Biomedical subjects

J Fred Dice

Publications and source records attributed to J Fred Dice.

8 recordsLinked to original sources

PubMed2006

Extracellular matrix remodeling--methods to quantify cell-matrix interactions.

Tissue turnover during wound healing, regeneration or integration of biomedical materials depends on the rate and extent of materials trafficking into and out of cells involved in extracellular matrix (ECM) remodeling. To exploit these processes, we report the first model for matrix trafficking in which these issues are quantitatively assessed for cells grown on both native collagen (normal tissue) and denatured collagen (wound state) substrates. Human fibroblasts more rapidly remodeled denatured versus normal collagen type I to form new ECM. Fluxes to and from the cells from the collagen substrates and the formation of new ECM were quantified using radioactively labeled substrates. The model can be employed for the systematic and quantitative study of the impact of a broad range of physiological factors and disease states on tissue remodeling, integrating extracellular matrix structures and cell biology.

Cell Communication↗

PubMed2006

Akt and Mammalian target of rapamycin regulate separate systems of proteolysis in renal tubular cells.

EGF suppresses proteolysis via class 1 phosphatidylinositol 3-kinase (PI3K) in renal tubular cells. EGF also increases the abundance of glycolytic enzymes (e.g., glyceraldehyde-3-phosphate dehydrogenase [GAPDH]) and transcription factors (e.g., pax2) that are degraded by the lysosomal pathway of chaperone-mediated autophagy. To determine if EGF regulates chaperone-mediated autophagy through PI3K signaling, this study examined the effect of inhibiting PI3K and its downstream mediators Akt and the mammalian target of rapamycin (mTOR). Inhibition of PI3K with LY294002 prevented EGF-induced increases in GAPDH and pax2 abundance in NRK-52E renal tubular cells. Similar results were seen with an adenovirus encoding a dominant negative Akt (DN Akt). Expression of a constitutively active Akt increased GAPDH and pax2 abundance. An mTOR inhibitor, rapamycin, did not prevent EGF-induced increases in these proteins. Neither DN Akt nor rapamycin alone had an effect on total cell protein degradation, but both partially reversed EGF-induced suppression of proteolysis. DN Akt no longer affected proteolysis after treatment with a lysosomal inhibitor, methylamine. In contrast, methylamine or the inhibitor of macroautophagy, 3-methyladenine, did not prevent rapamycin from partially reversing the effect of EGF on proteolysis. Notably, rapamycin did not increase autophagasomes detected by monodansylcadaverine staining. Blocking the proteasomal pathway with either MG132 or lactacystin prevented rapamycin from partially reversing the effect of EGF on proteolysis. It is concluded that EGF regulates pax2 and GAPDH abundance and proteolysis through a PI3K/Akt-sensitive pathway that does not involve mTOR. Rapamycin has a novel effect of regulating proteasomal proteolysis in cells that are stimulated with EGF.

Acetylcysteine↗

PubMed2005

Effects of small molecules on chaperone-mediated autophagy.

Autophagy, including macroautophagy (MA), chaperone-mediated autophagy (CMA), crinophagy, pexophagy and microautophagy, are processes by which cells select internal components such as proteins, secretory vesicles, organelles, or foreign bodies, and deliver them to lysosomes for degradation. MA and CMA are activated during conditions of serum withdrawal in cell culture and during short-term and prolonged starvation in organisms, respectively. Although MA and CMA are activated under similar conditions, they are regulated by different mechanisms. We used pulse/chase analysis under conditions in which most intracellular proteolysis is due to CMA to test a variety of compounds for effects on this process. We show that inhibitors of MA such as 3-methyladenine, wortmannin, and LY294002 have no effect on CMA. Protein degradation by MA is sensitive to microtubule inhibitors such as colcemide and vinblastine, but protein degradation by CMA is not. Activators of MA such as rapamycin also have no effect on CMA. We demonstrate that CMA, like MA, is inhibited by protein synthesis inhibitors anisomycin and cycloheximide. CMA is also partially inhibited when the p38 mitogen activated protein kinase is blocked. Finally we demonstrate that the glucose-6-phophate dehydrogenase inhibitor, 6-aminonicotinamide, and heat shock protein of 90 kilodaltons inhibitor, geldanamycin, have the ability to activate CMA.

6-Aminonicotinamide↗

PubMed2005

Ketone bodies stimulate chaperone-mediated autophagy.

Chaperone-mediated autophagy (CMA) is a selective lysosomal protein degradative process that is activated in higher organisms under conditions of prolonged starvation and in cell culture by the removal of serum. Ketone bodies are comprised of three compounds (beta-hydroxybutyrate, acetoacetate, and acetone) that circulate during starvation, especially during prolonged starvation. Here we have investigated the hypothesis that ketone bodies induce CMA. We found that physiological concentrations of beta-hydroxybutyrate (BOH) induced proteolysis in cells maintained in media with serum and without serum; however, acetoacetate only induced proteolysis in cells maintained in media with serum. Lysosomes isolated from BOH-treated cells displayed an increased ability to degrade both glyceraldehyde-3-phosphate dehydrogenase and ribonuclease A, substrates for CMA. Isolated lysosomes from cells maintained in media without serum also demonstrated an increased ability to degrade glyceraldehyde-3-phosphate dehydrogenase and ribonuclease A when the reaction was supplemented with BOH. Such treatment did not affect the levels of lysosome-associated membrane protein 2a or lysosomal heat shock cognate protein of 70 kDa, two rate-limiting proteins in CMA. However, pretreatment of glyceraldehyde-3-phosphate and ribonuclease A with BOH increased their rate of degradation by isolated lysosomes. Lysosomes pretreated with BOH showed no increase in proteolysis, suggesting that BOH acts on the substrates to increase their rates of proteolysis. Using OxyBlot analysis to detect carbonyl formation on proteins, one common marker of protein oxidation, we showed that treatment of substrates with BOH increased their oxidation. Neither glycerol, another compound that increases in circulation during prolonged starvation, nor butanol or butanone, compounds closely related to BOH, had an effect on CMA. The induction of CMA by ketone bodies may provide an important physiological mechanism for the activation of CMA during prolonged starvation.

Antigens, CD↗

PubMed2005

Unifying nomenclature for the isoforms of the lysosomal membrane protein LAMP-2.

The present nomenclature of the splice variants of the lysosome-associated membrane protein type 2 (LAMP-2) is confusing. The LAMP-2a isoform is uniformly named in human, chicken, and mouse, but the LAMP-2b and LAMP-2c isoforms are switched in human as compared with mouse and chicken. We propose to change the nomenclature of the chicken and mouse b and c isoforms to agree with that currently used for the human isoforms. To avoid confusion in the literature, we further propose to adopt the use of capital letters for the updated nomenclature of all the isoforms in all three species: LAMP-2A, LAMP-2B, and LAMP-2C.

Alternative Splicing↗

PubMed2004

Mechanisms of chaperone-mediated autophagy.

Chaperone-mediated autophagy is one of several lysosomal pathways of proteolysis. This pathway is activated by physiological stresses such as prolonged starvation. Cytosolic proteins with particular peptide sequence motifs are recognized by a complex of molecular chaperones and delivered to lysosomes. No vesicular traffic is required for this protein degradation pathway, so it differs from microautophagy and macroautophagy. Protein substrates bind to a receptor in the lysosomal membrane, the lysosome-associated membrane protein (lamp) type 2a. Levels of lamp2a in the lysosomal membrane are controlled by alterations in the lamp2a half-life as well as by the dynamic distribution of the protein between the lysosomal membrane and the lumen. Substrate proteins are unfolded before transport into the lysosome lumen, and the transport of substrate proteins requires a molecular chaperone within the lysosomal lumen. The exact roles of this lysosomal chaperone remain to be defined. The mechanisms of chaperone-mediated autophagy are similar to mechanisms of protein import into mitochondria, chloroplasts, and the endoplasmic reticulum.

Amino Acid Motifs↗

PubMed2003

Cathepsin A regulates chaperone-mediated autophagy through cleavage of the lysosomal receptor.

Protective protein/cathepsin A (PPCA) has a serine carboxypeptidase activity of unknown physiological function. We now demonstrate that this protease activity triggers the degradation of the lysosome-associated membrane protein type 2a (lamp2a), a receptor for chaperone-mediated autophagy (CMA). Degradation of lamp2a is important because its level in the lysosomal membrane is a rate-limiting step of CMA. Cells defective in PPCA show reduced rates of lamp2a degradation, higher levels of lamp2a and higher rates of CMA. Restoration of PPCA protease activity increases rates of lamp2a degradation, reduces levels of lysosomal lamp2a and reduces rates of CMA. PPCA associates with lamp2a on the lysosomal membrane and cleaves lamp2a near the boundary between the luminal and transmembrane domains. In addition to the well-studied role of PPCA in targeting and protecting two lysosomal glycosidases, we have defined a role for the proteolytic activity of this multifunctional protein.

Amino Acid Sequence↗

PubMedDate not supplied

Proteolytic and lipolytic responses to starvation.

Mammals survive starvation by activating proteolysis and lipolysis in many different tissues. These responses are triggered, at least in part, by changing hormonal and neural statuses during starvation. Pathways of proteolysis that are activated during starvation are surprisingly diverse, depending on tissue type and duration of starvation. The ubiquitin-proteasome system is primarily responsible for increased skeletal muscle protein breakdown during starvation. However, in most other tissues, lysosomal pathways of proteolysis are stimulated during fasting. Short-term starvation activates macroautophagy, whereas long-term starvation activates chaperone-mediated autophagy. Lipolysis also increases in response to starvation, and the breakdown of triacylglycerols provides free fatty acids to be used as an energy source by skeletal muscle and other tissues. In addition, glycerol released from triacylglycerols can be converted to glucose by hepatic gluconeogenesis. During long-term starvation, oxidation of free fatty acids by the liver leads to the production of ketone bodies that can be used for energy by skeletal muscle and brain. Tissues that cannot use ketone bodies for energy respond to these small molecules by activating chaperone-mediated autophagy. This is one form of interaction between proteolytic and lipolytic responses to starvation.

Acyl Coenzyme A↗