Discrete GPCR-triggered endocytic modes enable β-arrestins to flexibly regulate cell signaling

{beta}-arrestins are master regulators of cellular signaling that operate by desensitizing ligand-activated G protein-coupled receptors (GPCRs) at the plasma membrane and promoting their subsequent endocytosis. The endocytic activity of {beta}-arrestins is ligand-dependent, triggered by GPCR binding, and increasingly recognized to have a multitude of downstream signaling and trafficking consequences that are specifically programmed by the bound GPCR. However, only one biochemical mode for GPCR-mediated triggering of the endocytic activity is presently known- displacement of the {beta}-arrestin C-terminus (CT) to expose CCP-binding determinants that are masked in the inactive state. Here we revise this view by uncovering a second mode of GPCR-triggered endocytic activity that is independent of the {beta}-arrestin CT and, instead, requires the cytosolic base of the {beta}-arrestin C-lobe (CLB). We further show each of the discrete endocytic modes is triggered in a receptor-specific manner, with GPCRs that bind {beta}-arrestin transiently ( class A) primarily triggering the CLB-dependent mode and GPCRs that bind more stably ( class B) triggering both the CT and CLB-dependent modes in combination. Moreover, we show that each mode has opposing effects on the net signaling output of receptors- with the CLB-dependent mode promoting rapid signal desensitization and the CT-dependent mode enabling prolonged signaling. Together, these results fundamentally revise understanding of how {beta}-arrestins operate as efficient endocytic adaptors while facilitating diversity and flexibility in the control of cell signaling.