PubMed Health⌕ Search

Biomedical subjects

M B Yaffe

Publications and source records attributed to M B Yaffe.

At least 37 records · Page 2Linked to original sources
PubMed2000

14-3-3 proteins and survival kinases cooperate to inactivate BAD by BH3 domain phosphorylation.

The Bcl-2 homology 3 (BH3) domain of prodeath Bcl-2 family members mediates their interaction with prosurvival Bcl-2 family members and promotes apoptosis. We report that survival factors trigger the phosphorylation of the proapoptotic Bcl-2 family member BAD at a site (Ser-155) within the BAD BH3 domain. When BAD is bound to prosurvival Bcl-2 family members, BAD Ser-155 phosphorylation requires the prior phosphorylation of Ser-136, which recruits 14-3-3 proteins that then function to increase the accessibility of Ser-155 to survival-promoting kinases. Ser-155 phosphorylation disrupts the binding of BAD to prosurvival Bcl-2 proteins and thereby promotes cell survival. These findings define a mechanism by which survival signals inactivate a proapoptotic Bcl-2 family member, and suggest a role for 14-3-3 proteins as cofactors that regulate sequential protein phosphorylation events.

14-3-3 Proteins↗
PubMed1999

Affinity-driven peptide selection of an NFAT inhibitor more selective than cyclosporin A.

The flow of information from calcium-mobilizing receptors to nuclear factor of activated T cells (NFAT)-dependent genes is critically dependent on interaction between the phosphatase calcineurin and the transcription factor NFAT. A high-affinity calcineurin-binding peptide was selected from combinatorial peptide libraries based on the calcineurin docking motif of NFAT. This peptide potently inhibited NFAT activation and NFAT-dependent expression of endogenous cytokine genes in T cells, without affecting the expression of other cytokines that require calcineurin but not NFAT. Substitution of the optimized peptide sequence into the natural calcineurin docking site increased the calcineurin responsiveness of NFAT. Compounds that interfere selectively with the calcineurin-NFAT interaction without affecting calcineurin phosphatase activity may be useful as therapeutic agents that are less toxic than current drugs.

Amino Acid Sequence↗
PubMed1999

Crystal structures of the XLP protein SAP reveal a class of SH2 domains with extended, phosphotyrosine-independent sequence recognition.

SAP, the product of the gene mutated in X-linked lymphoproliferative syndrome (XLP), consists of a single SH2 domain that has been shown to bind the cytoplasmic tail of the lymphocyte coreceptor SLAM. Here we describe structures that show that SAP binds phosphorylated and nonphosphorylated SLAM peptides in a similar mode, with the tyrosine or phosphotyrosine residue inserted into the phosphotyrosine-binding pocket. We find that specific interactions with residues N-terminal to the tyrosine, in addition to more characteristic C-terminal interactions, stabilize the complexes. A phosphopeptide library screen and analysis of mutations identified in XLP patients confirm that these extended interactions are required for SAP function. Further, we show that SAP and the similar protein EAT-2 recognize the sequence motif TIpYXX(V/I).

Amino Acid Sequence↗
PubMed1999

Structural analysis of 14-3-3 phosphopeptide complexes identifies a dual role for the nuclear export signal of 14-3-3 in ligand binding.

We have solved the high-resolution X-ray structure of 14-3-3 bound to two different phosphoserine peptides, representing alternative substrate-binding motifs. These structures reveal an evolutionarily conserved network of peptide-protein interactions within all 14-3-3 isotypes, explain both binding motifs, and identify a novel intrachain phosphorylation-mediated loop structure in one of the peptides. A 14-3-3 mutation disrupting Raf signaling alters the ligand-binding cleft, selecting a different phosphopeptide-binding motif and different substrates than the wild-type protein. Many 14-3-3: peptide contacts involve a C-terminal amphipathic alpha helix containing a putative nuclear export signal, implicating this segment in both ligand and Crm1 binding. Structural homology between the 14-3-3 NES structure and those within I kappa B alpha and p53 reveals a conserved topology recognized by the Crm1 nuclear export machinery.

14-3-3 Proteins↗
PubMed1999

Priming of the neutrophil respiratory burst is species-dependent and involves MAP kinase activation.

BACKGROUND: Priming of the neutrophil respiratory burst has been implicated in the pathogenesis of multi-system organ failure (MSOF) after sepsis and trauma. The intracellular signal transduction pathways that mediate priming are unclear. METHODS: Human, porcine, rabbit, rat, and mouse neutrophils were assayed by luminol-dependent chemiluminescence in whole blood and purified neutrophil preparations. Multiple priming agents and agonists were studied, as was inhibition of priming by the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 and the Mek 1/2 inhibitor PD98059. RESULTS: Priming by tumor necrosis factor alpha (TNF-alpha), interleukin-8 (IL-8), and granulocyte-macrophage colony-stimulating factor (GM-CSF) was significantly inhibited by SB203580, whereas platelet-activating factor (PAF) priming was unaffected. Neither TNF-alpha nor PAF primed polymorphonuclear neutrophils (PMNs) within whole blood for N-formyl-methionyl-leucyl-phenylalanine (f-MLP) activation, in contrast to activation by complement-opsonized zymosan (OPZ) or low-dose phorbolmyristate acetate (PMA). Both TNF-alpha and PAF, however, primed purified neutrophils for f-MLP activation. In contrast to human and porcine PMNs, rabbit, rat, and mouse PMNs could not be primed by TNF-alpha or PAF, regardless of the final agonist. CONCLUSIONS: Priming of the PMN respiratory burst proceeds through multiple signaling pathways, depending on the particular priming agent and agonist pair. Differences in priming between PMNs in whole blood and purified preparations may be physiologically significant. There is a pronounced species dependency in the ability to prime the neutrophil respiratory burst.

Animals↗
PubMed1998

Analysis of an activator:coactivator complex reveals an essential role for secondary structure in transcriptional activation.

Ser-133 phosphorylation of CREB within the kinase-inducible domain (KID) promotes target gene activation via complex formation with the KIX domain of the coactivator CBP. Concurrent phosphorylation of CREB at Ser-142 inhibits transcriptional induction via an unknown mechanism. Unstructured in the free state, KID folds into a helical structure upon binding to KIX. Using site-directed mutagenesis based on the NMR structure of the KID:KIX complex, we have examined the mechanisms by which Ser-133 and Ser-142 phosphorylation regulate CREB activity. Our results indicate that phospho-Ser-133 stablizes whereas phospho-Ser-142 disrupts secondary structure-mediated interactions between CREB and CBP. Thus, differential phosphorylation of CREB may form the basis by which upstream signals regulate the specificity of target gene activation.

Amino Acid Sequence↗
PubMed1997

The structural basis for 14-3-3:phosphopeptide binding specificity.

The 14-3-3 family of proteins mediates signal transduction by binding to phosphoserine-containing proteins. Using phosphoserine-oriented peptide libraries to probe all mammalian and yeast 14-3-3s, we identified two different binding motifs, RSXpSXP and RXY/FXpSXP, present in nearly all known 14-3-3 binding proteins. The crystal structure of 14-3-3zeta complexed with the phosphoserine motif in polyoma middle-T was determined to 2.6 A resolution. The bound peptide is in an extended conformation, with a tight turn created by the pS +2 Pro in a cis conformation. Sites of peptide-protein interaction in the complex rationalize the peptide library results. Finally, we show that the 14-3-3 dimer binds tightly to single molecules containing tandem repeats of phosphoserine motifs, implicating bidentate association as a signaling mechanism with molecules such as Raf, BAD, and Cbl.

14-3-3 Proteins↗
PubMed1997

Sequence-specific and phosphorylation-dependent proline isomerization: a potential mitotic regulatory mechanism.

Pin1 is an essential and conserved mitotic peptidyl-prolyl isomerase (PPIase) that is distinct from members of two other families of conventional PPIases, cyclophilins and FKBPs (FK-506 binding proteins). In response to their phosphorylation during mitosis, Pin1 binds and regulates members of a highly conserved set of proteins that overlaps with antigens recognized by the mitosis-specific monoclonal antibody MPM-2. Pin1 is here shown to be a phosphorylation-dependent PPIase that specifically recognizes the phosphoserine-proline or phosphothreonine-proline bonds present in mitotic phosphoproteins. Both Pin1 and MPM-2 selected similar phosphorylated serine-proline-containing peptides, providing the basis for the specific interaction between Pin1 and MPM-2 antigens. Pin1 preferentially isomerized proline residues preceded by phosphorylated serine or threonine with up to 1300-fold selectivity compared with unphosphorylated peptides. Pin1 may thus regulate mitotic progression by catalyzing sequence-specific and phosphorylation-dependent proline isomerization.

Amino Acid Isomerases↗
PubMed1997

Insulin receptor substrate proteins create a link between the tyrosine phosphorylation cascade and the Ca2+-ATPases in muscle and heart.

Following phosphorylation by the insulin receptor kinase, the insulin receptor substrates (IRS)-1 and IRS-2 bind to and activate several Src homology 2 (SH2) domain proteins. To identify novel proteins that interact with IRS proteins in muscle, a human skeletal muscle cDNA expression library was created in the lambdaEXlox system and probed with baculovirus-produced and tyrosine-phosphorylated human IRS-1. One clone of the 10 clones which was positive through three rounds of screening represented the C terminus of the human homologue of the adult fast twitch skeletal muscle Ca2+-ATPase (SERCA1) including the cytoplasmic tail and part of transmembrane region 10. Western blot analysis of extracts of rat muscle demonstrated co-immunoprecipitation of both IRS-1 and IRS-2 with the skeletal muscle Ca2+-ATPase (SERCA1) and the cardiac muscle isoform (SERCA2). In both cases, injection of insulin stimulated a 2- to 6-fold increase in association of which was maximal within 5 min. In primary cultures of aortic smooth muscle cells and C2C12 cells, the insulin-stimulated interaction between IRS proteins and SERCA1 and -2 was dose-dependent with a maximum induction at 100 nM insulin. This interaction was confirmed in a "pull down" experiment using a glutathione S-transferase fusion protein containing the C terminus of the human SERCA isoform and phosphorylated IRS-1 in vitro and could be blocked by a FLVRES-like domain peptide present in the human SERCA sequence. Affinity chromatography of phosphopeptide libraries using the glutathione S-transferase fusion protein of the C terminus of SERCA1 indicated a consensus sequence for binding of XpYGSS; this is identical to potential tyrosine phosphorylation sites at position 431 of human IRS-1 and at position 500 of human IRS-2. In streptozotocin diabetic rats the interaction between IRS proteins and SERCA1 in skeletal muscle and SERCA2 in cardiac muscle was significantly reduced. Taken together, these results indicate that the IRS proteins bind to the Ca2+-ATPase of the sarcoplasmic reticulum in an insulin-regulated fashion, thus creating a potential link between the tyrosine phosphorylation cascade and effects of insulin on calcium.

Animals↗
PubMed1997

Small-bowel diverticulosis: perceptions and reality.

BACKGROUND: Small-bowel diverticulosis is a rare entity that can be discovered incidentally during celiotomy, endoscopy, or radiographic imaging studies. The reported complication rate is low, giving rise to the current recommendation not to treat uncomplicated small-bowel diverticula. STUDY DESIGN: A retrospective review was performed of patients with small-bowel diverticulosis seen during 23 years at three major institutions. RESULTS: Two hundred eight patients were identified. Diverticula were located in the duodenum in 79 percent; in the jejunum or ileum in 18 percent; and in duodenum, jejunum, and ileum in 3 percent. Complications developed in 42 of the 208 patients (20 percent) including bleeding in 14, diverticulitis with perforation and abscess formation in 12, and malabsorption in 8. When assessed by location, jejunoileal diverticula were more likely to have complications than duodenal diverticula: 46 percent compared to 13 percent (p < .01). Bleeding accounted for 52 percent of the duodenal complications compared to 12 percent of the jejunoileal complications (p < 05). Jejunoileal diverticula were more likely to perforate and develop abscesses (21 percent compared to 1.2 percent; p < .001). CONCLUSIONS: The low incidence of complications associated with duodenal diverticula justifies a nonoperative approach. The higher complication rate associated with jejunoileal diverticula will be necessary to define that approach more exactly.

Adult↗
PubMed1997

Pancreatic trauma: a ten-year multi-institutional experience.

Our objective was to determine the incidence, management, and outcome of traumatic pancreatic injury. A retrospective review was performed of all patients with pancreatic injury admitted to two Level I trauma hospitals over a 10-year period. Comparisons were made with Chi square or Fisher's exact tests. Of 16,188 trauma admissions, 72 patients (0.4%) had pancreatic injury. The mean age was 30 years, and 30 patients (69%) were male. Mechanism of injury was gunshot in 32 (45%), blunt in 27 (37%), and stab wound in 13 (18%). The pancreas was involved in 1.1 per cent of patients with penetrating injuries compared to 0.2 per cent with blunt injuries (P < 0.01). There were 18 grade I (25%), 32 grade II (45%), 16 grade III (22%), and 5 grade IV (7%) injuries. Initial diagnosis was made intraoperatively in 63 patients and by computed tomography in 8. The mean injury grade was significantly lower on computed tomography compared to surgical exploration (0.4 vs 2.0; P < 0.05). Operative procedures included distal pancreatectomy in 23 (32%), exploration only in 22 (31%), external drainage in 13 (18%), pancreatorrhaphy in 4, internal drainage in 2, and proximal resection in 2. Mortality was 16.6 per cent and was not related to the mechanism or grade of injury. Mean Injury Severity Score and transfusion requirements were significantly greater in patients who died (P < 0.05). Morbidity occurred in 30 patients (42%), including pancreatic fistula (11%), pancreatitis (7%), and pancreatic pseudocyst (3%). Six patients (8%) developed intra-abdominal abscesses, and all had associated liver or intestinal injuries. In patients with grade I and II injuries, morbidity was higher with external drainage compared to exploration without drainage. Pancreatic injury is infrequent and is more often associated with penetrating trauma. Diagnosis is most commonly made by exploration and cannot be excluded by computed tomography. Drainage of low-grade injuries may not be necessary. Morbidity and mortality in patients with pancreatic trauma is significant and is primarily due to associated injuries.

Adolescent↗
PubMed1996

Injury induces rapid changes in hepatocyte nuclear factor-1: DNA binding.

BACKGROUND: Transcriptional regulation in the liver plays a critical role in mediating the acute phase response to injury. The molecular mechanisms driving these transcriptional events, however, are poorly defined in vivo. The liver-specific transcription factor hepatocyte nuclear factor (HNF)-1 binds to the 5' upstream region of many acute phase genes. To explore the connection between injury and transcriptional regulatory mechanisms, we investigated the effect of injury on HNF-1 binding activity. METHODS: Liver nuclear extracts were prepared from animals after burn or anesthetized sham burn injury. HNF-1 binding activity, affinity, and off rate were assessed by electrophoretic mobility shift analysis. RESULTS: HNF-1 binding activity decreased by 28% 1 1/2 hours after injury. The dissociation constant for HNF-1 increased from 0.6 nm to 11.8 nm at 1 1/2 hours after burn injury partly because of an increase in off rate for the HNF-1: DNA complex. CONCLUSIONS: Burn injury leads to a significant decrease in HNF-1 binding activity as a result of decreased affinity of HNF-1 for DNA. These injury-induced alterations in binding of a liver-specific transcription factor for its DNA binding site represent a mechanism for rapidly modulating acute phase gene transcription in vivo.

Animals↗
PubMed1993

The t-complex polypeptide 1 complex is a chaperonin for tubulin and actin in vivo.

A role in folding newly translated cytoskeletal proteins in the cytosol of eukaryotes has been proposed for t-complex polypeptide 1 (TCP1). In this study, we investigated tubulin and actin biogenesis in Chinese hamster ovary (CHO) cells. When extracts of pulse-labeled cells were analyzed by anion-exchange and size-exclusion chromatography, newly synthesized alpha-tubulin, beta-tubulin, and actin were observed to enter a large molecular mass complex (approximately 900 kDa). These proteins were released from this complex capable, in the case of tubulin, of forming heterodimers. The large molecular mass complexes coeluted with TCP1 and could be immunoprecipitated by using an anti-TCP1 antibody. These findings demonstrate that there is a cytosolic pathway for folding tubulin and actin in vivo that involves the TCP1 complex.

Actins↗
PubMed1993

Site-directed mutagenesis of alpha-tubulin. Reductive methylation studies of the Lys 394 region.

Previous studies have implicated at least two regions in alpha-tubulin that are important for the regulation of microtubule assembly. These regions include a cluster of basic residues consisting of Arg 390, His 393, and Lys 394 and the highly acidic carboxyl terminus. Lys 394 is highly reactive to HCHO and NaCNBH3. The reductive methylation of Lys 394 by these reagents is thought to be responsible for the profound inhibitory effects of low concentrations of HCHO on microtubule assembly (cf. Szasz J., M. B. Yaffe, M. Elzinga, G. S. Blank, and H. Sternlicht. 1986. Biochemistry. 25:4572-4582). In this study we reexamined the basis for this inhibition. Lys 394 in a human keratinocyte alpha-tubulin (k alpha 1) was replaced by a glutamic acid residue using site-directed mutagenesis. The mutant K394E was synthesized in vitro using rabbit reticulocyte lysates, and its ability to coassemble with bovine brain microtubule protein (MTP) before and after reaction with HCHO and NaCNBH3 was compared with that of wild-type. No differences in the coassemblies of the unmethylated proteins were detected suggesting that Lys 394 is not essential for microtubule assembly. However, methylated K394E prepared at low HCHO concentrations (< 1 mM) incorporated into microtubules to a greater extent (approximately 30-40%) than methylated wild-type. This result is consistent with the hypothesis that methylation of Lys 394 interferes with microtubule assembly. However, the extent of protection afforded by the replacement of Lys 394 with Glu 394 was less than half as large as that predicted from the earlier studies. We tentatively conclude that another residue(s) besides Lys 394 contributes significantly to the assembly-inhibition observed with low concentrations of HCHO. Since this residue(s) is less reactive than Lys 394, it would have to inhibit assembly substoichiometrically when methylated. Potential candidates for this residue include bulk lysyl residue(s), a lysyl residue(s) with intermediate reactivity toward HCHO, and the NH2-termini. The NH2-termini are especially attractive candidates since they appear to have a structural role in microtubule assembly.

Animals↗
PubMed1993

Evidence that involucrin is a covalently linked constituent of highly purified cultured keratinocyte cornified envelopes.

The cornified envelop, the terminal product of keratinocyte differentiation, is composed of a variety of covalently cross-linked proteins that form a rigid three-dimensional structure. Our present studies show that preparations of intact envelopes prepared from cultured human keratinocytes contain soluble involucrin, keratin, and filaggrin. Sequential extraction with sodium dodecyl sulfate (SDS) and urea followed by sonication produces envelope fragments that are largely free of soluble proteins, including involucrin. Digestion of these highly purified envelope fragments with cyanogen bromide (CNBr) releases a smear of anti-involucrin immunoreactive material (40-180 kDa) with two enriched clusters of bands at approximately 52 and 70 kDa. The 52-kDa band cluster co-migrates with products released by CNBr digestion of purified involucrin. The CNBr-mediated release of discrete (52- and 70-kDa) involucrin-immunoreactive bands suggests that many involucrin molecules may be cross-linked at relatively few glutamyl residues/molecule in envelopes prepared from cultured keratinocytes. Moreover, what appears to be cross-linked involucrin can be localized on highly purified sonicated envelope fragments using colloidal gold electron microscopy. These results provide evidence that involucrin is a cross-linked component of the keratinocyte marginal band.

Cells, Cultured↗
PubMed1993

Involucrin--structure and role in envelope assembly.

Recent findings have revealed much about the structure of involucrin. These findings make it possible to propose specific models regarding the role of involucrin and the mechanism of its crosslinking as an envelope precursor. These models provide clearly testable hypotheses that are expected to provide additional insights into the mechanism of cornified envelope assembly.

Amino Acid Sequence↗
PubMed1992

TCP1 complex is a molecular chaperone in tubulin biogenesis.

A role in folding of newly translated proteins in the cytosol of eukaryotes has been proposed for t-complex polypeptide-1 (TCP1), although its molecular targets have not yet been identified. Tubulin is a major cytosolic protein whose assembly into microtubules is critical to many cellular processes. Although numerous studies have focused on the expression of tubulin, little is known about the processes whereby newly translated tubulin subunits acquire conformations that enable them to form alpha-beta-heterodimers. We examined the biogenesis of alpha- and beta-tubulin in rabbit reticulocyte lysate, and report here that newly translated tubulin subunits entered a 900K complex in a protease-sensitive conformation. Addition of Mg-ATP, but not nonhydrolysable analogues, released the tubulin subunits as assembly-competent protein with a conformation that was relatively protease-resistant. The 900K complex purified from reticulocyte lysate contained as its major constituent a 58K protein that cross-reacted with a monoclonal antiserum against mouse TCP1. We conclude that TCP1 functions as a cytosolic chaperone in the biogenesis of tubulin.

Adenosine Triphosphate↗