Hrs regulates multivesicular body formation via ESCRT recruitment to endosomes

Hrs and the endosomal sorting complexes required for transport, ESCRT-I, -II, and -III, are involved in the endosomal sorting of membrane proteins into multivesicular bodies and lysosomes or vacuoles. The ESCRT complexes are also required for formation of intraluminal endosomal vesicles and for budding of certain enveloped RNA viruses such as HIV. Here, we show that Hrs binds to the ESCRT-I subunit Tsg101 via a PSAP motif that is conserved in Tsg101-binding viral proteins. Depletion of Hrs causes a reduction in membrane-associated ESCRT-I subunits, a decreased number of multivesicular bodies and an increased size of late endosomes. Even though Hrs mainly localizes to early endosomes and Tsg101 to late endosomes, the two proteins colocalize on a subpopulation of endosomes that contain lyso-bisphosphatidic acid. Overexpression of Hrs causes accumulation of Tsg101 on early endosomes and prevents its localization to late endosomes. We conclude that Hrs mediates the initial recruitment of ESCRT-I to endosomes and, thereby, indirectly regulates multivesicular body formation

Circulating Factor Seven Activating Protease (FSAP) in the Hyperacute Phase of Stroke

Background. Factor VII activating protease (FSAP) is a circulating serine protease that could be involved in the pathophysiology of stroke. We analyzed the temporal changes in FSAP antigen and FSAP activity after acute cerebral ischemia (ACI) and tested if FSAP could be used to differentiate between stroke subtypes in the hyperacute phase (<4.5 hours after symptom onset). Methods. Of the 118 suspected stroke patients enrolled, 76 had ACI; of which 20 suffered from large vessel occlusion (LVO), 19 had intracerebral hemorrhage (ICH), and 23 had stroke mimics. Median time from symptom onset to the two plasma sample collections, <4.5 hours, were 66 and 107 minutes for the entire study population. Additional samples were collected up to 90 days post stroke in a subset of ACI patients (). FSAP antigen, FSAP activity, FSAP-α2-antiplasmin-complex (FSAP-AP complex), and nucleosomes were measured by activity assays or ELISA. Results. ACI patients treated with tissue plasminogen activator (tPA) had elevated FSAP hours () that subsequently normalized after 6 hours. FSAP-AP complex levels decreased significantly from <4.5 hours () to 6 hours after symptom onset. tPA did not increase FSAP activity significantly in plasma in vitro. FSAP antigen significantly hours after symptom onset in LVO () and ICH () patients. FSAP could not differentiate ACI from ICH or strokes (ACI and ICH) from stroke mimics. FSAP did not correlate with stroke severity. Conclusion. LVO and ICH seem to influence FSAP levels in the hyperacute phase of stroke, but FSAP does not differentiate between stroke subtypes in a hyperacute setting.publishedVersio

Cost-Effectiveness of Mobile Stroke Unit Care in Norway

Background: Acute ischemic stroke treatment in mobile stroke units (MSUs) reduces time-to-treatment and increases thrombolytic rates, but implementation requires substantial investments. We wanted to explore the cost-effectiveness of MSU care incorporating novel efficacy data from the Norwegian MSU study, Treat-NASPP (the Norwegian Acute Stroke Prehospital Project). Methods: We developed a Markov model linking improvements in time-to-treatment and thrombolytic rates delivered by treatment in an MSU to functional outcomes for the patients in a lifetime perspective. We estimated incremental costs, health benefits, and cost-effectiveness of MSU care as compared with conventional care. In addition, we estimated a minimal MSU utilization level for the intervention to be cost-effective in the publicly funded health care system in Norway. Results: MSU care was associated with an expected quality-adjusted life-year-gain of 0.065 per patient, compared with standard care. Our analysis suggests that about 260 patients with ischemic stroke need to be treated with MSU annually to result in an incremental cost-effectiveness ratio of about NOK385 000 (US$43 780) per quality-adjusted life-year for MSU compared with standard care. The incremental cost-effectiveness ratio varies between some NOK1 000 000 (US$113 700) per quality-adjusted life-year if an MSU treats 100 patients per year and to about NOK340 000 (US$38 660) per quality-adjusted life-year if 300 patients with acute ischemic stroke are treated. Conclusions: MSU care in Norwegian settings is potentially cost-effective compared with conventional care, but this depends on a relatively high annual number of treated patients with acute ischemic stroke per vehicle. These results provide important information for MSU implementation in government-funded health care systems.publishedVersio

Ultraearly thrombolysis by an anesthesiologist in a mobile stroke unit: A prospective, controlled intervention study

Background Acute stroke treatment in mobile stroke units (MSU) is feasible and reduces time-to-treatment, but the optimal staffing model is unknown. We wanted to explore if integrating thrombolysis of acute ischemic stroke (AIS) in an anesthesiologist-based emergency medical services (EMS) reduces time-to-treatment and is safe. Methods A nonrandomized, prospective, controlled intervention study. Inclusion criteria: age ≥18 years, nonpregnant, stroke symptoms with onset ≤4 h. The MSU staffing is inspired by the Norwegian Helicopter Emergency Medical Services crew with an anesthesiologist, a paramedic-nurse and a paramedic. Controls were included by conventional ambulances in the same catchment area. Primary outcome was onset-to-treatment time. Secondary outcomes were alarm-to-treatment time, thrombolytic rate and functional outcome. Safety outcomes were symptomatic intracranial hemorrhage and mortality. Results We included 440 patients. MSU median (IQR) onset-to-treatment time was 101 (71–155) minutes versus 118 (90–176) minutes in controls, p = 0.007. MSU median (IQR) alarm-to-treatment time was 53 (44–65) minutes versus 74 (63–95) minutes in controls, p < 0.001. Golden hour treatment was achieved in 15.2% of the MSU patients versus 3.7% in the controls, p = 0.005. The thrombolytic rate was higher in the MSU (81% vs 59%, p = 0.001). MSU patients were more often discharged home (adjusted OR [95% CI]: 2.36 [1.11–5.03]). There were no other significant differences in outcomes. Conclusions Integrating thrombolysis of AIS in the anesthesiologist-based EMS reduces time-to-treatment without negatively affecting outcomes. An MSU based on the EMS enables prehospital assessment of acute stroke in addition to other medical and traumatic emergencies and may facilitate future implementation.publishedVersio

Misfolding diverts CFTR from recycling to degradation: quality control at early endosomes

To investigate the degradation mechanism of misfolded membrane proteins from the cell surface, we used mutant cystic fibrosis transmembrane conductance regulators (CFTRs) exhibiting conformational defects in post-Golgi compartments. Here, we show that the folding state of CFTR determines the post-endocytic trafficking of the channel. Although native CFTR recycled from early endosomes back to the cell surface, misfolding prevented recycling and facilitated lysosomal targeting by promoting the ubiquitination of the channel. Rescuing the folding defect or down-regulating the E1 ubiquitin (Ub)-activating enzyme stabilized the mutant CFTR without interfering with its internalization. These observations with the preferential association of mutant CFTRs with Hrs, STAM-2, TSG101, hVps25, and hVps32, components of the Ub-dependent endosomal sorting machinery, establish a functional link between Ub modification and lysosomal degradation of misfolded CFTR from the cell surface. Our data provide evidence for a novel cellular mechanism of CF pathogenesis and suggest a paradigm for the quality control of plasma membrane proteins involving the coordinated function of ubiquitination and the Ub-dependent endosomal sorting machinery

The Growth-Regulatory Protein HCRP1/hVps37A Is a Subunit of Mammalian ESCRT-I and Mediates Receptor Down-Regulation

The biogenesis of multivesicular bodies and endosomal sorting of membrane cargo are driven forward by the endosomal sorting complexes required for transport, ESCRT-I, -II, and -III. ESCRT-I is characterized in yeast as a complex consisting of Vps23, Vps28, and Vps37. Whereas mammalian homologues of Vps23 and Vps28 (named Tsg101 and hVps28, respectively) have been identified and characterized, a mammalian counterpart of Vps37 has not yet been identified. Here, we show that a regulator of proliferation, hepatocellular carcinoma related protein 1 (HCRP1), interacts with Tsg101, hVps28, and their upstream regulator Hrs. The ability of HCRP1 (which we assign the alternative name hVps37A) to interact with Tsg101 is conferred by its mod(r) domain and is shared with hVps37B and hVps37C, two other mod(r) domain-containing proteins. HCRP1 cofractionates with Tsg101 and hVps28 by size exclusion chromatography and colocalizes with hVps28 on LAMP1-positive endosomes. Whereas depletion of Tsg101 by siRNA reduces cellular levels of both hVps28 and HCRP1, depletion of HCRP1 has no effect on Tsg101 or hVps28. Nevertheless, HCRP1 depletion strongly retards epidermal growth factor (EGF) receptor degradation. Together, these results indicate that HCRP1 is a subunit of mammalian ESCRT-I and that its function is essential for lysosomal sorting of EGF receptors

Defective downregulation of receptor tyrosine kinases in cancer

Most growth factors control cellular functions by activating specific receptor tyrosine kinases (RTKs). While overactivation of RTK signalling pathways is strongly associated with carcinogenesis, it is becoming increasingly clear that impaired deactivation of RTKs may also be a mechanism in cancer. A major deactivation pathway, receptor downregulation, involves ligand-induced endocytosis of the RTK and subsequent degradation in lysosomes. A complex molecular machinery that uses the small protein ubiquitin as a key regulator assures proper endocytosis and degradation of RTKs. Here we discuss evidence that implicates deregulation of this machinery in cancer