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Growth suppression by Lkb1 is mediated by a G(1) cell cycle arrest
M Tiainen1, A Ylikorkala, T P Mäkelä
1Haartman Institute and Biocentrum Helsinki, P.O. Box 21, 00014 University of Helsinki, Helsinki, Finland.
Abstract:
Germ-line mutations of LKB1 (STK11) lead to Peutz-Jeghers syndrome characterized by gastrointestinal polyps and cancer of different organ systems. The mutations lead to loss or severe impairment of Lkb1 serine/threonine kinase activity. Therefore LKB1 has been implicated as a tumor suppressor gene, but only a few mutations in the coding exons of LKB1 have been detected in sporadic tumors. Here, we have identified tumor cell lines with severely reduced mRNA levels and impaired Lkb1 kinase activity. Reintroducing Lkb1 into these cells suppressed cell growth. The Lkb1-mediated growth inhibition was caused by a G(1) cell cycle block and was not detected with several naturally occurring Lkb1 mutants. These results indicate that LKB1 has functional and specific growth-suppressing activity.
Insights
Germ-line mutations in the LKB1 (STK11) gene cause Peutz-Jeghers syndrome. This study shows LKB1 exhibits tumor suppressor activity by inhibiting cancer cell growth and causing a G1 cell cycle block.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Germ-line mutations in LKB1 (STK11) are linked to Peutz-Jeghers syndrome, characterized by gastrointestinal polyps and increased cancer risk.
- LKB1 is a serine/threonine kinase implicated as a tumor suppressor, though mutations are rarely found in sporadic tumors.
Purpose of the Study:
- To investigate the role of LKB1 in sporadic tumors.
- To determine if LKB1 possesses functional tumor-suppressive activity in cancer cell lines.
Main Methods:
- Identified tumor cell lines with reduced LKB1 mRNA and kinase activity.
- Reintroduced functional LKB1 into these cells.
- Assessed the impact of LKB1 reintroduction on cell growth and cell cycle progression.
Main Results:
- Tumor cell lines with impaired LKB1 exhibited reduced mRNA levels and kinase activity.
- Restoring LKB1 expression suppressed tumor cell growth.
- LKB1-mediated growth inhibition was associated with a G1 cell cycle block.
- Naturally occurring LKB1 mutants did not show this growth-inhibitory effect.
Conclusions:
- LKB1 demonstrates functional and specific growth-suppressing activity in cancer cells.
- These findings support LKB1's role as a tumor suppressor beyond Peutz-Jeghers syndrome.
- LKB1's kinase activity is crucial for its tumor suppressor function.