Fig. 4. p38 is expressed and effectively inhibited by SB202190 in primary limb mesenchymal, G8 and C2C12 cells. Limb mesenchymal cultures, G8 and C2C12 cells express at least p38, as determined by western analysis using a pan-p38 and p38-specific antibodies (A). A band corresponding to a molecular weight of 42 kDa, consistent with the reported size of p38 isoforms, was observed with both antibodies. The expression of p38 in limb mesenchymal cultures does not noticeably change upon treatment with 10 µM SB202190. To control for loading all blots were subsequently incubated with an antibody against ß-actin. SB202190 effectively inhibits p38 activity in limb mesenchymal cultures (B) and G8 and C2C12 cells (C). Activity of a GAL4-CHOP fusion protein, measured by pG5-luc activity, is induced by co-transfection with MKK6E and p38 and ß in primary cultures and in G8 and C2C12 cultures (data shown only for MKK6E). This induction is attenuated by 10 µM SB202190 in all cell types.