Internalization and degradation of heparin is not required for stimulus of heparan sulfate proteoglycan synthesis.
In vitro, heparin and antithrombotic drugs specifically stimulate the synthesis of an antithrombotic heparan sulfate proteoglycan (HSPG) produced by endothelial cells. The putative heparin binding site(s) that may be related to this phenomenon were investigated. In the preceding article, using various heparin probes, it was shown that the heparin does not bind to the endothelial cell surface, but only to the extracellular matrix. The present study demonstrated that, when the cells were exposed to heparin at 37 degrees C, the heparin was internalized and with time was localized in lysosomes. However, endocytosis of heparin was not required for the stimulation of HSPG synthesis. The requirement for heparin degradation in the stimulus of HSPG synthesis was also investigated. When the cells were incubated with chloroquine, a lysosomotropic amine that raises the lysosomal pH thus inhibiting enzymatic degradation of internalized compounds, stimulation of HSPG synthesis was still observed. These combined results indicate that neither internalization nor degradation of heparin is required for stimulation of HSPG synthesis, and suggests that its binding to the extracellular matrix could be responsible for this effect.
Departamento de Bioquímica, Universidade Federal de São Paulo, São Paulo, SP, Brazil.
Edvaldo S
ES
Trindade
Rodrigo I
RI
Bouças
Hugo A O
HA
Rocha
Juliana A
JA
Dominato
Edgar J
EJ
Paredes-Gamero
Célia Regina C
CR
Franco
Constance
C
Oliver
Maria C
MC
Jamur
Carl P
CP
Dietrich
Helena B
HB
Nader
D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D002738:Chloroquine / Q000494:pharmacology; D004705:Endocytosis; D042783:Endothelial Cells / Q000187:drug effects* / Q000201:enzymology / Q000648:ultrastructure; D005109:Extracellular Matrix / Q000378:metabolism; D005343:Fibrinolytic Agents / Q000378:metabolism / Q000494:pharmacology*; D006493:Heparin / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D008247:Lysosomes / Q000187:drug effects* / Q000201:enzymology / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D018715:Microscopy, Video; D011485:Protein Binding; D011509:Proteoglycans / Q000378:metabolism*; D011817:Rabbits; D013997:Time Factors
D005343:Fibrinolytic Agents; D011509:Proteoglycans; C036090:heparin proteoglycan; D002738:Chloroquine; D006493:Heparin