title: LKB1 suppresses p21-activated kinase-1 (PAK1) by phosphorylation of Thr109 in the p21-binding domain.
abstract: The serine/threonine protein kinase LKB1 is a tumor suppressor gene mutated in Peutz-Jeghers syndrome patients. The mutations are found also in several types of sporadic cancer. Although LKB1 is implicated in suppression of cell growth and metastasis, the detailed mechanisms have not yet been elucidated. In this study, we investigated the effect of LKB1 on cell motility, whose acquisition occurs in early metastasis. The knockdown of LKB1 enhanced cell migration and PAK1 activity in human colon cancer HCT116 cells, whereas forced expression of LKB1 in Lkb1-null mouse embryonic fibroblasts suppressed PAK1 activity and PAK1-mediated cell migration simultaneously. Notably, LKB1 directly phosphorylated PAK1 at Thr(109) in the p21-binding domain in vitro. The phosphomimetic T109E mutant showed significantly lower protein kinase activity than wild-type PAK1, suggesting that the phosphorylation at Thr(109) by LKB1 was responsible for suppression of PAK1. Consistently, the nonphosphorylatable T109A mutant was resistant to suppression by LKB1. Furthermore, we found that PAK1 was activated in the hepatocellular carcinomas and the precancerous liver lesions of Lkb1(+/-) mice. Taken together, these results suggest that PAK1 is a direct downstream target of LKB1 and plays an essential role in LKB1-induced suppression of cell migration.
authors.affiliation: Department of Pharmacology, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan.
authors.forename: Atsuko
authors.initials: A
authors.lastname: Deguchi
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Miyoshi
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Kojima
authors.forename: Katsuya
authors.initials: K
authors.lastname: Okawa
authors.forename: Masahiro
authors.initials: M
authors.lastname: Aoki
authors.forename: Makoto M
authors.initials: MM
authors.lastname: Taketo
mesh_terms: D000091162:AMP-Activated Protein Kinase Kinases; D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D002465:Cell Movement; D005260:Female; D006801:Humans; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009369:Neoplasms / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry* / Q000235:genetics; D015398:Signal Transduction; D013912:Threonine / Q000737:chemistry*; D054462:p21-Activated Kinases / Q000737:chemistry* / Q000235:genetics
chemical_list: D013912:Threonine; D017346:Protein Serine-Threonine Kinases; C109790:STK11 protein, human; D054462:p21-Activated Kinases; D000091162:AMP-Activated Protein Kinase Kinases
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