Xiaobei Wang

Beta-arrestin 1 (ARRB1) is a multifunctional adaptor protein that regulates diverse signaling pathways beyond its canonical role in G-protein-coupled receptor desensitization. While ARRB1 has been implicated in cancer progression, its role in modulating host immunity against multiple myeloma (MM) remains unexplored. Here, we demonstrate that host ARRB1 deficiency significantly enhances anti-myeloma immunity and prolongs survival in a syngeneic murine MM model. Using Vk*MYC myeloma cells transplanted into wild-type and ARRB1 knockout mice, we show that ARRB1 deficiency in the host microenvironment promotes robust T cell infiltration and activation while reducing immunosuppressive myeloid populations. Notably, ARRB1 knockout mice exhibited markedly decreased programmed cell death protein-1 (PD-1) expression on both T cells and myeloid-derived suppressor cells, indicating reduced immune exhaustion. Furthermore, ARRB1 deficiency conferred protection against myeloma-induced bone disease, suggesting a dual role in immune regulation and bone homeostasis. These findings establish ARRB1 as a critical negative regulator of host anti-myeloma immunity and identify it as a potential therapeutic target for enhancing immunotherapy efficacy in MM.

β-arrestin 2 (ARRB2) is involved in the desensitization and trafficking of G protein-coupled receptors (GPCRs) and plays a critical role in cell proliferation, apoptosis, chemotaxis, and immune response modulation. The role of ARRB2 in the pathogenesis of multiple myeloma (MM) has not been elucidated. This study addressed this question by evaluating the expression of ARRB2 in bone marrow (BM) samples from newly diagnosed MM patients and deriving correlations with key clinical outcomes. In light of recent trends towards the use of immune checkpoint inhibitors across malignancies, the effect of ARRB2 in the regulation of the PD-1/PD-L1 axis was also investigated. The expression of ARRB2 was significantly higher in MM patients resistant to proteosome inhibitor (bortezomib) treatment compared to those who responded. Higher ARRB2 expression in the BM of newly diagnosed MM patients was associated with inferior progression-free survival and overall survival. PD-1 expression was downregulated in CD3 T cells isolated from ARRB2 knockout (KO) mice. Furthermore, knockdown of ARRB2 with siRNA reduced PD-1 expression in murine CD3 T cells and PD-L1 expression in murine myeloid-derived suppressor cells. These findings suggest an important role of ARRB2 in MM pathogenesis, potentially mediated via modulation of immune checkpoints in the tumor microenvironment. Our study provides new evidence that ARRB2 may have non-canonical functions independent of GPCRs with relevance to the understanding of MM pathobiology as well as immunotherapy and checkpoint inhibitor escape/resistance more broadly.