Ki-67 Contributes to Normal Cell Cycle Progression and Inactive X Heterochromatin in p21 Checkpoint-Proficient Human Cells

Abstract

The Ki-67 protein is widely used as a tumor proliferation marker. However, whether Ki-67 affects cell cycle progression has been controversial. Here we demonstrate that depletion of Ki-67 in human hTERT-RPE1, WI-38, IMR90, and hTERT-BJ cell lines and primary fibroblast cells slowed entry into S phase and coordinately downregulated genes related to DNA replication. Some gene expression changes were partially relieved in Ki-67-depleted hTERT-RPE1 cells by codepletion of the Rb checkpoint protein, but more thorough suppression of the transcriptional and cell cycle defects was observed upon depletion of the cell cycle inhibitor p21. Notably, induction of p21 upon depletion of Ki-67 was a consistent hallmark of cell types in which transcription and cell cycle distribution were sensitive to Ki-67; these responses were absent in cells that did not induce p21. Furthermore, upon Ki-67 depletion, a subset of inactive X (Xi) chromosomes in female hTERT-RPE1 cells displayed several features of compromised heterochromatin maintenance, including decreased H3K27me3 and H4K20me1 labeling. These chromatin alterations were limited to Xi chromosomes localized away from the nuclear lamina and were not observed in checkpoint-deficient 293T cells. Altogether, our results indicate that Ki-67 integrates normal S-phase progression and Xi heterochromatin maintenance in p21 checkpoint-proficient human cells.KEYWORDS cell cycle, heterochromatin K i-67 was first identified via an antibody raised against Hodgkin's lymphoma cell nuclei (1). Because Ki-67 is generally expressed strongly in proliferating cells and poorly in quiescent cells (2), anti-Ki-67 antibodies are frequently used to detect proliferative cells in clinical studies (3, 4). In interphase cells, Ki-67 primarily localizes to the nucleolus (5-7), whereas during mitosis, it coats the chromosomes (8-10). In the past few years, several studies have greatly increased our understanding of Ki-67 function. This is particularly true for its mitotic roles. Specifically, Ki-67 is required for formation of the mitotic perichromosomal layer (11, 12), a proteinaceous sheath that coats mitotic chromosomes (13,14). In this layer, Ki-67's large size and highly positively charged amino acid composition keep individual mitotic chromosomes dispersed rather than aggregated upon nuclear envelope disassembly, thereby ensuring normal kinetics of anaphase progression (15). At anaphase onset, Ki-67 binds protein phosphatase 1␥ (PP1␥) to form a holoenzyme (16) important for targeting substrates that must be dephosphorylated during mitotic exit (10). In contrast to its structural role on the

Expression Profile of Cell Cycle-Related Genes in Human Fibroblasts Exposed Simultaneously to Radiation and Simulated Microgravity

“…Nine genes ( ABL1 [39], CCNB1 [40], CCND1 [41], CDKN1A [40,41], KPNA2 [42], MCM4 [43], MDM2 [44], MKI67 [45], and STMN1 [46]) were calculated by considering the effect of simulated μ G alone with several processes of Step 5 in judgement criteria (Figure 2). Table 2 provides summary information on the nine selected genes.…”

Vitamin C and B3 as new biomaterials to alter intestinal stem cells

“…The CD44 protein is a cell-surface glycoprotein that is related to cell-cell interaction and lymphocyte activity (Goodison, Urquidi, & Tarin, 1999). Ki67 contributes to controlling cell proliferation and the cell cycle (Sun et al, 2017). NF-kB, which is nuclear factor kappa light enhancer of activated B cells, is a complex of proteins that controls DNA transcription, cytokine production, and cell survival fate (Lawrence, 2009).…”

Ki67 is a Graded Rather than a Binary Marker of Proliferation versus Quiescence

“…Ki67 depletion results in reduced proliferation in hTERT-RPE1, hTERT-BJ, Swiss-3T3, WI-38, IMR90, MCF7, IM-9, RT-4, and 786–0 cells, but not in others such as MCF10A, DLD-1, HeLa, U2OS, and 293T cells (Cidado et al, 2016; Schlüter et al, 1993; Sobecki et al, 2016; Starborg et al, 1996; Sun et al, 2017; Zheng et al, 2006). Additionally, Ki67 knockout mice develop normally and are fertile (Sobecki et al, 2016).…”