G-protein-coupled receptors (GPCRs) constitute the largest superfamily of cell-surface signaling proteins. However, mechanisms underlying their surface targeting and sorting are poorly understood. Here, we screen the Rab family of small GTPases in the surface transport of multiple GPCRs. We find that manipulation of Rab43 function significantly alters the surface presentation and signaling of all GPCRs studied without affecting non-GPCR membrane proteins. Rab43 specifically regulates the transport of nascent GPCRs from the endoplasmic reticulum (ER) to the Golgi. More interestingly, Rab43 directly interacts with GPCRs in an activation-dependent fashion. The Rab43-binding domain identified in the receptors effectively converts non-GPCR membrane protein transport into a Rab43-dependent pathway. These data reveal a crucial role for Rab43 in anterograde ER-Golgi transport of nascent GPCRs, as well as the ER sorting of GPCR members by virtue of its ability to interact directly.

ARF1 promotes prostate tumorigenesis via targeting oncogenic MAPK signaling

Background: Proliferation of vascular smooth muscle cells (VSMCs) is a hallmark of arterial diseases, especially in arterial restenosis after angioplasty or stent placement. VSMCs reprogram their metabolism to meet the increased requirements of lipids, proteins, and nucleotides for their proliferation. De novo purine synthesis is one of critical pathways for nucleotide synthesis. However, its role in proliferation of VSMCs in these arterial diseases has not been defined. Methods: De novo purine synthesis in proliferative VSMCs was evaluated by liquid chromatography-tandem mass spectrometry. The expression of ATIC (5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/inosine monophosphate cyclohydrolase), the critical bifunctional enzyme in the last 2 steps of the de novo purine synthesis pathway, was assessed in VSMCs of proliferative arterial neointima. Global and VSMC-specific knockout of Atic mice were generated and used for examining the role of ATIC-associated purine metabolism in the formation of arterial neointima and atherosclerotic lesions. Results: In this study, we found that de novo purine synthesis was increased in proliferative VSMCs. Upregulated purine synthesis genes, including ATIC, were observed in the neointima of the injured vessels and atherosclerotic lesions both in mice and humans. Global or specific knockout of Atic in VSMCs inhibited cell proliferation, attenuating the arterial neointima in models of mouse atherosclerosis and arterial restenosis. Conclusions: These results reveal that de novo purine synthesis plays an important role in VSMC proliferation in arterial disease. These findings suggest that targeting ATIC is a promising therapeutic approach to combat arterial diseases.

G-protein-coupled receptors (GPCRs) constitute the largest superfamily of cell surface signaling proteins. However, the molecular mechanisms underlying their cell surface delivery after synthesis remain poorly understood. Here, we screen the TBC domain-containing proteins, putative Rab GTPase-activating proteins (GAPs), in the intracellular trafficking of GPCRs and identify several TBC proteins that activity-dependently regulate the anterograde transport, en route from the endoplasmic reticulum to the Golgi or from the Golgi to the cell surface, of several prototypic GPCR members without affecting other plasma membrane proteins. We also show that TBC1D6 functions as a GAP for Rab26, physically associates with Rab26, and attenuates Rab26 interaction with GPCRs. Furthermore, both overexpression and depletion of TBC1D6 inhibit the post-Golgi traffic of GPCRs. These data demonstrate important roles of the TBC proteins in forward trafficking of nascent GPCRs and reveal regulatory mechanisms of GPCR targeting to the functional destination.

Interleukin-4 (IL-4)–exposed microglia acquire neuroprotective properties, but their functions and regulation in Parkinson’s disease (PD) are poorly understood. In this study, we demonstrate that IL-4 enhances anti-inflammatory microglia reactivity, ameliorates the pathological features of PD, and reciprocally affects expression of β-arrestin 1 and β-arrestin 2 in microglia in PD mouse models. We also show that manipulation of two β-arrestins produces contrary effects on the anti-inflammatory states and neuroprotective action of microglia induced by IL-4 in vivo and in vitro. We further find that the functional antagonism of two β-arrestins is mediated through sequential activation of sterile alpha motif domain containing 4 (Samd4), mammalian target of rapamycin (mTOR), and mitochondrial oxidative phosphorylation (OXPHOS). Collectively, these data reveal opposing functions of two closely related β-arrestins in regulating the IL-4–induced microglia reactivity via the Samd4/mTOR/OXPHOS axis in PD mouse models and provide important insights into the pathogenesis and therapeutics of PD.