ADP-ribosylation Factor Family Research Articles

Mapping the global interactome of the ARF family reveals spatial organization in cellular signaling pathways.

The ADP-ribosylation factors (ARFs) and ARF-like (ARLs) GTPases serve as essential molecular switches governing a wide array of cellular processes. In this study, we utilized proximity-dependent biotin identification (BioID) to comprehensively map the interactome of 28 out of 29 ARF and ARL proteins in two cellular models. Through this approach, we identified ∼3000 high-confidence proximal interactors, enabling us to assign subcellular localizations to the family members. Notably, we uncovered previously undefined localizations for ARL4D and ARL10. Clustering analyses further exposed the distinctiveness of the interactors identified with these two GTPases. We also reveal that the expression of the understudied member ARL14 is confined to the stomach and intestines. We identified phospholipase D1 (PLD1) and the ESCPE-1 complex, more precisely SNX1, as proximity interactors. Functional assays demonstrated that ARL14 can activate PLD1 in cellulo and is involved in cargo trafficking via the ESCPE-1 complex. Overall, the BioID data generated in this study provide a valuable resource for dissecting the complexities of ARF and ARL spatial organization and signaling.

Brefeldin A and M-COPA block the export of RTKs from the endoplasmic reticulum via simultaneous inactivation of ARF1, ARF4, and ARF5

Normal receptor tyrosine kinases (RTKs) need to reach the plasma membrane (PM) for ligand-induced activation, whereas its cancer-causing mutants can be activated before reaching the PM in organelles, such as the Golgi/trans-Golgi network (TGN). Inhibitors of protein export from the endoplasmic reticulum (ER), such as brefeldin A (BFA) and 2-methylcoprophilinamide (M-COPA), can suppress the activation of mutant RTKs in cancer cells, suggesting that RTK mutants cannot initiate signaling in the ER. BFA and M-COPA block the function of ADP-ribosylation factors (ARFs) that play a crucial role in ER–Golgi protein trafficking. However, among ARF family proteins, the specific ARFs inhibited by BFA or M-COPA, that is, the ARFs involved in RTKs transport from the ER, remain unclear. In this study, we showed that M-COPA blocked the export of not only KIT but also PDGFRA/EGFR/MET RTKs from the ER. ER-retained RTKs could not fully transduce anti-apoptotic signals, thereby leading to cancer cell apoptosis. Moreover, single knockdown of ARF1, ARF3, ARF4, ARF5, or ARF6 could not block ER export of RTKs, indicating that BFA/M-COPA treatment cannot be mimicked by knockdown of only one ARF member. Interestingly, simultaneous transfection of ARF1, ARF4, and ARF5 siRNAs mirrored the effect of BFA/M-COPA treatment. Consistent with these results, in vitro pulldown assays showed that BFA/M-COPA blocked the function of ARF1, ARF4, and ARF5. Taken together, these results suggest that BFA/M-COPA targets at least ARF1, ARF4, and ARF5; in other words, RTKs require the simultaneous activation of ARF1, ARF4, and ARF5 for their ER export.

Membrane trafficking alterations in breast cancer progression.

Breast cancer (BC) is the most common type of cancer in women, and remains one of the major causes of death in women worldwide. It is now well established that alterations in membrane trafficking are implicated in BC progression. Indeed, membrane trafficking pathways regulate BC cell proliferation, migration, invasion, and metastasis. The 22 members of the ADP-ribosylation factor (ARF) and the >60 members of the rat sarcoma (RAS)-related in brain (RAB) families of small GTP-binding proteins (GTPases), which belong to the RAS superfamily, are master regulators of membrane trafficking pathways. ARF-like (ARL) subfamily members are involved in various processes, including vesicle budding and cargo selection. Moreover, ARFs regulate cytoskeleton organization and signal transduction. RABs are key regulators of all steps of membrane trafficking. Interestingly, the activity and/or expression of some of these proteins is found dysregulated in BC. Here, we review how the processes regulated by ARFs and RABs are subverted in BC, including secretion/exocytosis, endocytosis/recycling, autophagy/lysosome trafficking, cytoskeleton dynamics, integrin-mediated signaling, among others. Thus, we provide a comprehensive overview of the roles played by ARF and RAB family members, as well as their regulators in BC progression, aiming to lay the foundation for future research in this field. This research should focus on further dissecting the molecular mechanisms regulated by ARFs and RABs that are subverted in BC, and exploring their use as therapeutic targets or prognostic markers.

Integrated analysis and validation reveal CYTH4 as a potential prognostic biomarker in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a clonal hematological malignancy with high mortality rates. The identification of novel markers is urgent for AML. Cytohesins are a subfamily of guanine nucleotide exchange factors activating the ADP-ribosylation factor family GTPases. While the important roles of cytohesins have been reported in various cancers, their function in AML remains unclear. The present study aimed to explore the prognostic impact of cytohesin-4 (CYTH4) and the underlying molecular functions. RNA sequencing and AML clinical data were obtained from The Cancer Genome Atlas and Gene Expression Omnibus databases to investigate gene expression and survival. Using the R software, differentially expressed genes were identified between the high- and the low-CYTH4 group. Functional enrichment analysis was conducted by Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and Gene Set Enrichment Analyses. The CIBERSORTx tool was used to explore the proportions of different immune cell types. The molecular function of CYTH4 was also validated in vitro by examining cell growth, cell cycle, apoptosis and colony-forming ability. CYTH4 was significantly upregulated in AML compared with other cancers and normal tissues. High CYTH4 expression was associated with high white blood count (P=0.004) and higher risk status (P<0.001). Patients with high CYTH4 expression had poor overall survival (OS; HR=2.19; 95% CI, 1.40-3.44; P=0.0006; high vs. low) and event-free survival (EFS; HR=2.32; 95% CI, 1.43-3.75; P=0.0006; high vs. low), and these patients could benefit from transplantation (HR=0.29; 95% CI, 0.18-0.47; P<0.0001; transplantation vs. chemotherapy). Multivariate analysis showed that high CYTH4 expression was independently associated with inferior OS (HR=2.49; 95% CI, 1.28-4.83; P=0.007) and EFS (HR=2.56; 95% CI, 1.48-4.42; P=0.001). Functional analysis showed that CYTH4 was involved in immunoregulation. In vitro validation showed knockdown of CYTH4 adversely affected cell growth and induced cell apoptosis, while overexpression of CYTH4 enhanced cell growth. Taken together, CYTH4 is expressed at high levels in AML and can potentially function as a prognostic biomarker.

An ARF24-ZmArf2 module influences kernel size in different maize haplotypes.

Members of the ADP-ribosylation factor family, which are GTP-binding proteins, are involved in metabolite transport, cell division, and expansion. Although there has been a significant amount of research on small GTP-binding proteins, their roles and functions in regulating maize kernel size remain elusive. Here, we identified ZmArf2 as a maize ADP-ribosylation factor-like family member that is highly conserved during evolution. Maize zmarf2 mutants showed a characteristic smaller kernel size. Conversely, ZmArf2 overexpression increased maize kernel size. Furthermore, heterologous expression of ZmArf2 dramatically elevated Arabidopsis and yeast growth by promoting cell division. Using expression quantitative trait loci (eQTL) analysis, we determined that ZmArf2 expression levels in various lines were mainly associated with variation at the gene locus. The promoters of ZmArf2 genes could be divided into two types, pS and pL, that were significantly associated with both ZmArf2 expression levels and kernel size. In yeast-one-hybrid screening, maize Auxin Response Factor 24 (ARF24) is directly bound to the ZmArf2 promoter region and negatively regulated ZmArf2 expression. Notably, the pS and pL promoter types each contained an ARF24 binding element: an auxin response element (AuxRE) in pS and an auxin response region (AuxRR) in pL, respectively. ARF24 binding affinity to AuxRR was much higher compared with AuxRE. Overall, our results establish that the small G-protein ZmArf2 positively regulates maize kernel size and reveals the mechanism of its expression regulation.

ADP-ribosylation factor D1 modulates Golgi morphology, cell plate formation, and plant growth in Arabidopsis.

ADP-ribosylation factor (ARF) family proteins, one type of small guanine-nucleotide-binding (G) proteins, play a central role in regulating vesicular traffic and organelle structures in eukaryotes. The Arabidopsis (Arabidopsis thaliana) genome contains more than 21 ARF proteins, but relatively little is known about the functional heterogeneity of ARF homologs in plants. Here, we characterized the function of a unique ARF protein, ARFD1B, in Arabidopsis. ARFD1B exhibited both cytosol and punctate localization patterns, colocalizing with a Golgi marker in protoplasts and transgenic plants. Distinct from other ARF1 homologs, overexpression of a dominant-negative mutant form of ARFD1B did not alter the localization of the Golgi marker mannosidase I (ManI)-RFP in Arabidopsis cells. Interestingly, the ARFD1 artificial microRNA knockdown mutant arfd1 displayed a deleterious growth phenotype, while this phenotype was restored in complemented plants. Further, confocal imaging and transmission electron microscopy analyses of the arfd1 mutant revealed defective cell plate formation and abnormal Golgi morphology. Pull-down and liquid chromatography-tandem mass spectrometry analyses identified Coat Protein I (COPI) components as interacting partners of ARFD1B, and subsequent bimolecular fluorescence complementation, yeast (Saccharomyces cerevisiae) two-hybrid, and co-immunoprecipitation assays further confirmed these interactions. These results demonstrate that ARFD1 is required for cell plate formation, maintenance of Golgi morphology, and plant growth in Arabidopsis.

The Arf-GAP Proteins AoGcs1 and AoGts1 Regulate Mycelial Development, Endocytosis, and Pathogenicity in Arthrobotrys oligospora.

Small GTPases from the ADP-ribosylation factor (Arf) family and their activating proteins (Arf-GAPs) regulate mycelial development, endocytosis, and virulence in fungi. Here, we identified two orthologous Arf-GAP proteins, AoGcs1 and AoGts1, in a typical nematode-trapping fungus Arthrobotrys oligospora. The transcription of Aogcs1 and Aogts1 was highly expressed in the sporulation stage. The deletion of Aogcs1 and Aogts1 caused defects in DNA damage, endocytosis, scavenging of reactive oxygen species, lipid droplet storage, mitochondrial activity, autophagy, serine protease activity, and the response to endoplasmic reticulum stress. The combined effects resulted in slow growth, decreased sporulation capacity, increased susceptibility to chemical stressors and heat shock, and decreased pathogenicity of the mutants compared with the wild-type (WT) strain. Although deletion of Aogcs1 and Aogts1 produced similar phenotfypic traits, their roles varied in conidiation and proteolytic activity. The ΔAogts1 mutant showed a remarkable reduction in conidial yield compared with the WT strain but not in proteolytic activity; in contrast, the ΔAogcs1 mutant showed an increase in proteolytic activity but not in sporulation. In addition, the growth of ΔAogcs1 and ΔAogts1 mutants was promoted by rapamycin, and the ΔAogts1 mutant was sensitive to H-89. Collectively, the ΔAogts1 mutant showed a more remarkable difference compared with the WT strain than the ΔAogcs1 mutant. Our study further illustrates the importance of Arf-GAPs in the growth, development, and pathogenicity of nematode-trapping fungi.

ADP-Ribosylation Factor Family of Small GTP-Binding Proteins: Their Membrane Recruitment, Activation, Crosstalk and Functions.

Members of the ADP-ribosylation factor (ARF) family of guanine-nucleotide binding proteins play critical roles in various cellular processes, especially in regulating the secretory, and endocytic pathways. The fidelity of intracellular vesicular trafficking depends on proper activations and precise subcellular distributions of ARF family proteins regulated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Here we review recent progress in understanding the membrane recruitment, activation, crosstalk, and functions of ARF family proteins.

The ARF GAPs ELMOD1 and ELMOD3 act at the Golgi and cilia to regulate ciliogenesis and ciliary protein traffic.

ELMODs are a family of three mammalian paralogues that display GTPase-activating protein (GAP) activity toward a uniquely broad array of ADP-ribosylation factor (ARF) family GTPases that includes ARF-like (ARL) proteins. ELMODs are ubiquitously expressed in mammalian tissues, highly conserved across eukaryotes, and ancient in origin, being present in the last eukaryotic common ancestor. We described functions of ELMOD2 in immortalized mouse embryonic fibroblasts (MEFs) in the regulation of cell division, microtubules, ciliogenesis, and mitochondrial fusion. Here, using similar strategies with the paralogues ELMOD1 and ELMOD3, we identify novel functions and locations of these cell regulators and compare them to those of ELMOD2, allowing the determination of functional redundancy among the family members. We found strong similarities in phenotypes resulting from deletion of either Elmod1 or Elmod3 and marked differences from those arising in Elmod2 deletion lines. Deletion of either Elmod1 or Elmod3 results in the decreased ability of cells to form primary cilia, loss of a subset of proteins from cilia, and accumulation of some ciliary proteins at the Golgi, predicted to result from compromised traffic from the Golgi to cilia. These phenotypes are reversed upon activating mutant expression of either ARL3 or ARL16, linking their roles to ELMOD1/3 actions.

Cross-Kingdom Activation of Vibrio Toxins by ADP-Ribosylation Factor Family GTPases.

Pathogenic Vibrio species use many different approaches to subvert, attack, and undermine the host response. The toxins they produce are often responsible for the devastating effects associated with their diseases. These toxins target a variety of host proteins, which leads to deleterious effects, including dissolution of cell organelle integrity and inhibition of protein secretion. Becoming increasingly prevalent as cofactors for Vibrio toxins are proteins of the small GTPase families. ADP-ribosylation factor small GTPases (ARFs) in particular are emerging as a common host cofactor necessary for full activation of Vibrio toxins. While ARFs are not the direct target of Vibrio cholerae cholera toxin (CT), ARF binding is required for its optimal activity as an ADP-ribosyltransferase. The makes caterpillars floppy (MCF)-like and the domain X (DmX) effectors of the Vibrio vulnificus multifunctional autoprocessing repeats-in-toxin (MARTX) toxin also both require ARFs to initiate autoprocessing and activation as independent effectors. ARFs are ubiquitously expressed in eukaryotes and are key regulators of many cellular processes, and as such they are ideal cofactors for Vibrio pathogens that infect many host species. In this review, we cover in detail the known Vibrio toxins that use ARFs as cross-kingdom activators to both stimulate and optimize their activity. We further discuss how these contrast to toxins and effectors from other bacterial species that coactivate, stimulate, or directly modify host ARFs as their mechanisms of action.

Coordination of Grp1 recruitment mechanisms by its phosphorylation.

The action of guanine nucleotide exchange factors (GEFs) on the ADP-ribosylation factor (ARF) family of small GTPases initiates intracellular transport pathways. This role requires ARF GEFs to be recruited from the cytosol to intracellular membrane compartments. An ARF GEF known as General receptor for 3-phosphoinositides 1 (Grp1) is recruited to the plasma membrane through its pleckstrin homology (PH) domain that recognizes phosphatidylinositol 3,4,5-trisphosphate (PIP3). Here, we find that the phosphorylation of Grp1 induces its PH domain to recognize instead phosphatidylinositol 4-phosphate (PI4P). This phosphorylation also releases an autoinhibitory mechanism that results in the coil–coil (CC) domain of Grp1 engaging two peripheral membrane proteins of the recycling endosome. Because the combination of these actions results in Grp1 being recruited preferentially to the recycling endosome rather than to the plasma membrane, our findings reveal the complexity of recruitment mechanisms that need to be coordinated in localizing an ARF GEF to an intracellular compartment to initiate a transport pathway. Our elucidation is also remarkable for having revealed that phosphoinositide recognition by a PH domain can be switched through its phosphorylation.

GTPases Arf5 and Arl2 function partially distinctly during oocyte meiosis.

Mammalian female meiosis must be tightly regulated to produce high-quality mature oocytes for subsequent regular fertilization and healthy live birth of the next generation. GTPases control many important signal pathways involved in diverse cellular activities. ADP-ribosylation factor family members (Arfs) in mice possess GTPase activities, and some members have been found to function in meiosis. However, whether other Arfs play a role in meiosis is unknown. In this study, we found that Arl2 and Arf5 are the richest among Arfs in mouse oocytes, and they are more abundant in oocytes than in granular cells. Furthermore, Arl2 and Arf5 depletion both impeded meiotic progression, but by affecting spindles and microfilaments, respectively. Moreover, Arl2 and Arf5 depletion both significantly increased regular reactive oxygen species levels and decreased mitochondrial membrane potential and autophagy, indicating that oocyte quality was damaged by Arl2 and Arf5 depletion. These results suggest that Arl2 and Arf5 are two novel essential GTPases required for oocyte meiosis and quality control.

De Novo and Inherited Variants in GBF1 are Associated with Axonal Neuropathy Caused by Golgi Fragmentation

SummaryDistal hereditary motor neuropathies (HMNs) and axonal Charcot-Marie-Tooth neuropathy (CMT2) are clinically and genetically heterogeneous diseases characterized primarily by motor neuron degeneration and distal weakness. The genetic cause for about half of the individuals affected by HMN/CMT2 remains unknown. Here, we report the identification of pathogenic variants in GBF1 (Golgi brefeldin A-resistant guanine nucleotide exchange factor 1) in four unrelated families with individuals affected by sporadic or dominant HMN/CMT2. Genomic sequencing analyses in seven affected individuals uncovered four distinct heterozygous GBF1 variants, two of which occurred de novo. Other known HMN/CMT2-implicated genes were excluded. Affected individuals show HMN/CMT2 with slowly progressive distal muscle weakness and musculoskeletal deformities. Electrophysiological studies confirmed axonal damage with chronic neurogenic changes. Three individuals had additional distal sensory loss. GBF1 encodes a guanine-nucleotide exchange factor that facilitates the activation of members of the ARF (ADP-ribosylation factor) family of small GTPases. GBF1 is mainly involved in the formation of coatomer protein complex (COPI) vesicles, maintenance and function of the Golgi apparatus, and mitochondria migration and positioning. We demonstrate that GBF1 is present in mouse spinal cord and muscle tissues and is particularly abundant in neuropathologically relevant sites, such as the motor neuron and the growth cone. Consistent with the described role of GBF1 in Golgi function and maintenance, we observed marked increase in Golgi fragmentation in primary fibroblasts derived from all affected individuals in this study. Our results not only reinforce the existing link between Golgi fragmentation and neurodegeneration but also demonstrate that pathogenic variants in GBF1 are associated with HMN/CMT2.

ARF family GTPases with links to cilia.

The ADP-ribosylation factor (ARF) superfamily of regulatory GTPases, including both the ARF and ARF-like (ARL) proteins, control a multitude of cellular functions, including aspects of vesicular traffic, lipid metabolism, mitochondrial architecture, the assembly and dynamics of the microtubule and actin cytoskeletons, and other pathways in cell biology. Considering their general utility, it is perhaps not surprising that increasingly ARF/ARLs have been found in connection to primary cilia. Here, we critically evaluate the current knowledge of the roles four ARF/ARLs (ARF4, ARL3, ARL6, ARL13B) play in cilia and highlight key missing information that would help move our understanding forward. Importantly, these GTPases are themselves regulated by guanine nucleotide exchange factors (GEFs) that activate them and by GTPase-activating proteins (GAPs) that act as both effectors and terminators of signaling. We believe that the identification of the GEFs and GAPs and better models of the actions of these GTPases and their regulators will provide a much deeper understanding and appreciation of the mechanisms that underly ciliary functions and the causes of a number of human ciliopathies.

Function of Arl4aa in the Initiation of Hematopoiesis in Zebrafish byMaintaining Golgi Complex Integrity in Hemogenic Endothelium.

SummaryADP-ribosylation factor-like 4aa (Arl4aa) is a member of the ADP-ribosylation factor family. It is expressed in hematopoietic tissue during embryonic development, but its function was unknown. Zebrafish arl4aa is preferentially expressed in the ventral wall of the dorsal aorta (VDA) at 24 and 36 hpf and in caudal hematopoietic tissue at 48 hpf. Morpholino knockdown and transcription activator-like effector nuclease (TALEN) knockout of arl4aa significantly reduced expression of genes associated with definitive hematopoietic stem cells (HSCs). Golgi complex integrity in VDA was disrupted as shown by transmission electron microscopy and immunostaining of Golgi membrane Giantin. Mechanistically, arl4aa knockdown reduced Notch signaling in the VDA and its target gene expression. Protein expression of NICD was also reduced. Effects of arl4aa knockdown on definitive hematopoiesis could be restored by NICD expression. This study identified arl4aa as a factor regulating initiation of definitive HSCs by maintaining the integrity of Golgi complex and, secondarily, maturation of the Notch receptor.

The Arf-GAP AoGlo3 regulates conidiation, endocytosis, and pathogenicity in the nematode-trapping fungus Arthrobotrys oligospora

Small GTPases of the ADP-ribosylation factor (Arf) family and their activating proteins (Arf-GAPs) regulate mycelial development and pathogenicity in yeast and filamentous fungi; however, little is known about their roles in nematode-trapping (NT) fungi. In this study, an ortholog of Arf-GAP Glo3 (AoGlo3) in Saccharomyces cerevisiae was characterized in the NT fungus Arthrobotrys oligospora. Deletion of the Aoglo3 gene resulted in growth defects and an increase in hyphal septum. Meanwhile, the sporulation capacity of the ΔAoglo3 mutant was decreased by 98%, and 67.1–71.2% spores became gourd or claviform in shape (from obovoid), which was accompanied by a significant decrease in the spore germination rate. This reduced sporulation capacity correlated with the transcriptional repression of several sporulation-related genes including fluG, rodA, abaA, medA, and lreA. The ΔAoglo3 mutant was also sensitive to several chemical stressors such as Congo red, NaCl, and sorbitol. Additionally, AoGlo3 was found to be involved in endocytosis, and more myelin figures were observed in the ΔAoglo3 mutant than in the wild-type strain, which was consistent with the presence of more autophagosomes observed in the mutant. Importantly, AoGlo3 affected the production of mycelial traps and serine proteases for nematode predation. In summary, AoGlo3 is involved in the regulation of multiple cellular processes such as mycelial growth, conidiation, environmental adaption, endocytosis, and pathogenicity in A. oligospora.

Silencing of ARL14 Gene Induces Lung Adenocarcinoma Cells to a Dormant State.

Recently, a growing number of ADP ribosylation factor (ARF) family members has been suggested to be critical in tumorigenesis. However, the effects of most ARF members on lung adenocarcinoma pathogenesis are still not well disclosed yet. In this study, ARF-like GTPase 14 (ARL14) was screened as an important prognostic factor of lung adenocarcinoma from The Cancer Genome Atlas (TCGA) database and validated by our in vitro experiments. It was found that silencing of ARL14 gene inhibited cell proliferation and the abilities of cell migration and invasion, and it also attenuated radiation damage of lung adenocarcinoma cells but had no effect on the proliferation of normal lung cells. Notably, ARL14 siRNA blocked the extracellular signal-regulated kinase (ERK)/p38 signaling pathway and induced cell cycle arrest in G0 phase, ultimately leading to cell dormancy. Moreover, ARL14 siRNA enhanced the expression of cell death activator DFFA-like effector (CIDEC) that had opposite roles in cell proliferation and migration to ALR14. Collectively, our results suggest that ARL14 has an important role in the pathogenesis of lung adenocarcinoma through CIDEC/ERK/p38 signaling pathway, and thus it could be applied as a new candidate of prognosis indicator and/or therapeutic target of lung adenocarcinoma.

Ancient complement and lineage-specific evolution of the Sec7 ARF GEF proteins in eukaryotes.

Guanine nucleotide exchange factors (GEFs) are the initiators of signaling by every regulatory GTPase, which in turn act to regulate a wide array of essential cellular processes. To date, each family of GTPases is activated by distinct families of GEFs. Bidirectional membrane trafficking is regulated by ADP-ribosylation factor (ARF) GTPases and the development throughout eukaryotic evolution of increasingly complex systems of such traffic required the acquisition of a functionally diverse cohort of ARF GEFs to control it. We performed phylogenetic analyses of ARF GEFs in eukaryotes, defined by the presence of the Sec7 domain, and found three subfamilies (BIG, GBF1, and cytohesins) to have been present in the ancestor of all eukaryotes. The four other subfamilies (EFA6/PSD, IQSEC7/BRAG, FBX8, and TBS) are opisthokont, holozoan, metazoan, and alveolate/haptophyte specific, respectively, and each is derived from cytohesins. We also identified a cytohesin-derived subfamily, termed ankyrin repeat-containing cytohesin, that independently evolved in amoebozoans and members of the SAR and haptophyte clades. Building on evolutionary data for the ARF family GTPases and their GTPase-­activating proteins allowed the generation of hypotheses about ARF GEF protein function(s) as well as a better understanding of the origins and evolution of cellular complexity in eukaryotes.

A Common Variant of ASAP1 Is Associated with Tuberculosis Susceptibility in the Han Chinese Population.

Background ASAP1 (also known as AMAP1 or DDEF1) encodes an Arf GTPase-activating protein (Arf GAP), a multifunctional scaffold protein that induces hydrolysis of GTP bound to the ADP-ribosylation factor (Arf) family GTP-binding proteins. Reduction of ASAP1 expression in vitro was related to suppression of cell migration and invasiveness. The genetic variant rs4733781 of the ASAP1 gene was revealed as a significant locus for tuberculosis (TB) susceptibility, but the results still need to be validated. Methods Blood samples from a total of 1914 active TB and healthy controls (HC) were collected to evaluate rs4733781 and the risk of TB. Meanwhile, a total of 48 noninfected HC, latent TB-infected (LTBI) controls, and active TB were collected to assay ASAP1 expression difference among the three groups. The QuantiFERON-TB Gold In-Tube was adopted to identify noninfected HC and LTBI. Results The genetic variant of rs4733781 was found to be significantly associated with TB, and the A allele of rs4733781 (C>A) was 0.38 and 0.43 among TB cases and HC, respectively (P = 0.0035). Meanwhile, the peripheral blood monocyte RNA fold changes for the ASAP1 gene among the 16 HC, 16 LTBI, and 16 active TB were 1.088 ± 0.4919, 2.237 ± 0.6505, and 10.12 ± 10.98 (F = 9.559, P = 0.0003), respectively, and the expression of ASAP1 was increased by 2.06-fold (P < 0.0001) and 9.30-fold (P < 0.0052) for LTBI and active TB, when compared to the HC. Conclusions Our data indicated that the A allele of rs4733781 for the ASAP1 gene was in association with a decreased risk of TB. But not only that, the overexpression of the ASAP1 gene among LTBI and TB was related to the progression of TB, which further implies that the expression of ASAP1 would be a potential biomarker for LTBI and TB diagnoses.

FAM134B promotes adipogenesis by increasing vesicular activity in porcine and 3T3-L1 adipocytes.

Family with sequence similarity 134, Member B (FAM134B), is a cis-Golgi transmembrane protein that is known to be necessary for the long-term survival of nociceptive and autonomic ganglion neurons. Recent work has shown that FAM134B plays a pivotal role in autophagy-mediated turnover of endoplasmic reticulum (ER) membranes, tumor inhibition and lipid homeostasis. In this study, we provide mechanistic links between FAM134B and ARF-related protein 1 (ARFRP1) and further show that FAM134B resides in the Golgi apparatus. Here, we found that FAM134B increased lipid accumulation in adipocytes. Transport vehicle number and ADP-ribosylation factor (ARF) family gene expression were also increased by FAM134B overexpression, suggesting that vesicular transport activity enhanced lipid accumulation. ARF-related protein 1 (ARFRP1) is a GTPase that promotes protein trafficking. We show that FAM134B regulates the expression of ARFRP1, and the knockdown of ARFRP1 abolishes enhancement on lipid accumulation caused by FAM134B. In addition, FAM134B upregulates the PAT family protein (PAT), which associates with the lipid droplets (LDs) surface and promotes lipolysis by recruiting adipocyte triglyceride lipase (ATGL). These findings indicate that FAM134B promotes lipid accumulation and adipogenic differentiation by increasing vesicle transport activity in the Golgi apparatus and inhibiting the lipolysis of LDs.