Sani B P, Shealy Y F, Hill D L
Kettering-Meyer Laboratory, Southern Research Institute, Birmingham, AL 35255-5305, USA.
Carcinogenesis. 1995 Oct;16(10):2531-4. doi: 10.1093/carcin/16.10.2531.
The cellular transport, metabolism and biological activity of retinoids are mediated by their specific binding proteins and nuclear receptors. For an understanding of the mode of action of retinoids with potential cancer chemopreventive or other biological activity, it is important to study their interactions with these binding proteins and receptors. In our attempts to understand the action of N-(4-hydroxyphenyl)retinamide (4HPR) and other retinamides in the prevention of cancer, we observed that 4HPR binds to a serum protein with a molecular size of approximately 20,000. The retinoid, however, did not show any binding affinity for cellular retinol-binding protein (CRABP) or for cellular retinoic acid-binding protein (CRABP). However, it showed binding affinity for the nuclear receptors of retinoic acid (RARs) equivalent to 15% of that of retinoic acid. The physicochemical properties of the 4HPR binding protein in the serum were identical to those of serum retinol binding protein (RBP). Antibodies against RBP quantitatively immunoprecipitated the protein-4HPR complex, confirming that the retinoid specifically binds to RBP. Although retinol and 4HPR cross-competed for RBP binding, N-phenylretinamide, in which the 4-hydroxyl group is absent, and N-(4-methoxyphenyl)retinamide, a major cellular metabolite of 4HPR, in which the hydroxyl group is blocked, did not show affinity for the binding protein. The results indicate that the hydroxyl group of 4HPR is essential for binding of this type of retinoid to RBP. Thus, our studies suggest that serum transport of 4HPR may be facilitated by RBP. To bind more efficiently to CRBP, CRABP, or RARs/RXRs, the retinoid may require further metabolic change.
类视黄醇的细胞转运、代谢及生物活性由其特定的结合蛋白和核受体介导。为了解具有潜在癌症化学预防或其他生物活性的类视黄醇的作用模式，研究它们与这些结合蛋白和受体的相互作用很重要。在我们试图了解N-(4-羟基苯基)视黄酰胺(4HPR)及其他视黄酰胺预防癌症的作用时，我们观察到4HPR与一种分子大小约为20,000的血清蛋白结合。然而，该类视黄醇对细胞视黄醇结合蛋白(CRABP)或细胞视黄酸结合蛋白(CRABP)均未表现出任何结合亲和力。不过，它对视黄酸核受体(RARs)的结合亲和力相当于视黄酸的15%。血清中4HPR结合蛋白的物理化学性质与血清视黄醇结合蛋白(RBP)相同。抗RBP抗体能定量免疫沉淀蛋白-4HPR复合物，证实该类视黄醇特异性结合RBP。虽然视黄醇和4HPR在与RBP结合上存在交叉竞争，但缺乏4-羟基的N-苯基视黄酰胺以及4HPR的主要细胞代谢产物、羟基被封闭的N-(4-甲氧基苯基)视黄酰胺，对该结合蛋白均无亲和力。结果表明，4HPR的羟基对于这类视黄醇与RBP的结合至关重要。因此，我们的研究提示RBP可能有助于4HPR的血清转运。为了更有效地与CRBP、CRABP或RARs/RXRs结合；该类视黄醇可能需要进一步的代谢变化。
