title: Growth arrest by the LKB1 tumor suppressor: induction of p21(WAF1/CIP1).
abstract: Germline mutations of the LKB1 tumor suppressor gene lead to Peutz-Jeghers syndrome (PJS), with a predisposition to cancer. LKB1 encodes for a nuclear and cytoplasmic serine/threonine kinase, which is inactivated by mutations observed in PJS patients. Restoring LKB1 activity into cancer cell lines defective for its expression results in a G(1) cell cycle arrest. Here we have investigated molecular mechanisms leading to this arrest. Reintroduced active LKB1 was cytoplasmic and nuclear, whereas most kinase-defective PJS mutants of LKB1 localized predominantly to the nucleus. Moreover, when LKB1 was forced to remain cytoplasmic through disruption of the nuclear localization signal, it retained full growth suppression activity in a kinase-dependent manner. LKB1-mediated G(1) arrest was found to be bypassed by co-expression of the G(1) cyclins cyclin D1 and cyclin E. In addition, the protein levels of the CDK inhibitor p21(WAF1/CIP1) and p21 promoter activity were specifically upregulated in LKB1-transfected cells. Both the growth arrest and the induction of the p21 promoter were found to be p53-dependent. These results suggest that growth suppression by LKB1 is mediated through signaling of cytoplasmic LKB1 to induce p21 through a p53-dependent mechanism.
authors.affiliation: Haartman Institute and Helsinki University Central Hospital, Biomedicum Helsinki, PO Box 63, 00014 University of Helsinki, Finland.
authors.forename: Marianne
authors.initials: M
authors.lastname: Tiainen
authors.forename: Kari
authors.initials: K
authors.lastname: Vaahtomeri
authors.forename: Antti
authors.initials: A
authors.lastname: Ylikorkala
authors.forename: Tomi P
authors.initials: TP
authors.lastname: Mäkelä
mesh_terms: D000091162:AMP-Activated Protein Kinase Kinases; D000818:Animals; D019556:COS Cells; D002453:Cell Cycle / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D019938:Cyclin D1 / Q000502:physiology; D019927:Cyclin E / Q000502:physiology; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D009154:Mutation; D010770:Phosphotransferases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000502:physiology; D015854:Up-Regulation
chemical_list: D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D016159:Tumor Suppressor Protein p53; D019938:Cyclin D1; D010770:Phosphotransferases; D017346:Protein Serine-Threonine Kinases; C109790:STK11 protein, human; D000091162:AMP-Activated Protein Kinase Kinases