Gerard A
Faculté de Médecine de Nancy I, Laboratoire d'Histologie-Embryologie II, Morphogénèse et Reproduction, Vandoeurve-lès-Nancy, France.
J Steroid Biochem Mol Biol. 1995 Jun;53(1-6):533-42. doi: 10.1016/0960-0760(95)00109-d.
To test whether Sertoli cell-secreted ABP could serve as steroid carrier to the germ cell (GC) lineage, radiolabeled ABP and SHBG and gold SHBG were used for binding studies and for internalization studies based on transmission electron microscope analyses and autoradiography of the radiolabeled samples. The data clearly showed that: (1) rat and human germ cells possess a single class of binding sites for rat ABP and human SHBG respectively (Kd of 0.78 and 0.56 nM); (2) 1.7 x 10(10) and 2.7 x 10(10) sites/mg protein was found in the corresponding plasma membrane preparations; (3) the receptor peak was eluted in the same position as dextran blue: 2000 kDa (M(r) = 2 x 106) for labeled rat ABP; (4) in the whole GC lineage, the labeled ligand was internalized through an endocytic pathway involving clathrin coated structures and the distribution was similar throughout the maturation step, however striking differences in the internalization rate were revealed with regard to the maturation step; and (5) this internalization occurred even in ligated seminiferous tubules, via the Sertoli cells cytoplasm. When isolated rat GC were incubated in the presence of ABP, a dose dependent increase in labeled secreted protein was observed for spermatocytes (50-250%) whereas ABP had no effect on spermatids. Addition of steroids and ABP caused a 200 and 50% increase in labeled secreted proteins for spermatocytes and spermatids respectively. 2-D SDS-PAGE analysis revealed that ABP alone increased the secretion of specific spermatocyte proteins whereas steroids in the presence of ABP resulted in the synthesis of new spermatocyte secreted proteins. Taken together these results strongly suggest that ABP may be required for spermatogenesis either as a steroid transmembrane carrier or on its own.
为了测试支持细胞分泌的雄激素结合蛋白（ABP）是否可作为向生殖细胞（GC）谱系转运类固醇的载体，基于透射电子显微镜分析和放射性标记样品的放射自显影，使用放射性标记的ABP和性激素结合球蛋白（SHBG）以及金标记的SHBG进行结合研究和内化研究。数据清楚地表明：（1）大鼠和人类生殖细胞分别具有一类针对大鼠ABP和人类SHBG的结合位点（解离常数分别为0.78和0.56 nM）；（2）在相应的质膜制剂中发现每毫克蛋白质有1.7×10¹⁰和2.7×10¹⁰个位点；（3）受体峰在与葡聚糖蓝相同的位置洗脱：标记的大鼠ABP为2000 kDa（相对分子质量 = 2×10⁶）；（4）在整个GC谱系中，标记的配体通过涉及网格蛋白包被结构的内吞途径内化，并且在整个成熟步骤中的分布相似，然而在内化速率方面，关于成熟步骤显示出显著差异；（5）即使在结扎的生精小管中，这种内化也通过支持细胞的细胞质发生。当在ABP存在的情况下孵育分离的大鼠GC时，观察到精子细胞中标记的分泌蛋白呈剂量依赖性增加（50 - 250%），而ABP对精子细胞没有影响。添加类固醇和ABP分别使精子细胞和精子细胞中标记的分泌蛋白增加200%和50%。二维SDS - 聚丙烯酰胺凝胶电泳分析表明，单独的ABP增加了特定精子细胞蛋白的分泌，而在ABP存在下的类固醇导致了新的精子细胞分泌蛋白的合成。综上所述，这些结果强烈表明，ABP可能是精子发生所必需的，要么作为类固醇跨膜载体，要么自身发挥作用。
