The MAP kinase pathway is required for entry into mitosis and cell survival

Abstract

In this communication, we examined the role of the MAP kinase pathway in the G2/M phase of the cell cycle. Activation of the Plk1 and MAP kinase pathways was initially evaluated in FT210 cells, which arrest at G2 phase at the restrictive temperature (391C), due to a mutation in the cdc2 gene. Previous studies had shown that these cells enter mitosis at the nonpermissive temperature upon incubation with okadaic acid, a protein phosphatase 1 and 2A inhibitor. We show that treatment of FT210 cells at 391C with okadaic acid activated Plk1, as shown by hyperphosphorylation and elevated protein kinase activity, and also induced activation of the MAP kinase pathway. The specific Mek inhibitor PD98059 antagonized the okadaic acid-induced activation of both Plk1 and MAP kinases. This suggests that activation of the MAP kinase pathway may contribute to the okadaic acid-induced activation of Plk1 in FT210 cells at 391C. We also found that PD98059 strongly attenuated progression of HeLa cells through mitosis, and active Mek colocalizes with Plk1 at mitotic structures. To study the potential function of the MAP kinase pathway during mitosis, RNAi was used to specifically deplete five members of this pathway (Raf1, Mek1/2, Erk1/2). Each of these five protein kinases is required for cell proliferation and survival, and depletion of any of these proteins eventually leads to apoptosis. Treatment with Mek inhibitors also inhibited cell proliferation and caused apoptosis. A dramatic increase of Plk1 activities and a moderate increase of Cdc2 activities in Raf1-depleted cells indicate that Raf1-depleted cells arrest in the late G2 or M phase. Mek1 and Erk1 depletion also caused cell cycle arrest at G2, suggesting that these enzymes are required for the G2/M transition, whereas the loss of Mek2 or Erk2 caused arrest at G1.

Transcriptional Repression of Mad-Max Complex by Human Umbilical Cord Blood Stem Cells Downregulates Extracellular Signal-Regulated Kinase in Glioblastoma

“…Notably, the addition of rERK to shERK-transfected U251 and 5310 cells induced an obvious increase in the G 0 -G 1 peak. These results support previous findings by Liu et al [29] who demonstrated that inhibition of MEK1/2 in ERKdepleted cells arrest cells at the G 1 phase. This suggests that downregulation of ERK by hUCBSC may be regarded as a key step for the regulation of glioblastoma progression.…”

RNAi-mediated ERK2 knockdown inhibits growth of tumor cells in vitro and in vivo

“…This model of competition is based on observations that inactivation of ERK1 by either genetic disruption or RNAi silencing increases the proliferation rate of fibroblasts, whereas knockdown of ERK2 expression dramatically inhibits cell proliferation. However, these findings are discrepant with observations showing no difference in the proliferation rate of ERK1-deficient embryonic fibroblasts (Pages et al, 1999) whereas RNAi silencing of ERK1 inhibited the proliferation of HeLa cells to the same extent as ERK2 silencing (Liu et al, 2004). Recent studies emphasize this controversy (Sanjo et al, 2007).…”

“…In FT210 cells, ERK1 depletion caused cell-cycle arrest at G 2 , whereas the loss of ERK2 induced arrest at G 1 (Liu et al, 2004). In NIH 3T3, knockdown of ERK2 almost completely abolished normal and Ras-dependent cell proliferation.…”

Mitogen-activated Protein Kinase Kinase 1-dependent Golgi Unlinking Occurs in G2Phase and Promotes the G2/M Cell Cycle Transition

“…Activation is independent of extracellular growth factor input (Dangi and Shapiro, 2005), and inhibition causes spindle defects (Horne and Guadagno, 2003). Additionally, interfering with MEK1 signaling via expression of dominant-negative mutants, use of chemical inhibitors, or RNA interference (RNAi) significantly delays mitotic entry (Wright et al, 1999;Roberts et al, 2002;Liu et al, 2004), suggesting the existence of a novel mitotic target of MEKmediated signaling that promotes mitotic entry. Surprisingly, one apparent mitotic target of MEK1 is the mammalian Golgi apparatus (Acharya et al, 1998).…”