PubMed Health⌕ Search

Biomedical subjects

David B Sacks

Publications and source records attributed to David B Sacks.

30 records · Page 2Linked to original sources
PubMed2003

IQGAP1 promotes cell motility and invasion.

The dynamic processes of cell migration and invasion are largely coordinated by Rho family GTPases. The scaffolding protein IQGAP1 binds to Cdc42, increasing the amount of active Cdc42 both in vitro and in cells. Here we show that overexpression of IQGAP1 in mammalian cells enhances cell migration in a Cdc42- and Rac1-dependent manner. Importantly, cell motility was significantly decreased both by knock down of endogenous IQGAP1 using small interfering RNA and by transfection of a dominant negative IQGAP1 construct, IQGAP1DeltaGRD. Cell invasion was similarly altered by manipulating intracellular IQGAP1 concentrations. Moreover, invasion mediated by constitutively active Cdc42 was attenuated by IQGAP1DeltaGRD. Thus, IQGAP1 has a fundamental role in cell motility and invasion.

Animals↗
PubMed2003

Identification and characterization of the Cdc42-binding site of IQGAP1.

IQGAP1 is a multi-domained protein that integrates signaling of the Rho family GTPase Cdc42 with regulation of the cytoskeleton. Using SPOT analysis and in vitro peptide competition assays we have identified a 24 amino acid region of IQGAP1 that is necessary for Cdc42 binding. Both in vitro and in vivo analyses reveal that deletion of this sequence abolishes binding of IQGAP1 to Cdc42. In addition, the ability of IQGAP1 to increase the amount of active Cdc42 in cells is abrogated upon removal of this region. An IQGAP1 mutant lacking the Cdc42 binding site mislocalizes to the cell periphery. These observations specifically define a short sequence of IQGAP1 that is required for its interaction with Cdc42 and demonstrate that Cdc42 binding is necessary for the normal subcellular distribution of IQGAP1.

Animals↗
PubMed2003

IQGAP1 as signal integrator: Ca2+, calmodulin, Cdc42 and the cytoskeleton.

A family of proteins known as IQGAPs have been identified in yeast, amebas and mammals. IQGAPs are multidomain molecules that contain several protein-interacting motifs which mediate binding to target proteins. Mammalian IQGAP1 is a component of signaling networks that are integral to maintaining cytoskeletal architecture and cell-cell adhesion. Published data suggest that IQGAP1 is a scaffolding protein that modulates cross-talk among diverse pathways in complex regulatory circuits. These pathways include modulating the actin cytoskeleton, mediating signaling by Rho family GTPases and calmodulin, regulating E-cadherin and beta-catenin function and organizing microtubules.

Animals↗
PubMed2003

Transcriptional activity and DNA binding of heat shock factor-1 involve phosphorylation on threonine 142 by CK2.

Heat shock factor-1 (HSF-1) is the regulator of hsp molecular chaperone transcription, although the intracellular mechanisms involved in HSF-1 activation have not been fully elucidated. As HSF1 is activated by heat shock simultaneously with the nuclear translocation of the protein kinase CK2, we have investigated the role of CK2 in HSF1 activation. We demonstrate that HSF-1 is phosphorylated by CK2 on both serine and threonine residues and has characterized a phosphorylation site at threonine 142. Mutation of Thr-142 to alanine (T142A) inhibits trans-activation of the HSP70 gene by HSF1 and in addition inhibits the accumulation of HSF-1 competent to bind heat shock elements in the nucleus. HSF1 activation by heat is correlated with the thermal activation of nuclear CK2 and overexpression of CK2 activates HSF1. Phosphorylation by CK2 on threonine 142 may therefore be an essential step in the thermal activation of latent HSF1 by stresses.

Alanine↗
PubMed2003

IQGAP proteins are integral components of cytoskeletal regulation.

IQGAP1 is a scaffolding protein that binds to a diverse array of signalling and structural molecules. By interacting with its target proteins, human IQGAP1 participates in multiple cellular functions, including Ca(2+)/calmodulin signalling, cytoskeletal architecture, CDC42 and Rac signalling, E-cadherin-mediated cell-cell adhesion and beta-catenin-mediated transcription. Yeast IQGAP homologues are important regulators of cellular morphogenesis because they are required for budding and cytokinesis. Here we discuss the structure and function of IQGAP1 as a member of the family of IQGAP proteins and summarize the current knowledge about IQGAP1 and IQGAP2. Collectively, these data reveal that IQGAP1 is a fundamental regulator of cytoskeletal function.

Animals↗
PubMed2002

Elucidation of the interaction of calmodulin with the IQ motifs of IQGAP1.

Calmodulin regulates the function of numerous proteins by binding to short regions on the target molecule. IQ motifs, which are found in over 100 human proteins, appear in tandem repeats and bind calmodulin in the absence of Ca(2+). One of these IQ-containing proteins, IQGAP1, interacts with several targets, including Cdc42, beta-catenin, E-cadherin, and actin, in a calmodulin-regulated manner. To elucidate the molecular mechanism by which apocalmodulin and Ca(2+)/calmodulin differentially regulate IQGAP1, a series of constructs of IQGAP1 with selected point mutations of the four tandem IQ motifs were generated. Mutating the basic charged arginine residues in all four IQ motifs abrogated binding of IQGAP1 to apocalmodulin, but had no effect on its interaction with Ca(2+)/calmodulin. Analysis of IQGAP1 constructs with point mutations in single, double, or triple IQ motifs revealed that apocalmodulin bound only to IQ3 and IQ4. By contrast to the arginine mutant constructs, mutation of selected hydrophobic residues in the IQ motifs produced an IQGAP1 protein incapable of binding either apocalmodulin or Ca(2+)/calmodulin. These results, which differ from the conventional model of Ca(2+)-independent binding of calmodulin to IQ motifs, provide insight into the complexity of the molecular interactions between calmodulin and IQ motifs.

Amino Acid Motifs↗
PubMed2002

Calmodulin regulates the transcriptional activity of estrogen receptors. Selective inhibition of calmodulin function in subcellular compartments.

The steroid hormone estrogen elicits biological effects in cells by binding to and activating the estrogen receptor (ER). Estrogen binding induces a conformational change in the receptor, inducing nuclear translocation and transcriptional activation of ER. The ubiquitous Ca(2+)-binding protein calmodulin has been shown to interact directly with ER and enhance its stability. To further elucidate the functional sequelae of the association between calmodulin and ER, we examined the effect on ER transcriptional activation of specifically inhibiting calmodulin. The cell-permeable calmodulin antagonist CGS9343B prevented estrogen-induced transcriptional activation by ER, without altering basal transcription. The inhibition was dose-dependent and independent of the time of estrogen stimulation. To validate these findings, calmodulin function was also neutralized by targeted expression of a specific inhibitor peptide. By inserting localization signals, the inhibitor peptide was selectively targeted to different subcellular domains. Inactivation of calmodulin function in the nucleus virtually eliminated estrogen-stimulated ER transcriptional activation. By contrast, when membrane calmodulin was specifically neutralized, estrogen-stimulated transcriptional activation by ER was only slightly attenuated. Importantly, the inhibitor peptides did not significantly reduce the amount of ER in the cells. Together, these data demonstrate that calmodulin is a fundamental component of ER transcriptional activation.

Animals↗
PubMed2002

IQGAP1 is a component of Cdc42 signaling to the cytoskeleton.

The Ras-GAP related protein IQGAP1 binds several proteins, including actin, calmodulin, E-cadherin and the Rho family GTPase Cdc42. To gain insight into its in vivo function, IQGAP1 was overexpressed in mammalian cells. Transfection of IQGAP1 significantly increased the levels of active, GTP-bound Cdc42, resulting in the formation of peripheral actin microspikes. By contrast, transfection of an IQGAP1 mutant lacking part of the GAP-related domain (IQGAP1deltaGRD) substantially decreased the amount of GTP-bound Cdc42 in cell lysates. Consistent with these findings, IQGAP1DeltaGRD blocked Cdc42 function in cells that stably overexpress constitutively active Cdc42 and abrogated the effect of bradykinin on Cdc42. In cells transfected with IQGAP1deltaGRD, bradykinin was unable to activate Cdc42, translocate Cdc42 to the membrane fraction, or induce filopodia production. IQGAP1deltaGRD transfection altered cellular morphology, producing small, round cells that closely resemble Cdc42-/- cells. Some insight into the mechanism was provided by in vitro analysis, which revealed that IQGAP1deltaGRD increased the intrinsic GTPase activity of Cdc42, thereby increasing the amount of inactive, GDP-bound Cdc42. These data imply that IQGAP1 has a crucial role in transducing Cdc42 signaling to the cytoskeleton.

Amino Acid Sequence↗
PubMed2002

Screening for diabetes: is it warranted?

BACKGROUND: Diabetes mellitus is estimated to have a worldwide prevalence of 4.6% and afflict 200 million people. The prevalence is accelerating rapidly and the disease has reached epidemic proportions. While type 1 diabetes usually has a dramatic clinical onset, almost half of all those individuals with type 2 diabetes have not been diagnosed. This observation, coupled with the presence of complications at diagnosis and the significant reduction of microvascular complications obtained with tight glycemic control, has led to the recommendation that screening for diabetes be instituted. The American Diabetes Association recommends that adults aged 45 years or more should be evaluated for diabetes by measuring fasting plasma glucose concentrations. CONCLUSIONS: The rationale for screening, evidence that tight glycemic control reduces complications, and the possible roles of Hb A(1c) and autoantibodies in screening strategies are addressed in this review.

Blood Glucose↗
PubMed2002

Guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus.

BACKGROUND: Multiple laboratory tests are used in the diagnosis and management of patients with diabetes mellitus. The quality of the scientific evidence supporting the use of these assays varies substantially. APPROACH: An expert committee drafted evidence-based recommendations for the use of laboratory analysis in patients with diabetes. An external panel of experts reviewed a draft of the guidelines, which were modified in response to the reviewers' suggestions. A revised draft was posted on the Internet and was presented at the AACC Annual Meeting in July, 2000. The recommendations were modified again in response to oral and written comments. The guidelines were reviewed by the Professional Practice Committee of the American Diabetes Association. CONTENT: Measurement of plasma glucose remains the sole diagnostic criterion for diabetes. Monitoring of glycemic control is performed by the patients, who measure their own plasma or blood glucose with meters, and by laboratory analysis of glycated hemoglobin. The potential roles of noninvasive glucose monitoring, genetic testing, autoantibodies, microalbumin, proinsulin, C-peptide, and other analytes are addressed. SUMMARY: The guidelines provide specific recommendations based on published data or derived from expert consensus. Several analytes are of minimal clinical value at the present time, and measurement of them is not recommended.

Blood Glucose↗
PubMed2001

IQGAP1-mediated stimulation of transcriptional co-activation by beta-catenin is modulated by calmodulin.

Beta-catenin, an oncoprotein integral to cell-cell adhesion and proliferative signaling, is increased in several malignancies. The recently discovered calmodulin-binding protein IQGAP1 binds stoichiometrically to beta-catenin and regulates the association of beta-catenin with the cell-cell adhesion complex. In the present work, we investigated the role of IQGAP1 on the transcriptional co-activator function of beta-catenin, and whether calmodulin modulated the functional interaction between IQGAP1 and beta-catenin. In vitro competition assays revealed that both Ca(2+)/calmodulin and apo-calmodulin, when pre-bound to IQGAP1, prevented binding of beta-catenin to IQGAP1, and partially displaced beta-catenin pre-bound to IQGAP1 when added subsequently. Conversely, beta-catenin partially displaced apo-calmodulin, but not Ca(2+)/calmodulin, from IQGAP1. Overexpression of IQGAP1 in SW480 colon carcinoma cells enhanced beta-catenin-mediated transcriptional co-activation by 1.72-fold, and this stimulation was significantly attenuated upon antagonism of calmodulin using the cell-permeable antagonist CGS9343B. Moreover, an IQGAP1 mutant that does not bind calmodulin was unable to stimulate beta-catenin transcriptional function. Results of pulse-chase analyses suggested that IQGAP1 slowed the turnover of soluble, but not total, beta-catenin. Immunocytochemistry revealed that IQGAP1 overexpression increased the amount of beta-catenin located in the nucleus, whereas incubation of cells with CGS9343B blocked this accumulation. Together, our results imply that IQGAP1 enhances the function of beta-catenin in the nucleus and that calmodulin regulates this stimulation.

Antidiarrheals↗