β-arrestin mediates communication between plasma membrane and intracellular GPCRs to regulate signaling

Abstract

It has become increasingly apparent that G protein-coupled receptor (GPCR) localization is a master regulator of cell signaling. However, the molecular mechanisms involved in this process are not well understood. To date, observations of intracellular GPCR activation can be organized into two categories: a dependence on OCT3 cationic channelpermeable ligands or the necessity of endocytic trafficking. Using CXC chemokine receptor 4 (CXCR4) as a model, we identified a third mechanism of intracellular GPCR signaling. We show that independent of membrane permeable ligands and endocytosis, upon stimulation, plasma membrane and internal pools of CXCR4 are post-translationally modified and collectively regulate EGR1 transcription. We found that β-arrestin-1 (arrestin 2) is necessary to mediate communication between plasma membrane and internal pools of CXCR4. Notably, these observations may explain that while CXCR4 overexpression is highly correlated with cancer metastasis and mortality, plasma membrane localization is not. Together these data support a model were a small initial pool of plasma membrane-localized GPCRs are capable of activating internal receptordependent signaling events.3 While extracellular inputs, cell membrane receptors, and resulting transcriptional programs are diverse, many receptor-signaling events converge to a reduced number of signaling hubs. Cellular mechanisms that mediate this process as well as strategies to control these actions remain outstanding questions. Over the last decade, we have learned that GPCR spatiotemporal signaling is one mechanism used by cells to translate diverse environmental information into actionable intracellular decisions while using seemingly redundant signaling cascades 1 . Extensive research has illustrated that GPCRs elicit distinct signaling events at different plasma membrane micro-domains as well as endocytic compartments that are important for cell physiology and disease pathogenesis [1][2][3][4][5][6][7][8][9] . These studies support a model where the location, in addition to magnitude, of a signaling event is important for cellular decision-making. Others have shown that GPCR site-specific post-translational modifications (PTMs) modulate adaptor protein recruitment, GPCR localization, and consequently receptor signaling events 10-12 .Together these observations motivated us to reexamine some confounding observations pertaining to the relationship of receptor localization, PTM, and signaling for CXCR4.CXCR4 is a type 1 GPCR that regulates a variety of biological processes such as cell migration, embryogenesis, and immune cell homeostasis 10,[13][14][15][16] . It is deregulated in 23 different cancers and overexpression is often correlated with metastasis and mortality 17-21 . However, surprisingly, plasma membrane expression is not correlated with metastasis 21 and in some cancer tumor specimens as well as cell culture models, samples with poor CXCR4 plasma membrane localization remain responsive to CXCR4 agonist 22-26 . CXCR4 is activated by a highly rec...

Deciphering the signaling mechanisms of β‐arrestin1 and β‐arrestin2 in regulation of cancer cell cycle and metastasis

“…This communication was found to be mediated by β‐arr1 between the membrane receptor and internal pools of CXCR4. Additionally, this implies that overexpression of CXCR4 is strongly associated with cancer metastasis and death, regardless of the localization of the plasma membrane (DeNies et al, 2020). In solid tumor progression, angiogenesis is stimulated by proangiogenic agents produced by the tumor such as thrombin and PG, which act on GPCRs, namely PAR1, S1PR, CXCR4, and CXCR7 cause the stimulation and release of MMPs, VEGF, and FGF which are the angiogenic mediators.…”