A dimensional investigation of error-related negativity (ERN) and self-reported psychiatric symptoms.

Alterations in error processing are implicated in a range of DSM-defined psychiatric disorders. For instance, obsessive-compulsive disorder (OCD) and generalised anxiety disorder show enhanced electrophysiological responses to errors-i.e. error-related negativity (ERN)-while others like schizophrenia have an attenuated ERN. However, as diagnostic categories in psychiatry are heterogeneous and also highly intercorrelated, the precise mapping of ERN enhancements/impairments is unclear. To address this, we recorded electroencephalograms (EEG) from 196 participants who performed the Flanker task and collected scores on 9 questionnaires assessing psychiatric symptoms to test if a dimensional framework could reveal specific transdiagnostic clinical manifestations of error processing dysfunctions. Contrary to our hypothesis, we found non-significant associations between ERN amplitude and symptom severity of OCD, trait anxiety, depression, social anxiety, impulsivity, eating disorders, alcohol addiction, schizotypy and apathy. A transdiagnostic approach did nothing to improve signal; there were non-significant associations between all three transdiagnostic dimensions (anxious-depression, compulsive behaviour and intrusive thought, and social withdrawal) and ERN magnitude. In these same individuals, we replicated a previously published transdiagnostic association between goal-directed learning and compulsive behaviour and intrusive thought. Possible explanations discussed are (i) that associations between the ERN and psychopathology might be smaller than previously assumed, (ii) that these associations might depend on a greater level of symptom severity than other transdiagnostic cognitive biomarkers, or (iii) that task parameters, such as the ratio of compatible to incompatible trials, might be crucial for ensuring the sensitivity of the ERN to clinical phenomena.

Qualitative Evaluation of a Community-Based Physical Activity and Yoga Program for Men Living With Prostate Cancer: Survivor Perspectives.

PURPOSE: Physical activity (PA) programs for prostate cancer survivors have positive effects on many aspects of health-related quality of life. Translating this research into sustainable community-based settings is necessary to ensure access to programs for survivors. This study examines patient perspectives in the community-based TrueNTH Lifestyle Management (TrueNTH LM) program in Calgary, Canada. METHODS: Eleven men from programs at civic wellness centers participated in 2 small semistructured focus groups (n = 5 and 6) at the University of Calgary. Motivation for program initiation and adherence, benefits and barriers to participation, and individual satisfaction and feedback on program improvement were discussed. Audio recordings were transcribed and analyzed using thematic methodology guided by a pragmatic philosophy on the patient experience in the program. RESULTS: Themes identified included perceived benefits of participating (physical, psychological, and social), facilitators for involvement in the PA program (program design, initial free access, tailored to prostate cancer specific needs, psychosocial environment), and opportunities for improvement and sustainability (exercise as a part of standard care, cost structure, home-based options). CONCLUSIONS: These findings provide valuable insight into patient perspectives on effective characteristics of prostate cancer and exercise programs. TrueNTH LM has implemented findings, and ensuring needs (benefits and barriers) are addressed for prostate cancer survivors when entering community-based PA programs.

Structural and mechanistic studies on the peroxisomal oxygenase phytanoyl-CoA 2-hydroxylase (PhyH).

Phytanic acid (PA) is an epimeric metabolite of the isoprenoid side chain of chlorophyll. Owing to the presence of its epimeric beta-methyl group, PA cannot be metabolized by beta-oxidation. Instead, it is metabolized in peroxisomes via alpha-oxidation to give pristanic acid, which is then oxidized by beta-oxidation. PhyH (phytanoyl-CoA 2-hydroxylase, also known as PAHX), an Fe(II) and 2OG (2-oxoglutarate) oxygenase, catalyses hydroxylation of phytanoyl-CoA. Mutations of PhyH ablate its role in alpha-oxidation, resulting in PA accumulation and ARD (adult Refsum's disease). The structure and function of PhyH is discussed in terms of its clinical importance and unusual selectivity. Most point mutations of PhyH causing ARD cluster in two distinct groups around the Fe(II)- and 2OG-binding sites. Therapaeutic possibilities for the treatment of Refsum's disease involving PhyH are discussed.

Substance abuse in young patients with type 1 diabetes: easily neglected in complex medical management.

The use of recreational drugs has become increasingly popular among young people. As a centre caring for a large group of young patients with type 1 diabetes, we have become concerned about the number of patients presenting with drug-related metabolic problems. We present a case series highlighting the issues of substance abuse in young patients with type 1 diabetes.

Oxidation by 2-oxoglutarate oxygenases: non-haem iron systems in catalysis and signalling.

The 2-oxoglutarate (2OG) and ferrous iron dependent oxygenases are a superfamily of enzymes that catalyse a wide range of reactions including hydroxylations, desaturations and oxidative ring closures. Recently, it has been discovered that they act as sensors in the hypoxic response in humans and other animals. Substrate oxidation is coupled to conversion of 2OG to succinate and carbon dioxide. Kinetic, spectroscopic and structural studies are consistent with a consensus mechanism in which ordered binding of (co)substrates enables control of reactive intermediates. Binding of the substrate to the active site triggers the enzyme for ligation of dioxygen to the metal. Oxidative decarboxylation of 2OG then generates the ferryl species thought to mediate substrate oxidation. Structural studies reveal a conserved double-stranded beta-helix core responsible for binding the iron, via a 2His-1carboxylate motif and the 2OG side chain. The rigidity of this core contrasts with the conformational flexibility of surrounding regions that are involved in binding the substrate. Here we discuss the roles of 2OG oxygenases in terms of the generic structural and mechanistic features that render the 2OG oxygenases suited for their functions.

Factor inhibiting hypoxia-inducible factor (FIH) and other asparaginyl hydroxylases.

FIH (Factor inhibiting hypoxia-inducible factor), an asparaginyl beta-hydroxylase belonging to the super-family of 2-oxoglutarate and Fe(II)-dependent dioxygenases, catalyses hydroxylation of Asn-803 of hypoxia-inducible factor, a transcription factor that regulates the mammalian hypoxic response. Only one other asparaginyl beta-hydroxylase, which catalyses hydroxylation of both aspartyl and asparaginyl residues in EGF (epidermal growth factor)-like domains, has been characterized. In the light of recent crystal structures of FIH, we compare FIH with the EGFH (EGF beta-hydroxylase) and putative asparagine/asparaginyl hydroxylases. Sequence analyses imply that EGFH does not contain the HXD/E iron-binding motif characteristic of most of the 2-oxoglutarate oxygenases.

Saving clinicians' time by delegating routine aspects of therapy to a computer: a randomized controlled trial in phobia/panic disorder.

BACKGROUND: The demand for time-consuming psychotherapy of phobia/panic exceeds the supply of trained therapists. Delegating routine therapy aspects to a computer might ease this problem. METHOD: Ninety-three out-patients with phobia or panic disorder were randomized in a 2: 2 : 1 ratio to have self-exposure therapy guided either mainly by a stand-alone computer system (FearFighter) or entirely face-to-face by a clinician, or to have mainly computer-guided self-relaxation as a placebo. Both computer groups (FearFighter and relaxation) had brief back-up advice from a clinician. Primary outcome measures were self- and blind-assessor ratings of Main Problem and Goals, and Global Phobia. RESULTS: Drop-outs occurred significantly more often in the two self-exposure groups (43% if mainly computer-guided, 24% if entirely clinician-guided) than with self-relaxation (6%); the difference between the two self-exposure groups was not significant. Even with all drop-outs included, the mainly computer-guided exposure group and the relaxation group had 73% less clinician time per patient than did the entirely clinician-guided exposure group. The two self-exposure groups had comparable improvement and satisfaction at post-treatment and at 1-month follow-up, while relaxation was ineffective. Mean improvement on the primary outcome measures (self- and assessor-rated) was 46% computer, 49% clinician, 9% relaxation at post-treatment (week 10) and 58% computer, 53% clinician and -4% relaxation at 1-month follow-up (week 14). Mean effect sizes on the primary outcome measures were 2.9 computer, 3.5 clinician and 0.5 relaxation at post-treatment; and 3.7 computer, 3.5 clinician and 0.5 relaxation at 1-month follow-up. The assessor did not rate patients at follow-up. CONCLUSIONS: Despite its (non-significantly) higher dropout rate, self-exposure therapy for panic/ phobia cut clinician time per patient by 73% without losing efficacy when guided mainly by a computer rather than entirely by a clinician. The finding needs confirmation at a follow-up that is longer and includes a blind assessor. Self-relaxation had the highest rate of completers but was ineffective.

Pharmacological management of obsessive-compulsive disorder: a review for clinicians.

Obsessive-compulsive disorder (OCD) has been treated pharmacologically with drugs that enhance availability of the neurotransmitter serotonin. This review summarizes the available literature on the pharmacological treatments of OCD. Numerous randomized controlled trials have attested to the efficacy of serotonin-reuptake inhibitors (SRIs) in treating this disorder, although a coherent model of serotonin dysfunction in OCD has not been established. Meta-analyses of randomized controlled trials have found better results with clomipramine than with other SRIs, but comparative studies have so far not replicated this finding. Aspects of the methodology in these studies that might explain this discrepancy are considered. Tolerability, side effects, dosing, and safety during pregnancy of the SRIs are discussed. Treatment of OCD with poor insight and of OCD comorbid with a tic disorder, augmentation strategies, and management of partial response to SRIs are reviewed. Finally, the available interventions for refractory OCD are considered.

Erotomania revisited: clinical course and treatment.

Erotomania is a rare disorder in which an individual has a delusional belief that a person of higher social status falls in love and makes amorous advances towards him/her. Little is known about the background, classification, treatment, or outcome of individuals with this disorder. The purpose of this study was to evaluate current criteria for diagnosing and classifying primary and secondary erotomania in addition to examining course, outcome, and impact on victims of erotomania. Semistructured interviews covering personal and family details in addition to treatment and outcome to date were performed on a series of erotomanic patients identified in a defined area. Evaluation of diagnosis used DSM-IV and other criteria. Fifteen erotomanic subjects (11 female, four male) were identified. Most were isolated, without a partner or full-time occupation. Forty percent had a first-degree relative with a psychiatric history and of those half had a first-degree relative with a mono-delusional disorder. Less than half of the objects of their affection, mainly noncelebrities, were subject to harassment. Subjects with primary erotomania and erotomania secondary to other psychiatric diagnoses were identified using DSM-IV criteria. Ellis and Mellsop's criteria were found to be useful in assessing erotomania but we could not replicate Seeman's fixed and recurrent groups. Treatment and outcome was better than expected particularly for those with primary erotomania and erotomanics with a diagnosis of bipolar affective disorder. In this series, erotomanic symptoms largely occurred in the context of other psychiatric disorders, although subjects with pure erotomanic symptoms were seen. Subjects were less dangerous and engaged in less harassment of victims than the literature suggests. Subjects were often isolated, unemployed, and with few social contacts. Strong family psychiatric histories were seen particularly with regard to mono-delusional disorders raising the possibility of genetic inheritance. An adaptation of Ellis and Mellsop's criteria was suggested for the diagnosis of primary and secondary erotomania. Response to treatment and prognosis was good, particularly for primary erotomania and erotomania secondary to bipolar affective disorder.

Salvage external beam radiotherapy for clinical failure after cryosurgery for prostate cancer.

PURPOSE: To investigate the role of external beam radiotherapy (EBRT) as salvage treatment of prostate cancer after cryosurgery failure. METHODS AND MATERIALS: Between 1993 and 1998, 6 patients underwent EBRT with curative intent for local recurrence of prostate cancer after cryosurgery. All 6 patients had biopsy-proven recurrence and palpable disease on digital rectal examination at the time of EBRT. The median follow-up was 34 months (range 8-46). The median prostate-specific antigen level was 2.3 ng/mL (range 0.8-4.1). No patient had evidence of metastatic disease. Two patients received hormonal therapy before beginning EBRT. No patient received hormonal therapy after EBRT completion. The median elapsed time between cryosurgery and EBRT was 3 years (range 1.5-4). The median delivered dose was 66 Gy (range 62-70.2) using a 10-MeV photon beam. An in-house-developed three-dimensional treatment planning system was used to plan delivery of the prescribed dose with conformal radiotherapy techniques. RESULTS: After EBRT, all patients had complete resolution of palpable disease. Four patients (66%) were disease free at the time of the last follow-up. Two patients developed biochemical failure as defined by the American Society for Therapeutic Radiology and Oncology consensus definition. One of these patients had a prostate-specific antigen level of 97 ng/mL before cryosurgery. No patient developed distant metastasis during follow-up. Two patients (33%) developed proctitis; 1 case resolved with Rowasa suppositories and 1 required blood transfusion. CONCLUSIONS: Our preliminary results suggest that EBRT can render a significant number of patients biochemically free of disease and can cause complete resolution of clinically palpable disease after initial cryosurgery. The results also showed that EBRT can be given without excessive morbidity. EBRT should be considered as a treatment option in these potentially curable cases.

A 1.2-A snapshot of the final step of bacterial cell wall biosynthesis.

The cell wall imparts structural strength and shape to bacteria. It is made up of polymeric glycan chains with peptide branches that are cross-linked to form the cell wall. The cross-linking reaction, catalyzed by transpeptidases, is the last step in cell wall biosynthesis. These enzymes are members of the family of penicillin-binding proteins, the targets of beta-lactam antibiotics. We report herein the structure of a penicillin-binding protein complexed with a cephalosporin designed to probe the mechanism of the cross-linking reaction catalyzed by transpeptidases. The 1.2-A resolution x-ray structure of this cephalosporin bound to the active site of the bifunctional serine type D-alanyl-D-alanine carboxypeptidase/transpeptidase (EC ) from Streptomyces sp. strain R61 reveals how the two peptide strands from the polymeric substrates are sequestered in the active site of a transpeptidase. The structure of this complex provides a snapshot of the enzyme and the bound cell wall components poised for the final and critical cross-linking step of cell wall biosynthesis.

Olanzapine for chronic, stereotypic self-injurious behaviour: a pilot study in seven adults with intellectual disability.

Dopamine one (D1) receptor supersensitvity in the corpus striatum is said to be the primary mechanism within the dopamine model proposed for chronic, refractory self-injurious behaviour (SIB), which may explain why conventional neuroleptics have proven largely ineffective. In common with other atypical antipsychotic agents, olanzapine has more affinity for the D1 receptor. The present study explored whether olanzapine could reduce rates of the stereotypic form of chronic SIB, a subtype where dopamine dysfunction is the most likely underlying mechanism. A clinical sample of seven patients with various levels of learning disability who displayed features of stereotypic SIB were assessed over a 6-week period of baseline measurement and a 15-week treatment phase during which olanzapine was added to existing medication. Both SIB and other aberrant behaviours were measured by daily nurse rating and the Self-Injury Trauma Scale (SITS). All measurements were unblind. Doses ranged from 5 to 15 mg. Out of the seven subjects, three showed a clear improvement, one showed a marginal improvement, one deteriorated, and the data was equivocal for the remaining two individuals. The means of the SITS Number and Severity Indices (NI and SI, respectively) reduced significantly from baseline during both the 5- and 10-mg treatment phases, and taking treatment as a whole, by 53% and 48%, respectively (NI: mean = 0.7 units reduction, P = 0.02; SI: mean = 0.9 units reduction, P = 0.04). The risk index also reduced, but did not reach significance. A modest reduction in mean nurse-rated SIB was not significant for either phase or for treatment as a whole. At doses above 5mg, mean scores deteriorated on balance, although two responders showed a marginal additional improvement. Olanzapine was well tolerated with one adverse event reported (somnolence) which was mild and transient. The present pilot study suggests that olanzapine can reduce stereotypic SIB. A larger trial is indicated.

Species-specific identification of human adenoviruses by a multiplex PCR assay.

A multiplex PCR assay was developed by using primers to the fiber gene that could differentiate human adenovirus (Ad) species A through F in a single amplification reaction. The assay correctly identified the species of all 49 recognized Ad prototype strains as well as 180 geographically and temporally diverse Ad field isolates. Ad serotype 6 (Ad6) (species C), Ad16 (species B), Ad31 (species A), and Ad40 and Ad41 (species F) could also be distinguished by amplicon size within each respective species. In comparison, a previously described Ad species-specific multiplex PCR assay that used primers to the Ad hexon gene gave equivocal results with several serotypes of species B, whereas our multiplex assay amplified all species B serotypes equally well. Our multiplex PCR assay will permit rapid, accurate, and cost-effective classification of Ad isolates.

Molecular and antigenic characterization of a highly evolved derivative of the type 2 oral poliovaccine strain isolated from sewage in Israel.

An unusual, highly diverged derivative of the Sabin type 2 oral poliovaccine (OPV) strain was recovered from environmental samples during routine screening for wild polioviruses. Virus was cultivated in L20B cells and then passaged on BGM cells at 40 degrees C (RCT [reproductive capacity at supraoptimal temperature]-positive marker) to select against most OPV strains. All but 1 of 25 RCT-positive OPV-derived environmental isolates were antigenically and genetically (>99.5% VP1 sequence match) similar to the respective Sabin strains. However, isolate PV2/4568-1/ISR98 (referred to below as 4568-1) escaped neutralization with Sabin 2-specific monoclonal antibodies and cross-adsorbed sera, and had multiple nucleotide substitutions (220 of 2,646; 8.3%) in the P1 capsid region. Fourteen of the 44 associated amino acid substitutions in the capsid mapped to neutralizing antigenic sites. Neutralizing titers in the sera of 50 Israeli children 15 years old were significantly lower to 4568-1 (geometric mean titer [GMT], 47) than to Sabin 2 (GMT, 162) or to the prototype wild strain, PV2/MEF-1/EGY42 (GMT, 108). Two key attenuating sites had also reverted in 4568-1 (A(481) to G in the 5' untranslated region and the VP1 amino acid I(143) to T), and the isolate was highly neurovirulent for transgenic mice expressing the poliovirus receptor (PVR-Tg21 mice). The extensive genetic divergence of 4568-1 from the parental Sabin 2 strain suggested that the virus had replicated in one or more people for approximately 6 years. The presence in the environment of a highly evolved, neurovirulent OPV-derived poliovirus in the absence of polio cases has important implications for strategies for the cessation of immunization with OPV following global polio eradication.

Hyperbaric oxygen in the treatment of delayed radiation injuries of the extremities.

Hyperbaric oxygen (HBO2) is used as an adjunct in the treatment of radiation injury at many sites, including the mandible, larynx, chest wall, bladder, and rectum. In these disorders, HBO2 is effective in stimulating neovascularization and reducing fibrosis. No previous publications report the application of HBO2 to radiation injuries of the extremities. From 1979 until 1997, 17 patients were treated at the Southwest Texas Methodist and Nix Hospitals for nonhealing necrotic wounds of the extremities within previously irradiated fields. All but one wound involved a lower extremity. Most of the patients had been irradiated for soft tissue sarcomas or skin cancers. The rest were irradiated for a variety of malignancies. HBO2 was delivered in a multiplace chamber at 2.4 atm abs daily for 90 min of 100% oxygen at pressure. This report is a retrospective, uncontrolled review of these patients. Eleven patients (65%) healed completely whereas five (29%) failed to heal and one (6%) was lost to follow-up. Three (60%) of those who failed were found to have local or distant recurrence of their tumor early in their course of hyperbaric treatment and were discontinued from therapy at that time. When last seen in the clinic, the wound of the patient who was lost to follow-up was improved but not completely healed. Four of those who failed (including the two with local tumor recurrence) required amputation. If we exclude those with active cancer and the patient lost to follow-up, the success rate was 11 of 13 or 85%. HBO2 was applied successfully with complete wound healing and the avoidance of amputation in a majority of these patients. The consequences of failure in patients suffering from radiation necrosis of the extremities (some complicated by the presence of tumor) are significant, with 80% of the five failures requiring amputation. In radiation injuries of the extremities as in delayed radiation injury at other sites, HBO2 is a useful adjunct and should be part of the overall management.

Spontaneous tandem amplification and deletion of the shiga toxin operon in Shigella dysenteriae 1.

Only one species of Shigella, Shigella dysenteriae 1, has been demonstrated to produce Shiga toxin (Stx). Stx is closely related to the toxins produced by Shiga toxin-producing Escherichia coli (STEC). In STEC, these toxins are often encoded on lambdoid bacteriophages and are major virulence factors for these organisms. Although the bacteriophage-encoded stx genes of STEC are highly mobile, the stx genes in S. dysenteriae 1 have been believed to be chromosomally encoded and not transmissible. We have located the toxin genes of S. dysenteriae 1 to a region homologous to minute 30 of the E. coli chromosome, within a 22.4 kbp putative composite transposon bracketed by IS600 insertion sequences. This region is present in all the S. dysenteriae 1 strains examined. Tandem amplification occurs via the flanking insertion sequences, leading to increased toxin production. The global regulatory gene, fnr, is located within the stx region, allowing deletions of the toxin genes to be created by anaerobic growth on chlorate-containing medium. Deletions occur by recombination between the flanking IS600 elements. Lambdoid bacteriophage genes are found both upstream and within the region, and we demonstrate the lysogeny of Shigella species with STEC bacteriophages. These observations suggest that S. dysenteriae 1 originally carried a Stx-encoding lambdoid prophage, which became defective due to loss of bacteriophage sequences after IS element insertions and rearrangements. These insertion sequences have subsequently allowed the amplification and deletion of the stx region.

Crystal structure of penicillin G acylase from the Bro1 mutant strain of Providencia rettgeri.

Penicillin G acylase is an important enzyme in the commercial production of semisynthetic penicillins used to combat bacterial infections. Mutant strains of Providencia rettgeri were generated from wild-type cultures subjected to nutritional selective pressure. One such mutant, Bro1, was able to use 6-bromohexanamide as its sole nitrogen source. Penicillin acylase from the Bro1 strain exhibited an altered substrate specificity consistent with the ability of the mutant to process 6-bromohexanamide. The X-ray structure determination of this enzyme was undertaken to understand its altered specificity and to help in the design of site-directed mutants with desired specificities. In this paper, the structure of the Bro1 penicillin G acylase has been solved at 2.5 A resolution by molecular replacement. The R-factor after refinement is 0.154 and R-free is 0.165. Of the 758 residues in the Bro1 penicillin acylase heterodimer (alpha-subunit, 205; beta-subunit, 553), all but the eight C-terminal residues of the alpha-subunit have been modeled based on a partial Bro1 sequence and the complete wild-type P. rettgeri sequence. A tightly bound calcium ion coordinated by one residue from the alpha-subunit and five residues from the beta-subunit has been identified. This enzyme belongs to the superfamily of Ntn hydrolases and uses Ogamma of Ser beta1 as the characteristic N-terminal nucleophile. A mutation of the wild-type Met alpha140 to Leu in the Bro1 acylase hydrophobic specificity pocket is evident from the electron density and is consistent with the observed specificity change for Bro1 acylase. The electron density for the N-terminal Gln of the alpha-subunit is best modeled by the cyclized pyroglutamate form. Examination of aligned penicillin acylase and cephalosporin acylase primary sequences, in conjunction with the P. rettgeri and Escherichia coli penicillin acylase crystal structures, suggests several mutations that could potentially allow penicillin acylase to accept charged beta-lactam R-groups and to function as a cephalosporin acylase and thus be used in the manufacture of semi-synthetic cephalosporins.

Prolonged replication of a type 1 vaccine-derived poliovirus in an immunodeficient patient.

VP1 sequences were determined for poliovirus type 1 isolates obtained over a 189-day period from a poliomyelitis patient with common variable immunodeficiency syndrome (a defect in antibody formation). The isolate from the first sample, taken 11 days after onset of paralysis, contained two poliovirus populations, differing from the Sabin 1 vaccine strain by approximately 10%, differing from diverse type 1 wild polioviruses by 19 to 24%, and differing from each other by 5.5% of nucleotides. Specimens taken after day 11 appeared to contain only one major poliovirus population. Evolution of VP1 sequences at synonymous third-codon positions occurred at an overall rate of approximately 3.4% per year over the 189-day period. Assuming this rate to be constant throughout the period of infection, the infection was calculated to have started approximately 9.3 years earlier. This estimate is about the time (6. 9 years earlier) the patient received his last oral poliovirus vaccine dose, approximately 2 years before the diagnosis of immunodeficiency. These findings may have important implications for the strategy to eliminate poliovirus immunization after global polio eradication.

A role for POR1, a Rac1-interacting protein, in ARF6-mediated cytoskeletal rearrangements.

The ARF6 GTPase, the least conserved member of the ADP ribosylation factor (ARF) family, associates with the plasma membrane and intracellular endosome vesicles. Mutants of ARF6 defective in GTP binding and hydrolysis have a marked effect on endocytic trafficking and the gross morphology of the peripheral membrane system. Here we report that expression of the GTPase-defective mutant of ARF6, ARF6(Q67L), remodels the actin cytoskeleton by inducing actin polymerization at the cell periphery. This cytoskeletal rearrangement was inhibited by co-expression of ARF6(Q67L) with deletion mutants of POR1, a Rac1-interacting protein involved in membrane ruffling, but not with the dominant-negative mutant of Rac1, Rac1(S17N). A synergistic effect between POR1 and ARF6 for the induction of actin polymerization was detected. Furthermore, we observed that ARF6 interacts directly with POR1 and that this interaction was GTP dependent. These findings indicate that ARF6 and Rac1 function on distinct signaling pathways to mediate cytoskeletal reorganization, and suggest a role for POR1 as an important regulatory element in orchestrating cytoskeletal rearrangements at the cell periphery induced by ARF6 and Rac1.