β-arrestin1-medieated inhibition of FOXO3a contributes to prostate cancer cell growth in vitro and in vivo

β-Arrestin2 promotes docetaxel resistance of castration-resistant prostate cancer via promoting hnRNP A1-mediated PKM2 alternative splicing

PURPOSE

To investigate the influence of β-arrestin2 on the docetaxel resistance in castration-resistant prostate cancer (CRPC) and elucidate the underlying molecular mechanisms.

METHODS

PC3 and DU145 cells with stable β-arrestin2 overexpression and C4-2 cells with stable β-arrestin2 knockdown, were constructed via using lentivirus and puromycin selection. MTT and colony formation assays were carried out to investigate the effect of β-arrestin2 expression on the docetaxel resistance of CRPC cells. Glycolysis analysis was used to assess the glycolytic capacity modulated by β-arrestin2. GO enrichment analysis, gene set enrichment analysis and Spearman correlation test were carried out to explore the potential biological function and mechanism via using public data from GEO and TCGA. The expressions of PKM2, Phospho-PKM2, Phospho-ERK1/2 and hnRNP A1 were detected by western blot. Functional blocking experiments were carried out to confirm the roles of PKM2 and hnRNP A1 in the regulation of β-arrestin2's biological functions via silencing PKM2 or hnRNP A1 expression in cells with stable β-arrestin2 overexpression. Finally, nude mice xenograft models were established to confirm the experimental results of cell experiments.

RESULTS

β-Arrestin2 significantly decreased the sensitivity of CRPC cells to docetaxel stimulation, through enhancing the phosphorylation and expression of PKM2. Additionally, β-arrestin2 increased PKM2 phosphorylation via the ERK1/2 signaling pathway and induced PKM2 expression in a post-transcriptional manner through an hnRNP A1-dependent PKM alternative splicing mechanism, rather than by inhibiting its ubiquitination degradation.

CONCLUSION

Our findings indicate that the β-arrestin2/hnRNP A1/PKM2 pathway could be a promising target for treating docetaxel-resistant CRPC.

β-Arrestins: Structure, Function, Physiology, and Pharmacological Perspectives

The two β-arrestins, β-arrestin-1 and -2 (systematic names: arrestin-2 and -3, respectively), are multifunctional intracellular proteins that regulate the activity of a very large number of cellular signaling pathways and physiologic functions. The two proteins were discovered for their ability to disrupt signaling via G protein-coupled receptors (GPCRs) via binding to the activated receptors. However, it is now well recognized that both β-arrestins can also act as direct modulators of numerous cellular processes via either GPCR-dependent or -independent mechanisms. Recent structural, biophysical, and biochemical studies have provided novel insights into how β-arrestins bind to activated GPCRs and downstream effector proteins. Studies with β-arrestin mutant mice have identified numerous physiologic and pathophysiological processes regulated by β-arrestin-1 and/or -2. Following a short summary of recent structural studies, this review primarily focuses on β-arrestin-regulated physiologic functions, with particular focus on the central nervous system and the roles of β-arrestins in carcinogenesis and key metabolic processes including the maintenance of glucose and energy homeostasis. This review also highlights potential therapeutic implications of these studies and discusses strategies that could prove useful for targeting specific β-arrestin-regulated signaling pathways for therapeutic purposes. SIGNIFICANCE STATEMENT: The two β-arrestins, structurally closely related intracellular proteins that are evolutionarily highly conserved, have emerged as multifunctional proteins able to regulate a vast array of cellular and physiological functions. The outcome of studies with β-arrestin mutant mice and cultured cells, complemented by novel insights into β-arrestin structure and function, should pave the way for the development of novel classes of therapeutically useful drugs capable of regulating specific β-arrestin functions.

CSNK1D-mediated phosphorylation of HNRNPA2B1 induces miR-25-3p/miR-93-5p maturation to promote prostate cancer cell proliferation and migration through m6A-dependent manner

It has been reported that heterogeneous nuclear ribonucleoprotein A2/B1 (HNRNPA2B1) is highly expressed in prostate cancer (PCa) and associated with poor prognosis of patients with PCa. Nevertheless, the specific mechanism underlying HNRNPA2B1 functions in PCa remains not clear. In our study, we proved that HNRNPA2B1 promoted the progression of PCa through in vitro and in vivo experiments. Further, we found that HNRNPA2B1 induced the maturation of miR-25-3p/miR-93-5p by recognizing primary miR-25/93 (pri-miR-25/93) through N6-methyladenosine (m6A)-dependent manner. In addition, both miR-93-5p and miR-25-3p were proven as tumor promoters in PCa. Interestingly, by mass spectrometry analysis and mechanical experiments, we found that casein kinase 1 delta (CSNK1D) could mediate the phosphorylation of HNRNPA2B1 to enhance its stability. Moreover, we further proved that miR-93-5p targeted BMP and activin membrane-bound inhibitor (BAMBI) mRNA to reduce its expression, thereby activating transforming growth factor β (TGF-β) pathway. At the same time, miR-25-3p targeted forkhead box O3 (FOXO3) to inactivate FOXO pathway. These results collectively indicated that CSNK1D stabilized HNRNPA2B1 facilitates the processing of miR-25-3p/miR-93-5p to regulate TGF-β and FOXO pathways, resulting in PCa progression. Our findings supported that HNRNPA2B1 might be a promising target for PCa treatment.

Role of ARRB1 in prognosis and immunotherapy: A Pan-Cancer analysis

Background: β-arrestin1 (ARRB1), was originally identified as a multifunctional adaptor protein. Although ARRB1 has recently been shown to also play an important role in tumor growth, metastasis, inflammation, and immunity, its relationship with distinct tumor types and the tumor immune microenvironment remains unclear.

Methods: We analyzed the ARRB1 expression profile and clinical characteristics in 33 cancer types using datasets from The Cancer Genome Atlas (TCGA) database. Clinical parameters such as patient survival, tumor stage, age, and gender were used to assess the prognostic value of ARRB1. The Human Protein Atlas (HPA) database was used to explore ARRB1 protein expression data. ESTIMATE and CIBERSORT algorithms were performed to assess immune infiltration. Furthermore, putative correlations between ARRB1 and tumor-infiltrating immune cells, the signatures of T-cell subtypes, immunomodulators, the tumor mutation burden (TMB), Programmed cell death ligand 1 (PD-L1), and microsatellite instability (MSI) were also explored. Gene functional enrichment was determined using GSEA. GSE40435 and GSE13213 cohorts were used to validate the correlation of ARRB1 with KIRC and LUAD clinicopathological parameters. Finally, the relationship between ARRB1 and immunotherapeutic responses was assessed using three independent immunotherapy cohorts, namely, GSE67501, GSE168204, and IMvigor210.

Results: We found that ARRB1 expression levels were lower in 17 tumor tissues than in the corresponding normal tissues. We further found that ARRB1 expression was significantly correlated with tumor stage in BRCA, ESCA, KIRC, TGCT, and THCA, while in some tumors, particularly KIRC and LUAD, ARRB1 expression was associated with better prognosis. ARRB1 expression was also positively correlated with the stromal score or the immune score in some tumors. Regarding immune cell infiltration, ARRB1 expression in DLBC was positively correlated with M1 macrophage content and negatively correlated with B-cell infiltration. Additionally, there was a broad correlation between ARRB1 expression and three classes of immunomodulators. Furthermore, high ARRB1 expression levels were significantly correlated with some tumor immune-related pathways. Finally, ARRB1 expression was significantly associated with MSI, PD-L1, and TMB in some tumors and with the efficacy of immune checkpoint inhibitors (ICIs) in melanoma.

Conclusion: ARRB1 has prognostic value in malignant tumors, especially in KIRC and LUAD. At the same time, ARRB1 was closely correlated with the tumor immune microenvironment and indicators of immunotherapy efficacy, indicating its great potential as a reliable marker for predicting the efficacy of immunotherapy.

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

β-Arrestins are ubiquitously expressed intracellular proteins with many functions which interact directly and indirectly with a wide number of cellular partners and mediate downstream signaling. Originally, β-arrestins were identified for their contribution to GPCR desensitization to agonist-mediated activation, followed by receptor endocytosis and ubiquitylation. However, current investigations have now recognized that in addition to GPCR arresting (hence the name arrestin). β-Arrestins are adaptor proteins that control the recruitment, activation, and scaffolding of numerous cytoplasmic signaling complexes and assist in G-protein receptor signaling, thus bringing them into close proximity. They have participated in various cellular processes such as cell proliferation, migration, apoptosis, and transcription via canonical and noncanonical pathways. Despite their significant recognition in several physiological processes, these activities are also involved in the onset and progression of various cancers. This review delivers a concise overview of the role of β-arrestins with a primary emphasis on the signaling processes which underlie the mechanism of β-arrestins in the onset of cancer. Understanding these processes has important implications for understanding the therapeutic intervention and treatment of cancer in the future.

Structural basis and molecular mechanism of biased GPBAR signaling in regulating NSCLC cell growth via YAP activity

The G protein-coupled bile acid receptor (GPBAR) is the membrane receptor for bile acids and a driving force of the liver-bile acid-microbiota-organ axis to regulate metabolism and other pathophysiological processes. Although GPBAR is an important therapeutic target for a spectrum of metabolic and neurodegenerative diseases, its activation has also been found to be linked to carcinogenesis, leading to potential side effects. Here, via functional screening, we found that two specific GPBAR agonists, R399 and INT-777, demonstrated strikingly different regulatory effects on the growth and apoptosis of non-small cell lung cancer (NSCLC) cells both in vitro and in vivo. Further mechanistic investigation showed that R399-induced GPBAR activation displayed an obvious bias for β-arrestin 1 signaling, thus promoting YAP signaling activation to stimulate cell proliferation. Conversely, INT-777 preferentially activated GPBAR-Gs signaling, thus inactivating YAP to inhibit cell proliferation and induce apoptosis. Phosphorylation of GPBAR by GRK2 at S310/S321/S323/S324 sites contributed to R399-induced GPBAR-β-arrestin 1 association. The cryoelectron microscopy (cryo-EM) structure of the R399-bound GPBAR-Gs complex enabled us to identify key interaction residues and pivotal conformational changes in GPBAR responsible for the arrestin signaling bias and cancer cell proliferation. In summary, we demonstrate that different agonists can regulate distinct functions of cell growth and apoptosis through biased GPBAR signaling and control of YAP activity in a NSCLC cell model. The delineated mechanism and structural basis may facilitate the rational design of GPBAR-targeting drugs with both metabolic and anticancer benefits.

FOXO3a and Its Regulators in Prostate Cancer

Forkhead box O3 (FOXO3a) is a member of a subfamily of forkhead transcription factors involved in the basic processes within a cell, including proliferation, apoptosis, cell cycle regulation, and DNA damage. As a transcription factor, FOXO3a is involved in the response to cellular stress, UV radiation, or oxidative stress. Its regulation is based on the modification of proteins as well as regulation by other proteins, e.g., growth factors. FOXO3a is commonly deregulated in cancer cells, and its inactivation is associated with initiation and progression of tumorigenesis, suggesting its role as a tumor suppressor; however, its role is still disputed and seems to be dependent on upstream signaling. Nevertheless, FOXO3a serves as an interesting potential target in therapies as it is regulated during treatment with very common anti-cancer drugs such as paclitaxel, cisplatin, docetaxel, and doxorubicin. This review aims to update the reported role of FOXO3a in prostate cancer (PCa), with a focus on its regulators that might serve as potential therapeutic agents in PCa therapy.

Combined Anti-Cancer Effects of Platycodin D and Sorafenib on Androgen-Independent and PTEN-Deficient Prostate Cancer

Castration-resistant (androgen-independent) and PTEN-deficient prostate cancer is a challenge in clinical practice. Sorafenib has been recommended for the treatment of this type of cancer, but is associated with several adverse effects. Platycodin D (PD) is a triterpene saponin with demonstrated anti-cancer effects and a good safety profile. Previous studies have indicated that PC3 cells (PTEN -/-, AR -/-) are sensitive to PD, suggesting that it may also be a useful treatment for castration-resistance prostate cancer. We herein investigated the effects of combining PD with sorafenib to treat PTEN-deficient prostate cancer cells. Our data show that PD promotes sorafenib-induced apoptosis and cell cycle arrest in PC3 cells. Of interest, PD only promoted the anti-cancer effects of sorafenib in Akt-positive and PTEN-negative prostate cancer cells. Mechanistic studies revealed that PD promoted p-Akt ubiquitination by increasing the p-Akt level. PD also increased the protein and mRNA expression of FOXO3a, the downstream target of Akt. Meanwhile, PD promoted the activity of FOXO3a and increased the protein expression of Fasl, Bim and TRAIL. Interestingly, when FOXO3a expression was inhibited, the antitumor effects of both PD and sorafenib were individually inhibited, and the more potent effects of the combination treatment were inhibited. Thus, the combination of PD and sorafenib may exert potent anti-cancer effects specifically via FOXO3a. The use of Akt inhibitors or FOXO3a agonists, such as PD, may represent a promising approach for the treatment of androgen-independent and PTEN-deficient prostate cancer.

β-arrestin 2 is essential for fluoxetine-mediated promotion of hippocampal neurogenesis in a mouse model of depression

Over the last decade, the roles of β-arrestins in the treatment of neuropsychological diseases have become increasingly appreciated. Fluoxetine is the first selective serotonin reuptake inhibitor developed and is approved for the clinical treatment of depression. Emerging evidence suggests that fluoxetine can directly combine with the 5-HT receptor, which is a member of the G protein-coupled receptor (GPCR) family, in addition to suppressing the serotonin transporter. In this study, we prepared a chronic mild stress (CMS)-induced depression model with β-arrestin2-/- mice and cultured adult neural stem cells (ANSCs) to investigate the involvement of the 5-HT receptor-β-arrestin axis in the pathogenesis of depression and in the therapeutic effect of fluoxetine. We found that β-arrestin2 deletion abolished the fluoxetine-mediated improvement in depression-like behaviors and monoamine neurotransmitter levels, although β-arrestin2 knockout did not aggravate CMS-induced changes in mouse behaviors and neurotransmitters. Notably, the β-arrestin2-/- mice had a shortened dendritic length and reduced dendritic spine density, as well as decreased neural precursor cells, compared to the WT mice under both basal and CMS conditions. We further found that β-arrestin2 knockout decreased the number of proliferating cells in the hippocampal dentate gyrus and suppressed the proliferative capability of ANSCs in vitro. Moreover, β-arrestin2 knockout aggravated the impairment of cell proliferation induced by corticosterone and further blocked the fluoxetine-mediated promotion of mouse hippocampal neurogenesis. Mechanistically, we found that the 5-HT2BR-β-arrestin2-PI3K/Akt axis is essential to maintain the modulation of hippocampal neurogenesis in depressed mice. Our study may provide a promising target for the development of new antidepressant drugs.

Host versus cell-dependent effects of β-arrestin 1 expression in prostate tumorigenesis

Prostate cancer (PCa) constitutes a serious health challenge and remains one of the main causes of cancer-related death among men. The more aggressive form of the disease has been attributed to androgen independence, resulting in a lack of response to androgen deprivation therapy and sustained activation of other growth pathways. The scaffold proteins β-arrestin 1 and 2 (βarr1 and βarr2), which are known to mediate G protein-coupled receptor desensitization and internalization, were also shown to modulate prostate tumorigenesis. βarr1 is significantly overexpressed (>4-fold) in PCa cells relative to βarr2. In this study, we investigated the effect of βarr1 overexpression in PCa development and progression using the mouse and human PCa cell xenografts, and autochthonous transgenic adenocarcinoma of the mouse prostate (TRAMP) models deficient in β-arrestin depletion of βarr1 in TRAMP mice (TRAMP/βarr1-/-) increased PCa growth and decreased overall survival relative to control TRAMP or TRAMP/βarr2-/- animals. Prostate tissues from TRAMP/βarr1-/- tumors displayed an increase in androgen receptor (AR) expression, whereas overexpression of βarr1 in TRAMP-C1 (TRAMP-C1-βarr1-GFP) which derived from TRAMP decreased AR expression, cell proliferation and tumor growth in nude mice xenografts, relative to control TRAMP-C1-GFP. Knockdown of βarr1 expression in human MDA PCa 2b cells (MDA PCa 2b-βarr1-/-) also decreased AR expression cell proliferation and tumor growth relative to control (MDA PCa 2b-Sham) cells. Interestingly, both TRAMP-C1-βarr1-GFP and MDA PCa 2b-βarr1-/- xenografts showed a decrease in AKT phosphorylation but an increase in MAPK activation. Altogether, the data indicate that the effect of βarr1 in modulating AR signaling to regulate PCa aggressiveness is cell and host autonomous.

The Role of β-Arrestin1 in Esophageal Squamous Cell Carcinoma

Introduction

Esophageal squamous cell carcinoma (ESCC) is the predominant type of esophageal carcinoma with a low survival rate and a poor prognosis. Therefore, it is of great significance to explore the effective tumor markers in early diagnosis, treatment monitoring and prognosis evaluation of ESCC. The current study was designed to explore the important role of β-arrestin1 in ESCC and the underlying mechanism.

Methods

The defined effects of β-arrestin1 on cell proliferation, migration, invasion, EMT and tumor growth were investigated both in ESCC cells and in vivo model of ESCC. β-arrestin1 expression was detected using Western blot and immunohistochemistry assay. The cell proliferation ability was determined using CCK-8 assay. Wound healing assay and trans-well invasion assay were performed to determine cell migration and invasion. The key proteins related to cell migration, invasion and EMT were detected by Western blot. Tumor growth in vivo was also monitored by tumor volume and weight. In addition, the effects of β-arrestin1 on AKT/GSK3β/β-catenin pathway were evaluated.

Results

β-arrestin1 was aberrantly upregulated in human ESCC tissues, ESCC cell lines and animal model of ESCC. β-arrestin1 downregulation inhibited cell proliferation, migration, invasion and EMT of ESCC in vitro and vivo. β-arrestin downregulation also suppressed tumor growth in vivo model of ESCC. In addition, the inhibitory effects of β-arrestin1 downregulation were exerted via AKT/GSK3β/β-catenin signaling pathway.

Discussion

The results in the present study together confirmed the truth that β-arrestin1 interference may suppress ESCC cell proliferation, migration, invasion, EMT and tumor growth via AKT/GSK3β/β-catenin signaling pathway.

Blockade of MDM2 with inactive Cas9 prevents epithelial to mesenchymal transition in retinal pigment epithelial cells

Epithelial to mesenchymal transition (EMT) plays an important role in the pathogenesis of proliferative vitreoretinopathy (PVR). We aimed to demonstrate the role of mouse double minute 2 (MDM2) in transforming growth factor-beta 2 (TGF-β2)-induced EMT in human retinal pigment epithelial cells (RPEs). Immunofluorescence was used to assess MDM2 expression in epiretinal membranes (ERMs) from patients with PVR. A single guide (sg)RNA targeting the second promoter of MDM2 was cloned into a mutant lentiviral Clustered Regularly Interspaced Short Palindromic Repeats (lentiCRISPR) v2 (D10A and H840A) vector for expressing nuclease dead Cas9 (dCas9)/MDM2-sgRNA in RPEs. In addition, MDM2-sgRNA was also cloned into a pLV-sgRNA-dCas9-Kruppel associated box (KRAB) vector for expressing dCas9 fused with a transcriptional repressor KRAB/MDM2-sgRNA. TGF-β2-induced expression of MDM2 and EMT biomarkers were assessed by quantitative polymerase chain reaction (q-PCR), western blot, or immunofluorescence. Wound-healing and proliferation assays were used to evaluate the role of MDM2 in TGF-β2-induced responses in RPEs. As a result, we found that MDM2 was expressed obviously in ERMs, and that TGF-β2-induced expression of MDM2 and EMT biomarkers Fibronectin, N-cadherin and Vimentin in RPEs. Importantly, we discovered that the dCas9/MDM2-sgRNA blocked TGF-β2-induced expression of MDM2 and the EMT biomarkers without affecting their basal expression, whereas the dCas9-KRAB/MDM2-sgRNA suppressed basal MDM2 expression in RPEs. These cells could not be maintained continuously because their viability was greatly reduced. Next, we found that Nutlin-3, a small molecule blocking the interaction of MDM2 with p53, inhibited TGF-β2-induced expression of Fibronectin and N-cadherin but not Vimentin in RPEs, indicating that MDM2 functions in both p53-dependent and -independent pathways. Finally, our experimental data demonstrated that dCas9/MDM2-sgRNA suppressed TGF-β2-dependent cell proliferation and migration without disturbing the unstimulated basal activity. In conclusion, the CRISPR/dCas9 capability for blocking TGF-β2-induced expression of MDM2 and EMT biomarkers can be exploited for a therapeutic approach to PVR.

SPTLC1 inhibits cell growth via modulating Akt/FOXO1 pathway in renal cell carcinoma cells

Serine palmitoyltransferase long chain-1 (SPTLC1), which is the rate-limiting enzyme for sphingolipid biosynthesis, has been indicated to be essential for carcinoma cell survival and proliferation in recent, but its role in the regulation of renal cell carcinoma (RCC) remains unknown. In the present study, we found that SPTLC1 expression was significantly decreased in RCC tissues compared to non-tumor tissues, and low SPTLC1 expression was associated with poor overall survival of RCC patients. In addition, our results revealed that forced expression of SPTLC1 could significantly inhibit cell growth in vitro and in vivo via, at least in part, modulating Akt/FOXO1 signaling pathway, thus representing a novel role of SPTLC1 in the regulation of tumor growth in RCC for the first time.

Therapeutic Potential of Targeting ß-Arrestin

ß-arrestins are multifunctional proteins that modulate heptahelical 7 transmembrane receptors, also known as G protein-coupled receptors (GPCRs), a superfamily of receptors that regulate most physiological processes. ß-arrestin modulation of GPCR function includes termination of G protein-dependent signaling, initiation of ß-arrestin-dependent signaling, receptor trafficking to degradative or recycling pathways, receptor transactivation, transcriptional regulation, and localization of second messenger regulators. The pleiotropic influence ß-arrestins exert on these receptors regulates a breadth of physiological functions, and additionally, ß-arrestins are involved in the pathophysiology of numerous and wide-ranging diseases, making them prime therapeutic targets. In this review, we briefly describe the mechanisms by which ß-arrestins regulate GPCR signaling, including the functional cellular mechanisms modulated by ß-arrestins and relate this to observed pathophysiological responses associated with ß-arrestins. We focus on the role for ß-arrestins in transducing cell signaling; a pathway that is complementary to the classical G protein-coupling pathway. The existence of these GPCR dual signaling pathways offers an immense therapeutic opportunity through selective targeting of one signaling pathway over the other. Finally, we will consider several mechanisms by which the potential of dual signaling pathway regulation can be harnessed and the implications for improved disease treatments.

New Routes in GPCR/β-Arrestin-Driven Signaling in Cancer Progression and Metastasis

Tumor cells acquire invasive and metastatic behavior by sensing changes in the localization and activation of signaling pathways, which in turn determine changes in actin cytoskeleton. The core-scaffold machinery associated to β-arrestin (β-arr) is a key mechanism of G-protein coupled receptors (GPCR) to achieve spatiotemporal specificity of different signaling complexes driving cancer progression. Within different cellular contexts, the scaffold proteins β-arr1 or β-arr2 may now be considered organizers of protein interaction networks involved in tumor development and metastatic dissemination. Studies have uncovered the importance of the β-arr engagement with a growing number of receptors, signaling molecules, cytoskeleton regulators, epigenetic modifiers, and transcription factors in GPCR-driven tumor promoting pathways. In many of these molecular complexes, β-arrs might provide a physical link to active dynamic cytoskeleton, permitting cancer cells to adapt and modify the tumor microenvironment to promote the metastatic spread. Given the complexity and the multidirectional β-arr-driven signaling in cancer cells, therapeutic targeting of specific GPCR/β-arr molecular mechanisms is an important avenue to explore when considering future new therapeutic options. The focus of this review is to integrate the most recent developments and exciting findings of how highly connected components of β-arr-guided molecular connections to other pathways allow precise control over multiple signaling pathways in tumor progression, revealing ways of therapeutically targeting the convergent signals in patients.

β-arrestin1-medieated inhibition of FOXO3a contributes to prostate cancer cell growth in vitro and in vivo

Recently, β-arrestin1 has been indicated as a prostate cancer promoter through promoting cell proliferation and epithelial to mesenchymal transition, but its underlying mechanism remains unclear. Here, our data revealed that β-arrestin1 could promote cell growth through inhibiting the transcriptional activity and expression of FOXO3a in prostate cancer cells in vitro and in vivo. We found that β-arrestin1 could promote the cell and tumor growth of prostate cancer, and β-arrestin1 expression represented a negative correlation with FOXO3a expression but not FOXO1 expression in prostate cancer cell lines and tissues. In addition, forced expression of β-arrestin1 induced a significant decrease of FOXO3a expression but had no clear effect on FOXO1 expression. Mechanistically, β-arrestin1 could interact with FOXO3a and MDM2, respectively, and promote the interaction between FOXO3a and MDM2, whereas it had no obvious interaction with FOXO1. Furthermore, β-arrestin1 could inhibit the transcriptional activity of FOXO3a via Akt and ERK1/2 pathways. Together, our results revealed a novel mechanism for β-arrestin1 in the regulation of the prostate cancer procession through inhibiting FOXO3a.