The non-receptor tyrosine kinase Csk serves as an indispensable negative regulator of the Src family tyrosine kinases (SFKs) by specifically phosphorylating the negative regulatory site of SFKs, ...thereby suppressing their oncogenic potential. Csk is primarily regulated through its SH2 domain, which is required for membrane translocation of Csk via binding to scaffold proteins such as Cbp/PAG1. The binding of scaffolds to the SH2 domain can also upregulate Csk kinase activity. These regulatory features have been elucidated by analyses of Csk structure at the atomic levels. Although Csk itself may not be mutated in human cancers, perturbation of the regulatory system consisting of Csk, Cbp/PAG1, or other scaffolds, and certain tyrosine phosphatases may explain the upregulation of SFKs frequently observed in human cancers. This review focuses on the molecular bases for the function, structure, and regulation of Csk as a unique regulatory tyrosine kinase for SFKs.
Background Belimumab in conjunction with mycophenolate mofetil has been proven to be effective for treating systemic lupus erythematosus (SLE) in several randomized controlled trials. Usefulness of ...calcineurin inhibitors has also been reported in controlling the activity of SLE. However, the safety and effectiveness of belimumab-calcineurin inhibitor combination therapy have not been addressed. Therefore, we conducted a single-center retrospective study to analyze the safety/efficacy profile of belimumab-tacrolimus (B-T) combination therapy in patients with SLE. Methods Patients with SLE administered belimumab and tacrolimus during their treatment were included in the study, and samples collected were analyzed for the drug retention rate/SLE flare rate/infection incidence rate/glucocorticoid-sparing effect of the B-T combination therapy. Results Thirty-three patients with SLE were treated with B-T combination therapy at our institution. Four patients discontinued the treatment because of insufficient response/adverse events. The drug retention rate was over 90% at week 52 and approximately 80% at day 1000. Only one patient developed serious infection. The lupus low disease activity state (LLDAS) achievement ratio was 9.1% on the day of initiation and improved to 64.0% at 52 weeks after initiation. SLE flares were observed in only three patients (9.1%) in the first 52 weeks after initiation, and in five patients (15.2%) throughout the study period. A glucocorticoid-reducing effect was also observed in patients treated with B-T combination therapy. Conclusions In most patients with SLE, B-T combination therapy was well tolerated, and showed a good efficacy profile and glucocorticoid-reducing effect. Thus, B-T combination therapy can be a feasible option for patients with refractory lupus.
Ragulator is a heteropentameric protein complex consisting of two roadblock heterodimers wrapped by the membrane anchor p18/Lamtor1. The Ragulator complex functions as a lysosomal membrane scaffold ...for Rag GTPases to recruit and activate mechanistic target of rapamycin complex 1 (mTORC1). However, the roles of Ragulator structure in the regulation of mTORC1 function remain elusive. In this study, we disrupted Ragulator structure by directly anchoring RagC to lysosomes and monitored the effect on amino acid-dependent mTORC1 activation. Expression of lysosome-anchored RagC in p18-deficient cells resulted in constitutive lysosomal localization and amino acid-independent activation of mTORC1. Co-expression of Ragulator in this system restored the amino acid dependency of mTORC1 activation. Furthermore, ablation of Gator1, a suppressor of Rag GTPases, induced amino acid-independent activation of mTORC1 even in the presence of Ragulator. These results demonstrate that Ragulator structure is essential for amino acid-dependent regulation of Rag GTPases via Gator1. In addition, our genetic analyses revealed new roles of amino acids in the regulation of mTORC1 as follows: amino acids could activate a fraction of mTORC1 in a Rheb-independent manner, and could also drive negative-feedback regulation of mTORC1 signalling via protein phosphatases. These intriguing findings contribute to our overall understanding of the regulatory mechanisms of mTORC1 signalling.
The objective of the study is to evaluate the sensitivity of the new criteria for the classification of systemic lupus erythematosus (SLE), when applied to real SLE cases. We retrospectively reviewed ...the electronic medical records of 100 consecutive patients who visited St. Luke’s International Hospital. Patients were included if they were clinically diagnosed as having SLE and excluded if they had other autoimmune disease or if they were less than 18 years old. Each patient was evaluated if they satisfied the American College of Rheumatology (ACR) 1997 classification criteria (1997 criteria), 2012 Systemic Lupus International Collaborating Clinics criteria (2012 criteria), or 2019 ACR/European League Against Rheumatism (EULAR) criteria. Among the 100 patients, the sensitivity of the 1997, 2012, and 2019 criteria was, 97, 99, and 92%, respectively. The total patient score with the 2019 criteria ranged from 12 to 44 (mean, 27.3). All patients who were classified as non-SLE with the 2019 criteria had an anti-nuclear antibody (ANA) titre of < 1:80. The 2019 criteria for SLE accomplished modestly high sensitivity in the real-world practice, but not as high as the 1997 and 2012 criteria. They possibly misclassify the real SLE cases as non-SLE, especially if patients have a low titre (< 1:80) of ANA.
Key Points
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The 2019 criteria for the classification of SLE achieve modestly high sensitivity in real-world practice.
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The entry criteria (ANA ≥ 1:80) possibly misclassify the real SLE cases as non-SLE, as the sensitivity of IIF-ANA in SLE varies widely depending on the staining kit.
Objective
To assess the efficacy and safety of subcutaneous (SC) belimumab in patients with systemic lupus erythematosus (SLE).
Methods
Patients with moderate‐to‐severe SLE (score of ≥8 on the Safety ...of Estrogens in Lupus Erythematosus National Assessment SELENA version of the SLE Disease Activity Index SLEDAI) were randomized 2:1 to receive weekly SC belimumab 200 mg or placebo by prefilled syringe in addition to standard SLE therapy for 52 weeks. The primary end point was the SLE Responder Index (SRI4) at week 52. Secondary end points were reduction in the corticosteroid dosage and time to severe flare. Safety was assessed according to the adverse events (AEs) reported and the laboratory test results.
Results
Of 839 patients randomized, 836 (556 in the belimumab group and 280 in the placebo group) received treatment. A total of 159 patients withdrew before the end of the study. At entry, mean SELENA–SLEDAI scores were 10.5 in the belimumab group and 10.3 in the placebo group. More patients who received belimumab were SRI4 responders than those who received placebo (61.4% versus 48.4%; odds ratio OR 1.68 95% confidence interval (95% CI) 1.25–2.25; P = 0.0006). In the belimumab group, both time to and risk of severe flare were improved (median 171.0 days versus 118.0 days; hazard ratio 0.51 95% CI 0.35–0.74; P = 0.0004), and more patients were able to reduce their corticosteroid dosage by ≥25% (to ≤7.5 mg/day) during weeks 40–52 (18.2% versus 11.9%; OR 1.65 95% CI 0.95–2.84; P = 0.0732), compared with placebo. AE incidence was comparable between treatment groups; serious AEs were reported by 10.8% of patients taking belimumab and 15.7% of those taking placebo. A worsening of IgG hypoglobulinemia by ≥2 grades occurred in 0.9% of patients taking belimumab and 1.4% of those taking placebo.
Conclusion
In patients with moderate‐to‐severe SLE, weekly SC doses of belimumab 200 mg plus standard SLE therapy significantly improved their SRI4 response, decreased severe disease flares as compared with placebo, and had a safety profile similar to placebo plus standard SLE therapy.
The regulation of endosome dynamics is crucial for fundamental cellular functions, such as nutrient intake/digestion, membrane protein cycling, cell migration and intracellular signalling. Here, we ...show that a novel lipid raft adaptor protein, p18, is involved in controlling endosome dynamics by anchoring the MEK1–ERK pathway to late endosomes. p18 is anchored to lipid rafts of late endosomes through its N‐terminal unique region. p18−/− mice are embryonic lethal and have severe defects in endosome/lysosome organization and membrane protein transport in the visceral endoderm. p18−/− cells exhibit apparent defects in endosome dynamics through perinuclear compartment, such as aberrant distribution and/or processing of lysosomes and impaired cycling of Rab11‐positive recycling endosomes. p18 specifically binds to the p14–MP1 complex, a scaffold for MEK1. Loss of p18 function excludes the p14–MP1 complex from late endosomes, resulting in a downregulation of the MEK–ERK activity. These results indicate that the lipid raft adaptor p18 is essential for anchoring the MEK–ERK pathway to late endosomes, and shed new light on a role of endosomal MEK–ERK pathway in controlling endosome dynamics.
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