Non-canonical Golgi-compartmentalized Gβγ signaling: mechanisms, functions, and therapeutic targets

MTX-induced gastrointestinal reactions in RA: Prevotella enrichment, gut dysbiosis, and PI3K/Akt/Ras/AMPK pathways

OBJECTIVES

To investigate the role of gut microbiota in methotrexate (MTX)-induced gastrointestinal reactions (MRGR) in patients with rheumatoid arthritis (RA).

METHODS

As a prospective, single-center, convenience sampling study, stool samples were obtained from 28 RA patients (male: female = 10:18) at Lanzhou University Second Hospital who were undergoing MTX treatment for analysis of their gut microbiota using 16S rRNA gene sequencing. Clinical disease activity (CDAI) and MRGR were assessed after two months of MTX therapy. All data collection periods exceeded one year. Intestinal germ-free mice, generated through antibiotic treatment, received fecal microbiota transplantation (FMT) from the patients, followed by varying doses of MTX to observe MRGR. Intestinal transcriptomics and markers related to intestinal barrier function were subsequently examined.

RESULTS

Females (84.6%) and high disease activity (CDAI scores, 39.6 ± 11.2 vs 26.3 ± 9.2) were prone to have MRGR in RA patients. Patients with MRGR (PT-GR) showed lower gut microbial diversity versus non-MRGR (PT-noGR). Prevotella abundance, positively correlated with CDAI and MRGR (p < 0.05), was elevated in PT-GR. Administering 10 mg/kg MTX to mice caused intestinal damage. FMT-GR-MTX mice exhibited weight loss (95.2%), morphological deterioration (86.4%), and reduced tight junction proteins (Claudin-1:72.4%; ZO-1:81.2%). Transcriptomics linked upregulated Gβγ/CREB/Atp4b to PI3K/Akt/Ras pathways and downregulated PFK2/PP2 to AMPK signaling in MRGR.

CONCLUSION

Our study identified notable gut microbiota alterations in RA patients prone to MRGR, with changes in intestinal gene expression and reduced intestinal barrier function potentially contributing to MRGR. These findings suggest potential strategies to mitigate MRGR in RA patients undergoing MTX treatment. Key Points • The RA-related MRGR is correlated with the intestinal microbiota. • Females, low gut diversity, and Prevotella enrichment are MRGR risks in RA. • Upregulated DEGs in MRGR linked to PI3K/Akt, Ras pathways. • Downregulated DEGs in MRGR focus on the AMPK pathway.

A visual cortical-lateral posterior thalamic nucleus circuit regulates depressive-like behaviors in male mice

Depression, a prevalent psychiatric disorder of ambiguous etiology and high heterogeneity, has been recently linked to the primary visual cortex (V1). However, the precise circuits mediating the impact of V1 on depressive-like behaviors are poorly understood. Here, we demonstrate that the V1, specifically the lateral posterior nucleus of the thalamus (LP)-projecting V1 glutamatergic subpopulation (GluV1→LP neurons), shows reduced activity after chronic restraint stress (CRS) in male mice, leading to depressive-like behaviors. Optogenetic or chemogenetic activation of these neurons ameliorated depressive-like behaviors in CRS-depressed mice, whereas reducing activity exacerbated these behaviors. This reduction in GluV1→LP neurons activity was predominantly due to a decrease in the guanine nucleotide-binding protein subunit gamma-4 (Gγ4). Overexpression of Gγ4 in the GluV1→LP neurons produced antidepressant-like effects, suggesting that Gγ4 is a crucial regulator of mood. Collectively, these results reveal a V1→LP circuit that modulates depressive-like behaviors, suggesting potential targets for therapeutic interventions.

The role of Golgi complex proteins in cell division and consequences of their dysregulation

The GC (Golgi complex) plays a pivotal role in the trafficking and sorting of proteins and lipids until they reach their final destination. Additionally, the GC acts as a signalling hub to regulate a multitude of cellular processes, including cell polarity, motility, apoptosis, DNA repair and cell division. In light of these crucial roles, the GC has garnered increasing attention, particularly given the evidence that a dysregulation of GC-regulated signalling pathways may contribute to the onset of various pathological conditions. This review examines the functions of the GC and GC-localised proteins in regulating cell cycle progression, in both mitosis and meiosis. It reviews the involvement of GC-resident proteins in the formation and orientation of the spindle during cell division. In light of the roles played by the GC in controlling cell division, this review also addresses the involvement of the GC in cancer development. Furthermore, TCGA (The Cancer Genome Atlas) database has been queried in order to retrieve information on the genetic alterations and the correlation between the expression of GC-localised proteins and the survival of cancer patients. The data presented in this review highlight the relevance of the GC in regulating cell cycle progression, cellular differentiation and tumourigenesis.

Protocol to visualize and quantify the COPII concentration and anterograde transport of nascent G protein-coupled receptors

Here, we present a protocol for visualization and quantification of the recruitment of newly synthesized G protein-coupled receptors (GPCRs) to coat protein complex II vesicles and GPCR transport from the endoplasmic reticulum through the Golgi to the cell surface in the retention using the selective hooks assay. We describe steps for plasmid construction, cell transfection, transport synchronization, confocal microscope imaging, and quantification. This protocol is also applicable for studying the transport of non-GPCR cargoes. For complete details on the use and execution of this protocol, please refer to Xu et al.1,2.

The ufmylation cascade controls COPII recruitment, anterograde transport, and sorting of nascent GPCRs at ER

Ufmylation is implicated in multiple cellular processes, but little is known about its functions and regulation in protein trafficking. Here, we demonstrate that the genetic depletion of core components of the ufmylation cascade, including ubiquitin-fold modifier 1 (UFM1), UFM1 activation enzyme 5, UFM1-specific ligase 1 (UFL1), UFM1-specific protease 2, and UFM1-binding protein 1 (UFBP1) each markedly inhibits the endoplasmic reticulum (ER)-Golgi transport, surface delivery, and recruitment to COPII vesicles of a subset of G protein-coupled receptors (GPCRs) and UFBP1's function partially relies on UFM1 conjugation. We also show that UFBP1 and UFL1 interact with GPCRs and UFBP1 localizes at COPII vesicles coated with specific Sec24 isoforms. Furthermore, the UFBP1/UFL1-binding domain identified in the receptors effectively converts non-GPCR protein transport into the ufmylation-dependent pathway. Collectively, these data reveal important functions for the ufmylation system in GPCR recruitment to COPII vesicles, biosynthetic transport, and sorting at ER via UFBP1 ufmylation and interaction directly.

Non-canonical G protein signaling

The original paradigm of classical - also referred to as canonical - cellular signal transduction of heterotrimeric G proteins (G protein) is defined by a hierarchical, orthograde interaction of three players: the agonist-activated G protein-coupled receptor (GPCR), which activates the transducing G protein, that in turn regulates its intracellular effectors. This receptor-transducer-effector concept was extended by the identification of regulators and adapters such as the regulators of G protein signaling (RGS), receptor kinases like βARK, or GPCR-interacting arrestin adapters that are integrated into this canonical signaling process at different levels to enable fine-tuning. Finally, the identification of atypical signaling mechanisms of classical regulators, together with the discovery of novel modulators, added a new and fascinating dimension to the cellular G protein signal transduction. This heterogeneous group of accessory G protein modulators was coined "activators of G protein signaling" (AGS) proteins and plays distinct roles in canonical and non-canonical G protein signaling pathways. AGS proteins contribute to the control of essential cellular functions such as cell development and division, intracellular transport processes, secretion, autophagy or cell movements. As such, they are involved in numerous biological processes that are crucial for diseases, like diabetes mellitus, cancer, and stroke, which represent major health burdens. Although the identification of a large number of non-canonical G protein signaling pathways has broadened the spectrum of this cellular communication system, their underlying mechanisms, functions, and biological effects are poorly understood. In this review, we highlight and discuss atypical G protein-dependent signaling mechanisms with a focus on inhibitory G proteins (Gi) involved in canonical and non-canonical signal transduction, review recent developments and open questions, address the potential of new approaches for targeted pharmacological interventions.

Segregation of nascent GPCRs in the ER-to-Golgi transport by CCHCR1 via direct interaction

G protein-coupled receptors (GPCRs) constitute the largest superfamily of cell surface signaling proteins that share a common structural topology. When compared with agonist-induced internalization, how GPCRs are sorted and delivered to functional destinations after synthesis in the endoplasmic reticulum (ER) is much less well understood. Here, we demonstrate that depletion of coiled-coil α-helical rod protein 1 (CCHCR1) by siRNA and CRISPR-Cas9 significantly inhibits surface expression and signaling of α2A-adrenergic receptor (α2A-AR; also known as ADRA2A), without affecting α2B-AR. Further studies show that CCHCR1 depletion specifically impedes α2A-AR export from the ER to the Golgi, but not from the Golgi to the surface. We also demonstrate that CCHCR1 selectively interacts with α2A-AR. The interaction is mediated through multiple domains of both proteins and is ionic in nature. Moreover, mutating CCHCR1-binding motifs significantly attenuates ER-to-Golgi export, surface expression and signaling of α2A-AR. Collectively, these data reveal a novel function for CCHCR1 in intracellular protein trafficking, indicate that closely related GPCRs can be sorted into distinct ER-to-Golgi transport routes by CCHCR1 via direct interaction, and provide important insights into segregation and anterograde delivery of nascent GPCR members.

Sequence-directed concentration of G protein-coupled receptors in COPII vesicles

G protein-coupled receptors (GPCRs) constitute the largest superfamily of plasma membrane signaling proteins. However, virtually nothing is known about their recruitment to COPII vesicles for forward delivery after synthesis in the endoplasmic reticulum (ER). Here, we demonstrate that some GPCRs are highly concentrated at ER exit sites (ERES) before COPII budding. Angiotensin II type 2 receptor (AT2R) and CXCR4 concentration are directed by a di-acidic motif and a 9-residue domain, respectively, and these motifs also control receptor ER-Golgi traffic. We further show that AT2R interacts with Sar1 GTPase and that distinct GPCRs have different ER-Golgi transport rates via COPII which is independent of their concentration at ERES. Collectively, these data demonstrate that GPCRs can be actively captured by COPII via specific motifs and direct interaction with COPII components that in turn affects their export dynamics, and provide important insights into COPII targeting and forward trafficking of nascent GPCRs.

Gβγ signaling regulates microtubule-dependent control of Golgi integrity

Gβγ subunits regulate several non-canonical functions at distinct intracellular organelles. Previous studies have shown that Gβγ signaling at the Golgi is necessary to mediate vesicular protein transport function and to regulate mitotic Golgi fragmentation. Disruption of Golgi structure also occurs in response to microtubule depolymerizing agents, such as nocodazole. In this study, we use siRNA against Gβ1/2 or specific Gγ subunits to deplete their expression, and show that their knockdown causes a significant reduction in nocodazole-induced Golgi fragmentation. We establish that knockdown of Gβγ or inhibition of Gβγ with gallein resulted in decreased activation of protein kinase D (PKD) in response to nocodazole treatment. We demonstrate that restricting the amount of free Gβγ available for signaling by either inhibiting Gαi activation using pertussis toxin or by knockdown of the non-GPCR GEF, Girdin/GIV protein, results in a substantial decrease in nocodazole-induced Golgi fragmentation and PKD phosphorylation. Our results also indicate that depletion of Gβγ or inhibition with gallein or pertussis toxin significantly reduces the microtubule disruption-dependent Golgi fragmentation phenotype observed in cells transfected with mutant SOD1, a major causative protein in familial amyotrophic lateral sclerosis (ALS). These results provide compelling evidence that Gβγ signaling is critical for the regulation of Golgi integrity.