The prolactin receptor scaffolds Janus kinase 2 via co-structure formation with phosphoinositide-4,5-bisphosphate

Class 1 cytokine receptors transmit signals through the membrane by a single transmembrane helix to an intrinsically disordered cytoplasmic domain that lacks kinase activity. While specific binding to phosphoinositides has been reported for the prolactin receptor (PRLR), the role of lipids in PRLR signalling is unclear. Using an integrative approach combining NMR spectroscopy, cellular signalling experiments, computational modelling and simulation, we demonstrate co-structure formation of the disordered intracellular domain of the human PRLR, the membrane constituent phosphoinositide-4,5-bisphosphate (PI(4,5)P₂) and the FERM-SH2 domain of the Janus kinase 2 (JAK2). We find that the complex leads to accumulation of PI(4,5)P₂ at the transmembrane helix interface and that mutation of residues identified to interact specifically with PI(4,5)P₂ negatively affects PRLR-mediated activation of signal transducer and activator of transcription 5 (STAT5). Facilitated by co-structure formation, the membrane-proximal disordered region arranges into an extended structure. We suggest that the co-structure formed between PRLR, JAK2 and PI(4,5)P₂ locks the juxtamembrane disordered domain of the PRLR in an extended structure, enabling signal relay from the extracellular to the intracellular domain upon ligand binding. We find that the co-structure exists in different states which we speculate could be relevant for turning signalling on and off. Similar co-structures may be relevant for other non-receptor tyrosine kinases and their receptors.

Tyrosine kinases compete for growth hormone receptor binding and regulate receptor mobility and degradation

Growth hormone (GH) acts via JAK2 and LYN to regulate growth, metabolism, and neural function. However, the relationship between these tyrosine kinases remains enigmatic. Through an interdisciplinary approach combining cell biology, structural biology, computation, and single-particle tracking on live cells, we find overlapping LYN and JAK2 Box1-Box2-binding regions in GH receptor (GHR). Our data implicate direct competition between JAK2 and LYN for GHR binding and imply divergent signaling profiles. We show that GHR exhibits distinct mobility states within the cell membrane and that activation of LYN by GH mediates GHR immobilization, thereby initiating its nanoclustering in the membrane. Importantly, we observe that LYN mediates cytokine receptor degradation, thereby controlling receptor turnover and activity, and this applies to related cytokine receptors. Our study offers insight into the molecular interactions of LYN with GHR and highlights important functions for LYN in regulating GHR nanoclustering, signaling, and degradation, traits broadly relevant to many cytokine receptors.

Assessment of models for calculating the hydrodynamic radius of intrinsically disordered proteins

Diffusion measurements by pulsed-field gradient NMR and fluorescence correlation spectroscopy can be used to probe the hydrodynamic radius of proteins, which contains information about the overall dimension of a protein in solution. The comparison of this value with structural models of intrinsically disordered proteins is nonetheless impaired by the uncertainty of the accuracy of the methods for computing the hydrodynamic radius from atomic coordinates. To tackle this issue, we here build conformational ensembles of 11 intrinsically disordered proteins that we ensure are in agreement with measurements of compaction by small-angle x-ray scattering. We then use these ensembles to identify the forward model that more closely fits the radii derived from pulsed-field gradient NMR diffusion experiments. Of the models we examined, we find that the Kirkwood-Riseman equation provides the best description of the hydrodynamic radius probed by pulsed-field gradient NMR experiments. While some minor discrepancies remain, our results enable better use of measurements of the hydrodynamic radius in integrative modeling and for force field benchmarking and parameterization.

Orchestration of signaling by structural disorder in class 1 cytokine receptors

BACKGROUND

Class 1 cytokine receptors (C1CRs) are single-pass transmembrane proteins responsible for transmitting signals between the outside and the inside of cells. Remarkably, they orchestrate key biological processes such as proliferation, differentiation, immunity and growth through long disordered intracellular domains (ICDs), but without having intrinsic kinase activity. Despite these key roles, their characteristics remain rudimentarily understood.

METHODS

The current paper asks the question of why disorder has evolved to govern signaling of C1CRs by reviewing the literature in combination with new sequence and biophysical analyses of chain properties across the family.

RESULTS

We uncover that the C1CR-ICDs are fully disordered and brimming with SLiMs. Many of these short linear motifs (SLiMs) are overlapping, jointly signifying a complex regulation of interactions, including network rewiring by isoforms. The C1CR-ICDs have unique properties that distinguish them from most IDPs and we forward the perception that the C1CR-ICDs are far from simple strings with constitutively bound kinases. Rather, they carry both organizational and operational features left uncovered within their disorder, including mechanisms and complexities of regulatory functions.

CONCLUSIONS

Critically, the understanding of the fascinating ability of these long, completely disordered chains to orchestrate complex cellular signaling pathways is still in its infancy, and we urge a perceptional shift away from the current simplistic view towards uncovering their full functionalities and potential. Video abstract.

Production of Intrinsically Disordered Proteins for Biophysical Studies: Tips and Tricks

Intrinsically disordered proteins (IDPs) have no single, fixed tertiary structure, yet they take on many vital functions in biology. In recent years, considerable effort has been put into the structural characterization of their conformational ensembles, to understand the link between the transient, short- and long-range organizations of IDPs and their functions. Such biophysical studies require substantial amounts of pure protein, representing a major bottleneck in the studies of IDPs. However, the unique physicochemical properties resulting from their compositional bias may be exploited for simple yet effective purification strategies. In this chapter, we provide tips and tricks for IDP production and describe the most important analyses to carry out before bringing an IDP of interest to the laboratory. We outline four purification protocols utilizing the unique properties of IDPs as well as some commonly encountered challenges and pitfalls.

Septic shock in children in an urban area in Western Germany--outcome, risk factors for mortality and infection epidemiology

BACKGROUND

Only sparse data exist about children with septic shock in Europe. The present study aimed to evaluate demographics, treatment, outcome and risk factors for mortality in Western Germany.

PATIENTS

Children with septic shock aged 2 months to 17 years.

METHODS

In a multi-center retrospective study of 20 children's hospitals data were obtained and analyzed by chart review. Risk factors for mortality were identified and assessed by multivariate regression analysis.

RESULTS

Overall mortality in 83 cases with septic shock was 25% (21 patients). Significant risk factors were high PRISM III score, low pH, low arterial systolic blood pressure, presence of disseminated intravascular coagulation and extent of multi-organ failure, but not lactate (p=0.05) and base excess (p=0.065). Mortality in hospitals which treated 10 or more patients (category 1) was 17% and increased to 22% in hospitals which treated 3-6 patients (category 2). In hospitals with only 1 or 2 patients (category 3) mortality rate was 61% (p<0.01 when compared to category 1 or 2). A stepwise increase was also seen in the severely sick patients according to PRISM III (>19): category 1: 23%, category 2: 40%, category 3: 62.5% (p<0.05 for comparison of category 1 and 3). Multivariate analysis of significant risk factors revealed low number of treated patients as the only individual risk factor for mortality.

CONCLUSION

Mortality from pediatric septic shock in an urban area in Western Germany is high. Disease severity and treatment in a department with few cases were associated with increased mortality.

Pulmonary sarcoidosis in a 14-year-old boy diagnosed by low-dose CT-guided transthoracic lung biopsy

Pulmonary sarcoidosis is a rare disease in the pediatric age group, characterized by the presence of epitheloid-cell granulomas. In stage 3 sarcoidosis, pulmonary infiltrates without hilar lymphadenopathy occur. Definitive diagnosis requires a histopathological specimen, which might be difficult to obtain by transbronchial biopsy. Multidetector computed tomography (MDCT)-guided transthoracic lung biopsy (TLB) is a well-established procedure in adults, but has only rarely been applied in children.A 14-year-old boy was admitted to hospital for evaluation of a chronic systemic disease with severe pulmonary manifestation. All investigations, including bronchosopy and bronchoalveolar lavage with microbiological and virological testing, had been negative. MDCT-guided TLB was performed on a 16-section scanner with a low-dose protocol (single slices, 120 kV, 20 mAs), using a 16-gauge biopsy device. The total effective dose was 0.4 mSv for the biopsy procedure. Histopathological examination revealed multiple epitheloid-cell granulomas with giant cells in the absence of microbiological or virological abnormalities. A diagnosis of stage 3 pulmonary sarcoidosis was made and systemic anti-inflammatory therapy was administered, which led to complete remission within weeks. MDCT-guided TLB can be a valuable instrument in assessing pulmonary manifestations of pediatric sarcoidosis, enabling precise histopathological diagnosis and adequate therapy. The use of low-dose protocols can substantially reduce radiation exposure without relevant loss of image information. MDCT-guided lung biopsy should be considered prior to open-lung surgery in selected patients with unclear pulmonary disease.

Hydrocephalus internus in two patients with 5,10-methylenetetrahydrofolate reductase deficiency

Hydrocephalus internus (HCI) of all four ventricles in association with early neurological abnormalities is described as the presenting symptom in two patients with 5,10-methylenetetrahydrofolate reductase (MTHFR) deficiency. Decreased activity of MTHFR leads to reduction of 5-methyltetrahydrofolate, the main methyl donor for methionine synthesis necessary for synthesis of S-adenosyl-methionine (SAM). Demyelination in MTHFR deficiency has been attributed to low SAM levels in the brain. The biochemical hallmarks of the disorder are hyperhomocystinemia, homocystinuria and low levels of plasma methionine. Hydrocephalus internus requiring neurosurgical intervention has to our knowledge not been reported as a presenting feature of homocystinuria due to deficiency of MTHFR so far. The surprising finding of HCI of all four ventricles in MTHFR deficiency must be kept in mind when evaluating patients with hydrocephalus of unknown origin.

Deficiency of cartilage in the segmental bronchi of a child: congenital or acquired?

The case of a 4-year-old girl suffering from a severe bronchopneumonia of the left lower lobe is presented. Microscopically no cartilage was found in the resected lobe distal to the lobar bronchus. The case is unusual because a congenital lobar emphysema associated with an aplasia of bronchial cartilage has to be considered as well as secondary cartilage destruction due to chronic relapsing inflammations.

[Effects of amrinone in myocardial insufficiency following heart surgery in children]

11 infants and children with severe congestive heart failure after cardiac surgery were treated with Amrinone. Cardiac and circulatory effects were monitored by quantitative echocardiography and blood pressure measurements. Within 1 day after the initial dose ventricular ejection fractions (EF) increased. Left ventricle: EF = 0.35 +/- 0.06 to EF = 0.49 +/- 0.06; right ventricle: EF = 0.30 +/- 0.12 to EF = 0.56 +/- 0.12. Vascular resistance dropped from R = 1527 +/- 517 dyn.s.cm-5.m2 to R = 1071 +/- 399 dyn.s.cm-5.m2. Blood pressure and heart rate remained almost unchanged. It is concluded, that Amrinone acts as a positive inotropic and vasodilating drug with the potential for effective treatment in children where conventional therapy has failed.

Verapamil-induced ventricular tachycardia in hypertrophic cardiomyopathy

A 17-year old boy with hypertrophic obstructive cardiomyopathy (HOCM) developed repeated short runs of self terminating ventricular tachycardia 12 hours after starting oral verapamil, which was substituted for propranolol therapy. It is suggested that alterations in sympathetic tone induced by changing from a beta-blocker to a calcium antagonist might have increased myocardial irritability thus favouring genesis of severe ventricular arrhythmias. Verapamil is often considered to be more effective than propranolol in the treatment of HOCM. However, if propranolol is replaced by verapamil one has to take account of the possibility of serious arrhythmias as demonstrated by our case.