The LIM-only protein FHL2 mediates ras-induced transformation through cyclin D1 and p53 pathways.
BACKGROUND
Four and a half LIM-only protein 2 (FHL2) has been implicated in multiple signaling pathways that regulate cell growth and tissue homeostasis. We reported previously that FHL2 regulates cyclin D1 expression and that immortalized FHL2-null mouse embryo fibroblasts (MEFs) display reduced levels of cyclin D1 and low proliferative activity.


RESULTS
Here we address the contribution of FHL2 in cell transformation by investigating the effects of oncogenic Ras in FHL2-null context. We show that H-RasV12 provokes cell cycle arrest accompanied by accumulation of p53 and p16(INK4a) in immortalized FHL2(-/-) MEFs. These features contrast sharply with Ras transforming activity in wild type cell lines. We further show that establishment of FHL2-null cell lines differs from conventional immortalization scheme by retaining functional p19(ARF)/p53 checkpoint that is required for cell cycle arrest imposed by Ras. However, after serial passages of Ras-expressing FHL2(-/-) cells, dramatic increase in the levels of D-type cyclins and Rb phosphorylation correlates with the onset of cell proliferation and transformation without disrupting the p19(ARF)/p53 pathway. Interestingly, primary FHL2-null cells overexpressing cyclin D1 undergo a classical immortalization process leading to loss of the p19(ARF)/p53 checkpoint and susceptibility to Ras transformation.


CONCLUSIONS
Our findings uncover a novel aspect of cellular responses to mitogenic stimulation and illustrate a critical role of FHL2 in the signalling network that implicates Ras, cyclin D1 and p53.
Labalette
Charlotte
C
Institut Pasteur, Unité d'Oncogenèse et Virologie Moléculaire, Paris, France.
Nouët
Yann
Y
Levillayer
Florence
F
Armengol
Carolina
C
Renard
Claire-Angélique
CA
Soubigou
Guillaume
G
Xia
Tian
T
Buendia
Marie-Annick
MA
Wei
Yu
Y
D000818:Animals; D002460:Cell Line; D002461:Cell Line, Transformed; D002467:Cell Nucleus / Q000378:metabolism; D019938:Cyclin D1 / Q000378:metabolism*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D018398:Homeodomain Proteins / Q000378:metabolism / Q000502:physiology*; D060850:LIM-Homeodomain Proteins; D054461:Lim Kinases / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D009124:Muscle Proteins / Q000378:metabolism / Q000502:physiology*; D010641:Phenotype; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism*
C417743:Cdkn2a protein, mouse; D019941:Cyclin-Dependent Kinase Inhibitor p16; C491382:Fhl2 protein, mouse; D018398:Homeodomain Proteins; D060850:LIM-Homeodomain Proteins; D009124:Muscle Proteins; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D019938:Cyclin D1; D054461:Lim Kinases; D018631:ras Proteins