solution to a final concentration of 20 nM prior to blotting. A commercial b-catenin antibody was used for comparison at 1:2000 dilution. The phospho-S33/S37/T41 bcatenin antibody was used at dilution of 1:200 for western blot. Monoclonal 9720791 antibody 8E7 that recognizes unphosphorylated S37/T41 b-catenin was used at 1:800 for blotting. The HA-tagged wild type b-catenin in pCS2 mammalian expression vector, T120I and T102I/T112R/T120I mutants were described previously. The shRNA constructs targeting PKD1 were purchased from Open Biosystems/Thermo Scientific. Human recombinant Wnt-3a was purchased from R&D Systems and used at 50 ng/ml in cell culture. Materials and Methods Development of the pT120 antibody An antigen peptide correspondent to the b-catenin T120 region, 109-IPSTQFDAAHPpTNVQRLAEPSQML was synthesized. The peptide was injected into two rabbits to raise antisera. A corresponding nonphospho-peptide was also synthesized for antibody screening and purification. The peptide synthesis and antibody generation was performed by commercial contractor Millipore. Cell cultures, treatment and Topflash assay Prostate cancer cell lines LNCaP C42 and a benign prostate hyperplastic epithelial cell line BPH-1 
were cultured in RPMI1640 medium plus 10% bovine fetal serum. C4-2 cells that stably express PKD1-GFP was previously described. Normal prostate epithelial cell line RWPE-1 was maintained in Keratinocyte Serum Free Medium and supplied with bovine pituitary extract and human recombinant epidermal growth factor. Mouse NIH 3T3 cell line was cultured in DMEM medium with 10% FBS. Transient transfection was performed by Lipofectamine 2000 reagent overnight. Topflash assay conditions were described previously. HC030031 Briefly, LNCaP cells were transfected by 50 ng Topflash reporter, 5 ng Renilla luciferase vector and 100 ng either PKD1 expression vector or empty vector ” control for overnight. Luciferase activity was measured 2 days later. Relative luciferase activity was obtained by averaging of normalized firefly luciferase activities from three samples. Normalization was performed with Renilla luciferase from Promega. Western blotting and protein sample preparation To prepare whole cell lysates, cells cultured on monolayer were washed by phosphoate buffered saline and dissolved in RIPA buffer plus protease inhibitor cocktail. For fractionation experiments, a commercial cell fractionation kit was used according to manufacturer’s recommendation. Briefly, cultured cells were collected by scratching and washed with PBS plus a protease inhibitor cocktail and a phosphatase inhibitor cocktail. Cell pellet was resuspended in 250 microliter of a hypotonic buffer and homogenized with a plastic pestle. After incubation 15 min on ice, cells were centrifuged at 8,0006g for 5 min. The supernatant was collected and centrifuged again at 16,0006g for 10 min and supernatant is used as soluble cytosol fraction. The initial pellet was washed with a wash buffer, spinned down, resuspended in 125 microliter of Nuclear Buffer 3 and homogenized. After incubating on ice for 30 min, the lysate was centrifuged at 16,0006g for 10 min. The supernatant Immunofluorescence and immunohistochemistry For immunofluorescence, cultured cells were fixed in 5% formalin in PBS for 10 minutes at room temperature. Human normal prostate tissues were deparafinized and rehydrated. The pT120 and H102 antibodies were diluted 2000-fold in PBS with 0.1% Triton X-100 and 10 mg/ml BSA. Antibody to transGolgi
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