β-arrestin2 regulates TRAIL-induced HepG2 cell apoptosis via the Src-extracellular signal-regulated signaling pathway

beta-arrestins, including beta-arrestin1 and beta-arrestin2, two ubiquitously expressed members of the arrestin family in various types of tissue, are adaptor proteins that modulate the desensitization and trafficking of seven membrane-spanning receptors. Recently, beta-arrestins have been shown to bind to numerous signaling molecules, including c-Src and mitogen-activated protein kinase family members. In addition, accumulating evidence has suggested that beta-arrestins are involved in the anti-apoptosis signaling pathway by associating with kinases, such as Akt and ERK, and altering their activities. However, the role of beta-arrestins in tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) -induced apoptosis remains unclear. In the present study, beta-arrestin2, but not beta-arrestin1, was observed to modulate TRAIL-triggered HepG2 cell apoptosis by regulating activation of the Src-extracellular signal-regulated kinase (ERK) signaling pathway. Using overexpression and RNA interference experiments, beta-arrestin2 was demonstrated to prevent TRAIL-induced HepG2 cell apoptosis. Additionally, beta-arrestin2 exerted an additive effect on TRAIL-induced activation of Src and ERK. Furthermore, downregulating beta-arrestin2 expression attenuated the TRAIL-induced activation of Src and ERK survival signaling and enhanced TRAIL-induced apoptosis. PP2, a pharmacological inhibitor of Src, reduced activation of the Src-ERK signaling pathway and enhanced TRAIL-induced HepG2 cell apoptosis. Co-immunoprecipitation experiments demonstrated a physical association between beta-arrestin2 and Src, and TRAIL stimulation resulted in enhanced quantities of the beta-arrestin2/Src complex. A notable interaction was identified between beta-arrestin2 and death receptors (DR) 4 and 5, but only in the presence of TRAIL stimulation. To the best of our knowledge, these findings are the first to demonstrate that beta-arrestin2 mediates TRAIL-induced apoptosis by combing with DRs and Src, and regulates the activation of Src-ERK signaling in HepG2 cells. It is hypothesized that the formation of a signaling complex comprising DR, beta-arrestin2 and Src is required for the action of TRAIL on HepG2 cell apoptosis, which provides a novel insight into analyzing the effects of beta-arrestin2 on protecting cells from TRAIL-induced apoptosis.