Phosphoinositide 3-kinases (PI3-Ks) are an important emerging class of drug targets, but the unique roles of PI3-K isoforms remain poorly defined. We describe here an approach to pharmacologically interrogate the PI3-K family. A chemically diverse panel of PI3-K inhibitors was synthesized, and their target selectivity was biochemically enumerated, revealing cryptic homologies across targets and chemotypes. Crystal structures of three inhibitors bound to p110gamma identify a conformationally mobile region that is uniquely exploited by selective compounds. This chemical array was then used to define the PI3-K isoforms required for insulin signaling. We find that p110alpha is the primary insulin-responsive PI3-K in cultured cells, whereas p110beta is dispensable but sets a phenotypic threshold for p110alpha activity. Compounds targeting p110alpha block the acute effects of insulin treatment in vivo, whereas a p110beta inhibitor has no effect. These results illustrate systematic target validation using a matrix of inhibitors that span a protein family.

STIM1, a recently identified endoplasmic reticulum (ER) protein, rapidly translocates to a plasma membrane-adjacent ER compartment upon depletion of the ER Ca2؉ stores. Here we use a novel means, namely a chemically inducible bridge formation between the plasma and ER membranes, to highlight the plasma membrane-adjacent ER compartment and show that this is the site where STIM1 and its Ca 2؉ channel partner, Orai1, form a productive interaction upon store depletion. By changing the length of the linkers connecting the plasma and ER membranes, we show that Orai1 requires a larger space than STIM1 between the two membranes. This finding suggests that Orai1 is part of a larger macromolecular cluster with an estimated 11-14-nm protrusion to the cytoplasm, whereas the cytoplasmic domain of STIM1 fits in a space calculated to be less than 6 nm. We finally show that agonist-induced translocation of STIM1 is rapidly reversible and only partially affects STIM1 in the juxtanuclear ER compartment. These studies are the first to detect juxtaposed areas between the ER and the plasma membrane in live cells, revealing novel details of STIM1-Orai1 interactions.It has long been known that Ca 2ϩ -mobilizing agonists activate a Ca 2ϩ entry pathway subsequent to their mobilization of intracellular Ca 2ϩ stores by a mechanism that has eluded identification until most recently. In 1986, Putney (1) had postulated that enhanced Ca 2ϩ entry is a consequence of the depletion of the intracellular Ca 2ϩ stores, introducing the term capacitative Ca 2ϩ entry or store-operated Ca 2ϩ entry pathway (SOCE).3 Most recent developments began to shed light on the molecular details underlying the SOCE phenomenon. Screening with libraries of RNA interference, two groups have identified proteins, previously known as stromal-interacting molecule (STIM) 1 and -2 (2, 3), as essential components of SOCE (4 -6). STIM1 and STIM2 are ER-resident proteins that contain a single membrane-spanning domain and an EF hand motif in the luminal side of the ER that serves as a Ca 2ϩ sensor. Remarkably, STIM1 shows rapid translocation to a plasma membrane (PM)-adjacent region of the ER upon depletion of the ER luminal Ca 2ϩ (4, 5, 7), but it does not have the structural hallmarks of an ion channel. In parallel studies, another protein necessary for SOCE and with a channel-like structure has been identified and named Orai1 (8) or CRACM1 (9). Although overexpression of STIM1 alone is a poor enhancer of SOCE, together with Orai1, it dramatically enhances store-operated Ca 2ϩ entry consistent with the hypothesis that STIM and Orai form a functional complex, (10, 11). Finally, three groups have recently provided strong evidence that Orai1 indeed is the molecular entity forming the channel pore through which Ca 2ϩ enters the cells upon store depletion (12)(13)(14). These studies have laid the groundwork for the molecular definition of the capacitative Ca 2ϩ entry process. Several questions have been raised concerning the movements of STIM1 within the ER and between the ER and ...

Barley ( Hordeum vulgare subsp. vulgare) is an economically important diploid model for the Triticeae; and a better understanding of low-temperature tolerance mechanisms could significantly improve the yield of fall-sown cereals. We developed a new resource for genetic analysis of winter hardiness-related traits, the 'Nure' x 'Tremois' linkage map, based on a doubled-haploid population that is segregating for low-temperature tolerance and vernalization requirement. Three measures of low-temperature tolerance and one measure of vernalization requirement were used and, for all traits, QTLs were mapped on chromosome 5H. The vernalization response QTL coincides with previous reports at the Vrn-1/Fr1 region of the Triticeae. We also found coincident QTLs at this position for all measures of low-temperature tolerance. Using Composite Interval Mapping, a second proximal set, of coincident QTLs for low-temperature tolerance, and the accumulation of two different COR proteins (COR14b and TMC-Ap3) was identified. The HvCBF4 locus, or another member of the CBF loci clustered in this region, is the candidate gene underlying this QTL. There is a CRT/DRE recognition site in the promoter of cor14b with which a CBF protein could interact. These results support the hypothesis that highly conserved regulatory factors, such as members of the CBF gene family, may regulate the stress responses of a wide range of plant species.

Transient receptor potential melastatin 2 (TRPM2) is a Ca2+-permeable cation channel required for immune cell activation, insulin secretion, and body heat control. TRPM2 is activated by cytosolic Ca2+, phosphatidyl-inositol-4,5-bisphosphate and ADP ribose. Here, we present the ~3 Å resolution electron cryo-microscopic structure of TRPM2 from Nematostella vectensis, 63% similar in sequence to human TRPM2, in the Ca2+-bound closed state. Compared to other TRPM channels, TRPM2 exhibits unique structural features that correlate with its function. The pore is larger and more negatively charged, consistent with its high Ca2+ selectivity and larger conductance. The intracellular Ca2+ binding sites are connected to the pore and cytosol, explaining the unusual dependence of TRPM2 activity on intra- and extracellular Ca2+. In addition, the absence of a post-filter motif is likely the cause of the rapid inactivation of human TRPM2. Together, our cryo-EM and electrophysiology studies provide a molecular understanding of the unique gating mechanism of TRPM2.

Several pleckstrin-homology (PH) domains with the ability to bind phosphatidylinositol (3,4,5)-trisphosphate [PtdIns(3,4,5)P3, PIP3] were expressed as green fluorescent protein (GFP) fusion proteins to determine their effects on various cellular responses known to be activated by PIP3. These proteins comprised the PH domains of Akt, ARNO, Btk or GRP1, and were found to show growth-factor-stimulated and wortmannin-sensitive translocation from the cytosol to the plasma membrane in several cell types, indicating their ability to recognize PIP3. Remarkably, although overexpressed Akt-PH–GFP and Btk-PH–GFP were quite potent in antagonizing the PIP3-mediated activation of the Akt protein kinase, such inhibition was not observed with the other PH domains. By contrast, expression of the PH domains of GRP1 and ARNO, but not of Akt or Btk, inhibited the attachment and spreading of freshly seeded cells to culture dishes. Activation of PLCγ by epidermal growth factor (EGF) was attenuated by the PH domains of GRP1, ARNO and Akt, but was significantly enhanced by the Btk PH domain. By following the kinetics of expression of the various GFP-fused PH domains for several days, only the PH domain of Akt showed a lipid-binding-dependent self-elimination, consistent with its interference with the anti-apoptotic Akt signaling pathway. Mutations of selective residues that do not directly participate in PIP3 binding in the GRP1-PH and Akt-PH domain were able to reduce the dominant-negative effects of these constructs yet retain their lipid binding. These data suggest that interaction with and sequestration of PIP3 may not be the sole mechanism by which PH domains interfere with cellular responses and that their interaction with other membrane components, most probably with proteins, allows a more specific participation in the regulation of specific signaling pathways.

The recently identified ceramide transfer protein, CERT, is responsible for the bulk of ceramide transport from the endoplasmic reticulum (ER) to the Golgi. CERT has a C-terminal START domain for ceramide binding and an N-terminal pleck-strin homology domain that binds phosphatidylinositol 4-phosphate suggesting that phosphatidylinositol (PI) 4-kinases are involved in the regulation of CERT-mediated ceramide transport. In the present study fluorescent analogues were used to follow the ER to Golgi transport of ceramide to determine which of the four mammalian PI 4-kinases are involved in this process. Overexpression of pleckstrin homology domains that bind phosphatidylinositol 4-phosphate strongly inhibited the transport of C5-BODIPY-ceramide to the Golgi. A newly identified PI 3-kinase inhibitor, PIK93 that selectively inhibits the type III PI 4-kinase beta enzyme, and small interfering RNA-mediated down-regulation of the individual PI 4-kinase enzymes, revealed that PI 4-kinase beta has a dominant role in ceramide transport between the ER and Golgi. Accordingly, inhibition of PI 4-kinase III beta either by wortmannin or PIK93 inhibited the conversion of [3H]serine-labeled endogenous ceramide to sphingomyelin. Therefore, PI 4-kinase beta is a key enzyme in the control of spingomyelin synthesis by controlling the flow of ceramide from the ER to the Golgi compartment.

Transient receptor potential melastatin 2 (TRPM2) is a Ca2؉ -permeable cation channel involved in physiological and pathophysiological processes linked to oxidative stress. TRPM2 channels are co-activated by intracellular Ca 2؉ and ADP-ribose (ADPR) but also modulated in intact cells by several additional factors. Superfusion of TRPM2-expressing cells with H 2 O 2 or intracellular dialysis of cyclic ADPR (cADPR) or nicotinic acid adenine dinucleotide phosphate (NAADP) activates, whereas dialysis of AMP inhibits, TRPM2 whole-cell currents. Additionally, H 2 O 2 , cADPR, and NAADP enhance ADPR sensitivity of TRPM2 currents in intact cells. Because in whole-cell recordings the entire cellular machinery for nucleotide and Ca 2؉homeostasis is intact, modulators might affect TRPM2 activity either directly, by binding to TRPM2, or indirectly, by altering the local concentrations of the primary ligands ADPR and Ca 2؉ . To identify direct modulators of TRPM2, we have studied the effects of H 2 O 2 , AMP, cADPR, NAADP, and nicotinic acid adenine dinucleotide in inside-out patches from Xenopus oocytes expressing human TRPM2, by directly exposing the cytosolic faces of the patches to these compounds. H 2 O 2 (1 mM) and enzymatically purified cADPR (10 M) failed to activate, whereas AMP (200 M) failed to inhibit TRPM2 currents. NAADP was a partial agonist (maximal efficacy, ϳ50%), and nicotinic acid adenine dinucleotide was a full agonist, but both had very low affinities (K 0.5 ‫؍‬ 104 and 35 M). H 2 O 2 , cADPR, and NAADP did not enhance activation by ADPR. Considering intracellular concentrations of these compounds, none of them are likely to directly affect the TRPM2 channel protein in a physiological context. TRPM22 is a member of the transient receptor potential family of proteins and forms a nonselective cation channel that is permeable to Ca 2ϩ (1). TRPM2 channels are abundantly expressed in the brain, in hematopoietic tissues, and in leukocytes (1-4) and activate under conditions of oxidative stress to cause elevations in intracellular [Ca 2ϩ ] ([Ca 2ϩ ] i ) that contribute to chemotactic responses (5) and chemokine production (6) of immune cells, as well as to neuronal cell death following ischemia (4,7,8).The primary activators of TRPM2 are ADP-ribose (ADPR) and Ca 2ϩ (2-4); simultaneous binding of both agonists is required for channel opening (9). TRPM2 channels are homotetramers (10), and ADPR binds to the NUDT9-H domains located at the cytosolic C termini of the subunits, named based on sequence homology to the mitochondrial enzyme NUDT9 (2). Both NUDT9 and isolated NUDT9-H bind ADPR and convert it to AMP and ribose-5-phosphate (2, 11), but the role in TRPM2 channel gating of the very slow ADPR hydrolase (ADPRase) activity of NUDT9-H is unknown. In intact cells ADPR activates TRPM2 only in the presence of either intra-or extracellular Ca 2ϩ (4, 12, 13); biophysical studies in inside-out patches have shown that the activatory Ca 2ϩ -binding sites are located intracellularly of the gate, such that extracellular...

Two populations of single chromosome recombinant lines were used to map genes controlling flowering time on chromosome 5B of wheat, and one of the populations was also used to map a new frost resistance gene. Genetic maps were developed, mainly using microsatellite markers, and QTL analysis was applied to phenotypic data on the performance of each population collected from growth-room tests of flowering time and frost tolerance. Using a recombinant substitution-line mapping population derived from a cross between the substitution-line 'Chinese Spring' ('Cheyenne' 5B) and 'Chinese Spring' (CS), the gene Vrn-B1, affecting vernalization response, an earliness per se locus, Eps-5BL1, and a gene, Fr-B1, affecting frost resistance, were mapped. Using a 'Hobbit Sib' ('Chinese Spring' 5BL) x 'Hobbit Sib' recombinant substitution line mapping population, an earliness per se locus, Eps-5BL2 was mapped. The Vrn-B1 locus was mapped on the distal portion of the long arm of chromosome 5B, to a region syntenous with the segments of chromosomes 5A and 5D containing Vrn-A1 and Vrn-D1 loci, respectively. The two Eps-5BL loci were mapped close to the centromere with a 16-cM distance from each other, one in agreement with the position of a homoeologous locus previously mapped on chromosome 5H of barley, and suggested by the response of 'Chinese Spring' deletion lines. The Fr-B1 gene was mapped on the long arm of chromosome 5B, 40 cM from the centromeric marker. Previous comparative mapping data with rice chromosome 9 would suggest that this gene could be orthologous to the other Fr genes mapped previously by us on chromosomes 5A or 5D of wheat, although in a more proximal position. This study completes the mapping of these homoeoallelic series of vernalization requirement genes and frost resistance genes on the chromosomes of the homoeologous group 5 in wheat.