Human alpha-defensin regulates smooth muscle cell contraction: a role for low-density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor.
We have previously identified alpha-defensin in association with medial smooth muscle cells (SMCs) in human coronary arteries. In the present paper we report that alpha-defensin, at concentrations below those found in pathological conditions, inhibits phenylephrine (PE)-induced contraction of rat aortic rings. Addition of 1 microM alpha-defensin increased the half-maximal effective concentration (EC(50)) of PE on denuded aortic rings from 32 to 630 nM. The effect of alpha-defensin was dose dependent and saturable, with a half-maximal effect at 1 microM. alpha-Defensin binds to human umbilical vein SMCs in a specific manner. The presence of 1 microM alpha-defensin inhibited the PE-mediated Ca(++) mobilization in SMCs by more than 80%. The inhibitory effect of alpha-defensin on contraction of aortic rings and Ca(++) mobilization was completely abolished by anti-low-density lipoprotein receptor-related protein/alpha(2-)macroglobulin receptor (LRP) antibodies as well as by the antagonist receptor-associated protein (RAP). alpha-Defensin binds directly to isolated LRP in a specific and dose-dependent manner; the binding was inhibited by RAP as well as by anti-LRP antibodies. alpha-Defensin is internalized by SMCs and interacts with 2 intracellular subtypes of protein kinase C (PKC) involved in muscle contraction, alpha and beta. RAP and anti-LRP antibodies inhibited the binding and internalization of alpha-defensin by SMCs and its interaction with intracellular PKCs. These observations suggest that binding of alpha-defensin to LRP expressed in SMCs leads to its internalization; internalized alpha-defensin binds to PKC and inhibits its enzymatic activity, leading to decreased Ca(++) mobilization and SMC contraction in response to PE.
Nassar
Taher
T
Department of Clinical Biochemistry, Interdepartmental Unit, Hadassah University Hospital and Hebrew University-Hadassah Medical School, Jerusalem, Israel.
Akkawi
Sa'ed
S
Bar-Shavit
Rachel
R
Haj-Yehia
Abdullah
A
Bdeir
Khalil
K
Al-Mehdi
Abu-Bakr
AB
Tarshis
Mark
M
Higazi
Abd Al-Roof
AA
D000818:Animals; D001011:Aorta; D020013:Calcium Signaling / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007457:Iodine Radioisotopes; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000378:metabolism / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000502:physiology*; D010656:Phenylephrine / Q000037:antagonists & inhibitors; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D014471:Umbilical Veins; D014662:Vasoconstrictor Agents / Q000037:antagonists & inhibitors; D023084:alpha-Defensins / Q000378:metabolism / Q000493:pharmacokinetics* / Q000494:pharmacology
D007457:Iodine Radioisotopes; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D014662:Vasoconstrictor Agents; D023084:alpha-Defensins; D010656:Phenylephrine; D011493:Protein Kinase C