The Cyclin-Dependent Kinase Inhibitor p57Kip2 Regulates Cell Cycle Exit, Differentiation, and Migration of Embryonic Cerebral Cortical Precursors

As a broad-acting cyclin-dependent kinase inhibitor, p21WAF1 occupies a central position in the cell cycle regulation of self-renewing tissues such as oral mucosa and skin. In addition to regulating normal cell cycle progression decisions, p21WAF1 integrates genotoxic insults into growth arrest and apoptotic signaling pathways that ultimately determine cell fate. As a result of its complex interactions with cell cycle machinery and response to mutagenic agents, p21WAF1 also has stage-specific roles in epithelial carcinogenesis. Finally, a view is emerging of p21WAF1 as not merely a cyclin-dependent kinase inhibitor, but also as a direct participant in regulating genes involved in growth arrest, senescence, and aging, thus providing an additional layer of control over matters of the cell cycle. This review discusses these various roles played by p21WAF1 in cell cycle control, and attempts to relate these to epithelial cell biology, with special emphasis on keratinocytes. (Abbreviations used include the following: Brdu, 5-Bromo-2-deoxyuridine; cdk, cyclin-dependent kinase; EGF, epidermal growth factor; KIP, kinase inhibitor protein; PCNA, proliferating cell nuclear antigen; and TPA, 12-O-tetradecanoylphorbol-13-acetate.)

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A comprehensive model for the proliferation–quiescence decision in response to endogenous DNA damage in human cells

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1715345115 ◽

2018 ◽

Vol 115 (10) ◽

pp. 2532-2537 ◽

Cited By ~ 29

Author(s):

Frank S. Heldt ◽

Alexis R. Barr ◽

Sam Cooper ◽

Chris Bakal ◽

Béla Novák

Keyword(s):

Cell Cycle ◽

Dna Damage ◽

Kinase Inhibitor ◽

Human Cells ◽

Cyclin Dependent Kinase ◽

Restriction Point ◽

Cyclin Dependent Kinase Inhibitor ◽

Serum Stimulation ◽

G1 Cells ◽

External Stimuli

Human cells that suffer mild DNA damage can enter a reversible state of growth arrest known as quiescence. This decision to temporarily exit the cell cycle is essential to prevent the propagation of mutations, and most cancer cells harbor defects in the underlying control system. Here we present a mechanistic mathematical model to study the proliferation–quiescence decision in nontransformed human cells. We show that two bistable switches, the restriction point (RP) and the G1/S transition, mediate this decision by integrating DNA damage and mitogen signals. In particular, our data suggest that the cyclin-dependent kinase inhibitor p21 (Cip1/Waf1), which is expressed in response to DNA damage, promotes quiescence by blocking positive feedback loops that facilitate G1 progression downstream of serum stimulation. Intriguingly, cells exploit bistability in the RP to convert graded p21 and mitogen signals into an all-or-nothing cell-cycle response. The same mechanism creates a window of opportunity where G1 cells that have passed the RP can revert to quiescence if exposed to DNA damage. We present experimental evidence that cells gradually lose this ability to revert to quiescence as they progress through G1 and that the onset of rapid p21 degradation at the G1/S transition prevents this response altogether, insulating S phase from mild, endogenous DNA damage. Thus, two bistable switches conspire in the early cell cycle to provide both sensitivity and robustness to external stimuli.

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345 GENE EXPRESSION IN OOCYTES AFTER MEIOTIC INHIBITION WITH THE CYCLIN-DEPENDENT KINASE INHIBITOR BUTYROLACTONE I

Reproduction Fertility and Development ◽

10.1071/rdv22n1ab345 ◽

2010 ◽

Vol 22 (1) ◽

pp. 329

Author(s):

C. L. V. Leal ◽

S. Mamo ◽

T. Fair ◽

P. Lonergan

Keyword(s):

Gene Expression ◽

Cell Cycle ◽

Relative Abundance ◽

Kinase Inhibitor ◽

Expression Profiles ◽

Cyclin Dependent Kinase ◽

Oocyte Competence ◽

Cyclin Dependent Kinase Inhibitor ◽

Bovine Oocytes

Once removed from the follicle, mammalian oocytes resume meiosis spontaneously and progress through breakdown of the germinal vesicle to the matured state at metaphase II. The ability to reversibly inhibit such meiotic resumption has been reported and is a potentially useful method for studying developmental competence acquisition in oocytes as well as in some cases allowing flexibility in an IVF system where oocytes are collected from distant locations or on different days. The aim of the present study was to determine the effect of temporary inhibition of meiotic resumption using the cyclin-dependent kinase inhibitor butyrolactone I (BLI) on gene expression in bovine oocytes. Immature bovine oocytes were recovered from the ovaries of slaughtered heifers at a commercial abattoir and assigned to 1 of 4 groups: (1) Control: immature oocytes were collected either immediately or (2) after IVM for 24 h in TCM-199 containing 10 ng mL-1 EGF and 10% (v/v) FCS, (3) Inhibited oocytes collected either 24 h after incubation in the presence of 100 μM BLI in TCM-199 with 3 mg mL-1 BSA or (4) after meiotic inhibition for 24 h followed by in vitro maturation. All cultures were carried out at 38.5°C under 5% CO2 in air and maximum humidity. For mRNA relative abundance analysis, cumulus cells were removed and pools of 10 denuded oocytes were snap frozen in liquid nitrogen and stored at -80°C until use. A total of 42 transcripts, previously reported to be related to cell cycle regulation and/or oocyte competence were evaluated by quantitative real time PCR. Differences in relative abundance were analyzed by ANOVA and Student’s t-test. The majority of transcripts were downregulated (P < 0.05) after IVM in control oocytes (23 out of 42) and the same pattern was observed in inhibited oocytes that were allowed to mature. Twelve transcripts remained stable (P > 0.05) after IVM in control oocytes; of these, only two (PTTG1 and INHBA) did not show the same pattern in inhibited and matured oocytes. Few genes (7) were upregulated after IVM in control oocytes (P < 0.05) and of these, three (PLAT1, RBP1, and INHBB) were not upregulated in inhibited oocytes after IVM. Inhibited oocytes showed similar levels of expression (P > 0.05) as immature control oocytes, except for two genes (LUM and INHBB), which were increased in these oocytes (P < 0.05). The expression profiles of cell cycle genes were mostly unaffected by the BLI treatment. The few genes affected were previously reported as competence-related and could be useful markers of oocyte competence following pretreatment. In conclusion, the changes occurring in transcript abundance during oocyte maturation in vitro were to a large extent mirrored following inhibition of meiotic resumption prior to IVM and subsequent release from inhibition and maturation. CLV Leal was supported by CNPq, Brazil (PDE 201487/2007-1); Supported by Science Foundation Ireland (07/SRC/B1156).

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