Figure 4

p38β specifically activates C/EBPβ-binding to the atrogin1/MAFbx promoter. (A) C2C12 myoblasts were transfected with a plasmid encoding constitutively active p38α, p38β or the empty vector (control). After differentiation, ChIP assay was carried out to evaluate C/EBPβ binding in myotubes to a 190-base pair fragment of the atrogin1/MAFbx promoter that contains the previously identified C/EBPβ-responsive cis-enhancer element [17] using control and the target PCR primers. Pre-immune IgG used as the control to the antibody against C/EBPβ did not pull down the target fragment (data not shown). (B) C2C12 myoblasts were transfected with siRNA as indicated. After differentiation, myotubes were treated with LCM or control medium for 1 h and ChIP assay was carried out to evaluate C/EBPβ binding to the atrogin1/MAFbx promoter. ChIP, chromosome immunoprecipitation; LCM, Lewis lung carcinoma cell-conditioned medium.