Assessing the prevalence and predicting factors of an abnormal gated myocardial perfusion SPECT in asymptomatic patients with type 2 diabetes

Considering the significant prevalence of silent myocardial ischemia and its related morbidity and mortality in asymptomatic type 2 diabetic patients, it is not well known whether early screening with MPI is cost-effective and predicting factors are not well elucidated. This was a cross-sectional study including 63 asymptomatic patients with type 2 diabetes mellitus (T2DM), with normal ECG and ejection fraction. Patients with any history of documented valvular, congestive or ischemic heart disease, renal or hepatic failure were excluded. At first all patients were interviewed and checked for risk factors and then patients underwent a two-day rest/stress 99mTc-MIBI gated MPI SPECT. Data was assessed by QPS/QGS and 4DM software and evaluated by a nuclear medicine specialist with summed stress score (SSS) of more than 4 defined as CAD. There were 42 females (67%) and 21 males (33%), with a mean age of 61.33 ± 6.98 years and 7.97 ± 4.86 years history of T2DM. CAD was detected in 26 (41.3%) patients and was significantly associated with male gender, smoking and requiring insulin therapy (P-value = 0.019, 0.046, 0.05, respectively). A significant association was found between the duration of diabetes, especially when > 15 years, and the probability of having CAD. Multivariable logistic regression revealed that smoking; male gender and diabetes duration were the strongest independent predictors of abnormal MPI results. We found a high (46%) prevalence of abnormal stress MPI SPECT in patients with type 2 diabetes mellitus, despite being asymptomatic. Asymptomatic patients with a history of smoking, long duration of diabetes, being under insulin treatment and male gender might benefit from MPI for early detection of silent ischemia.

An update on radiation absorbed dose to patients from diagnostic nuclear medicine procedures in Tehran: A study on four academic centers

Purpose:

Use of radiopharmaceuticals for diagnostic nuclear medicine procedures is one of the main sources of radiation exposure. We performed this study with respect to the rapid growth in nuclear medicine in Iran and lack of updated statistics.

Materials and Methods:

The data were obtained for all active Nuclear Medicine Centers affiliated to Shahid Beheshti University of Medical Sciences during 2009 and 2010.

Results:

The most frequently performed procedures were bone (30.16%), cardiac (28.96%), renal (17.97%), and thyroid (7.93%) scans. There was a significant decrease in the number of thyroid scintigraphies with ¹³¹I and ^99mTc-sulfur colloid liver/spleen scans and tremendous increase in the frequencies of cardiac and bone scintigraphies compared to one decade ago.

Conclusion:

Compared to previous studies, there were striking changes in trends of diagnostic nuclear medicine procedures in Tehran. This field is still evolving in the country, and this trend will further change with the introduction of positron emission tomography scanners in future.

Differential phosphorylation of IRS-1 by insulin and insulin-like growth factor I receptors in Chinese hamster ovary cells

Insulin receptor (IR) and insulin-like growth factor I receptor (IGF-IR) are closely related receptor tyrosine kinases. Despite their high degree of homology, recent evidence suggests that the two receptors have distinct biological roles. In several recent studies, the cytoplasmic tyrosine kinase domains of the two receptors have been shown to possess different signalling specificities. In this study, we examine the hypothesis that differential phosphorylation of insulin receptor substrate 1 (IRS-1) may contribute to these differences in signalling between the two receptors. Using Chinese hamster ovary (CHO) cells stably expressing human IR or IGF-IR and activated by their respective ligands, we show that there are differences between the two receptors with regard to the complement of SH2-containing proteins recruited to IRS-1. In particular, IGF-IR appears to couple IRS-1 preferentially to Grb2 whereas, in contrast, IR appears to couple IRS-1 preferentially to the p85 subunit of phosphatidyl inositol 3-kinase (PI3-kinase) and to Nck. The two receptors couple IRS-1 equally to the tyrosine phosphatase SHP2. We have also generated phosphospecific antibodies to three important tyrosine phosphorylation sites on IRS-1 (pY608, pY895 and pY1172). We used these antibodies to probe the phosphorylation status of these sites in intact CHO/IR and CHO/IGF-IR cells. In the case of pY608, these results also show evidence for differential phosphorylation of IRS-1 by the two receptors. Taken together, the results presented here support the notion that the cytoplasmic domains of IR and IGF-IR have differences in their intrinsic signalling potentials.

Dach1 mutant mice bear no gross abnormalities in eye, limb, and brain development and exhibit postnatal lethality

Drosophila dachshund is necessary and sufficient for compound eye development and is required for normal leg and brain development. A mouse homologue of dachshund, Dach1, is expressed in the developing retina and limbs, suggesting functional conservation of this gene. We have generated a loss-of-function mutation in Dach1 that results in the abrogation of the wild-type RNA and protein expression pattern in embryos. Homozygous mutants survive to birth but exhibit postnatal lethality associated with a failure to suckle, cyanosis, and respiratory distress. The heart, lungs, kidneys, liver, and skeleton were examined to identify factors involved in postnatal lethality, but these organs appeared to be normal. In addition, blood chemistry tests failed to reveal differences that might explain the lethal phenotype. Gross examination and histological analyses of newborn eyes, limbs, and brains revealed no detectable abnormalities. Since Dach1 mutants die shortly after birth, it remains possible that Dach1 is required for postnatal development of these structures. Alternatively, an additional Dach homologue may functionally compensate for Dach1 loss of function.

The substrate specificity of the catalytic domain of Abl plays an important role in directing phosphorylation of the adaptor protein Crk

c-Abl preferentially phosphorylates peptide substrates that contain proline at the P+3 site (relative to the phosphorylated tyrosine). We previously described a mutant form of the Abl catalytic domain (Y569W) with altered substrate specificity at the P+3 position, as measured using synthetic peptides. In this study, we examine the phosphorylation of Crk, a protein substrate of Abl that is phosphorylated in the sequence Tyr221-Ala-Gln-Pro. In vitro, phosphorylation of Crk by Y569W Abl is greatly reduced relative to wild-type Abl. Overexpression of Y569W mutant Abl in 293T kidney cells produces a similar overall pattern of tyrosine phosphorylation as wild-type Abl, indicating that not all cellular proteins depend on Pro at P+3 for Abl recognition. However, phosphorylation of Crk by Y569W Abl in these cells is markedly reduced relative to wild-type Abl. A truncated form of Abl lacking the C-terminal polyproline region is not able to phosphorylate Crk in these assay conditions. Thus, proper phosphorylation of Crk by Abl depends not only on the interaction of the Crk SH3 domain with the Abl polyproline region, but also on the recognition of amino acids surrounding tyrosine by the Abl catalytic domain.

Improving SH3 domain ligand selectivity using a non-natural scaffold

BACKGROUND

Src homology 3 (SH3) domains bind sequences bearing the consensus motif PxxP (where P is proline and x is any amino acid), wherein domain specificity is mediated largely by sequences flanking the PxxP core. This specificity is limited, however, as most SH3 domains show high ligand cross-reactivity. We have recently shown that diverse N-substituted residues (peptoids) can replace the prolines in the PxxP motif, yielding a new source of ligand specificity.

RESULTS

We have tested the effects of combining multiple peptoid substitutions with specific flanking sequences on ligand affinity and specificity. We show that by varying these different elements, a ligand can be selectively tuned to target a single SH3 domain in a test set. In addition, we show that by making multiple peptoid substitutions, high-affinity ligands can be generated that completely lack the canonical PxxP motif. The resulting ligands can potently disrupt natural SH3-mediated interactions.

CONCLUSIONS

Peptide-peptoid hybrid scaffolds yield SH3 ligands with markedly improved domain selectivity, overcoming one of the principal challenges in designing inhibitors against these domains. These compounds represent important leads in the search for orthogonal inhibitors of SH3 domains, and can serve as tools for the dissection of complex signaling pathways.

Dachshund and eyes absent proteins form a complex and function synergistically to induce ectopic eye development in Drosophila

The eyeless, dachshund, and eyes absent genes encode conserved, nuclear proteins that are essential for eye development in Drosophila. Misexpression of eyeless or dachshund is also sufficient to induce the formation of ectopic compound eyes. Here we show that the dachshund and eyes absent genes act synergistically to induce ectopic retinal development and positively regulate the expression of each other. Moreover, we show that the Dachshund and Eyes Absent proteins can physically interact through conserved domains, suggesting a molecular basis for the genetic synergy observed and that a similar complex may function in mammals. We propose that a conserved regulatory network, rather than a linear hierarchy, controls retinal specification and involves multiple protein complexes that function during distinct steps of eye development.

Src family-selective tyrosine kinase inhibitor, PP1, inhibits both Fc epsilonRI- and Thy-1-mediated activation of rat basophilic leukemia cells

Cross-linking of the surface receptor with high affinity for IgE (Fc epsilonRI) by multivalent antigen/immunoglobulin E complexes, as well as aggregation of Thy-1 glycoprotein by monoclonal antibodies lead in rat basophilic leukemia cells, clone RBL-2H3, to tyrosine phosphorylation of several cellular proteins, followed by a release of secretory components. To investigate the molecular mechanisms of Fc epsilonRI- and Thy-1-mediated transmembrane signaling and to map a step at which they converge into a common secretory pathway, we used a novel Src family-selective tyrosine kinase inhibitor, 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1), and analyzed its inhibitory activity on cell activation. Here we show that in RBL-2H3 cells PP1 demonstrates substrate specificity for a Src family kinase Lyn. In immunocomplex kinase assays in vitro, PP1 inhibited the Lyn kinase activity at nanomolar levels without any effect on Syk kinase activity. However, in RBL cells activated via aggregation of Fc epsilonRI, phosphorylation of both Syk and Lyn kinases was inhibited. Fc epsilonRI- and Thy-1-mediated early (protein-tyrosine phosphorylation) and late (release of beta-hexosaminidase) activation events were similarly affected by PP1. The inhibition was specific for membrane receptor-mediated signaling and was not observed in cells activated by an exposure to pervanadate. The combined data suggest that activation of Lyn is the early activation step at which the Fc epsilonRI- and Thy-1-mediated activation pathways of mast cells and basophils may converge.

Direct interaction of Syk and Lyn protein tyrosine kinases in rat basophilic leukemia cells activated via type I Fc epsilon receptors

Activation of rat mast cells through the receptor with high affinity for IgE (Fc epsilonRI) requires a complex set of interactions involving transmembrane subunits of the Fc epsilonRI and two classes of nonreceptor protein tyrosine kinase (PTK). the Src family PTK p53/p56(lyn) (Lyn) and the Syk/ZAP-family PTK p72(syk) (Syk). Early activation events involve increased activity of Lyn and Syk kinases and their translocation into membrane domains containing aggregated Fc epsilonRI, but the molecular mechanisms responsible for these changes have remained largely unclear. To determine the role of Fc epsilonRI subunits in this process, we have analyzed Syk- and Lyn-associated proteins in activated rat basophilic leukemia (RBL) cells and their variants deficient in the expression of Fc epsilonRI beta or gamma subunits. Sepharose 4B gel chromatography of postnuclear supernatants from Nonidet-P40-solubilized antigen (Ag)- or pervanadate-activated RBL cells revealed extensive changes in the size of complexes formed by Lyn and Syk kinases and other cellular components. A fusion protein containing Src homology 2 (SH2) and SH3 domains of Lyn bound Syk from lysates of nonactivated RBL cells; an increased binding was observed when lysates from Ag- or pervanadate-activated cells were used. A similar amount of Syk was bound when lysates from pervanadate-activated variant cells deficient in the expression of Fc epsilonRI beta or gamma subunits were used, suggesting that Fc epsilonRI does not function as the only intermediate in the formation of the Syk-Lyn complexes. Further experiments have indicated that Syk-Lyn interactions occur in Ag-activated RBL cells under in vivo conditions and that these interactions could involve direct binding of the Lyn SH2 domain with phosphorylated tyrosine of Syk. The physical association of Lyn and Syk during mast-like cell activation supports the recently proposed functional cooperation of these two tyrosine kinases in Fc epsilonRI signaling.

The functional expression of sodium-dependent bile acid transport in Madin-Darby canine kidney cells transfected with the cDNA for microsomal epoxide hydrolase

Previous studies have suggested that the enzyme microsomal epoxide hydrolase (mEH) is able to mediate sodium-dependent transport of bile acids such as taurocholate into hepatocytes (von Dippe, P., Amoui, M., Alves, C., and Levy, D.(1993) Am. J. Physiol. 264, G528-G534). In order to characterize directly the putative transport properties of the enzyme, a pCB6 vector containing the cDNA for this protein (pCB6-mEH) was transfected into Madin-Darby canine kidney (MDCK) cells, and stable transformants were isolated that could express mEH at levels comparable with the levels expressed in hepatocytes. Sodium-dependent transport of taurocholate was shown to be dependent on the expression of mEH and to be inhibited by the bile acid transport inhibitor 4,4'-diisothiocyanostilbene-2,2'disulfonic acid (DIDS), as well as by other bile acids. Kinetic analysis of this system indicated a Km of 26.3 microM and a Vmax of 117 pmol/mg protein/min. The Km value is essentially the same as that observed in intact hepatocytes. The transfected MDCK cells also exhibited sodium-dependent transport of cholate at levels 150% of taurocholate in contrast to hepatocytes where cholate transport is only 30% of taurocholate levels, suggesting that total hepatocyte bile acid transport is a function of multiple transport systems with different substrate specificities, where mEH preferentially transports cholate. This hypothesis is further supported by the observation that a monoclonal antibody that partially protects (26%) taurocholate transport from inhibition by DIDS in hepatocytes provides almost complete protection (88%) from DIDS inhibition of hepatocyte cholate transport, suggesting that taurocholate is also taken up by an alternative system not recognized by this antibody. Additional support for this concept is provided by the observation that the taurocholate transport system is almost completely protected (92%) from DIDS inhibition by this antibody in MDCK cells that express mEH as the only bile acid transporter. These results demonstrate that mEH is expressed on the surface of hepatocytes as well as on transfected MDCK cells and is able to mediate sodium-dependent transport of taurocholate and cholate.

Thy-1-mediated activation of rat mast cells: the role of Thy-1 membrane microdomains

The glycosyl-phosphatidylinositol (GPI)-anchored glycoprotein Thy-1 is one of the most abundant molecules expressed on the surface of rat mast cells and rat basophilic leukemia (RBL) cells. The finding that Thy-1 from detergent-solubilized RBL-2H3 cells forms complexes with src-related protein-tyrosine kinase p56/p53lyn suggested that this kinase may play a key role in Thy-1-mediated mast-cell activation. The molecular mechanism of this activation is, however, unknown. Here we show that in RBL-2H3-derived cells extracted by the standard procedure with several non-ionic detergents, the majority of Thy-1 and p56/p53lyn were not released into postnuclear supernatant but remained associated with the detergent-resistant cytoskeletal/nuclear fraction. Pretreatment of the cells with the cholesterol-complexing agents, saponin or digitonin, resulted in complete solubilization of Thy-1 and p56/p53lyn in non-ionic detergents and dissociation of the complexes; this implies that cholesterol plays a crucial role in stabilization of the complexes. This conclusion was supported by double immunofluorescence colocalization experiments which also allowed us to estimate the size of the insoluble complexes to be about 0.1 micron. Sequential treatment with saponin and Nonidet P-40 was used to fractionate tyrosine-phosphorylated proteins during Thy-1-mediated activation of RBL-2H3 cells. Among the soluble cytoplasmic proteins the most dramatic change in tyrosine phosphorylation was found in pp72, whereas pp40 and pp33 were found mainly in the membrane fraction. Our data suggest that surface aggregation of GPI-anchored Thy-1 molecules leads to aggregation of p56/p53lyn kinase located in the same membrane microdomain, followed by transphosphorylation of both soluble and membrane-bound substrates.

Bile acid transport into hepatocyte smooth endoplasmic reticulum vesicles is mediated by microsomal epoxide hydrolase, a membrane protein exhibiting two distinct topological orientations

Bile acids, such as taurocholate, have been shown to be transported into hepatocyte smooth endoplasmic reticulum (SER) vesicles. This process is Na(+)-independent, electrogenic, inhibitable by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and taurochenodeoxycholate, with a Km of 352 microM and a Vmax of 29.6 nmol/mg protein/min. The observed transport is mediated by the bifunctional protein, microsomal epoxide hydrolase (mEH) which can also mediate bile acid transport into hepatocytes across the sinusoidal plasma membrane (von Dippe, P., Amoui, M., Alves, C., and Levy, D. (1993) Am. J. Physiol. 264, G528-G534). mEH was isolated from SER membranes by immunoprecipitation with monoclonal antibody (mAb) 25D-1 which recognizes this protein on the surface of intact hepatocytes. The SER-derived protein exhibited an apparent molecular weight, isoelectric point, N-terminal amino acid sequence, and mEH-specific activity that were indistinguishable from the plasma membrane form of the enzyme. Proteoliposome reconstitution of the SER taurocholate transport system indicated that mEH was absolutely required for the expression of transport capacity. The interaction of mAb 25D-1 with mEH on intact right-side-out SER vesicles demonstrated that the epitope found on the surface of hepatocytes was also found on the cytoplasmic surface of these vesicles (80%) and in the lumen (20%) suggesting the presence of two forms of this protein in the SER, the latter from being sorted to the cell surface. The existence of two orientations of this protein in the SER was confirmed by the sensitivity to tryptic digestion, where 75% of the mAb epitope was accessible to the enzyme. The loss of the 25D-1 epitope correlated with loss of taurocholate transport capacity. The role of mEH in the transport process and the orientation of the transporting isoform was further established by demonstrating that mAb 25A-3, which also reacts with mEH on the hepatocyte surface, was able to directly inhibit taurocholate transport in the SER vesicle system. These and previous results thus establish that isoforms of mEH can mediate taurocholate transport at the sinusoidal plasma membrane and in SER vesicles and that this bifunctional protein can exist in two orientations in the SER membrane. The association of bile acids with the SER suggests a possible role of intracellular vesicles in the transhepatocellular movement of bile acids from the sinusoidal to the canalicular compartment.

Na(+)-dependent bile acid transport by hepatocytes is mediated by a protein similar to microsomal epoxide hydrolase

A protein mediating hepatocyte sodium-dependent bile acid transport across the sinusoidal plasma membrane has been purified by immunoprecipitation with monoclonal antibody (MAb) 25D-1, which specifically recognizes this protein on the surface of intact hepatocytes (Ananthanarayanan et al. J. Biol. Chem. 263: 8338-8343, 1988). The function of this protein was further established by proteoliposome reconstitution (von Dippe et al. J. Biol. Chem. 265: 14812-14816, 1990). NH2-terminal amino acid sequence analysis and amino acid composition revealed this protein to be closely related to the enzyme microsomal epoxide hydrolase (mEH). Both proteins exhibited the same elution times on a reverse-phase high-pressure liquid chromatography column, comigrated with an apparent molecular weight of 49,000 as measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and possessed identical isoelectric points of 8.2. The MAb was capable of immunoprecipitating chromatographically purified mEH, as well as a protein derived from the sinusoidal plasma membrane that exhibited mEH activity comparable to that of the protein isolated from the endoplasmic reticulum. The subtilisin fragmentation patterns derived from chromatographically purified mEH and the MAb-precipitated plasma membrane protein were also identical. Hydropathy profile analysis of the amino acid sequence of mEH suggested the presence of four transmembrane domains. The results of these studies indicate that a protein that is involved in mediating sodium-dependent bile acid transport is closely related to mEH.