Differential Subcellular Localization of Threonine-120 Phosphorylated β-catenin in Human Prostate Cancer is a Novel Functional Marker
Cheng Du, Ph.D, Chuanyou Zhang, Ph D, K.C. Balaji, MD.
U Mass Med, Worcester, MA, USA.
We previously identified that Protein kinase D1 (PKD1) phosphorylated β-catenin, a critical protein in the regulation of cell proliferation, apoptosis, adhesion and migration. The phosphorylation sites were mapped to threonine-112 and -120. Mutation of the phosphorylation sites altered β-catenin subcellular localization, transcription activity, cell proliferation and migration. The aim of this study was to develop and evaluate a phospho-threonine antibody specifically targeting phospho-threonine-120 of β-catenin (pT120), and compare distribution of pT120 β-catenin in normal and malignant prostate tissues.
METHODS: We characterized the pT120 antibody by Western blot, peptide competition binding, immunofluoresence staining and immunohistochemistry. The tissue staining pattern of pT120 antibody was compared to a conventional β-catenin antibody, which characteristically stains β-catenin on plasma membrane of normal tissue
The pT120 antibody specifically recognizes pT120 β-catenin whose accumulation was dependent on PKD1 activity. In 16/22 (72%) of normal prostate tissues, the pT120 β-catenin is enriched at trans Golgi network (TGN). In contrast, only 15/200 (7.5%; p < 0.001) of prostate cancer samples had accumulation of pT120 β-catenin in TGN. A vast majority of cancer samples (92.5%) lacking of TGN staining showed the pT120 β-catenin distributed diffusely in cytoplasm, nucleus and plasma membrane.
T120 phosphorylated β-catenin distribution at TGN is significantly decreased in malignant prostate tissue compared to normal. The pT120 antibody is clearly more sensitive than conventional β-catenin antibodies in detecting alteration in subcellular distribution of β-catenin and can be used in studying prostate and other tissues and may facilitate risk stratification or predict disease outcomes.