A single blinded, phase IV, adaptive randomised control trial to evaluate the safety of coadministration of seasonal influenza and COVID-19 vaccines (The FluVID study).

OBJECTIVES: We evaluated the frequency of moderate and severe adverse events following coadministration of seasonal influenza vaccine (SIV) versus placebo with COVID-19 vaccines among adults to support practice guidelines. METHODS: FluVID is a participant-blinded, phase IV, randomised control trial. On the same day as the participant's scheduled COVID-19 vaccine, participants were randomised to receive SIV or saline placebo; those assigned placebo at visit one then received SIV a week later, and vice versa. Self-reported adverse events were collected daily for seven days following each visit. The primary endpoint was any solicited adverse event of at least moderate severity occurring up to seven days following receipt of SIV or placebo. This was modelled using a Bayesian logistic regression model. Analyses were performed by COVID-19 vaccine type and dose number. RESULTS: Overall, 248 participants were enrolled; of these, 195 had received BNT162b2 and 53 had received mRNA1273 COVID-19 vaccines according to national guidelines. After randomisation, 119 were assigned to receive SIV and 129 were assigned to receive placebo at visit one. Adverse events were most frequently reported as mild (grade 1) in nature. Among 142 BNT162b2 booster dose one and 43 BNT162b2 booster dose two recipients, the posterior median risk difference for moderate/severe adverse events following SIV versus placebo was 13% (95% credible interval [CrI] -0.03 to 0.27) and 13% (95%CrI -0.37 to 0.12), respectively. Among 18 mRNA1273 booster dose one and 35 mRNA1273 booster dose two recipients, the posterior median risk difference of moderate/severe adverse events following influenza vaccine versus placebo was 6% (95%CrI -0.29 to 0.41) and -4% (95%CrI -0.30 to 0.23), respectively. CONCLUSION: Adverse events following SIV and COVID-19 co-administration were generally mild and occurred with similar frequency to events following COVID-19 vaccine alone. We found no evidence to justify routine separation of SIV and COVID-19 vaccine doses. CLINICAL TRIAL REGISTRATION: ACTRN12621001063808.

The effects of the DNA Demethylating reagent, 5-azacytidine on SMCHD1 genomic localization.

BACKGROUND: DNA methylation is an epigenetic modification that mainly repress expression of genes essential during embryogenesis and development. There are key ATPase-dependent enzymes that read or write DNA methylation to remodel chromatin and regulate gene expression. Structural maintenance of chromosome hinge domain containing 1 (SMCHD1) is an architectural protein that regulates expression of numerous genes, some of which are imprinted, that are sensitive to DNA methylation. In addition, SMCHD1 germline mutations lead to developmental diseases; facioscapulohumoral muscular dystrophy (FSHD), bosma arhinia and micropthalmia (BAMS). Current evidence suggests that SMCHD1 functions through maintenance or de novo DNA methylation required for chromatin compaction. However, it is unclear if DNA methylation is also essential for genomic recruitment of SMCHD1 and its role as an architectural protein. We previously isolated SMCHD1 using a methylated DNA region from mouse pituitary growth hormone (Gh1) promoter, suggesting that methylation is required for SMCHD1 DNA binding. The goal of this study was to further understand DNA methylation directed role of SMCHD1 in regulating gene expression. Therefore, we profiled SMCHD1 genome wide occupancy in human neuroblastoma SH-SY5Y cells and evaluated if DNA methylation is required for SMCHD1 genomic binding by treating cells with the DNA demethylating reagent, 5-azacytidine (5-azaC). RESULTS: Our data suggest that the majority of SMCHD1 binding occurs in intron and intergenic regions. Gene ontology analysis of genes associated with SMCHD1 genomic occupancy that is sensitive to 5-azaC treatment suggests SMCHD1 involvement in central nervous system development. The potassium voltage-gated channel subfamily Q member1 (KCNQ1) gene that associates with central nervous system is a known SMCHD1 target. We showed SMCHD1 binding to an intronic region of KCNQ1 that is lost following 5-azaC treatment suggesting DNA methylation facilitated binding of SMCHD1. Indeed, deletion of SMCHD1 by CRISPR- Cas9 increases KCNQ1 gene expression confirming its role in regulating KCNQ1 gene expression. CONCLUSION: These findings provide novel insights on DNA methylation directed function of SMCHD1 in regulating expression of genes associated with central nervous system development that impact future drug development strategies.

Retinoblastoma protein (Rb) links hypoxia to altered mechanical properties in cancer cells as measured by an optical tweezer.

Hypoxia modulates actin organization via multiple pathways. Analyzing the effect of hypoxia on the biophysical properties of cancer cells is beneficial for studying modulatory signalling pathways by quantifying cytoskeleton rearrangements. We have characterized the biophysical properties of human LNCaP prostate cancer cells that occur in response to loss of the retinoblastoma protein (Rb) under hypoxic stress using an oscillating optical tweezer. Hypoxia and Rb-loss increased cell stiffness in a fashion that was dependent on activation of the extracellular signal-regulated kinase (ERK) and the protein kinase B (AKT)- mammalian target of rapamycin (MTOR) pathways. Pharmacological inhibition of MEK1/2, AKT or MTOR impeded hypoxia-inducible changes in the actin cytoskeleton and inhibited cell migration in Rb-deficient cells conditioned with hypoxia. These results suggest that loss of Rb in transformed hypoxic cancer cells affects MEK1/2-ERK/AKT-MTOR signalling and promotes motility. Thus, the mechanical characterization of cancer cells using an optical tweezer provides an additional technique for cancer diagnosis/prognosis and evaluating therapeutic performance.

Rosuvastatin vs. protease inhibitor switching for hypercholesterolaemia: a randomized trial.

OBJECTIVES: The aim of the study was to compare the efficacy and safety of rosuvastatin initiation with those of switching of ritonavir-boosted protease inhibitors (PI/rs) in HIV-1-infected adults with hypercholesterolaemia and increased cardiovascular risk scores. METHODS: In this open-label, multicentre study, HIV-1-infected adults on PI/r-based therapy with viral load < 50 HIV-1 RNA copies/mL, fasting total cholesterol ≥ 5.5 mmol/L (both for ≥ 6 months) and elevated cardiovascular risk (Framingham score ≥ 8% or diabetes or family history), and not on lipid-lowering therapy, were randomized to open-label rosuvastatin 10 mg/day or to PI/r switching, both with standardized diet/exercise advice. The primary endpoint was change in total cholesterol at week 12 (intention to treat). RESULTS: There were 43 participants (23 on rosuvastatin). Baseline characteristics were: mean [± standard deviation (SD)] age 55 (8.5) years, 42 (98%) male, 41 (95%) white race, and mean (± SD) total cholesterol 6.2 (1.2) mmol/L. At enrolment, PI/rs were lopinavir/ritonavir (n = 22; 51%), atazanavir/ritonavir (n = 12; 28%) and darunavir/ritonavir (n = 9; 21%). The commonest PI/r substitutes were raltegravir (n = 9; 45%) and rilpivirine (n = 4; 20%). All participants were adherent through to week 12. Rosuvastatin yielded greater declines than PI/r switching in total (- 21.4% vs. - 8.7%, respectively; P = 0.003) and low-density lipoprotein (- 29.9% vs. - 1.0%, respectively; P < 0.001) cholesterol, but smaller declines in very low-density lipoprotein cholesterol and triglycerides (P < 0.01). Cholesterol lowering was greater in participants on atazanavir/ritonavir or once-daily darunavir/ritonavir (vs. lopinavir/ritonavir). More study drug-related adverse events (mostly grade 1 nausea/diarrhoea; 10 vs. one, respectively; P = 0.001) occurred with PI/r switching than with rosuvastatin. CONCLUSIONS: In adults receiving a PI/r, rosuvastatin 10 mg/day for 12 weeks yielded larger decreases in total and low-density lipoprotein cholesterol than PI/r switching, and was better tolerated.

Switch from tenofovir to raltegravir increases low bone mineral density and decreases markers of bone turnover over 48 weeks.

BACKGROUND: Tenofovir, particularly when given with a ritonavir-boosted protease inhibitor (rPI), reduces bone mineral density (BMD) and increases bone turnover markers (BTMs), both of which are associated with increased fracture risk. Raltegravir has not been associated with bone loss. METHODS: In an open-label, nonrandomized, pilot study, tenofovir was switched to raltegravir in adults also receiving a rPI for at least 6 months with a spine or hip T-score ≤ -1.0 and plasma HIV RNA < 50 HIV-1 RNA copies/mL for at least 3 months. The primary endpoint was BMD change by dual-energy X-ray absorptiometry. Student's paired t-test was used to compare continuous variables. Factors associated with BMD increase were assessed using linear regression. RESULTS: Thirty-seven patients were enrolled in the study: 97% were male, the mean age was 49 years, the mean T-scores were -1.4 (spine) and -1.3 (total left hip), and the mean tenofovir treatment duration was 3.1 years. BMD increases were significant at weeks 24 and 48. At week 48, spine BMD increased by 3.0% [95% confidence interval (CI) 1.9, 4.0%; P < 0.0001] and left total hip BMD increased by 2.5% (95% CI 1.6, 3.3%; P < 0.0001). BTMs (N-telopeptide, osteocalcin and bone alkaline phosphatase) all decreased significantly at week 24 (P ≤ 0.0017). There were no raltegravir-related serious or grade 3-4 adverse events. HIV viral load remained <50 copies/mL plasma on raltegravir/rPI therapy. CONCLUSIONS: Switching virologically suppressed HIV-infected adults with low BMD taking an rPI from tenofovir to raltegravir was safe and significantly improved hip and spine BMD and reduced markers of bone turnover over 48 weeks.

Fatal Nocardia cyriacigeorgica spontaneous bacterial peritonitis.

We report the first case of fatal spontaneous bacterial peritonitis and fulminant hepatitis caused by Nocardia cyriacigeorgica in a patient with hepatitis C-related liver cirrhosis.

Anesthetic management for cesarean delivery in a parturient with exacerbated hemophagocytic syndrome.

Hemophagocytic syndrome is an uncommon disease characterized by cytokine dysfunction and uncontrolled hemophagocytosis. It arises rarely during pregnancy, in which case maternal and fetal mortality are relatively high. It has some similarities with HELLP syndrome. Poor maternal condition increases the risk of preterm labor and the possibility of emergency cesarean delivery in non-optimal conditions, presenting a great challenge to the anesthesiologists. We report a 28-year-old primigravida with the onset of hemophagocytic syndrome and cyopenia at 23 weeks of gestation. A further exacerbation at 28 weeks of gestation brought on preterm labor. General anesthesia was provided successfully for cesarean delivery. The patient recovered completely after this episode. We suggest that early diagnosis, multi-disciplinary intervention, pre-operative correction of the hematological abnormalities, general anesthesia and close postoperative monitoring are necessary.

Direct interactions between NMDA and D1 receptors: a tale of tails.

Considerable evidence has accumulated describing a complex interaction between the dopaminergic and glutamatergic pathways. Efforts to describe the mechanisms underlying this complex interaction have implicated a functional interaction between dopamine and glutamate receptors. Classically, the interaction between D(1) and NMDA (N-methyl-D-aspartate) receptors has been proposed to involve the activation of second-messenger signalling cascades after receptor stimulation. However, in recent years, another paradigm has emerged which involves the direct interaction between D(1) and NMDA receptors. The physical association between D(1) and NMDA receptors is unique in that two different regions of the D(1) C-terminus are able to couple specifically and physically with two different NMDA subunits. The selective modulation of multiple NMDA receptor-mediated functions by direct interactions with D(1) receptors may form a new avenue to identify specific targets for therapeutics to modulate NMDA receptor-governed synaptic plasticity, neuronal development and disease states.

Direct binding and functional coupling of alpha-synuclein to the dopamine transporters accelerate dopamine-induced apoptosis.

Mutations in alpha-synuclein, a protein highly enriched in presynaptic terminals, have been implicated in the expression of familial forms of Parkinson's disease (PD) whereas native alpha-synuclein is a major component of intraneuronal inclusion bodies characteristic of PD and other neurodegenerative disorders. Although overexpression of human alpha-synuclein induces dopaminergic nerve terminal degeneration, the molecular mechanism by which alpha-synuclein contributes to the degeneration of these pathways remains enigmatic. We report here that alpha-synuclein complexes with the presynaptic human dopamine transporter (hDAT) in both neurons and cotransfected cells through the direct binding of the non-A beta amyloid component of alpha-synuclein to the carboxyl-terminal tail of the hDAT. alpha-Synuclein--hDAT complex formation facilitates the membrane clustering of the DAT, thereby accelerating cellular dopamine uptake and dopamine-induced cellular apoptosis. Since the selective vulnerability of dopaminergic neurons in PD has been ascribed in part to oxidative stress as a result of the cellular overaccumulation of dopamine or dopamine-like molecules by the presynaptic DAT, these data provide mechanistic insight into the mode by which the activity of these two proteins may give rise to this process.

Does learning a complex task have to be complex? A study in learning decomposition.

Many theories of skill acquisition have had considerable success in addressing the fine details of learning in relatively simple tasks, but can they scale up to complex tasks that are more typical of human learning in the real world? Some theories argue for scalability by making the implicit assumption that complex tasks consist of many smaller parts, which are learned according to basic learning principles. Surprisingly, there has been rather sparse empirical testing of this crucial assumption. In this article, we examine this assumption directly by decomposing the learning in the Kanfer-Ackerman Air-Traffic Controller Task (Ackerman, 1988) from the learning at the global level all the way down to the learning at the keystroke level. First, we reanalyze the data from Ackerman (1988) and show that the learning in this complex task does indeed reflect the learning of smaller parts at the keystroke level. Second, in a follow-up eye-tracking experiment, we show that a large portion of the learning at the keystroke level reflects the learning even at a lower, i.e., attentional level.

ARL4, an ARF-like protein that is developmentally regulated and localized to nuclei and nucleoli.

ADP-ribosylation factors (ARFs) are highly conserved approximately 20-kDa guanine nucleotide-binding proteins that participate in both exocytic and endocytic vesicular transport pathways via mechanisms that are only partially understood. Although several ARF-like proteins (ARLs) are known, their biological functions remain unclear. To characterize its molecular properties, we cloned mouse and human ARL4 (mARL4 and hARL4) cDNA. The appearance of mouse ARL4 mRNA during embryonic development coincided temporally with the sequential formation of somites and the establishment of brain compartmentation. Using ARL4-specific antibody for immunofluorescence microscopy, we observed that endogenous mARL4 in cultured Sertoli and neuroblastoma cells was mainly concentrated in nuclei. When expressed in COS7 cells, ARL4-T34N mutant, predicted to exist with GDP bound, was concentrated in nucleoli. Yeast two-hybrid screening and in vitro protein-interaction assays showed that hARL4 interacted with importin-alpha through its C-terminal NLS region and that the interaction was not nucleotide-dependent. Like ARL2 and -3, recombinant hARL4 did not enhance cholera toxin-catalyzed auto-ADP-ribosylation. Its binding of guanosine 5'-O-(thiotriphosphate) was modified by phospholipid and detergent, and the N terminus of hARL4, like that of ARF, was myristoylated. Our findings suggest that ARL4, with its distinctive nuclear/nucleolar localization and pattern of developmental expression, may play a unique role(s) in neurogenesis and somitogenesis during embryonic development and in the early stages of spermatogenesis in adults.

A cognate dopamine transporter-like activity endogenously expressed in a COS-7 kidney-derived cell line.

The activity of the dopamine transporter is an important mechanism for the maintenance of normal dopaminergic homeostasis by rapidly removing dopamine from the synaptic cleft. In kidney-derived COS-7, COS-1 and HEK-293 but not in other mammalian cell lines (CHO, Y1, Ltk-), we have characterized a putative functional dopamine transporter displaying a high affinity (Km approximately 250 nM) and a low capacity (approximately 0.1 pmol/10(5) cells/min) for [3H]dopamine uptake. Uptake displayed a pharmacological profile clearly indicative of the neuronal dopamine transporter. Estimated Ki values of numerous substrates and inhibitors for the COS-dopamine transporter and the cloned human neuronal transporter (human dopamine transporter) correlate well with the exception of a few notable compounds, including the endogenous neurotransmitter dopamine, the dopamine transporter inhibitor GBR 12,909 and the dopaminergic agonist apomorphine. As with native neuronal and cloned dopamine transporters, the uptake velocity was sodium-sensitive and reduced by phorbol ester pre-treatment. Two mRNA species of 3.8 and 4.0 kb in COS-7 cells were revealed by Northern blot analysis similar in size to that seen in native neuronal tissue. A reverse-transcribed PCR analysis confirmed the existence of a processed dopamine transporter. However, no immunoreactive proteins of expected dopamine transporter molecular size or [3H]WIN 35,428 binding activity were detected. A partial cDNA of 1.3 kb, isolated from a COS-1 cDNA library and encoding transmembrane domains 1-6, displayed a deduced amino acid sequence homology of approximately 96% to the human dopamine transporter. Taken together, the data suggest the existence of a non-neuronal endogenous high affinity dopamine uptake system sharing strong functional and molecular homology to that of the cloned neuronal dopamine transporter.

Structural elements of ADP-ribosylation factor 1 required for functional interaction with cytohesin-1.

ADP-ribosylation factor 1 (ARF1) is a 20-kDa guanine nucleotide-binding protein involved in vesicular trafficking. Conversion of inactive ARF-GDP to active ARF-GTP is catalyzed by guanine nucleotide exchange proteins such as cytohesin-1. Cytohesin-1 and its Sec7 domain (C-1Sec7) exhibit guanine nucleotide exchange protein activity with ARF1 but not ARF-like protein 1 (ARL1), which is 57% identical in amino acid sequence. With chimeric proteins composed of ARF1 (F) and ARL1 (L) sequences we identified three structural elements responsible for this specificity. Cytohesin-1 increased [35S]guanosine 5'-(gamma-thio)triphosphate binding to L28/F (first 28 residues of L, remainder F) and to a much lesser extent F139/L, and mut13F139/L (F139/L with random sequence in the first 13 positions) but not Delta13ARF1 that lacks the first 13 amino acids; therefore, a nonspecific ARF N terminus was required for cytohesin-1 action. The N terminus was not, however, required for that of C-1Sec7. Both C-1Sec7 and cytohesin-1 effectively released guanosine 5'-(gamma-thio)triphosphate from ARF1, but only C-1Sec7 displaced the nonhydrolyzable GTP analog bound to mut13F139/L, again indicating that structure in addition to the Sec7 domain is involved in cytohesin-1 interaction. Some element(s) of the C-terminal region is also involved, because replacement of the last 42 amino acids with ARL sequence in F139L decreased markedly the interaction with cytohesin-1. Participation of both termini is consistent with the crystallographic structure of ARF in which the two terminal alpha-helices are in close proximity. ARF1 residues 28-50 are also important in the interaction with cytohesin-1; replacement of Lys-38 with Gln, the corresponding residue in ARL1, abolished the ability to serve as substrate for cytohesin-1 or C-1Sec7. These studies have defined multiple structural elements in ARF1, including switch 1 and the N and C termini, that participate in functional interactions with cytohesin-1 (or its catalytic domain C-1Sec7), which were not apparent from crystallographic analysis.

Characterization of a novel ADP-ribosylation factor-like protein (yARL3) in Saccharomyces cerevisiae.

ADP-ribosylation factors (ARFs) are highly conserved, approximately 20-kDa guanine nucleotide-binding proteins that enhance the ADP-ribosyltransferase activity of cholera toxin and have an important role in vesicular transport. Several cDNAs for ARF-like proteins (ARLs) have been cloned from human, Drosophila, rat, and yeast, although the biological function(s) of ARLs is unknown. We have identified a yeast gene (yARL3) encoding a protein that is structurally related (>43% identical) to the mammalian ARF-like protein ARP. Biochemical studies of purified recombinant yARL3 protein revealed properties similar to those of ARF and ARL proteins, including the ability to bind and hydrolyze GTP. Like other ARLs, recombinant yARL3 did not stimulate cholera toxin-catalyzed auto-ADP-ribosylation. Anti-yARL3 antibodies did not cross-react with yARFs or yARL1. yARL3 was not essential for cell viability, but disruption of yARL3 resulted in cold-sensitive cell growth. At the nonpermissive temperature, processing of alkaline phosphatase and carboxypeptidase Y in arl3 mutant was slowed. yARL3 might be required for protein transport from endoplasmic reticulum to Golgi or from Golgi to vacuole at nonpermissive temperatures. On subcellular fractionation, unlike its mammalian homologue ARP, yARL3 was detected in the soluble fraction but not in the plasma membrane. Indirect immunofluorescence analysis revealed that yARL3 when overexpressed was associated in part with the endoplasmic reticulum-nuclear envelope. Thus, the structural and functional characteristics of yARL3 indicate that it may have a unique role(s) in vesicular trafficking.

Identification and subcellular localization of a novel Cu,Zn superoxide dismutase of Mycobacterium tuberculosis.

Periplasmic copper, zinc superoxide dismutases (Cu,ZnSOD) of several Gram-negative pathogens have been shown to play an important role in protection against exogenous superoxide radicals and in determining virulence of the pathogens. Here we report the cloning and characterization of the sodC gene, encoding Cu,ZnSOD, from the Gram-positive Mycobacterium tuberculosis. The predicted protein sequence contains 240 amino acids with a putative signal peptide at the N-terminus and shows approximately 25% identity to other bacterial sodC. Recombinant proteins of a full-length sodC and a truncated form lacking the putative signal peptide were overexpressed in Escherichia coli and affinity purified. Renatured recombinant M. tuberculosis sodC protein possessed characteristics of a Cu,ZnSOD. Immunoblotting with an antiserum against the recombinant M. tuberculosis Cu,ZnSOD allowed detection of a single polypeptide in the lysate of M. tuberculosis. This polypeptide has a similar size as the recombinant protein without the putative signal peptide indicating that the endogenous Cu,ZnSOD in M. tuberculosis might be processed and secreted. Furthermore, immunogold electron microscopic image showed that Cu,ZnSOD is located in the periphery of M. tuberculosis. The enzymatic activity and subcellular localization of this novel Cu,ZnSOD suggest that it may play a role in determining virulence of M. tuberculosis.

Protein kinase-mediated bidirectional trafficking and functional regulation of the human dopamine transporter.

Modification of the transport velocity of both the native neuronal and cloned presynaptic dopamine transporter (DAT) has been reported following activation/inhibition of second messenger system pathways. In order to identify the mechanism by which the functional activity of human DAT (hDAT) is regulated, we assessed the [3H]dopamine uptake kinetics, [3H] CFT binding characteristics, and, via immunofluorescent confocal microscopy, the cellular localization profiles of the hDAT expressed in both Sf9 and COS-7 cells following modulation of protein kinase C (PKC)- and protein kinase A (PKA)-dependent pathways. As with both native neuronal and cloned DATs, acute exposure of hDAT expressing Sf9 cells to the PKC activator PMA (1 microM), but not alphaPDD, reduced the Vmax (approximately 1 pmol/min/10(5) cells) for [3H]DA uptake by approximately 40%, an effect which was blocked by the protein kinase inhibitor staurosporine. Pretreatment of cells with staurosporine (500 nM) alone, however, increased [3H]DA uptake velocity by approximately 30%, an effect mimicked by the potent PKA inhibitor Rp-cAMPS. Activation of PKA-dependent pathways with Sp-cAMPS did not significantly modify DA uptake. Neither the Km of [3H]DA uptake (approximately 200 nM) nor the affinity of various substrates and transport inhibitors was altered by either PMA or staurosporine treatment. Despite changes in functional dopamine uptake velocity by PKC/PKA-dependent mechanisms, the estimated density of hDAT as indexed by whole-cell [3H] CFT binding was unchanged. Immunofluorescent confocal microscopy demonstrated that the observed functional consequence of PKC activation on [3H]DA uptake is associated with the rapid sequestration/internalization of hDAT protein from the cell surface, while the increase in DA uptake following PKC/PKA inhibition is the result of the recruitment of internalized or intracellular transporters to the plasma membrane. Identical rapid translocation patterns were observed in similarly treated COS-7 cells transiently expressing hDAT. These data suggest that the differential regulation of DAT transport capacity by both PKC- and PKA-dependent pathways are not a result of modifications in DAT catalytic activity. Moreover, the rapid shuttling of DATs between the plasma membrane and intracellular compartments provides an efficient means by which native DAT function may be regulated by second messenger systems, possibly following activation of presynaptic dopaminergic receptors, and suggests a role for cytoskeletal components in the dynamic regulation of DAT function.

Phospholipid- and GTP-dependent activation of cholera toxin and phospholipase D by human ADP-ribosylation factor-like protein 1 (HARL1).

ADP-ribosylation factors (ARFs), 20-kDa guanine nucleotide-binding proteins named for their ability to activate cholera toxin (CT) ADP-ribosyltransferase activity, have a critical role in vesicular transport and activate a phospholipase D (PLD) isoform. Although ARF-like (ARL) proteins are very similar in sequence to ARFs, they were initially believed not to activate CT or PLD. mRNA for human ARL1 (hARL1), which is 57% identical in amino acid sequence to hARF1, is present in all tissues, with the highest amounts in kidney and pancreas and barely detectable amounts in brain. Relative amounts of hARL1 protein were similar to mRNA levels. Purified hARL1 (rARL1) synthesized in Escherichia coli had less activity toward PLD than did rARF1, although PLD activation by both proteins was guanosine guanosine 5'-(gamma-thio)triphosphate (GTPgammaS)-dependent. ARL1 stimulation of CT-catalyzed ADP-ribosylation was considerably less than that by rARF1 and was phospholipid dependent. GTPgammaS-binding by rARL1 was also phospholipid- and detergent-dependent, and in assays containing phosphatidylserine, was greater than that by rARF1. In vitro, the activities of rARL1 and rARF1 are similar. Rather than being a member of a separate subfamily, hARL1, which activates PLD and CT in a phospholipiddependent manner, appears to be part of a continuum of ARF family proteins.