Characterization of the LDL receptor in rat promegakaryoblasts in culture

1991 ◽  
Vol 11 (1) ◽  
pp. 15-21 ◽  
Author(s):  
Tracy J. Budd ◽  
Frank W. Hemming ◽  
Bruce Middleton
Keyword(s):  
Cell Biology ◽  
Receptor Cell ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Classical Type ◽  
Lysosomal Degradation ◽  
High Affinity ◽  
Ldl Binding

Rat promegakaryoblasts (RPM, a precursor platelet cell line) in culture exhibited a capacity to bind, take up and degrade125I-LDL. The low density lipoprotein (LDL) binding showed the following characteristics: (a) high affinity, (b) saturability, (c) specificity, (d) down-regulation, after exposure to 25 hydroxycholesterol. Furthermore the proteolytic degradation of125I-LDL by RPMs was inhibited by chloroquine which interferes with the lysosomal degradation processes. These findings show LDL receptor cell biology of RPM to be of the classical type and to differ from that of platelets.

scholarly journals Characterization of SID-1-dependent and independent intergenerational RNA transport pathways in Caenorhabditis elegans

2017 ◽  
Author(s):  
Eddie Wang ◽  
Craig P. Hunter
Keyword(s):  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Epigenetic Inheritance ◽  
Transport Pathways ◽  
C Elegans ◽  
Early Embryos ◽  
Systemic Rna

AbstractSystemic RNA interference (RNAi) in C. elegans is dependent on sid-1 (Winstonet al. 2002), sid-3 (Joseet al. 2012) and sid-5 (Hinaset al. 2012). After injection, expression, or ingestion, double-stranded RNA (dsRNA) is transported between cells throughout the animal to enable RNAi in most tissues, including the germline and progeny. Here, we characterize the role of the Sid genes in transport of dsRNA to progeny. We previously reported that dsRNA injected directly in the germline unexpectedly requires sid-1 activity in the progeny to initiate RNAi (Winstonet al. 2002). We now show that germline injected dsRNA can travel by three independent pathways to silence gene expression in embryos. First, germline injected dsRNA is delivered, presumably by bulk flow, into oocytes and embryos. This means of delivery, which does not require sid-1, is limited by the amount and location of injected dsRNA. Second, maternal sid-1 transports extracellular dsRNA into the germline where it can silence maternal deposited mRNAs and segregate to embryos to silence embryonically expressed mRNAs. Third, extracellular dsRNA is also endocytosed into oocytes by the low-density lipoprotein (LDL) receptor superfamily homolog RME-2. The endocytosed dsRNA then requires sid-1 and sid-5 in embryos to silence embryonically expressed genes. Extracellular fluorescent dsRNA, once endocytosed into oocytes, does not co-localize with VIT2::GFP and it does not require sid-1 activity to segregate from the late endocytosis marker GFP::RAB-7 in early embryos. In conclusion, we identify genes and pathways that function redundantly for intergenerational RNA transfer that may represent mechanisms for transgenerational epigenetic inheritance.

Mutations that affect membrane receptor for LDL are useful for studying normal receptor function

1982 ◽  
Vol 243 (1) ◽  
pp. E5-E14
Author(s):  
R. G. Anderson
Keyword(s):  
Cell Biology ◽  
Cholesterol Metabolism ◽  
Plasma Cholesterol ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Cholesterol Transport ◽  
Low Density ◽  
Receptor Function ◽  
Coated Pits

Low-density lipoprotein (LDL), the major plasma cholesterol transport protein, is taken up by cells through a receptor-mediated process. After internalization through specialized segments of the cell surface called coated pits, the LDL is degraded in the lysosome and the released cholesterol is used by cells to meet various metabolic needs. The discovery of the LDL receptor and the studies of its function have provided new insights into both the biochemical aspects of cholesterol metabolism and the cell biology of receptor-mediated endocytosis. Of paramount importance in all of these studies has been the availability of human cells that express one or more allelic mutations that affect the function of the LDL receptor. These mutations have been valuable for assessing normal receptor function. Just as important, these mutations have been used as a reference point in the development of various cytochemical and biochemical techniques for studying receptor activity.

scholarly journals A transient amphipathic helix in the prodomain of PCSK9 facilitates binding to low-density lipoprotein particles

2020 ◽  
Vol 295 (8) ◽  
pp. 2285-2298
Author(s):  
Samantha K. Sarkar ◽  
Alexander C. Y. Foo ◽  
Angela Matyas ◽  
Ikhuosho Asikhia ◽  
Tanja Kosenko ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Low Density ◽  
Loss Of Function ◽  
Ldl Particles ◽  
Ldl Binding ◽  
Α Helix

Proprotein convertase subtilisin/kexin type-9 (PCSK9) is a ligand of low-density lipoprotein (LDL) receptor (LDLR) that promotes LDLR degradation in late endosomes/lysosomes. In human plasma, 30–40% of PCSK9 is bound to LDL particles; however, the physiological significance of this interaction remains unknown. LDL binding in vitro requires a disordered N-terminal region in PCSK9's prodomain. Here, we report that peptides corresponding to a predicted amphipathic α-helix in the prodomain N terminus adopt helical structure in a membrane-mimetic environment. This effect was greatly enhanced by an R46L substitution representing an atheroprotective PCSK9 loss-of-function mutation. A helix-disrupting proline substitution within the putative α-helical motif in full-length PCSK9 lowered LDL binding affinity >5-fold. Modeling studies suggested that the transient α-helix aligns multiple polar residues to interact with positively charged residues in the C-terminal domain. Gain-of-function PCSK9 mutations associated with familial hypercholesterolemia (FH) and clustered at the predicted interdomain interface (R469W, R496W, and F515L) inhibited LDL binding, which was completely abolished in the case of the R496W variant. These findings shed light on allosteric conformational changes in PCSK9 required for high-affinity binding to LDL particles. Moreover, the initial identification of FH-associated mutations that diminish PCSK9's ability to bind LDL reported here supports the notion that PCSK9-LDL association in the circulation inhibits PCSK9 activity.

Early Platelet Activation by Low Density Lipoprotein via p38MAP Kinase

1999 ◽  
Vol 82 (12) ◽  
pp. 1749-1756 ◽  
Author(s):  
Christian Hackeng ◽  
Ingrid Relou ◽  
Marc Pladet ◽  
Gertie Gorter ◽  
Herman van Rijn ◽  
...  
Keyword(s):  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Platelet Glycoprotein ◽  
Slight Reduction ◽  
Low Density ◽  
Density Lipoprotein Receptor ◽  
Arachidonate Metabolites ◽  
Ldl Binding ◽  
Dose Dependent

SummaryLow Density Lipoprotein (LDL) is known to sensitize platelets for physiological agonists. To clarify the basis of this sensitization, we investigated the involvement of p38MAP Kinase (p38MAPK). As dual phosphorylation on Thr180 and Tyr182 of p38MAPK is the trigger for activation of the kinase, p38MAPK-activity was measured with an antibody that recognizes the dual-phosphorylated sequence. LDL induced a rapid and dose dependent activation of p38MAPK. The activation was not inhibited by a wide variety of inhibitors of platelet signalling, including TxA2-formation, Phospholipase C-activation, Ca2+-mobilization and ERK 1/2-activation. Only a slight reduction in p38MAPK-activation was observed when protein kinase C was inhibited. Activation of p38MAPK was strongly inhibited by a rise in cAMP. Thus, p38MAPK-activation was upstream of most signalling pathways and close to the LDL-receptor. A number of platelet receptors was screened with the use of antibodies. Integrins αIIbβ3 and α2β1, as well as the FcγRII-receptor, CD36 (platelet glycoprotein IV), CD68 (gp110) and Low Density Lipoprotein-receptor related protein (LRP) were not implicated in LDL-induced p38MAPK-activation. Inhibition of LDL binding by modification of apo B100 lysines reduced p38MAPK-activation by 80 %. Activation of p38MAPK resulted in an increase in release of arachidonic acid, the precursor for thromboxane A2 synthesis. In conclusion, activation of p38MAPK might be the first step in platelet sensitization by LDL, leading to formation of arachidonate metabolites and increased aggregation and secretion responses to physiological agonists.

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