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J R Henley

Publications and source records attributed to J R Henley.

9 recordsLinked to original sources
PubMed1999

Participation of dynamin in the biogenesis of cytoplasmic vesicles.

Dynamin is a 100-kDa GTPase that has been implicated in endocytosis. To extend our understanding of its cellular functions, we have microinjected specific affinity-purified anti-dynamin antibodies into cultured mammalian epithelial cells. Using this approach, dynamin function can be inhibited specifically and rapidly in single cells. Effects of microinjected inhibitory antibodies on distinct endocytic processes and plasmalemmal morphology were then assayed by fluorescence microscopy (FM) and ultrastructural analysis. Micro-injected antibodies inhibit the clathrin-mediated endocytosis of fluorophore-labeled transferrin and cause a marked invagination of the plasma membrane. Many of these long plasmalemmal invaginations had clathrin-coated pits along their cytoplasmic surface. A number of distinct noncoated pits resembling plasmalemmal caveolae also accumulated in anti-dynamin antibody-injected cells. Further, the cellular uptake of cholera toxin B, which normally occurs by the internalization of caveolae, was inhibited in these cells. In support of these observations, immunoisolation techniques, double-label immuno-FM, and immunoelectron microscopy (immuno-EM) provided biochemical and morphological evidence that dynamin associates with plasmalemmal caveolae. Together, these observations indicate that dynamin mediates scission from the plasma membrane of both clathrin-coated pits and caveolae during distinct endocytic processes. These results demonstrate that dynamin isoforms are involved in an additional endocytic process that is distinct from clathrin-mediated endocytosis and provide significant insights into the molecular mechanisms governing the GTP-mediated internalization of caveolae. Evidence is provided demonstrating that dynamin isoforms have a differential distribution in mammalian cells. Targeting information for these isoforms is provided at least in part by regions of alternative splicing. Thus, the different dynamin isoforms may be localized to distinct cellular compartments but provide a similar scission function during the biogenesis of nascent cytoplasmic vesicles.

Animals↗
PubMed1998

Dynamin-mediated internalization of caveolae.

The dynamins comprise an expanding family of ubiquitously expressed 100-kD GTPases that have been implicated in severing clathrin-coated pits during receptor-mediated endocytosis. Currently, it is unclear whether the different dynamin isoforms perform redundant functions or participate in distinct endocytic processes. To define the function of dynamin II in mammalian epithelial cells, we have generated and characterized peptide-specific antibodies to domains that either are unique to this isoform or conserved within the dynamin family. When microinjected into cultured hepatocytes these affinity-purified antibodies inhibited clathrin-mediated endocytosis and induced the formation of long plasmalemmal invaginations with attached clathrin-coated pits. In addition, clusters of distinct, nonclathrin-coated, flask-shaped invaginations resembling caveolae accumulated at the plasma membrane of antibody-injected cells. In support of this, caveola-mediated endocytosis of labeled cholera toxin B was inhibited in antibody-injected hepatocytes. Using immunoisolation techniques an anti-dynamin antibody isolated caveolar membranes directly from a hepatocyte postnuclear membrane fraction. Finally, double label immunofluorescence microscopy revealed a striking colocalization between dynamin and the caveolar coat protein caveolin. Thus, functional in vivo studies as well as ultrastructural and biochemical analyses indicate that dynamin mediates both clathrin-dependent endocytosis and the internalization of caveolae in mammalian cells.

Amino Acid Sequence↗
PubMed1998

Role of dynamin in the formation of transport vesicles from the trans-Golgi network.

Dynamin guanosine triphosphatases support the scission of clathrin-coated vesicles from the plasmalemma during endocytosis. By fluorescence microscopy of cultured rat hepatocytes, a green fluorescent protein-dynamin II fusion protein localized with clathrin-coated vesicles at the Golgi complex. A cell-free assay was utilized to demonstrate the role of dynamin in vesicle formation at the trans-Golgi. Addition of peptide-specific anti-dynamin antibodies to the assay mixture inhibited both constitutive exocytic and clathrin-coated vesicle formation. Immunodepletion of dynamin proteins also inhibited vesicle formation, and budding efficiency was restored upon readdition of purified dynamin. These data suggest that dynamin participates in the formation of distinct transport vesicles from the trans-Golgi network.

Adenosine Triphosphate↗
PubMed1997

The dynamins: redundant or distinct functions for an expanding family of related GTPases?

In the 7 years since dynamin was first isolated from bovine brain in search of novel microtubule-based motors, our understanding of this enzyme has expanded significantly. We now know that brain dynamin belongs to a family of large GTPases, which mediate vesicle trafficking. Furthermore, this enzymatic activity is markedly increased through association with microtubules, acidic phospholipids, and certain regulatory proteins that contain Src homology 3 (SH3) domains. From functional, genetic, and cellular manipulations, it is now generally accepted that dynamin participates in the endocytic uptake of receptors, associated ligands, and plasma membrane following an exocytic event. These observations have confirmed at least one function of dynamin that was predicted from seminal studies on a pleiotropic mutant, shibire(ts) (shi(ts)) in Drosophila melanogaster. Of equal interest is the finding that there are multiple dynamin gene products, including two that are expressed in a tissue-specific manner, and they share marked homology with a larger family of distinct but related proteins. Therefore, it is attractive to speculate that the different dynamins may participate in related cellular functions, such as distinct endocytic processes and even secretion. In turn, dynamin could play an important role in cell growth, cell spreading, and neurite outgrowth. The purpose of this review is to enumerate on the expansive dynamin literature and to discuss the nomenclature, expression, and putative functions of this growing and interesting family of proteins.

Alternative Splicing↗
PubMed1996

Association of a dynamin-like protein with the Golgi apparatus in mammalian cells.

Dynamins are a family of 100-kD GTPases comprised of at least three distinct gene products and multiple alternatively spliced variants. Homologies with the shibire gene product in Drosophila melanogaster and with Vps1p and Dnm1p in Saccharomyces cerevisiae suggest that dynamins play an important role in vesicular transport. Morphological studies have localized brain dynamin to coated pits and tubular invaginations at the plasma membrane, where it is believed to facilitate the formation of endocytic vesicles. Because similar membrane-budding events occur at the Golgi apparatus and multiple dynamin isoforms exist, we have studied the distribution of dynamins in mammalian cells. To this end, we generated and characterized peptide-specific antibodies directed against conserved regions of the dynamin family. By immunoblot analysis, these antibodies reacted specifically with a 100-kD protein in fibroblasts that sedimented with membranes and microtubules in vitro in a manner similar to brain dynamin. By immunofluorescence microscopy, these antibodies strongly labeled the Golgi complex in cultured fibroblasts and melanocytes, as confirmed by double labeling with a Golgi-specific antibody. Furthermore, Western blot analysis showed significant enrichment of a 100-kD dynamin band in Golgi fractions isolated from the liver. To substantiate these findings, we use a specific antidynamin antibody to immunoisolate Golgi membranes from subcellular Golgi fractions, as determined by EM and immunoblot analysis. This study provides the first morphological and biochemical evidence that a dynamin-like protein associates with the Golgi apparatus in mammalian cells, and suggests that dynamin-related proteins may have multiple cytoplasmic distributions. The potential contributions of dynamin to the secretory and endocytic pathways are discussed.

Amino Acid Sequence↗
PubMed1995

Rapid endocytosis coupled to exocytosis in adrenal chromaffin cells involves Ca2+, GTP, and dynamin but not clathrin.

Rapid endocytosis (RE) occurs immediately after an exocytotic burst in adrenal chromaffin cells. Capacitance measurements of endoocytosis reveal that recovery of membrane is a biphasic process that is complete within 20 sec. The ultimate extent of membrane retrieval is precisely controlled and capacitance invariably returns to its prestimulation value. The mechanism of RE specifically requires intracellular Ca2+; Sr2+ and Ba2+ do not substitute, although all three cations support secretion. Thus the divalent cation receptors for RE and exocytosis must be distinct molecules. RE is dependent on GTP hydrolysis; it is blocked by GTP removal or replacement with guanosine 5'-[gamma-thio]triphosphate. In the presence of GTP, multiple rounds of secretion followed by RE could be elicited from the same cell. RE requires participation of dynamin, a guanine nucleotide binding protein, as revealed by intracellular immunological antagonism of this protein. Intact microtubules may be essential, as nocodazole also blocked RE. Whereas anti-dynamin antibodies blocked RE, anti-clathrin antibodies did not, suggesting that clathrin-coated vesicles are not involved in this form of endocytosis. RE may represent the initial step in the rapid recycling of secretory granules in the chromaffin cell.

Adrenal Glands↗
PubMed1977

Measuring various drug use dimensions with a calendar method.

This note presents a technique used to acquire a variety of time-specific data on drug use. The calendar technique involves self-reported patterns of consumption and any changes therein, including cessation. Advantages of this technique over other approaches are discussed, and examples of the variety of use measures that can be derived from the calendar method are illustrated.

Humans↗