Figure 6. β-arrestin-2 binds to BiP and promotes its polyubiquitination and degradation. (A) A co-immunoprecipitation assay revealed that β-arrestin-2 bound directly to BiP in LPS-stimulated cells. (B) An immunofluorescence assay demonstrated the colocalization of β-arrestin-2 and BiP in IEC-6 cells. (C) An immunofluorescence assay identified cells that were double-positive for β-arrestin-2 and BiP in NEC mouse intestinal specimens. (D) Salmeterol time-dependently improved the binding between β-arrestin-2 and BiP, and also increased apoptotic marker expression. (E) BiP mRNA expression was not significantly influenced by β-arrestin-2 overexpression. (F) β-arrestin-2 increased the ubiquitination of BiP in a dose-dependent manner in LPS-stimulated cells. (G) The ubiquitin-proteasome inhibitor MG132 increased BiP protein levels when β-arrestin-2 was overexpressed.