Regulation of Exit from Quiescence by p27 and Cyclin D1-CDK4

Abstract

The synthesis of cyclin D1 and its assembly with cyclin-dependent kinase 4 (CDK4) to form an active complex is a rate-limiting step in progression through the G 1 phase of the cell cycle. Using an activated allele of mitogen-activated protein kinase kinase 1 (MEK1), we show that this kinase plays a significant role in positively regulating the expression of cyclin D1. This was found both in quiescent serum-starved cells and in cells expressing dominant-negative Ras. Despite the observation that cyclin D1 is a target of MEK1, in cycling cells, activated MEK1, but not cyclin D1, is capable of overcoming a G 1 arrest induced by Ras inactivation. Either wild-type or catalytically inactive CDK4 cooperates with cyclin D1 in reversing the G 1 arrest induced by inhibition of Ras activity. In quiescent NIH 3T3 cells expressing either ectopic cyclin D1 or activated MEK1, cyclin D1 is able to efficiently associate with CDK4; however, the complex is inactive. A significant percentage of the cyclin D1-CDK4 complexes are associated with p27 in serum-starved activated MEK1 or cyclin D1 cell lines. Reduction of p27 levels by expression of antisense p27 allows for S-phase entry from quiescence in NIH 3T3 cells expressing ectopic cyclin D1, but not in parental cells.Both positive and negative extracellular growth factors exert their influence upon proliferation during the G 1 phase of the cell cycle. At a point in late G 1 , termed the restriction point (R), cells become largely refractory to these factors and once past R are committed to completing the mitotic cycle (62,87,97). The action of serum growth factors is mediated, in part, through their activation of receptor tyrosine kinases. Ras, an inner plasma membrane-bound GTPase, plays a significant role in receiving and transducing extracellular signals by functioning as a downstream mediator of several membrane-bound receptor and nonreceptor tyrosine kinases (5,45,46,69). Ras influences, and is required for, both the G 0 /G 1 transition and passage through G 1 to a point temporally coincident with the restriction point. In certain situations, Ras has been shown to be sufficient for progression from G 0 to S phase, as demonstrated by the ability of microinjected activated or wild-type Ras to induce DNA synthesis from quiescence in the absence of serum factors (19,84). Furthermore, microinjection of murine fibroblasts with anti-Ras neutralizing antibodies prevents efficient serum-induced S-phase entry from a G 0 state (16,52), and expression of a dominant-negative Ras protein (Ras N17 ) inhibits the proliferation of NIH 3T3 and 32D myeloid cells, resulting in a G 1 arrest (8,18,59).In terms of nuclear events influencing progression through the G 1 phase of the cell cycle, a key role is played by G 1 cyclins and their catalytic subunits, the cyclin-dependent kinases (CDKs). The three D-type cyclins associate with and activate CDK4 and CDK6. Cyclin E is required for the activation of CDK2. The synthesis of D-type cyclins, whose expression is rate limiting for G 1 progression, is ...

Retinoids arrest breast cancer cell proliferation: retinoic acid selectively reduces the duration of receptor tyrosine kinase signaling

“…Also consistent with a G 0 -like arrest of RA-treated cells are recent reports that the cyclin-dependent kinase inhibitor, p27, is elevated in RA-treated cells [4,[56][57][58][59]. Levels of p27 are typically high in quiescent cells and decrease following mitogen-stimulated reentry into G 1 [53,60].…”

“…Although our data do not rule out G 1 targets for retinoids in T-47D cells, we believe the critical block occurs in early G 1 . Cyclin D1, AP1 and MEK1 are all involved in regulating the G 0 / G 1 transition and G 1 progression [52][53][54]. Retinoid attenuation of MAP kinase activation, immediate early gene expression, AP1 transcriptional activity and cyclin D1 expression [55] supports our hypothesis that retinoids block cell cycle progression by disrupting the mitogenic signaling that is required for early G 1 progression (of cycling cells) or the transition from G 0 into G 1 (of quiescent cells).…”

Cyclin D1: polymorphism, aberrant splicing and cancer risk

“…Cyclin D1 expression is induced as a delayed early response to many mitogenic signals (Sherr et al, 1992;Sherr, 1995), and is universally associated with the transition from quiescence into the proliferative cycle (Won et al, 1992;Winston and Pledger, 1993;Lukas et al, 1994b;Ladha et al, 1998;Diehl, 2002). Among the cyclins that regulate G1 progression, it is hypothesized that stimulation of cyclin D1 expression represents the point at which mitogenic signal transduction cascades are integrated to mediate engagement of the cell cycle machinery (Figure 1).…”

Progressive and Inhibitory Cell Cycle Proteins Act Simultaneously to Regulate Neurotrophin-mediated Proliferation and Maturation of Neuronal Precursors

“…Mitogen-activated protein kinase (MAPK) signaling (ras/rap, raf, MEK1/2, Erk1/2) is implicated in mitogenic control of the cell cycle and regulation of cyclin D1 expression. 43,44 Our previous work showed that in vitro treatment of OSNs with BDNF leads to an increase in extracellular signal-related kinase (Erk1/2) phosphorylation/activation within 30 minutes after treatment, and that inclusion of the MAP kinase kinase (MEK) inhibitor, PD98059, results in inhibition of BDNF-induced proliferation. 16 We examined the effects of PD98059 on the number of neuronal precursors expressing cyclin D1 in response to either NGF (Fig.…”