FIGURE 4.

Arrestin-3 enhances MKK7-dependent phosphorylation of endogenous JNK1/2 in intact cells. A, a representative Western blot (IB) showing phosphorylation of endogenous JNK1/2 isoforms with or without arrestin-3 in COS-7 cells expressing varying amounts of MKK7. B, quantification of phosphorylation of JNK p46H and p54 isoforms with or without arrestin-3. Analysis of covariance with Arr3 as factor and MKK7 concentration as co-variate showed a significant effect of MKK7 concentration on the level of p46H and p54 phosphorylation (p < 0.0001). The presence of Arr3 significantly affected the level of p46H, but not p54, phosphorylation across MKK7 concentrations (F(1,38) = 8.592; p = 0.0057). Significant Arr3 × MKK7 interaction (p = 0.0335 for p46H and p < 0.0001 for p54) indicated a difference in slopes due to co-expression of arrestin-3. *, −p < 0.05 to −Arr3; Student's t test for individual points.