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G1 arrest and differentiation can occur independently of Rb family function.

ABSTRACT: The ability of progenitor cells to exit the cell cycle is essential for proper embryonic development and homeostasis, but the mechanisms governing cell cycle exit are still not fully understood. Here, we tested the requirement for the retinoblastoma (Rb) protein and its family members p107 and p130 in G0/G1 arrest and differentiation in mammalian cells. We found that Rb family triple knockout (TKO) mouse embryos survive until days 9-11 of gestation. Strikingly, some TKO cells, including in epithelial and neural lineages, are able to exit the cell cycle in G0/G1 and differentiate in teratomas and in culture. This ability of TKO cells to arrest in G0/G1 is associated with the repression of key E2F target genes. Thus, G1 arrest is not always dependent on Rb family members, which illustrates the robustness of cell cycle regulatory networks during differentiation and allows for the identification of candidate pathways to inhibit the expansion of cancer cells with mutations in the Rb pathway.

SUBMITTER: Wirt SE

PROVIDER: S-EPMC2983066 | biostudies-literature | 2010 Nov

REPOSITORIES: biostudies-literature

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G1 arrest and differentiation can occur independently of Rb family function.

Wirt Stacey E SE Adler Adam S AS Gebala Véronique V Weimann James M JM Schaffer Bethany E BE Saddic Louis A LA Viatour Patrick P Vogel Hannes H Chang Howard Y HY Meissner Alex A Sage Julien J

The Journal of cell biology 20101108 4

The ability of progenitor cells to exit the cell cycle is essential for proper embryonic development and homeostasis, but the mechanisms governing cell cycle exit are still not fully understood. Here, we tested the requirement for the retinoblastoma (Rb) protein and its family members p107 and p130 in G0/G1 arrest and differentiation in mammalian cells. We found that Rb family triple knockout (TKO) mouse embryos survive until days 9-11 of gestation. Strikingly, some TKO cells, including in epith ...[more]

PMID: 21059851

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Project description:Human diploid fibroblasts lose the capacity to proliferate and enter a state termed replicative senescence after a finite number of cell divisions in culture. When treated with sub-lethal concentrations of H2O2, pre-senescent human fibroblasts enter long-term growth arrest resembling replicative senescence. To understand the molecular basis for the H2O2-induced growth arrest, we determined the cell cycle distribution, levels of p53 tumour suppressor and p21 cyclin-dependent kinase inhibitor proteins, and the status of Rb phosphorylation in H2O2-treated cells. A 2-h pulse of H2O2 arrested the growth of IMR-90 fetal lung fibroblasts for at least 15 days. The arrested cells showed a G1 DNA content. The level of p53 protein increased 2- to 3-fold within 1.5 h after H2O2 exposure but returned to the control level by 48 h. The induction of p53 protein was dose dependent, beginning at 50-75 microM and reaching a maximum at 100-250 microM. The induction of p53 did not appear to correlate with the level of DNA damage as measured by the formation of 8-oxo-2'-deoxyguanosine in DNA. The level of p21 protein increased about 18 h after H2O2 exposure and remained elevated for at least 21 days. During this period, Rb remained underphosphorylated. The induction of p53 by H2O2 was abolished by the iron chelator deferoxamine and the protein synthesis inhibitor cycloheximide. The human papillomavirus protein E6, when introduced into the cells, abolished the induction of p53, reduced the induction of p21 to a minimal level and allowed Rb phosphorylation and entry of the cells into S-phase. The human papillomavirus protein E7 reduced the overall level of Rb and also abolished H2O2-induced G1 arrest. Inactivating G1 arrest by E6, E7 or both did not restore the replicative ability of H2O2-treated cells. Thus H2O2-treated cells show a transient elevation of p53, high level of p21, lack of Rb phosphorylation, G1 arrest and inability to replicate when G1 arrest is inactivated.

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G1 arrest and differentiation can occur independently of Rb family function.

Publications

G1 arrest and differentiation can occur independently of Rb family function.

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