Sequence variants of the axin gene in breast, colon, and other cancers: an analysis of mutations that interfere with GSK3 binding.
Axin is a recently discovered component of a multiprotein complex containing APC, beta-catenin, GSK3, and PP2A, which functions in the degradation of the beta-catenin protein. As part of WNT signal transduction, the function of the Axin complex is inhibited, leading to the accumulation of beta-catenin. The inappropriate stabilization of beta-catenin has been implicated in a range of human tumors. Two oncogenic mechanisms leading to beta-catenin stabilization are the loss of the APC tumor suppressor protein and the mutational activation of beta-catenin, such that the Axin/APC complex can no longer regulate it. Studies in Drosophila and mammalian tissue culture showed loss of Axin function interfered with beta-catenin turnover and activated beta-catenin/TCF-dependent transcription. Based on these observations, Axin was screened for mutations in a range of human tumor cell lines and primary breast tumor samples. We identified two sequence variants causing amino acid substitutions in four colon cancer cell lines, a Ser-to-Leu at residue 215 in LS513 and a Leu-to-Met at residue 396 in HCT-8, HCT-15, and DLD-1. The Axin L396M mutation was selected for further study since it lay within a region that was shown to interact with glycogen synthase kinase-3. Biochemical and functional studies showed that the L396M change interfered with Axin's ability to bind GSK3. Interestingly, this mutation and a neighboring L392M change differentially altered Axin's ability to interfere with two upstream activators of TCF-dependent transcription, Frat1 and Disheveled.
Webster
M T
MT
Developmental Biology, Section of Cell Biology and Experimental Pathology, Toby Robins Breakthrough Breast Cancer Research Centre, Institute of Cancer Research, London, England.
Rozycka
M
M
Sara
E
E
Davis
E
E
Smalley
M
M
Young
N
N
Dale
T C
TC
Wooster
R
R
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D060466:Axin Protein; D001483:Base Sequence; D001943:Breast Neoplasms / Q000235:genetics*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics*; D003110:Colonic Neoplasms / Q000235:genetics*; D005260:Female; D014644:Genetic Variation; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D006801:Humans; D007930:Leucine / Q000235:genetics; D008297:Male; D008715:Methionine / Q000235:genetics; D008869:Microtubule-Associated Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D010051:Ovarian Neoplasms / Q000235:genetics; D011485:Protein Binding; D011506:Proteins / Q000235:genetics*; D012097:Repressor Proteins; D014407:Tumor Cells, Cultured
D060466:Axin Protein; D008869:Microtubule-Associated Proteins; D011506:Proteins; D012097:Repressor Proteins; D008715:Methionine; D038341:Glycogen Synthase Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3; D007930:Leucine