scholarly journals A Skp2 autoinduction loop and restriction point control

2007 ◽  
Vol 178 (5) ◽  
pp. 741-747 ◽  
Author(s):  
Yuval Yung ◽  
Janice L. Walker ◽  
James M. Roberts ◽  
Richard K. Assoian
Keyword(s):  
S Phase ◽  
Cyclin Dependent Kinase ◽  
Embryonic Fibroblasts ◽  
Papilloma Virus ◽  
Restriction Point ◽  
Pocket Proteins ◽  
Serum Stimulation ◽  
Point Control ◽  
Phase Progression ◽  
Phase Entry

We describe a self-amplifying feedback loop that autoinduces Skp2 during G1 phase progression. This loop, which contains Skp2 itself, p27kip1 (p27), cyclin E–cyclin dependent kinase 2, and the retinoblastoma protein, is closed through a newly identified, conserved E2F site in the Skp2 promoter. Interference with the loop, by knockin of a Skp2-resistant p27 mutant (p27T187A), delays passage through the restriction point but does not interfere with S phase entry under continuous serum stimulation. Skp2 knock down inhibits S phase entry in nontransformed mouse embryonic fibroblasts but not in human papilloma virus–E7 expressing fibroblasts. We propose that the essential role for Skp2-dependent degradation of p27 is in the formation of an autoinduction loop that selectively controls the transition to mitogen-independence, and that Skp2-dependent proteolysis may be dispensable when pocket proteins are constitutively inactivated.

scholarly journals p107 inhibits G1 to S phase progression by down-regulating expression of the F-box protein Skp2

2005 ◽  
Vol 168 (1) ◽  
pp. 55-66 ◽  
Author(s):  
Geneviève Rodier ◽  
Constantin Makris ◽  
Philippe Coulombe ◽  
Anthony Scime ◽  
Keiko Nakayama ◽  
...  
Keyword(s):  
Cell Cycle Progression ◽  
Ectopic Expression ◽  
Inhibitory Effect ◽  
S Phase ◽  
Cycle Progression ◽  
Pocket Proteins ◽  
Phase Progression ◽  
F Box Protein ◽  
Serum Dependent ◽  
Phase Entry

Cell cycle progression is negatively regulated by the pocket proteins pRb, p107, and p130. However, the mechanisms responsible for this inhibition are not fully understood. Here, we show that overexpression of p107 in fibroblasts inhibits Cdk2 activation and delays S phase entry. The inhibition of Cdk2 activity is correlated with the accumulation of p27, consequent to a decreased degradation of the protein, with no change of Thr187 phosphorylation. Instead, we observed a marked decrease in the abundance of the F-box receptor Skp2 in p107-overexpressing cells. Reciprocally, Skp2 accumulates to higher levels in p107−/− embryonic fibroblasts. Ectopic expression of Skp2 restores p27 down-regulation and DNA synthesis to the levels observed in parental cells, whereas inactivation of Skp2 abrogates the inhibitory effect of p107 on S phase entry. We further show that the serum-dependent increase in Skp2 half-life observed during G1 progression is impaired in cells overexpressing p107. We propose that p107, in addition to its interaction with E2F, inhibits cell proliferation through the control of Skp2 expression and the resulting stabilization of p27.

scholarly journals Combined Inactivation of Pocket Proteins and APC/CCdh1 by Cdk4/6 Controls Recovery from DNA Damage in G1 Phase

Cells ◽  
2021 ◽  
Vol 10 (3) ◽  
pp. 550
Author(s):  
Indra A. Shaltiel ◽  
Alba Llopis ◽  
Melinda Aprelia ◽  
Rob Klompmaker ◽  
Apostolos Menegakis ◽  
...  
Keyword(s):  
Dna Damage ◽  
Normal Cell ◽  
S Phase ◽  
G1 Phase ◽  
Anaphase Promoting Complex ◽  
Inhibitory Effects ◽  
Pocket Proteins ◽  
Cyclin Dependent Kinases ◽  
Independent Functions ◽  
Phase Entry

Most Cyclin-dependent kinases (Cdks) are redundant for normal cell division. Here we tested whether these redundancies are maintained during cell cycle recovery after a DNA damage-induced arrest in G1. Using non-transformed RPE-1 cells, we find that while Cdk4 and Cdk6 act redundantly during normal S-phase entry, they both become essential for S-phase entry after DNA damage in G1. We show that this is due to a greater overall dependency for Cdk4/6 activity, rather than to independent functions of either kinase. In addition, we show that inactivation of pocket proteins is sufficient to overcome the inhibitory effects of complete Cdk4/6 inhibition in otherwise unperturbed cells, but that this cannot revert the effects of Cdk4/6 inhibition in DNA damaged cultures. Indeed, we could confirm that, in addition to inactivation of pocket proteins, Cdh1-dependent anaphase-promoting complex/cyclosome (APC/CCdh1) activity needs to be inhibited to promote S-phase entry in damaged cultures. Collectively, our data indicate that DNA damage in G1 creates a unique situation where high levels of Cdk4/6 activity are required to inactivate pocket proteins and APC/CCdh1 to promote the transition from G1 to S phase.

scholarly journals Anchorage-Independent Growth of Pocket Protein-Deficient Murine Fibroblasts Requires Bypass of G2 Arrest and Can Be Accomplished by Expression of TBX2

2008 ◽  
Vol 28 (24) ◽  
pp. 7263-7273 ◽  
Author(s):  
Tinke L. Vormer ◽  
Floris Foijer ◽  
Camiel L. C. Wielders ◽  
Hein te Riele
Keyword(s):  
Human Fibroblasts ◽  
Cyclin Dependent Kinase ◽  
Mouse Embryonic Fibroblasts ◽  
Embryonic Fibroblasts ◽  
Pocket Proteins ◽  
Anchorage Independent Growth ◽  
Pocket Protein ◽  
Murine Fibroblasts ◽  
Mouse Cells ◽  
Human And Mouse

ABSTRACT Mouse embryonic fibroblasts (MEFs) deficient for pocket proteins (i.e., pRB/p107-, pRB/p130-, or pRB/p107/p130-deficient MEFs) have lost proper G1 control and are refractory to RasV12-induced senescence. However, pocket protein-deficient MEFs expressing RasV12 were unable to exhibit anchorage-independent growth or to form tumors in nude mice. We show that depending on the level of pocket proteins, loss of adhesion induces G1 and G2 arrest, which could be alleviated by overexpression of the TBX2 oncogene. TBX2-induced transformation occurred only in the absence of pocket proteins and could be attributed to downregulation of the p53/p21CIP1 pathway. Our results show that a balance between the pocket protein and p53 pathways determines the level of transformation of MEFs by regulating cyclin-dependent kinase activities. Since transformation of human fibroblasts also requires ablation of both pathways, our results imply that the mechanisms underlying transformation of human and mouse cells are not as different as previously claimed.

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

2018 ◽  
Vol 115 (10) ◽  
pp. 2532-2537 ◽  
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.

scholarly journals Np95 is regulated by E1A during mitotic reactivation of terminally differentiated cells and is essential for S phase entry

2002 ◽  
Vol 157 (6) ◽  
pp. 909-914 ◽  
Author(s):  
Ian Marc Bonapace ◽  
Lucia Latella ◽  
Roberto Papait ◽  
Francesco Nicassio ◽  
Alessandra Sacco ◽  
...  
Keyword(s):  
S Phase ◽  
Cyclin Dependent Kinase ◽  
Gene Encoding ◽  
Adenovirus E1a ◽  
Differentiated Cells ◽  
Molecular Determinant ◽  
Tumor Viruses ◽  
Cdk2 Complex ◽  
Nih 3T3 ◽  
Phase Entry

Terminal differentiation exerts a remarkably tight control on cell proliferation. However, the oncogenic products of DNA tumor viruses, such as adenovirus E1A, can force postmitotic cells to proliferate, thus representing a powerful tool to study progression into S phase. In this study, we identified the gene encoding Np95, a murine nuclear phosphoprotein, as an early target of E1A-induced transcriptional events. In terminally differentiated (TD) cells, the activation of Np95 was specifically induced by E1A, but not by overexpression of E2F-1 or of the cyclin E (cycE)–cyclin-dependent kinase 2 (cdk2) complex. In addition, the concomitant expression of Np95 and of cycE–cdk2 was alone sufficient to induce S phase in TD cells. In NIH-3T3 cells, the expression of Np95 was tightly regulated during the cell cycle, and its functional ablation resulted in abrogation of DNA synthesis. Thus, expression of Np95 is essential for S phase entry. Previous evidence suggested that E1A, in addition to its well characterized effects on the pRb/E2F-1 pathway, activates a parallel and complementary pathway that is also required for the reentry in S phase of TD cells (Tiainen, M., D. Spitkousky, P. Jansen-Dürr, A. Sacchi, and M. Crescenzi. 1996. Mol. Cell. Biol. 16:5302–5312). From our results, Np95 appears to possess all the characteristics to represent the first molecular determinant identified in this pathway.

scholarly journals Cyclin A2/Cdk1 is Essential for the in vivo S Phase Entry by Phosphorylating Top2a

2019 ◽  
Author(s):  
Miaomiao Jin ◽  
Ruikun Hu ◽  
Baijie Xu ◽  
Weilai Huang ◽  
Hong Wang ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cyclin B1 ◽  
S Phase ◽  
Downstream Target ◽  
Early Embryonic Lethality ◽  
M Phase ◽  
Phase Progression ◽  
Cyclin A2 ◽  
Phase Entry

AbstractCyclin-dependent kinase 1 (CDK1) plays essential roles in cell cycle regulation. However, due to the early embryonic lethality of mouse Cdk1 mutants, the in vivo role of CDK1 in regulating cell cycle and embryonic development remains unclear. Here, by generating zebrafish cdk1 mutants using CRISPR/Cas9 system, we show that cdk1−/− embryos exhibit severe microphthalmia accompanied with multiple defects in polarized cell division, S phase entry and M phase progression, cell apoptosis and cell differentiation, but not in interkinetic nuclear migration (IKNM). By informatics analysis, we identified Top2a as a potential downstream target, and Cyclin A2 and Cyclin B1 as partners of Cdk1 in cell cycle. Depletion of either Cyclin A2 or Top2a leads to decreased S phase entry and increased DNA damage response in zebrafish retinal cells, and depletion of Cyclin B1 leads to M phase arrest. Immunoprecipitation shows that Cdk1 and Cyclin A2 physically interact in vivo. Moreover, phosphorylation of Top2a on Serine 1213 (S1213) site is almost absent in either cdk1 or ccna2 mutants, but in not ccnb1 mutants. Furthermore, overexpression of TOP2AS1213, the phosphomimetic form of human TOP2A, rescues S phase entry and microphthalmia defects in cdk1−/− and ccna2−/− embryos. Taken together, our data suggests that Cdk1 interacts with Cyclin A2 to regulate S phase entry through phosphorylating Top2a, and with Cyclin B1 to regulate M phase progression in vivo.

scholarly journals The Rice Cyclin-Dependent Kinase –Activating Kinase R2 Regulates S-Phase Progression

2002 ◽  
Vol 14 (1) ◽  
pp. 197-210 ◽  
Author(s):  
Tanja Fabian-Marwedel ◽  
Masaaki Umeda ◽  
Margret Sauter
Keyword(s):  
S Phase ◽  
Cyclin Dependent Kinase ◽  
Phase Progression

scholarly journals Cortactin Modulates RhoA Activation and Expression of Cip/Kip Cyclin-Dependent Kinase Inhibitors To Promote Cell Cycle Progression in 11q13-Amplified Head and Neck Squamous Cell Carcinoma Cells

2010 ◽  
Vol 30 (21) ◽  
pp. 5057-5070 ◽  
Author(s):  
David R. Croucher ◽  
Danny Rickwood ◽  
Carole M. Tactacan ◽  
Elizabeth A. Musgrove ◽  
Roger J. Daly
Keyword(s):  
Cell Cycle ◽  
Squamous Cell Carcinoma ◽  
Cell Carcinoma ◽  
Cell Cycle Progression ◽  
Kinase Inhibitors ◽  
S Phase ◽  
Cyclin Dependent Kinase ◽  
Cycle Progression ◽  
Fadu Cells ◽  
Phase Entry

ABSTRACT The cortactin oncoprotein is frequently overexpressed in head and neck squamous cell carcinoma (HNSCC), often due to amplification of the encoding gene (CTTN). While cortactin overexpression enhances invasive potential, recent research indicates that it also promotes cell proliferation, but how cortactin regulates the cell cycle machinery is unclear. In this article we report that stable short hairpin RNA-mediated cortactin knockdown in the 11q13-amplified cell line FaDu led to increased expression of the Cip/Kip cyclin-dependent kinase inhibitors (CDKIs) p21WAF1/Cip1, p27Kip1, and p57Kip2 and inhibition of S-phase entry. These effects were associated with increased binding of p21WAF1/Cip1 and p27Kip1 to cyclin D1- and E1-containing complexes and decreased retinoblastoma protein phosphorylation. Cortactin regulated expression of p21WAF1/Cip1 and p27Kip1 at the transcriptional and posttranscriptional levels, respectively. The direct roles of p21WAF1/Cip1, p27Kip1, and p57Kip2 downstream of cortactin were confirmed by the transient knockdown of each CDKI by specific small interfering RNAs, which led to partial rescue of cell cycle progression. Interestingly, FaDu cells with reduced cortactin levels also exhibited a significant diminution in RhoA expression and activity, together with decreased expression of Skp2, a critical component of the SCF ubiquitin ligase that targets p27Kip1 and p57Kip2 for degradation. Transient knockdown of RhoA in FaDu cells decreased expression of Skp2, enhanced the level of Cip/Kip CDKIs, and attenuated S-phase entry. These findings identify a novel mechanism for regulation of proliferation in 11q13-amplified HNSCC cells, in which overexpressed cortactin acts via RhoA to decrease expression of Cip/Kip CDKIs, and highlight Skp2 as a downstream effector for RhoA in this process.

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