Tumor suppressor protein Lgl mediates G1 cell cycle arrest at high cell density by forming an Lgl-VprBP-DDB1 complex

Lethal giant larvae (Lgl) is an evolutionarily conserved tumor suppressor whose loss of function causes disrupted epithelial architecture with enhanced cell proliferation and defects in cell polarity. A role for Lgl in the establishment and maintenance of cell polarity via suppression of the PAR-aPKC polarity complex is established; however, the mechanism by which Lgl regulates cell proliferation is not fully understood. Here we show that depletion of Lgl1 and Lgl2 in MDCK epithelial cells results in overproliferation and overproduction of Lgl2 causes G1 arrest. We also show that Lgl associates with the VprBP-DDB1 complex independently of the PAR-aPKC complex and prevents the VprBP-DDB1 subunits from binding to Cul4A, a central component of the CRL4 [VprBP] ubiquitin E3 ligase complex implicated in G1- to S-phase progression. Consistently, depletion of VprBP or Cul4 rescues the overproliferation of Lgl-depleted cells. In addition, the affinity between Lgl2 and the VprBP-DDB1 complex increases at high cell density. Further, aPKC-mediated phosphorylation of Lgl2 negatively regulates the interaction between Lgl2 and VprBP-DDB1 complex. These results suggest a mechanism protecting overproliferation of epithelial cells in which Lgl plays a critical role by inhibiting formation of the CRL4 [VprBP] complex, resulting in G1 arrest.

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Tumor suppressor protein VHL is induced at high cell density and mediates contact inhibition of cell growth

Oncogene ◽

10.1038/sj.onc.1204397 ◽

2001 ◽

Vol 20 (22) ◽

pp. 2727-2736 ◽

Cited By ~ 32

Author(s):

Masaya Baba ◽

Syu-ichi Hirai ◽

Satoshi Kawakami ◽

Takeshi Kishida ◽

Naoki Sakai ◽

...

Keyword(s):

Cell Growth ◽

Tumor Suppressor ◽

Cell Density ◽

High Cell Density ◽

Contact Inhibition ◽

Tumor Suppressor Protein ◽

High Cell

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Reduced Levels of ATF-2 Predispose Mice to Mammary Tumors

Molecular and Cellular Biology ◽

10.1128/mcb.01579-06 ◽

2006 ◽

Vol 27 (5) ◽

pp. 1730-1744 ◽

Cited By ~ 60

Author(s):

Toshio Maekawa ◽

Toshie Shinagawa ◽

Yuji Sano ◽

Takahiko Sakuma ◽

Shintaro Nomura ◽

...

Keyword(s):

Cell Density ◽

Target Genes ◽

High Cell Density ◽

Critical Role ◽

Susceptibility Gene ◽

Mammary Tumors ◽

Mrna Levels ◽

High Cell ◽

Wild Type ◽

Induced Apoptosis

ABSTRACT Transcription factor ATF-2 is a nuclear target of stress-activated protein kinases, such as p38, which are activated by various extracellular stresses, including UV light. Here, we show that ATF-2 plays a critical role in hypoxia- and high-cell-density-induced apoptosis and the development of mammary tumors. Compared to wild-type cells, Atf-2 −/− mouse embryonic fibroblasts (MEFs) were more resistant to hypoxia- and anisomycin-induced apoptosis but remained equally susceptible to other stresses, including UV. Atf-2 −/− and Atf-2 +/− MEFs could not express a group of genes, such as Gadd45α, whose overexpression can induce apoptosis, in response to hypoxia. Atf-2 −/− MEFs also had a higher saturation density than wild-type cells and expressed lower levels of Maspin, the breast cancer tumor suppressor, which is also known to enhance cellular sensitivity to apoptotic stimuli. Atf-2 −/− MEFs underwent a lower degree of apoptosis at high cell density than wild-type cells. Atf-2 +/− mice were highly prone to mammary tumors that expressed reduced levels of Gadd45α and Maspin. The ATF-2 mRNA levels in human breast cancers were lower than those in normal breast tissue. Thus, ATF-2 acts as a tumor susceptibility gene of mammary tumors, at least partly, by activating a group of target genes, including Maspin and Gadd45α.

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New primary culture systems to study the differentiation and proliferation of mouse fetal hepatoblasts

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00412.2007 ◽

2008 ◽

Vol 294 (2) ◽

pp. G529-G539 ◽

Cited By ~ 8

Author(s):

Rika Miki ◽

Norifumi Tatsumi ◽

Ken Matsumoto ◽

Yuji Yokouchi

Keyword(s):

Growth Factors ◽

Epithelial Cells ◽

Cell Density ◽

Culture System ◽

High Cell Density ◽

High Cell ◽

Culture Systems ◽

Biliary Epithelial Cells ◽

Low Cell Density ◽

E Cadherin

Hepatoblasts have the potential to differentiate into both hepatocytes and biliary epithelial cells through a differentiation program that has not been fully elucidated. With the aim to better define the mechanism of differentiation of hepatoblasts, we isolated hepatoblasts and established new culture systems. We isolated hepatoblasts from E12.5 fetal mouse liver by using E-cadherin. The E-cadherin+ cells expressed α-fetoprotein (AFP) and albumin (Alb) but not cytokeratin 19 (CK19). Transplantation of the E-cadherin+ cells into mice that had been subjected to liver injury or biliary epithelial injury led to differentiation of the cells into hepatocytes or biliary epithelial cells, respectively. In a low-cell-density culture system in the absence of additional growth factors, E-cadherin+ cells formed colonies of various sizes, largely comprising Alb-positive cells. Supplementation of the culture medium with hepatocyte growth factor and epidermal growth factor promoted proliferation of the cells. Thus the low-cell-density culture system should be useful to identify inductive factors that regulate the proliferation and differentiation of hepatoblasts. In a high-cell-density system in the presence of oncostatin M+dexamethasone, E14.5, but not E12.5, E-cadherin+ cells differentiated into mature hepatocytes, suggesting that unidentified factors are involved in hepatic maturation. Culture of E-cadherin+ cells derived from E12.5 or E14.5 liver under high-cell-density conditions should allow elucidation of the mechanism of hepatic differentiation in greater detail. These new culture systems should be of use to identify growth factors that induce hepatoblasts to proliferate or differentiate into hepatocytes and biliary epithelial cells.

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