Figure 1.

CYT-1 was degraded through both proteasomal and lysosomal pathways. A) Protein stability of full-length ErbB4 (180 kDa) and the 80-kDa ICD was measured by immunoblotting (IB) with anti-ErbB4 antibody at different time points after PMA administration. CYT-1 ICD was rapidly degraded 45 min after PMA-induced cleavage, while CYT-2 ICD levels remained relatively stable. B) The proteasome inhibitor, lactacystin, inhibited CYT-1 ICD degradation but had minimal effects on CYT-2 ICD level. C) The lysosome inhibitor, chloroquine, inhibited CYT-1 ICD degradation only at relatively late time points. D) Administration of the protein synthesis inhibitor, cytoheximide (CHX), decreased CYT-1 expression level. E) Simultaneous administration of lactacystin with CHX inhibited CYT-1 degradation, especially the 80-kDa ICD fragment.