Maintenance of β-catenin mRNA levels is required for HD5 expression in response to FGF9. A, Caco2 cells were treated with the FGFR-3 ligand, FGF9 (50 ng/ml), for the times indicated, and total protein preparations were resolved by gel electrophoresis and Western blotted for total and phospho-ERK1/2 and total and phospho-GSK3β as described under “Materials and Methods.” B, Western blot for phospho-β-catenin (Ser31/33 and Thr41) and total β-catenin in total protein extracts from Caco2 cells treated with FGF9 (50 ng/ml) for 24 h in the presence or absence of the proteasome inhibitor, MG132, as described under “Materials and Methods.” The phosphorylation status of neither GSK3β nor β-catenin was altered in response to FGFR-3. C, β-catenin mRNA levels determined by quantitative real-time PCR in total RNA isolated from cells treated with FGF9 (50 ng/ml) for the times indicated. All values are the mean ± S.D. (error bars) of n = 4. D, β-catenin and HD5 mRNA expression levels in response to β-catenin shRNA were determined by quantitative real-time PCR in total RNA isolated from cells treated with FGF9 for 3 days. Values are the mean ± S.D. of n = 3.