Functional correlates of mutations in beta-catenin exon 3 phosphorylation sites.
beta-Catenin-mediated signaling can be constitutively activated by truncation or mutation of serine and threonine residues in exon 3. Mutations in this region are observed in many human tumors. Examination of the locations of these mutations reveals interesting patterns; specifically, Ser45 and Thr41 appear more frequently in malignant tumors, and Ser37 and Ser33 are more common in benign entities. To test whether these patterns represent functional differences in beta-catenin signaling mechanisms, we generated mutations of each of these residues. Stable transformation of Madin-Darby canine kidney cells showed a transformed phenotype with each of the four mutations, as assessed by growth in soft agar and collagen. Functional assays including proliferation assays, cell shedding assays, and wounding assays demonstrated two groups. Ser45 and Thr41 represent a more transformed phenotype, whereas Ser37 and Ser33 behaved similarly to the vector in these assays. Assessment of downstream genes demonstrated increased activation of the beta-catenin target gene cyclin D1 by Ser45. Finally, we examined the kinase activity of I kappa B kinase-alpha and found that this kinase, unlike glycogen synthase kinase-3 beta, appears to preferentially phosphorylate Ser45 and Thr41, independent of priming by casein kinase-1. We conclude that these sites may represent an alternative (non-wnt) signaling pathway, which may be inappropriately activated in tumors with mutations of these residues.
Provost
Elayne
E
Department of Pathology, Yale University School of Medicine, New Haven, Connecticut 06520-8023, USA.
Yamamoto
Yumi
Y
Lizardi
Isabel
I
Stern
Jessica
J
D'Aquila
Thomas G
TG
Gaynor
Richard B
RB
Rimm
David L
DL
D000818:Animals; D019556:COS Cells; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004285:Dogs; D005091:Exons; D051550:I-kappa B Kinase; D009154:Mutation; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D013912:Threonine / Q000378:metabolism; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051176:beta Catenin
D003598:Cytoskeletal Proteins; D015534:Trans-Activators; D051176:beta Catenin; D013912:Threonine; D012694:Serine; D017346:Protein Serine-Threonine Kinases; D051550:I-kappa B Kinase