Ng Kwong-Man, Catalano Maria G, Pinós Tomàs, Selva David M, Avvakumov George V, Munell Francina, Hammond Geoffrey L
Department of Obstetrics and Gynecology, University of British Columbia, and Child and Family Research Institute, Vancouver V5Z 4H4, Canada.
J Biol Chem. 2006 Jun 9;281(23):15853-61. doi: 10.1074/jbc.M512370200. Epub 2006 Apr 6.
Sex hormone-binding globulin (SHBG) binds steroids in the blood but is also present in the extravascular compartments of some tissues. Mice expressing a human SHBG transgene in the liver have human SHBG in their blood. In these animals, human SHBG accumulates within the stromal matrix of the endometrium and epididymis. This is remarkable because these tissues do not express the transgene. Human SHBG administered intravenously to wild-type mice in the presence of estradiol is rapidly sequestered within the endometrial stroma, and this prompted us to search for SHBG interacting proteins. Yeast two-hybrid screens revealed that fibulin-1D and fibulin-2 interact with the amino-terminal laminin G domain of SHBG. These interactions were verified in GST-pull down assays in which human SHBG bound the carboxyl-terminal domains of fibulin-1D and fibulin-2 in a steroid-dependent manner, with estradiol being the most effective ligand, and were enhanced by reducing the N-glycosylation of human SHBG. Like human SHBG, fibulin-1 and fibulin-2 concentrate within the endometrial stroma. In addition, SHBG co-immunoprecipitates with these fibulins in a proestrus uterine extract. These matrix-associated proteins may therefore sequester plasma SHBG within uterine stroma where it can control sex-steroid access to target cells. Given the interplay between fibulins and numerous proteins within the basal lamina, interactions between SHBG and matrix proteins may exert novel biological effects.
性激素结合球蛋白（SHBG）在血液中结合类固醇，但在某些组织的血管外间隙中也有存在。在肝脏中表达人SHBG转基因的小鼠血液中有人类SHBG。在这些动物中，人SHBG在内膜和附睾的基质中积累。这很显著，因为这些组织不表达该转基因。在雌二醇存在的情况下，将人SHBG静脉注射到野生型小鼠体内，它会迅速被隔离在内膜基质中，这促使我们寻找与SHBG相互作用的蛋白质。酵母双杂交筛选显示，纤连蛋白-1D和纤连蛋白-2与SHBG的氨基末端层粘连蛋白G结构域相互作用。这些相互作用在GST下拉试验中得到验证，其中人SHBG以类固醇依赖的方式结合纤连蛋白-1D和纤连蛋白-2的羧基末端结构域，雌二醇是最有效的配体，并且通过减少人SHBG的N-糖基化而增强。与人类SHBG一样，纤连蛋白-1和纤连蛋白-2也集中在内膜基质中。此外，在动情前期子宫提取物中，SHBG与这些纤连蛋白共免疫沉淀。因此，这些与基质相关的蛋白质可能将血浆SHBG隔离在子宫基质中，在那里它可以控制性类固醇进入靶细胞。鉴于纤连蛋白与基膜内众多蛋白质之间的相互作用，SHBG与基质蛋白之间的相互作用可能会产生新的生物学效应。
