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 Ser431. We present pharmacological and genetic evidence that p90RSK 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. Ser431 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 Cys433. Our data suggest that phosphorylation of LKB1 at Ser431 does not affect farnesylation and that farnesylation does not affect phosphorylation at Ser431. Phosphorylation of LKB1 at Ser431 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 Ser431 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. 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 Ser431. We present pharmacological and genetic evidence that p90RSK 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. Ser431 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 Cys433. Our data suggest that phosphorylation of LKB1 at Ser431 does not affect farnesylation and that farnesylation does not affect phosphorylation at Ser431. Phosphorylation of LKB1 at Ser431 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 Ser431 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. cAMP-dependent protein kinase p90 ribosomal S6 kinase mitogen- and stress-activated protein kinase-1 p70 ribosomal S6 kinase extracellular signal-regulated kinase mitogen-activated protein kinase embryonic stem epidermal growth factor 12-O-tetradecanoylphorbol-13-acetate 2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)propane-1,3-diol cAMP response element-binding protein glutathioneS-transferase Dulbecco's modified Eagle's medium 3-phosphoinositide-dependent protein kinase glycogen synthase kinase-3 matrix-assisted laser desorption/ionization time-of-flight protein kinase B protein kinases similar to PKA, PKG, and PKC Peutz-Jeghers syndrome is an autosomal dominantly inherited disorder that predisposes to a wide spectrum of benign and malignant tumors (1Hemminki A. Cell. Mol. Life Sci. 1999; 55: 735-750Crossref PubMed Scopus (177) Google Scholar, 2Westerman A.M. Entius M.M. de Baar E. Boor P.P. Koole R. van Velthuysen M.L. Offerhaus G.J. Lindhout D. de Rooij F.W. Wilson J.H. Lancet. 1999; 353: 1211-1215Abstract Full Text Full Text PDF PubMed Scopus (123) Google Scholar). It is caused by mutation of a widely expressed protein kinase of unknown function termed LKB1 (also known as STK11) (3Hemminki A. Markie D. Tomlinson I. Avizienyte E. Roth S. Loukola A. Bignell G. Warren W. Aminoff M. Hoglund M. R. W. S. de A. PubMed Scopus Google Scholar, W. S. R. W. M. PubMed Scopus Google Scholar). to LKB1, of which be to LKB1 that LKB1 is to function in cells as a tumor and with of LKB1 in a of tumor cell to suppress cell growth by a cell M. A. Sci. S. A. 1999; PubMed Scopus Google Scholar). is known the mechanism by which LKB1 activity is regulated in and LKB1 LKB1 is a protein a kinase that is to The a A. S. A. Mol. 1999; PubMed Scopus Google and a putative A. M. 1999; PubMed Scopus Google Scholar). of LKB1, but putative with to E. Full Text Full Text PDF PubMed Scopus Google and with to LKB1 and in the kinase Google Scholar). In an protein kinase in the to a of LKB1 was to be at Ser431 by the cAMP-dependent protein kinase PubMed Scopus Google Scholar). Ser431 of LKB1 lies in the is which is in known LKB1 and did not full-length or endogenously expressed LKB1 was at Ser431 in response to that cAMP-dependent protein kinase or the that this phosphorylation in LKB1 to suppress cell growth. Ser431 lies in the phosphorylation by a group of kinases to PKA, p90 ribosomal S6 kinase mitogen- and protein kinase and p70 ribosomal S6 kinase M. PubMed Scopus Google Scholar, PubMed Scopus Google Scholar, M. PubMed Scopus Google that to the kinase p90RSK is in cells by growth and and by ERK1/2 M. S. Mol. Cell. 1999; PubMed Scopus Google is in by of ERK1/2 and the and M. PubMed Scopus Google Scholar). is in by growth a and by and a A. G. 1999; PubMed Scopus Google Scholar). Ser431 is the of LKB1, and the that Ser431 in LKB1 The Ser431 lies the of the protein in a known as the which the prenylation of E. Full Text PDF PubMed Google Scholar, PubMed Scopus Google Scholar). the is in of and and PubMed Scopus Google that a of LKB1, in 293 was prenylated at Cys433. did not full-length LKB1 was prenylated by addition of a or a farnesyl to or prenylation of LKB1 was LKB1 to suppress the growth of cells. Here, we that and phosphorylate full-length LKB1 at Ser431 in We that agonists that activate kinases in Rat-2 cells and embryonic stem cells the phosphorylation of LKB1 at Ser431. 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We that the of of wild-type was to that of and We and to protein kinases and the p53 tumor suppressor that was in by wild-type LKB1, but not by a mutant The to which p53 was by wild-type was similar to that to which was by and protein kinases phosphorylate but not in is to p53 is a this was the of an LKB1 In we demonstrate that stimulation of Rat-2 cells with and did not affect the to which the LKB1 cells or the to which that the of LKB1, into is prenylated and at cell PubMed Scopus Google of full-length LKB1 expressed in cell that LKB1 is expressed in the and at the M. A. Sci. S. A. 1999; PubMed Scopus Google Scholar, A. M. 1999; PubMed Scopus Google Scholar). endogenously expressed LKB1 is associated with cell we and of Rat-2 cells or Rat-2 cells with or amount of protein and protein was with LKB1, LKB1 at prenylated and was in the was in the LKB1 was in the was a but amount of LKB1 associated with the of Rat-2 cells with and did not alter the amount of LKB1 at the but phosphorylation of LKB1 at Ser431 was in the and not in the full-length LKB1 expressed in cells was we 293 cells with wild-type The cells were with in and was with an and was as a and were that were prenylated and expressed in 293 cells were to the as wild-type LKB1, that phosphorylation of LKB1 at not affect prenylation of mutant of LKB1 in which the predicted to be a of LKB1 was mutated to Ala was not that is to be the of and M. A. Sci. S. 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In and we demonstrate that was at growth of cells as wild-type LKB1, that the prenylation of LKB1 is not to suppress the growth of cells. prenylation was LKB1 to be at we 293 cells with wild-type and mutant of cells with to activate p90RSK or to activate induced phosphorylation of wild-type LKB1 and the we that and induced phosphorylation of but not of itself and p53 in to the as wild-type that prenylation of LKB1 is not the activity of the We to the LKB1 and to to was modified by farnesylation or the be in the as we to 293 cells wild-type LKB1, and with and to the Cys433. that phosphorylation of wild-type LKB1 and mutant but not mutant LKB1 was with and the were by a of were wild-type and mutant LKB1 cells the phosphorylation of of wild-type termed at as in and the termed at to the that is at Ser431 and in which is of the of of LKB1 with to with The of this by is predicted this is and was at the of not was the this the the as was not of this was as with the predicted of the that is at Ser431 and in which the to is an was in the wild-type LKB1, but was not in the and The of is to that of the of LKB1 that is at at of this with this and was the of not the that is not not be to to the and an of In the adjacent to in wild-type LKB1, the of LKB1 that is at with a of of was of the of this is that we Ser431 as an in phosphorylation in In of a of in the phosphorylation of LKB1, we that stimulation of Rat-2 cells and embryonic stem cells with an of PKA, induced the phosphorylation of LKB1 at that this was by induced the phosphorylation of and this is to be mediated by is by of kinase-1 and an of p90RSK and but not by of that We this by in cell and in an cell line PubMed Scopus Google p90RSK in cells and still induced the phosphorylation of LKB1 at Ser431 and that this phosphorylation was by and but not by In contrast, in a cell line A. van Full Text Full Text PDF PubMed Scopus Google in which ERK1/2 and but not this to phosphorylation of LKB1 at Ser431 the pharmacological and genetic data that we in Rat-2 and which in a or in the phosphorylation of LKB1 at Ser431 in response to agonists that activate LKB1 in at an p90RSK or but at an p90RSK that is a of p90RSK activity in cells with activity M. 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A. 1999; PubMed Scopus Google Scholar). is that LKB1 a and the expressed a of We that of that we the p53 tumor suppressor was by LKB1 293 at a mutant of in which a mutated was to phosphorylate p53 p53 was in by LKB1 Rat-2 cells. phosphorylation of p53 in the of but not with that LKB1 is in the of suggest that LKB1, a was the p53 in expressed in E. expressed in 293 did not phosphorylate itself or p53 not that the expressed is or that LKB1 expressed in cells or with a that to p53 is a The that LKB1 or activity p53 was not mutation of Ser431 to or or phosphorylation of Ser431 in that phosphorylation of not the activity of LKB1 mechanism by which phosphorylation of Ser431 LKB1 function be to alter or to to with a or a to a prenylation and phosphorylation of Ser431 prenylation of of LKB1 expressed as an protein was to be but was not in this full-length LKB1 was prenylated PubMed Scopus Google Scholar). We that full-length LKB1, in 293 is but that a mutant of LKB1 in which the predicted farnesyl is mutated to Ala is not prenylated B and and prenylated to a similar as wild-type LKB1 this that phosphorylation of LKB1 at Ser431 not affect prenylation of this which is prenylated and at the of that a of LKB1 in Rat-2 cells was associated with the stimulation of cells with or to phosphorylation of Ser431 did not alter the amount of LKB1 present in the of cells. of the LKB1 was in the of phosphorylation of LKB1 was stimulation of cells with and In contrast, induced of LKB1 associated with cell be LKB1 was a p90RSK and It is that and LKB1 but LKB1 be by a protein the of LKB1 be associated with protein that at Ser431. is evidence that P.P. S. PubMed Scopus Google Scholar, P.P. Sci. Full Text PDF PubMed Scopus Google as as p90RSK M. S. Mol. Cell. 1999; PubMed Scopus Google Scholar, Cell. 1999; PubMed Scopus Google Scholar, D. E. M. 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We and that mutation of Ser431 to Ala or greatly the of LKB1 to suppress the growth of cells is similar to in this is that mutation of Ser431 to is not to phosphorylation of LKB1 at this It cannot be that the phosphorylation and of Ser431 LKB1 to suppress growth. The that LKB1 is a of p90RSK and is and is to that of the of p90RSK and cell and be mediated phosphorylation of The that prenylation of LKB1 is not to suppress the growth of cells that farnesylation of LKB1 of of LKB1 a in inhibiting the function of LKB1 in mutant of LKB1 that is not prenylated still phosphorylate itself and p53 to a similar as wild-type LKB1 and is still at Ser431 in cells in response to agonists that activate and p90RSK as of LKB1 that is expressed in 293 cells is prenylated is not to or not prenylation of LKB1 LKB1 as be to a of LKB1 that was to a to this It is that prenylation the of LKB1, the of LKB1, or with a or In the be not to the function of phosphorylation of LKB1 at but to the that farnesylation of in LKB1 to cell We R. the and of We the of Life of
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