MAP3K4 and lipoprotein glomerulopathy: GADD45B interacts with MAPK upstream kinase MTK1/MEKK4, leading to the activation of p38 or c-jun N-terminal kinase signaling pathways.10, 11 MAPKs are known to have crucial roles in the progression of various glomerulopathies, and their inhibition is emerging as a promising therapeutic area for renal diseases.12 We found that GADD45B overexpression induced phosphorylation of p38 MAPK in podocytes (0.75±0.09 versus 0.37±0.10 normal control, P=0.008) (Figures 8d and e), but had no effect on activation of JNK and ERK phosphorylation (Figures 8d, f and g).