Homozygous deletion of glycogen synthase kinase 3β bypasses senescence allowing Ras transformation of primary murine fibroblasts

• Published in: Proceedings of the National Academy of Sciences - PNAS 2008-04, Vol.105 (13), p.5248-5253
• Main Authors: Liu, Shuying, Fang, Xianjun, Hall, Hassan, Yu, Shuangxing, Smith, Debra, Lu, Zhimin, Fang, Dexing, Liu, Jinsong, Stephens, L. Clifton, Woodgett, James R, Mills, Gordon B
• Format: Article
• Language: English
• Subjects: Biological Sciences; Cell growth; Cell lines; Cellular senescence; Cultured cells; Cyclins; Immunoblotting; Phosphorylation; Retroviridae; Tumors; Viruses
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0704242105

In primary mammalian cells, expression of oncogenes such as activated Ras induces premature senescence rather than transformation. We show that homozygous deletion of glycogen synthase kinase (GSK) 3β (GSK3β⁻/⁻) bypasses senescence induced by mutant RasV¹² allowing primary mouse embryo fibroblasts (MEFs) as well as immortalized MEFs to exhibit a transformed phenotype in vitro and in vivo. Both catalytic activity and Axin-binding of GSK3β are required to optimally suppress Ras transformation. The expression of RasV¹² in GSK3β⁻/⁻, but not in GSK3β⁺/⁺ MEFs results in translocation of β-catenin to the nucleus with concomitant up-regulation of cyclin D1. siRNA-mediated knockdown of β-catenin decreases both cyclin D1 expression and anchorage-independent growth of transformed cells indicating a causal role for β-catenin. Thus RasV¹² and the lack of GSK3β act in concert to activate the β-catenin pathway, which may underlie the bypass of senescence and tumorigenic transformation by Ras.