Gli2 has functional sites for PKA and GSK-3β phosphorylation. (A) NIH 3T3 cells were cotransfected with Gli2 and empty vector, PKA, GSK-3β or both and assayed for Gli-luciferase activity 48 h later. (B Upper) Immunoprecipitated myc-Gli2 was incubated in 40 mM Tris·HCl (pH 7.4), 20 mM magnesium acetate, and 0.2 mM [γ-32P]ATP (1 μCi/μmol) (control), with 10 units of PKA catalytic subunit or with PKA and 10 units of protein kinase inhibitor (PKI) for 30 min at 30°C. Beads were washed with 50 mM Tris·HCl (pH 7.5) and subjected to 5% SDS/PAGE and autoradiography. (B Lower) myc-Gli2 was incubated in 20 mM Tris·HCl (pH 7.5), 10 mM MgCl2, 5 mM DTT, and 200 μM [γ-32P]ATP (1 μCi/μmol) without (control) or with 500 units of GSK-3β for 30 min at 30°C, or Gli2 was phosphorylated first with PKA and cold ATP, as described above, followed by 10 units of PKI, 500 units of GSK-3β, and 200 μM [γ-32P]ATP and incubated for 30 min. Beads were processed as before. (C) Sequence of the Gli2 peptides corresponding to the four clusters with the conserved PKA and GSK-3β phosphorylation sites highlighted in boxes. (D) Phosphorylation of peptides shown in C and variant peptides in which each candidate residue was substituted by alanine. Peptides (1 mM) were treated with PKA and GSK-3β or both enzymes sequentially, as described for Gli2 in B. Reactions then were stopped by spotting onto P81 paper and washed with 50 mM H3PO4, and 32P incorporation was determined by liquid scintillation. PKA phosphorylation of kemptide was taken as 100%. (E) Gli2 WT, Gli2 PSM, and Gli2 GSM were expressed in 293 cells, immunoprecipated with Xpress antibody, and used as substrates for phosphorylation by PKA and GSK-3β as described in B. Phosphorylation and expression were assayed by autoradiography (Autorad.) and Western blot (WB) (Xpress Ab 1:5,000). Densitometric analysis of three experiments is shown in the graph. (F) Intact 293 cells were transfected with Gli2 WT or Gli2 PSM, labeled with [32P]orthophosphate, and stimulated with 10 μM forskolin for 2 h. Gli2 was immunoprecipitated with Xpress Ab, and 32P incorporation was determined by autoradiography. Quantification by densitometry of three experiments was performed by using the basal level of phosphorylation of Gli2 WT as 100%.