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Objective: To evaluate the efficacy and safety of tofacitinib in patients with ankylosing spondylitis (AS) by prior biologic disease‐modifying antirheumatic drug (bDMARD) use. Methods: Data from a placebo‐controlled, double‐blind study of patients with active AS were analyzed. Patients received tofacitinib 5 mg twice daily (BID) or placebo to week 16; all received open‐label tofacitinib 5 mg BID to week 48 and were stratified by prior treatment (bDMARD‐naive or tumor necrosis factor inhibitor [TNFi]–inadequate responder [IR], including bDMARD‐experienced [non‐IR]). Disease activity/safety were assessed throughout. Results: Of 269 patients, 207 (77%) were bDMARD‐naive; 62 (23%) were in the TNFi‐IR subgroup. TNFi‐IR patients had higher baseline BMI (28.0 vs. 26.1 kg/m2), longer symptom duration (14.4 vs. 13.2 years), and lower concomitant conventional synthetic DMARD use (14.5% vs. 30.9%) than bDMARD‐naive patients. At week 16, for most outcomes, tofacitinib efficacy exceeded placebo for both subgroups and was sustained to week 48. At week 16, tofacitinib versus placebo differences were similar between bDMARD‐naive and TNFi‐IR patients (Assessment in Spondyloarthritis international Society 40 treatment difference [95% confidence interval]: 30.8% [19.1%‐42.6%] vs. 19.4% [1.7%‐37.0%]). Adverse event (AE) proportions were similar between tofacitinib‐treated bDMARD‐naive/TNFi‐IR patients (77.5%/77.4%) at week 48 with no deaths. A numerically higher proportion of tofacitinib‐treated TNFi‐IR versus bDMARD‐naive patients discontinued study drug (12.9% vs. 3.9%) or dose reduced/temporarily discontinued due to AEs (19.4% vs. 11.8%). Conclusion: Tofacitinib efficacy exceeded placebo at week 16 for bDMARD‐naive/TNFi‐IR patients and was sustained to week 48. The absolute magnitude of responses was generally greater in bDMARD‐naive patients versus TNFi‐IR patients. More TNFi‐IR versus bDMARD‐naive patients discontinued or dose reduced/temporarily discontinued tofacitinib due to AEs. Small sample size and sample size differences between subgroups limited the interpretation. [ABSTRACT FROM AUTHOR]

Background: Tofacitinib is a Janus kinase inhibitor for the treatment of psoriatic arthritis (PsA) and has been investigated for psoriasis (PsO). Objectives: This post hoc analysis examined baseline cardiovascular (CV) disease risk and its association with the occurrence of major adverse cardiovascular events (MACE) and malignancies in tofacitinib-treated patients with PsA and PsO. Design: Included three phase III/long-term extension (LTE) PsA trials and seven phase II/phase III/LTE PsO trials of patients receiving ⩾ 1 dose of tofacitinib. Methods: Incidence rates (IRs: patients with events/100 patient-years) for MACE and malignancies (excluding non-melanoma skin cancer) were determined in subgroups according to history of atherosclerotic CV disease (ASCVD), baseline 10-year risk of ASCVD (in patients without history of ASCVD), and baseline metabolic syndrome (MetS). Results: For patients with PsA (N = 783) and PsO (N = 3663), respectively, tofacitinib exposure was 2038 and 8950 patient-years (median duration: 3.0 and 2.4 years), and 40.9% and 32.7% had MetS. Excluding missing CV risk profile data, 51/773 (6.6%) and 144/3629 (4.0%) patients had history of ASCVD, and in patients without history of ASCVD, around 20.0% had intermediate/high baseline 10-year ASCVD risk. For PsA and PsO, IRs of MACE were greatest in those with history of ASCVD or high baseline 10-year ASCVD risk. For PsA, five of six patients with MACE had baseline MetS. Malignancy IRs in patients with PsA were greatest in those with intermediate/high baseline 10-year ASCVD risk. Of these, eight of nine patients with malignancies had baseline MetS. In the PsO cohort, IR of malignancies was notably greater with high versus low/borderline/intermediate baseline 10-year ASCVD risk. Conclusion: In tofacitinib-treated patients with PsA/PsO, increased ASCVD risk and baseline MetS were associated with higher IRs for MACE and malignancies. Our results support assessing CV risk in patients with PsA/PsO and suggest enhanced cancer monitoring in those with increased ASCVD risk. Registration (ClinicalTrials.gov): NCT01877668/NCT01882439/NCT01976364/NCT00678210/NCT01710046/NCT01241591/NCT01186744/NCT01276639/NCT01309737/NCT01163253 Plain Language Summary: People who have psoriatic arthritis or psoriasis may have more heart-related problems and cancer if they have a higher risk of cardiovascular disease: A study in people with psoriatic arthritis or psoriasis receiving tofacitinib Why was this study done? • People with psoriatic arthritis (PsA) and psoriasis (PsO) are more likely than the general population to have a disease affecting the heart and blood vessels [cardiovascular (CV) disease]. • People who are more likely to have CV disease may also be more likely to have certain types of cancer. • Tofacitinib is a medicine to treat people with PsA and has been tested in people with PsO. • We wanted to know if the risk of CV disease affects the number of heart-related problems (including heart attack, stroke, or death) and cancer in people with PsA and PsO. What did the researchers do? • We used results from 10 clinical trials. • In these trials, people with PsA and PsO were taking tofacitinib 5 or 10 mg twice a day. • After the trials had ended, we measured people's risk of CV disease using a risk calculator. This risk calculator showed if they had a low, borderline, intermediate, or high risk of CV disease over the next 10 years. We also checked if they had had CV disease before treatment. • We checked if people had a group of conditions linked to CV disease: diabetes, high blood pressure, and obesity. • We counted the cases of heart-related problems and cancer in people once they started taking tofacitinib. What did the researchers find? In people with PsA and PsO taking tofacitinib: • There were more cases of heart-related problems and cancer in people who had intermediate or high risk of CV disease. • There were more cases of heart-related problems in people who had had CV disease before. • More people with diabetes, high blood pressure, and obesity had heart-related problems and cancer than people without those conditions. What do the findings mean? • It is important to measure risk and assess history of CV disease in people with PsA and PsO, including those taking tofacitinib. • We should test for cancer in people with high risk of CV disease. [ABSTRACT FROM AUTHOR]

Research has been conducted on the ubiquitin C-terminal hydrolase-L1 (UCH-L1). Results demonstrate that UCH-L1 exhibits dimerization-dependent ubiquityl ligase activity which may play role in proteasomal protein degradation.

Research is presented concerning the photochemistry of a number of o-phenol-containing alkoxyvinylsilanes which were prepared through the hydrosilylation of o-acetoxy arylacetylenes.

A study was conducted on the photochemical solid-phase phosphoramidite DNA synthesis technique. The findings indicate that the coupling efficiency of these amidites in the synthesis of homopolymers was in the range of 80-97%, with purines having lower efficiency than pyrimidines. Moreover, the results suggest that light-directed in situ synthesis of short oligonucleotides will be an effective approach in preparing hybridization surfaces for detection of complementary sequences.

An inverse 5'-3' photochemical phosphotriester DNA synthesis makes use of a photoremovable phosphate protecting group. The group is generated by fixing the 5'-hydroxyl of the DNA to a solid support thus making available the phosphate protecting group to the 3'-phosphate in the phosphotriester coupling method. The 3'-phosphodiester fused to the base is activated at the same time allowing the reaction between a 3'-activated phosphate and a 5'-hydroxyl. The method is able to synthesize short oligonucleotides which are attached to the support via their 5'-terminals.

Objective: To assess the efficacy/safety of tofacitinib in adult patients with active ankylosing spondylitis (AS).Methods: This phase III, randomised, double-blind, placebo-controlled study enrolled patients aged ≥18 years diagnosed with active AS, meeting the modified New York criteria, with centrally read radiographs, and an inadequate response or intolerance to ≥2 non-steroidal anti-inflammatory drugs. Patients were randomised 1:1 to receive tofacitinib 5 mg two times per day or placebo for 16 weeks. After week 16, all patients received open-label tofacitinib until week 48. The primary and key secondary endpoints were Assessment of SpondyloArthritis international Society ≥20% improvement (ASAS20) and ≥40% improvement (ASAS40) responses, respectively, at week 16. Safety was assessed throughout.Results: 269 patients were randomised and treated: tofacitinib, n=133; placebo, n=136. At week 16, the ASAS20 response rate was significantly (p<0.0001) greater with tofacitinib (56.4%, 75 of 133) versus placebo (29.4%, 40 of 136), and the ASAS40 response rate was significantly (p<0.0001) greater with tofacitinib (40.6%, 54 of 133) versus placebo (12.5%, 17 of 136). Up to week 16, with tofacitinib and placebo, respectively, 73 of 133 (54.9%) and 70 of 136 (51.5%) patients had adverse events; 2 of 133 (1.5%) and 1 of 136 (0.7%) had serious adverse events. Up to week 48, with tofacitinib, 3 of 133 (2.3%) patients had adjudicated hepatic events, 3 of 133 (2.3%) had non-serious herpes zoster, and 1 of 133 (0.8%) had a serious infection; with placebo→tofacitinib, 2 (1.5%) patients had non-serious herpes zoster. There were no deaths, malignancies, major adverse cardiovascular events, thromboembolic events or opportunistic infections.Conclusions: In adults with active AS, tofacitinib demonstrated significantly greater efficacy versus placebo. No new potential safety risks were identified.Trial Registration Number: NCT03502616. [ABSTRACT FROM AUTHOR]

Objectives: Tofacitinib is a Janus kinase inhibitor for the treatment of rheumatoid arthritis (RA), psoriatic arthritis (PsA) and ulcerative colitis, and has been investigated in psoriasis (PsO). Routine pharmacovigilance of an ongoing, open-label, blinded-endpoint, tofacitinib RA trial (Study A3921133; NCT02092467) in patients aged ≥50 years and with ≥1 cardiovascular risk factor identified a higher frequency of pulmonary embolism (PE) and all-cause mortality for patients receiving tofacitinib 10 mg twice daily versus those receiving tumour necrosis factor inhibitors and resulted in identification of a safety signal for tofacitinib. Here, we report the incidence of deep vein thrombosis (DVT), PE, venous thromboembolism (VTE; DVT or PE) and arterial thromboembolism (ATE) from the tofacitinib RA (excluding Study A3921133), PsA and PsO development programmes and observational studies. Data from an ad hoc safety analysis of Study A3921133 are reported separately within.Methods: This post-hoc analysis used data from separate tofacitinib RA, PsO and PsA programmes. Incidence rates (IRs; patients with events per 100 patient-years' exposure) were calculated for DVT, PE, VTE and ATE, including for populations stratified by defined baseline cardiovascular or VTE risk factors. Observational data from the US Corrona registries (including cardiovascular risk factor stratification), IBM MarketScan research database and the US FDA Adverse Event Reporting System (FAERS) database were analysed.Results: 12 410 tofacitinib-treated patients from the development programmes (RA: n=7964; PsO: n=3663; PsA: n=783) were included. IRs (95% CI) of thromboembolic events among the all tofacitinib cohorts' average tofacitinib 5 mg and 10 mg twice daily treated patients for RA, respectively, were: DVT (0.17 (0.09-0.27) and 0.15 (0.09-0.22)); PE (0.12 (0.06-0.22) and 0.13 (0.08-0.21)); ATE (0.32 (0.22-0.46) and 0.38 (0.28-0.49)). Among PsO patients, IRs were: DVT (0.06 (0.00-0.36) and 0.06 (0.02-0.15)); PE (0.13 (0.02-0.47) and 0.09 (0.04-0.19)); ATE (0.52 (0.22-1.02) and 0.22 (0.13-0.35)). Among PsA patients, IRs were: DVT (0.00 (0.00-0.28) and 0.13 (0.00-0.70)); PE (0.08 (0.00-0.43) and 0.00 (0.00-0.46)); ATE (0.31 (0.08-0.79) and 0.38 (0.08-1.11)). IRs were similar between tofacitinib doses and generally higher in patients with baseline cardiovascular or VTE risk factors. IRs from the overall Corrona populations and in Corrona RA patients (including tofacitinib-naïve/biologic disease-modifying antirheumatic drug-treated and tofacitinib-treated) with baseline cardiovascular risk factors were similar to IRs observed among the corresponding patients in the tofacitinib development programme. No signals of disproportionate reporting of DVT, PE or ATE with tofacitinib were identified in the FAERS database.Conclusions: DVT, PE and ATE IRs in the tofacitinib RA, PsO and PsA programmes were similar across tofacitinib doses, and generally consistent with observational data and published IRs of other treatments. As expected, IRs of thromboembolic events were elevated in patients with versus without baseline cardiovascular or VTE risk factors, and were broadly consistent with those observed in the Study A3921133 ad hoc safety analysis data, although the IR (95% CI) for PE was greater in patients treated with tofacitinib 10 mg twice daily in Study A3921133 (0.54 (0.32-0.87)), versus patients with baseline cardiovascular risk factors treated with tofacitinib 10 mg twice daily in the RA programme (0.24 (0.13-0.41)). [ABSTRACT FROM AUTHOR]

Objectives To describe characteristics, treatment patterns and persistence in patients with RA treated with tofacitinib, an oral Janus kinase inhibitor, in Canadian clinical practice between 1 June 2014 and 31 May 2017. Methods Data were obtained from the tofacitinib eXel support programme. Baseline demographics and medication history were collected via patient report/special authorization forms; reasons for discontinuation were captured by patient report. Treatment persistence was estimated using Kaplan–Meier methods, with data censored at last follow-up. Cox regression was applied to analyse baseline characteristics associated with treatment discontinuation. Results The number of patients with RA enrolled from 2014 to 2017 was 4276; tofacitinib utilization increased during that period, as did the proportion of biologic (b) DMARD-naïve patients prescribed tofacitinib. Of patients who initiated tofacitinib, 1226/3678 (33.3%) discontinued, mostly from lack of efficacy (35.7%) and adverse events (26.9%). Persistence was 62.7% and 49.6% after 1 and 2 years of treatment, respectively. Prior bDMARD experience predicted increased tofacitinib discontinuation (vs bDMARD-naïve, P < 0.001). Increased retention was associated with older age (56–65 years and >65 years vs ⩽45 years; P < 0.05), and time since diagnosis of 15 to <20 years (vs <5 years; P < 0.01). In bDMARD-naïve, post-1 bDMARD, post-2 bDMARD and post-⩾3 bDMARD patients, median survival was >730, 613, 667 and 592 days, respectively. Conclusion Since 2014, tofacitinib use in Canadian patients with RA increased, especially among bDMARD-naïve/post-1 bDMARD patients. Median drug survival was ∼2 years. Likelihood of persistence increased for bDMARD-naïve (vs bDMARD-experienced) patients and those aged ⩾56 (vs ⩽45) years. [ABSTRACT FROM AUTHOR]

Purpose: Current knowledge of the reasons for patients' preference for rheumatoid arthritis (RA) treatment modes is limited. This study was designed to identify preferences for four treatment modes, and to obtain in-depth information on the reasons for these preferences. Patients and Methods: In this multi-national, cross-sectional, qualitative study, in-depth interviews were conducted with adult patients with RA in the United States, France, Germany, Italy, Spain, Switzerland, the United Kingdom, and Brazil. Patients' strength of preference was evaluated using a 100-point allocation task (0– 100; 100=strongest) across four treatment modes: oral, self-injection, clinic-injection, and infusion. Qualitative descriptive analysis methods were used to identify, characterize, and summarize patterns found in the interview data relating to reasons for these preferences. Results: 100 patients were interviewed (female, 75.0%; mean age, 53.9 years; mean 11.6 years since diagnosis). Among the four treatment modes, oral administration was allocated the highest mean (standard deviation) preference points (47.3 [33.1]) and was ranked first choice by the greatest percentage of patients (57.0%), followed by self-injection (29.7 [27.7]; 29.0%), infusion (15.4 [24.6]; 16.0%), and clinic-injection (7.5 [14.1]; 2.0%). Overall, 56.0% of patients had a "strong" first-choice preference (ie, point allocation ≥ 70); most of these patients chose oral (62.5%) vs self-injection (23.2%), infusion (10.7%), or clinic-injection (3.6%). Speed and/or ease of administration were the most commonly reported reasons for patients choosing oral (52.6%) or self-injection (55.2%). The most common reasons for patients not choosing oral or self-injection were not wanting to take another pill (37.2%) and avoiding pain due to needles (46.5%), respectively. Conclusion: These data report factors important to patients regarding preferences for RA treatment modes. Patients may benefit from discussions with their healthcare professionals and/or patient support groups, regarding RA treatment modes, to facilitate shared decision-making. [ABSTRACT FROM AUTHOR]

Objective: Tofacitinib is an oral Janus kinase inhibitor for the treatment of rheumatoid arthritis (RA). This post hoc analysis evaluated tofacitinib persistence in patients with RA in long‐term extension (LTE) studies up to 9.5 years. Methods: Data were pooled from two LTE studies: ORAL Sequel (NCT00413699) and Study A3921041 (NCT00661661). Patients received tofacitinib 5 or 10 mg twice daily (BID), as monotherapy or with background conventional synthetic disease‐modifying antirheumatic drugs. Kaplan‐Meier estimates for tofacitinib drug survival and reasons for discontinuation were evaluated. Baseline factors were analyzed as predictors of persistence. Results: In 4967 tofacitinib‐treated patients entering LTE studies, mean (maximum) treatment duration was 3.5 (9.4) years. Median drug survival (95% confidence interval) was 4.9 (4.7, 5.1) years. Estimated 2‐ and 5‐year drug survival rates were 75.5% and 49.4%, respectively. Median drug survival was similar between the tofacitinib 5 and 10 mg BID groups, and slightly higher for patients receiving tofacitinib monotherapy versus combination therapy. Overall, 50.7% of patients discontinued tofacitinib; of these, 47.2% were due to adverse events and 7.1% for lack/loss of efficacy. An increased risk of discontinuation was associated with baseline diabetes, hypertension, negative anticyclic citrullinated peptide (anti‐CCP), negative rheumatoid factor (RF), and inadequate response to tumor necrosis factor inhibitors (TNFi‐IR). Conclusion: Median drug survival of tofacitinib‐treated patients participating in LTE studies was approximately 5 years and was similar for tofacitinib dosed at 5 and 10 mg BID. Reduced drug survival was associated with negative anti‐CCP/RF status, TNFi‐IR, and certain comorbidities. These data support tofacitinib use for long‐term management of RA. [ABSTRACT FROM AUTHOR]

Objective: Optimal targeted treatment in rheumatoid arthritis requires early identification of failure to respond. This post hoc analysis explored the relationship between early disease activity changes and the achievement of low disease activity (LDA) and remission targets with tofacitinib.Methods: Data were from 2 randomized, double-blind, phase III studies. In the ORAL Start trial, methotrexate (MTX)-naive patients received tofacitinib 5 or 10 mg twice daily, or MTX, for 24 months. In the placebo-controlled ORAL Standard trial, MTX inadequate responder patients received tofacitinib 5 or 10 mg twice daily or adalimumab 40 mg every 2 weeks, with MTX, for 12 months. Probabilities of achieving LDA (using a Clinical Disease Activity Index [CDAI] score ≤10 or the 4-component Disease Activity Score in 28 joints using the erythrocyte sedimentation rate [DAS28-ESR] ≤3.2) at months 6 and 12 were calculated, given failure to achieve threshold improvement from baseline (change in CDAI ≥6 or DAS28-ESR ≥1.2) at month 1 or 3.Results: In ORAL Start, 7.2% and 5.4% of patients receiving tofacitinib 5 and 10 mg twice daily, respectively, failed to show improvement in the CDAI ≥6 at month 3; of those who failed, 3.8% and 28.6%, respectively, achieved month 6 CDAI-defined LDA. In ORAL Standard, 18.8% and 17.5% of patients receiving tofacitinib 5 and 10 mg twice daily, respectively, failed to improve CDAI ≥6 at month 3; of those who failed, 0% and 2.9%, respectively, achieved month 6 CDAI-defined LDA. Findings were similar when considering improvements at month 1 or DAS28-ESR thresholds.Conclusion: In patients with an inadequate response to MTX, lack of response to tofacitinib after 1 or 3 months predicted a low probability of achieving LDA at month 6. Lack of an early response may be considered when deciding whether to continue treatment with tofacitinib. [ABSTRACT FROM AUTHOR]

Mutations in the parkin gene are responsible for a common familial form of Parkinson's disease. As parkin encodes an E3 ubiquitin ligase, defects in proteasome-mediated protein degradation are believed to have a central role in the pathogenesis of Parkinson's disease. Here, we report a novel role for parkin in a proteasome-independent ubiquitination pathway. We have identified a regulated interaction between parkin and Eps15, an adaptor protein that is involved in epidermal growth factor (EGF) receptor (EGFR) endocytosis and trafficking. Treatment of cells with EGF stimulates parkin binding to both Eps15 and the EGFR and promotes parkin-mediated ubiquitination of Eps15. Binding of the parkin ubiquitin-like (Ubl) domain to the Eps15 ubiquitin-interacting motifs (UIMs) is required for parkin-mediated Eps15 ubiquitination. Furthermore, EGFR endocytosis and degradation are accelerated in parkin-deficient cells, and EGFR signalling via the phosphoinositide 3-kinase (PI(3)K)–Akt pathway is reduced in parkin knockout mouse brain. We propose that by ubiquitinating Eps15, parkin interferes with the ability of the Eps15 UIMs to bind ubiquitinated EGFR, thereby delaying EGFR internalization and degradation, and promoting PI(3)K–Akt signalling. Considering the role of Akt in neuronal survival, our results have broad new implications for understanding the pathogenesis of Parkinson's disease. [ABSTRACT FROM AUTHOR]

Summarizes the results of a study on the interaction of ubiquilin, a type-2 ubiquitin-like protein containing a ubiquitin-like domain and a ubiquitin-associated domain, with both Eps15 and Eps15R. Colocalization of endogenous Eps15 and Hrs ubiquitin-interacting motif (UIM)-containing endocytic proteins with green-fluorescent-protein-fused ubiquilin in cytoplasmic aggregates that are not endocytic compartments; Characteristics of green-fluorescent-protein-fused-ubiquilin aggregates; Role of the interaction in the sequestration of certain UIM-containing endocytic proteins into cytoplasmic ubiquitin-rich protein aggregates.

Examines the enzymatic activities of neuronal enzyme ubiquitin C-terminal hydrolase-L1 (UCH-L1) to Parkison's disease. Applicability of UCH-L1 in Mammalian brain; Findings of the cell culture experiments of UCH-L1; Concentration-Dependent ubiquityl ligase activity of UCH-L1.

Objective: Optimal targeted treatment in rheumatoid arthritis requires early identification of failure to respond. This post hoc analysis explored the relationship between early disease activity changes and the achievement of low disease activity (LDA) and remission targets with tofacitinib., Methods: Data were from 2 randomized, double-blind, phase III studies. In the ORAL Start trial, methotrexate (MTX)-naive patients received tofacitinib 5 or 10 mg twice daily, or MTX, for 24 months. In the placebo-controlled ORAL Standard trial, MTX inadequate responder patients received tofacitinib 5 or 10 mg twice daily or adalimumab 40 mg every 2 weeks, with MTX, for 12 months. Probabilities of achieving LDA (using a Clinical Disease Activity Index [CDAI] score ≤10 or the 4-component Disease Activity Score in 28 joints using the erythrocyte sedimentation rate [DAS28-ESR] ≤3.2) at months 6 and 12 were calculated, given failure to achieve threshold improvement from baseline (change in CDAI ≥6 or DAS28-ESR ≥1.2) at month 1 or 3., Results: In ORAL Start, 7.2% and 5.4% of patients receiving tofacitinib 5 and 10 mg twice daily, respectively, failed to show improvement in the CDAI ≥6 at month 3; of those who failed, 3.8% and 28.6%, respectively, achieved month 6 CDAI-defined LDA. In ORAL Standard, 18.8% and 17.5% of patients receiving tofacitinib 5 and 10 mg twice daily, respectively, failed to improve CDAI ≥6 at month 3; of those who failed, 0% and 2.9%, respectively, achieved month 6 CDAI-defined LDA. Findings were similar when considering improvements at month 1 or DAS28-ESR thresholds., Conclusion: In patients with an inadequate response to MTX, lack of response to tofacitinib after 1 or 3 months predicted a low probability of achieving LDA at month 6. Lack of an early response may be considered when deciding whether to continue treatment with tofacitinib., (© 2018 Pfizer Inc. Arthritis Care & Research published by Wiley Periodicals, Inc. on behalf of American College of Rheumatology.)

Mutations in the gene encoding parkin cause an autosomal recessive juvenile-onset form of Parkinson's disease. Parkin functions as a RING-type E3 ubiquitin-ligase, coordinating the transfer of ubiquitin to substrate proteins and thereby targeting them for degradation by the proteasome. We now report that the extreme C terminus of parkin, which is selectively truncated by a Parkinson's disease-causing mutation, functions as a class II PDZ-binding motif that binds CASK, the mammalian homolog of Caenorhabditis elegans Lin-2, but not other PDZ proteins in brain extracts. Importantly, parkin co-localizes with CASK at synapses in cultured cortical neurons as well as in postsynaptic densities and lipid rafts in brain. Further, parkin associates not only with CASK but also with other postsynaptic proteins in the N-methyl d-aspartate (NMDA) receptor-signaling complex, in rat brain in vivo. Finally, despite exhibiting E2-dependent ubiquitin ligase activity, rat brain parkin does not ubiquitinate CASK, suggesting that CASK may function in targeting or scaffolding parkin within the postsynaptic complex rather than as a direct substrate for parkin-mediated ubiquitination. These data implicate for the first time a PDZ-mediated interaction between parkin and CASK in neurodegeneration and possibly in ubiquitination of proteins involved in synaptic transmission and plasticity.