Translational Control of p27
            <sup>Kip1</sup>
            Accumulation During the Cell Cycle

Hengst, Ludger; Reed, Steven I.

doi:10.1126/science.271.5257.1861

Cited by 817 publications

(617 citation statements)

References 23 publications

(7 reference statements)

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“…When this complex dissociates, p27 is freed and now available for interacting with and thereby inhibiting cdk2. In agreement with ®ndings by others (Polyak et al, 1994;Ko et al, 1993;Hengst and Reed, 1996) we have previously shown that contact-inhibition resulted in accumulation of p27 KIP1 , leading to reduced kinase activity of cdk2 and therefore to decreased phosphorylation of pRb, indicating that the observed inhibition of cdk2 in this study resulted from the action of p27 (Dietrich et al, 1997). If p16 INK4 was the critical molecule transmitting the growth-negative signals generated by cell-cell contacts, then impairing the function of p16 should lead to repression of contact-dependent inhibition of growth.…”

supporting

confidence: 93%

p16INK4 mediates contact-inhibition of growth

Wieser¹,

Faust²,

Dietrich³

et al. 1999

Oncogene

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Growth of non-transformed cells in vitro is regulated by density-dependent mechanisms via cell-cell contacts, leading to arrest in late G1-phase at con¯uency (contact-inhibition of growth). In the present study it is shown that this results from p16 INK4 -mediated dissociation of the complex cdk4-cyclin D1, which is responsible for the inactivation of the gate keeper of G1-S transition, the retinoblastoma protein pRb. As a consequence of the inactivation of cdk4, downstream the activation of cdk2 and hyperphosphorylation and thus inactivation of pRb was impaired. Direct evidence for the central role of p16 INK4 in growth control comes from the observation that a competitive inhibitor of p16 INK4 repressed contact inhibition of growth. These ®ndings provide an explanation for the high incidence of mutation or loss of INK4 in human tumours.Keywords: contact-inhibition; cdk4; p16 INK4 The cell cycle is regulated by an ordered cascade of phosphorylation reactions by a speci®c family of serine-threonine kinases, the cyclin-dependent kinases (cdks) (Lees, 1995;Sherr, 1996), and speci®c check points ensure that the cell's proper cycle is tightly controlled. In order to determine at which point of the G1-phase cells are arrested by contact-dependent inhibition of growth, time course studies were performed. In FH109 cells, human embryonal diploid lung ®broblasts (Wieser et al., 1985), contactdependent inhibition of growth is exclusively mediated by the interaction of two cell membrane proteins on adjacent cells, i.e. by the glycoprotein, contactinhibin (Wieser et al., 1990), which binds to its receptor referred to as contactinhibin receptor (Gradl et al., 1995).Cell-cell contacts were imitated by the addition of glutaraldehyde-®xed cells (in which contactinhibin remains active, as its growth inhibitory activity is mediated exclusively by its N-glycans not a ected by the ®xation process) to sparsely seeded ®broblasts in the presence of serum. In previous studies we have demonstrated that this system mimics physiological conditions concerning cell proliferation and differentiation which occur in con¯uent cultures (Wieser et al., 1985;Wieser and Oesch, 1986), thus enabling the study of early e ects of cell-cell contact-dependent signals. FH109 cells were sparsely seeded and cultured for 24 h in DMEM/0.5% FCS to achieve partial synchronization. Control cells were stimulated with 10% FCS in DMEM whereas contact-inhibited cells were generated by the addition of ®xed cells in DMEM/10% FCS prepared from con¯uent cultures (Wieser et al., 1985). These experiments revealed that when ®xed cells were added within the ®rst 8 h after serum-stimulation, proliferation was inhibited by 70 ± 80% as determined by [ 3 H]-thymidine incorporation, which correlates with the reduction of growth rate achieved by seeding ®broblasts to con¯uency (Figure 1). The addition of ®xed cells 10 h after serum stimulation no longer resulted in any growth inhibition, indicating that contact-dependent inhibition of growth is limited to a window in the cell ...

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supporting

confidence: 93%

p16INK4 mediates contact-inhibition of growth

Wieser¹,

Faust²,

Dietrich³

et al. 1999

Oncogene

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“…The abundance of p27 is thought to be regulated by translational and post-translational pathways, and less commonly at the level of transcription (Agrawal et al, 1996;Hengst and Reed, 1996;Roberts et al, 1994;Vlach et al, 1997). Our own observation suggests that the in vivo proteolysis of p27 by a CPP32-like caspase during early G 1 arrest could be an additional posttranslational regulation pathway of p27.…”

Section: Discussionmentioning

confidence: 75%

Evidence for a p23 caspase-cleaved form of p27[KIP1] involved in G1 growth arrest

et al. 1999

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p27 [KIP1] (p27) is a cyclin dependent kinase inhibitor, involved in the negative regulation of G 1 progression in response to a number of anti-proliferative signals. In this study we show, in growing mouse hybridoma (7TD1) and human myeloma (U266) cell lines, that p27 is highly expressed but slightly upregulated when cells are arrested, regardless to the phases of the cell cycle. In contrast, the speci®c blockade of these cells in early G 1 phase reveals the induction of a protein of 23 kDa (p23) speci®cally recognized by polyclonal anti-p27 antibodies raised against the NH2 terminal part of p27 but not by anti-p21 [CIP1] antibodies. Experiments using caspase inhibitors strongly suggest that p23 results from the proteolysis of p27 by a`caspase-3-like' protease. This cleavage leads to the cytosolic sequestration of p23 but does not alter its binding properties to CDK2 and CDK4 kinases. Indeed, p23 associated in vivo with high molecular weight complexes and coprecipitated with CDK2 and CDK4. We demonstrate by transfection experiments in SaOS-2 cells that p23 induces a G 1 phase growth arrest by inhibition of cyclin/CDK2 activity. In summary we describe here a caspase-cleaved form of p27, induced in absence of detectable apoptosis and likely involved in cell cycle regulation.

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“…Recent studies are uncovering a high genetic complexity of the CDKIs and their mechanisms of regulation and inactivation. In addition to deletions, rearrangements, mutations and CpG island hypermethylation, these show additional complex features, including posttranscriptional (p21 WAF1/CIP1 ) or post-translational (p27 KIP1 , p15 INK4b ) regulation or imprinting (p27 KIP1 ) (Hatada and Mukai 1995;Pagano et al, 1995;Hengst and Reed, 1996;Li et al, 1996;Matsuoka et al, 1996;Shandu et al, 1997;Cost et al, 1997;ReynisdoÂ ttir and MassagueÂ 1997). Regarding to untranslated regions, the transcriptional regulatory element proposed in this work for the p15 INK4b 3'-UTR is not unique in the CDKIs, since p21 WAF1/CIP1 has been shown to be not only posttranscriptionally regulated (Li et al, 1996) but also contains cis elements in its 3'-UTR involved in the regulation of transcription (Rishi et al, 1997).…”

Section: Discussionmentioning

confidence: 99%