The kidney filter represents a unique assembly of podocyte epithelial cells that tightly enwrap the glomerular capillaries with their complex foot process network. While deficiency of the polarity proteins Crumbs and aPKC result in impaired podocyte foot process architecture, the function of basolateral polarity proteins for podocyte differentiation and maintenance remained unclear. Here we report, that Scribble is expressed in developing podocytes, where it translocates from the lateral aspects of immature podocytes to the basal cell membrane and foot processes of mature podocytes. Immunogold electron microscopy reveals membrane associated localisation of Scribble predominantly at the basolateral site of foot processes. To further study the role of Scribble for podocyte differentiation Scribble(flox/flox) mice were generated by introducing loxP-sites into the Scribble introns 1 and 8 and these mice were crossed to NPHS2.Cre mice and Cre deleter mice. Podocyte-specific Scribble knockout mice develop normally and display no histological, ultrastructural or clinical abnormalities up to 12 months of age. In addition, no increased susceptibility to glomerular stress could be detected in these mice. In contrast, constitutive Scribble knockout animals die during embryonic development indicating the fundamental importance of Scribble for embryogenesis. Like in podocyte-specific Scribble knockout mice, the development of podocyte foot processes and the slit diaphragm was unaffected in kidney cultures from constitutive Scribble knockout animals. In summary these results indicate that basolateral polarity signaling via Scribble is dispensable for podocyte function, highlighting the unique feature of podocyte development with its significant apical membrane expansions being dominated by apical polarity complexes rather than by basolateral polarity signaling.

The kinase mammalian target of rapamycin (mTOR) exists in two multiprotein complexes (mTORC1 and mTORC2) and is a central regulator of growth and metabolism. Insulin activation of mTORC1, mediated by phosphoinositide 3-kinase (PI3K), Akt, and the inhibitory tuberous sclerosis complex 1/2 (TSC1-TSC2), initiates a negative feedback loop that ultimately inhibits PI3K. We present a data-driven dynamic insulin-mTOR network model that integrates the entire core network and used this model to investigate the less well understood mechanisms by which insulin regulates mTORC2. By analyzing the effects of perturbations targeting several levels within the network in silico and experimentally, we found that, in contrast to current hypotheses, the TSC1-TSC2 complex was not a direct or indirect (acting through the negative feedback loop) regulator of mTORC2. Although mTORC2 activation required active PI3K, this was not affected by the negative feedback loop. Therefore, we propose an mTORC2 activation pathway through a PI3K variant that is insensitive to the negative feedback loop that regulates mTORC1. This putative pathway predicts that mTORC2 would be refractory to Akt, which inhibits TSC1-TSC2, and, indeed, we found that mTORC2 was insensitive to constitutive Akt activation in several cell types. Our results suggest that a previously unknown network structure connects mTORC2 to its upstream cues and clarifies which molecular connectors contribute to mTORC2 activation.

G protein-coupled receptors (GPCRs) are dynamic membrane proteins that bind extracellular molecules to transduce signals. Although GPCRs represent the largest class of therapeutic targets only a small percentage of their ligand-binding sites are precisely defined. Here we describe the novel application of targeted photocrosslinking using unnatural amino acids to obtain structural information about the allosteric binding site of a small molecule drug, the CCR5-targeted HIV-1 co-receptor blocker maraviroc.

PURPOSE OF REVIEW: Mammalian target of rapamycin (mTOR) is an evolutionarily conserved protein kinase. mTOR forms two distinct functional multiprotein kinase complexes that mutually phosphorylate different substrates and regulate a wide array of essential cellular processes including translation, transcription and autophagy. mTOR is active in several types of cancer and plays a role in a variety of other serious human diseases, including diabetes, neurodegenerative disorders and polycystic kidney disease. However, until recently, only very little was known about the function of mTOR in glomerular homeostasis. RECENT FINDINGS: Emerging studies highlight the important roles of the mTOR signaling pathway in both maintaining and deregulating glomerular and podocyte function. SUMMARY: Here we review the current understanding of mTOR signaling in podocyte biology and discuss its implications for the development of glomerular diseases.

The pulse DEER (Double Electron-Electron Resonance) technique is frequently applied for measuring nanometer distances between specific sites in biological macromolecules. In this work we extend the applicability of this method to high field distance measurements in a protein assembly with mixed spin labels, i.e. a nitroxide spin label and a Gd(3+) tag. We demonstrate the possibility of spectroscopic selection of distance distributions between two nitroxide spin labels, a nitroxide spin label and a Gd(3+) ion, and two Gd(3+) ions. Gd(3+)-nitroxide DEER measurements possess high potential for W-band long range distance measurements (6 nm) by combining high sensitivity with ease of data analysis, subject to some instrumental improvements.

G protein-coupled receptors (GPCRs) form dimers and higher-order oligomers in native membranes, but the precise mode of receptor-receptor interaction remains unknown. To probe the intradimeric proximity of helix 8 (H8), we carried out chemical crosslinking of endogenous cysteines in rhodopsin in native disk membranes. We identified a Cys316-Cys316 crosslink using partial proteolysis and liquid chromatography-mass spectrometry (LC-MS). These results show that a symmetric dimer interface mediated by H1 and H8 contacts is present in native membranes.

Technological advancements allow new approaches to psychotherapy via electronic media. The eating disorder literature currently contains no studies on internet intervention in anorexia nervosa (AN). This study presents a RCT on an internet-based relapse prevention program (RP) over nine months after inpatient treatment for AN. The sample comprised 258 women, randomized to the RP or treatment as usual (TAU). Expert- and self-ratings were evaluated by intent-to-treat analyses. Concerning age, age at onset and comorbidity, both groups were comparable at randomization. During the RP, the intervention group gained weight while the TAU group had minimal weight loss. RP completers gained significantly more body weight than patients in the TAU condition. Group-by-time comparisons for eating-related cognitions and behaviors and general psychopathology showed a significantly more favorable course in the RP program for "sexual anxieties" and "bulimic symptoms"(interview), and "maturity fears" and "social insecurity"(EDI-2). General psychopathology showed no significant group-by-time interaction. Important factors for successful relapse prevention were adherence to the intervention protocol and increased spontaneity. Considering the unfavorable course and chronicity of anorexia nervosa (AN), internet-based relapse prevention in AN following inpatient treatment appears a promising approach. Future internet-based programs may be further improved and enhanced.

Paramagnetic metal ions generate pseudocontact shifts (PCSs) in nuclear magnetic resonance spectra that are manifested as easily measurable changes in chemical shifts. Metals can be incorporated into proteins through metal binding tags, and PCS data constitute powerful long-range restraints on the positions of nuclear spins relative to the coordinate system of the magnetic susceptibility anisotropy tensor (Δχ-tensor) of the metal ion. We show that three-dimensional structures of proteins can reliably be determined using PCS data from a single metal binding site combined with backbone chemical shifts. The program PCS-ROSETTA automatically determines the Δχ-tensor and metal position from the PCS data during the structure calculations, without any prior knowledge of the protein structure. The program can determine structures accurately for proteins of up to 150 residues, offering a powerful new approach to protein structure determination that relies exclusively on readily measurable backbone chemical shifts and easily discriminates between correctly and incorrectly folded conformations.

Loss of kidney function in renal ischemia/reperfusion injury is due to programmed cell death, but the contribution of necroptosis, a newly discovered form of programmed necrosis, has not been evaluated. Here, we identified the presence of death receptor-mediated but caspase-independent cell death in murine tubular cells and characterized it as necroptosis by the addition of necrostatin-1, a highly specific receptor-interacting protein kinase 1 inhibitor. The detection of receptor-interacting protein kinase 1 and 3 in whole-kidney lysates and freshly isolated murine proximal tubules led us to investigate the contribution of necroptosis in a mouse model of renal ischemia/reperfusion injury. Treatment with necrostatin-1 reduced organ damage and renal failure, even when administered after reperfusion, resulting in a significant survival benefit in a model of lethal renal ischemia/reperfusion injury. Unexpectedly, specific blockade of apoptosis by zVAD, a pan-caspase inhibitor, did not prevent the organ damage or the increase in urea and creatinine in vivo in renal ischemia/reperfusion injury. Thus, necroptosis is present and has functional relevance in the pathophysiological course of ischemic kidney injury and shows the predominance of necroptosis over apoptosis in this setting. Necrostatin-1 may have therapeutic potential to prevent and treat renal ischemia/reperfusion injury.Kidney International advance online publication, 11 January 2012; doi:10.1038/ki.2011.450.