Phosphorylation of the protein kinase mutated in Peutz-Jeghers cancer syndrome, LKB1/STK11, at Ser431 by p90(RSK) and cAMP-dependent protein kinase, but not its farnesylation at Cys(433), is essential for LKB1 to suppress cell vrowth.
Peutz-Jeghers syndrome is an inherited cancer syndrome that results in a greatly increased risk of developing tumors in those affected. The causative gene is a protein kinase termed LKB1, predicted to function as a tumor suppressor. The mechanism by which LKB1 is regulated in cells is not known. Here, we demonstrate that stimulation of Rat-2 or embryonic stem cells with activators of ERK1/2 or of cAMP-dependent protein kinase induced phosphorylation of endogenously expressed LKB1 at Ser(431). We present pharmacological and genetic evidence that p90(RSK) mediated this phosphorylation in response to agonists that activate ERK1/2 and that cAMP-dependent protein kinase mediated this phosphorylation in response to agonists that activate adenylate cyclase. Ser(431) of LKB1 lies adjacent to a putative prenylation motif, and we demonstrate that full-length LKB1 expressed in 293 cells was prenylated by addition of a farnesyl group to Cys(433). Our data suggest that phosphorylation of LKB1 at Ser(431) does not affect farnesylation and that farnesylation does not affect phosphorylation at Ser(431). Phosphorylation of LKB1 at Ser(431) did not alter the activity of LKB1 to phosphorylate itself or the tumor suppressor protein p53 or alter the amount of LKB1 associated with cell membranes. The reintroduction of wild-type LKB1 into a cancer cell line that lacks LKB1 suppressed growth, but mutants of LKB1 in which Ser(431) was mutated to Ala to prevent phosphorylation of LKB1 were ineffective in inhibiting growth. In contrast, a mutant of LKB1 that cannot be prenylated was still able to suppress the growth of cells.
Sapkota
G P
GP
Medical Research Council Protein Phosphorylation Unit, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland.
Kieloch
A
A
Lizcano
J M
JM
Lain
S
S
Arthur
J S
JS
Williams
M R
MR
Morrice
N
N
Deak
M
M
Alessi
D R
DR
D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases; D000818:Animals; D001665:Binding Sites; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002455:Cell Division; D002460:Cell Line; D003001:Cloning, Molecular; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D003545:Cysteine / Q000737:chemistry*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D007546:Isoquinolines / Q000494:pharmacology; D008798:Mevalonic Acid / Q000494:pharmacology; D051379:Mice; D008954:Models, Biological; D009154:Mutation; D010580:Peutz-Jeghers Syndrome / Q000235:genetics*; D010766:Phosphorylation; D011233:Precipitin Tests; D017368:Protein Prenylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D051381:Rats; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D012694:Serine / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013449:Sulfonamides; D013997:Time Factors; D014162:Transfection
D004791:Enzyme Inhibitors; D007546:Isoquinolines; D013449:Sulfonamides; D005576:Colforsin; D012694:Serine; D004815:Epidermal Growth Factor; D000242:Cyclic AMP; D005982:Glutathione Transferase; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C109790:STK11 protein, human; C491654:Stk11 protein, mouse; C116919:mitogen and stress-activated protein kinase 1; D017868:Cyclic AMP-Dependent Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases; D003545:Cysteine; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D008798:Mevalonic Acid