Human alpha-defensin regulates smooth muscle cell contraction: a role for low-density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor

• Published in: Blood 2002-12, Vol.100 (12), p.4026
• Main Authors: Nassar, Taher, Akkawi, Sa'ed, Bar-Shavit, Rachel, Haj-Yehia, Abdullah, Bdeir, Khalil, Al-Mehdi, Abu-Bakr, Tarshis, Mark, Higazi, Abd Al-Roof
• Format: Article
• Language: English
• Subjects: alpha-Defensins - metabolism; alpha-Defensins - pharmacokinetics; alpha-Defensins - pharmacology; Animals; Aorta; Calcium Signaling - drug effects; Dose-Response Relationship, Drug; Humans; Iodine Radioisotopes; Low Density Lipoprotein Receptor-Related Protein-1 - metabolism; Low Density Lipoprotein Receptor-Related Protein-1 - physiology; Male; Muscle Contraction - drug effects; Muscle, Smooth, Vascular - cytology; Muscle, Smooth, Vascular - physiology; Phenylephrine - antagonists & inhibitors; Protein Binding; Protein Kinase C - metabolism; Rats; Rats, Sprague-Dawley; Umbilical Veins; Vasoconstrictor Agents - antagonists & inhibitors
• ISSN: 0006-4971
• DOI: 10.1182/blood-2002-04-1080

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.