title: Dual alterations in casein kinase I-epsilon and GSK-3beta modulate beta-catenin stability in hyperproliferating colonic epithelia.
abstract: Casein kinase I (CKI)-epsilon and GSK-3beta phosphorylate beta-catenin at Ser(45) (beta-cat(45)) and Thr(41)/Ser(37,33) (beta-cat(33,37,41)) residues, thereby facilitating its ubiquitination and proteasomal degradation. We used a Citrobacter rodentium-induced transmissible murine colonic hyperplasia (TMCH) model to determine Ser/Thr phosphorylation and biological function of beta-catenin during crypt hyperproliferation. TMCH was associated with 3-fold and 3.3-fold increases in CKI-epsilon cellular abundance and 2-fold and 1.8-fold increase in its activity at 6 and 12 days after infection, respectively. beta-Catenin coimmunoprecipitated with both cellular and nuclear CKI-epsilon and cellular axin at these time points. Cellular beta-catenin was constitutively phosphorylated at Ser(45) and underwent subcellular redistribution to cytoskeletal and nuclear fractions at days 6 and 12 of TMCH, respectively. beta-cat(33,37,41), however, exhibited only subtle changes in either phosphorylation status or subcellular distribution even after blocking proteasomal degradation in vivo. Interestingly, GSK-3beta underwent increased phosphorylation at Ser(9), leading to 40% and 70% decreases in its activity at these time points, respectively. Coimmunoprecipitation studies exhibited strong association of GSK-3beta with PKC-zeta at either time point. Cellular beta-cat(45) stabilized and, along with unphosphorylated beta-catenin, underwent nuclear translocation, associated with nuclear accumulated Tcf-4 and cAMP response element binding protein binding protein, and was significantly acetylated, leading to increases in DNA binding. Priming of beta-catenin at Ser(45) exists in vivo. However, beta-cat(45) does not necessarily enter the degradation pathway. Impairment in linking beta-cat(45) to subsequent GSK-3beta-mediated phosphorylation and degradation may account for increased steady-state levels of both unphosphorylated as well as Ser(45)-phosphorylated beta-catenin, which may be causally linked to increases in cell census during TMCH.
authors.affiliation: Div of Gastroenterology, Univ of Texas Medical Branch, Galveston, TX 77555-0632, USA. shumar@utmb.edu
authors.forename: Shahid
authors.initials: S
authors.lastname: Umar
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Morris
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Sellin
mesh_terms: D000818:Animals; D060466:Axin Protein; D001897:Boronic Acids / Q000494:pharmacology; D000069286:Bortezomib; D048149:Casein Kinase 1 epsilon / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D044082:Citrobacter rodentium / Q000254:growth & development; D003106:Colon / Q000378:metabolism* / Q000473:pathology; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004756:Enterobacteriaceae Infections / Q000378:metabolism / Q000382:microbiology; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006965:Hyperplasia; D047468:Immunoprecipitation; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D010766:Phosphorylation / Q000187:drug effects; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism; D011719:Pyrazines / Q000494:pharmacology; D012097:Repressor Proteins / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D051820:TCF Transcription Factors / Q000378:metabolism; D013912:Threonine / Q000378:metabolism; D058118:Transcription Factor 7-Like 2 Protein; D051176:beta Catenin / Q000378:metabolism*; D000099221:Protein Kinase C zeta
chemical_list: D060466:Axin Protein; D001897:Boronic Acids; D000069286:Bortezomib; D048149:Casein Kinase 1 epsilon; D017362:Cyclic AMP Response Element-Binding Protein; D004247:DNA; D038362:Glycogen Synthase Kinase 3; D000071679:Glycogen Synthase Kinase 3 beta; D011480:Protease Inhibitors; D046988:Proteasome Endopeptidase Complex; D061988:Proteasome Inhibitors; D011493:Protein Kinase C; D011719:Pyrazines; D012097:Repressor Proteins; D012694:Serine; D051820:TCF Transcription Factors; D013912:Threonine; D058118:Transcription Factor 7-Like 2 Protein; D051176:beta Catenin; D000099221:Protein Kinase C zeta; C544895:Tcf7l2 protein, mouse; C000605507:Gsk3b protein, mouse