoses increases to a peak before a sharp fall as the cells change to the characteristic flat morphology indicative of replicative senescence [13, 14]. These data stimulated the hypothesis that telomeric loss at senescence may represent a ¡°genetic time bomb¡± causally involved in both cell senescence and malignant transformation [13, 15]. In is clear that CIN associated with
%U http://www.hindawi.com/journals/jar/2011/103253/