The assumption that each enzyme expresses a single enzymatic activity in vivo is challenged by the linkage of the neuronal enzyme ubiquitin C-terminal hydrolase-L1 (UCH-L1) to Parkinson's disease (PD). UCH-L1, especially those variants linked to higher susceptibility to PD, causes the accumulation of alpha-synuclein in cultured cells, an effect that cannot be explained by its recognized hydrolase activity. UCH-L1 is shown here to exhibit a second, dimerization-dependent, ubiquityl ligase activity. A polymorphic variant of UCH-L1 that is associated with decreased PD risk (S18Y) has reduced ligase activity but comparable hydrolase activity as the wild-type enzyme. Thus, the ligase activity as well as the hydrolase activity of UCH-L1 may play a role in proteasomal protein degradation, a critical process for neuronal health.

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.

ObjectivesTofacitinib 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.MethodsThis 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.Results12 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.ConclusionsDVT, 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)).