FIGURE 4.

β-Arrestin is required for SDF-1-induced cell signaling pathways activated by the CXCR4·CXCR7 complex. A, kinetics of SDF-1-induced ERK, p38 MAPK, and SAPK/JNK activation in cells expressing CXCR4/CXCR7 along with either nontargeting siRNA (nt siRNA) or β-arrestin2 targeting siRNA (βArr2 siRNA). Transfected cells were treated with 100 nm SDF-1 for 0, 5, 15, and 30 min. Cell lysates were subjected to Western immunoblot using phospho- and total ERK1/2, p38 MAPK, and SAPK/JNK antibodies. B, amount of ERK, p38 MAPK, and SAPK phosphorylation was quantified by densitometry and normalized by expressing the data as a ratio of the phosphorylated signal over the total signal. Results are expressed as a percentage of the maximum response at 5 min. Data represent means ± S.E. (n = 3). nt, nontargeting.